AP Sf Bio Cell to Cell Communication

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PROFESSIONAL DEVELOPMENT

Special Focus

AP BiologyCell-to-Cell Communication

Cell Signaling


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iii

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Jlia Kay Christensen Eichman

2. Introductory Lab: Cell-to-Cell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3


3. Cell Linkages: Integrins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Elizabeth A. Cowles

4. APBiology Free-Response Questions and Scoring Rubrics . . . . . . . . . . . 21


5. Additional Web Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Carolyn Schofeld Bronston

6. About the Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

7. About the Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51


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Introduction


Missouri Southern State University

Joplin, Missouri

Cell-to-cell communication, or signaling, is an important part o understanding cell

unctions as well as system unctions. There are several types o signaling, such as

neurotransmitters that are recognized in the synapse, antigens triggering antibody

responses, and target cells responding to specic hormones. This project provides

more inormation about the signaling process using integrins as the mechanism.

The document opens with a very eective introductory lab ocused on cell-

to-cell communication. Following this lab, author Elizabeth Cowles elaborates on

cell linkages and integrins in an attempt to oer students and teachers additional

background inormation and practical applications.

These materials also include appropriate AP Biology Exam ree-response

questions and their rubrics rom previous years, as well as inormative and interactive

Web sites. These resources provide teachers with additional inormation regarding

cell communication as well as animated examples o other types o signaling. I

access allows, teachers may use the activities and inormation presented on

these Web sites to introduce, develop, and reinorce concepts associated with cell

communication. Likewise, teachers may use the ree-response questions to not only

reinorce the concepts embedded within cell communication, but also to aid in the

understanding o this communication. These questions also serve to test students

analytical and reasoning skills while refecting appropriate lab experiences they

should possess.


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Introductory Lab: Cell-to-Cell



Joplin, Missouri

Is there an exchange o chemical inormation between cells?

Purpose

To determine i one cell has an eect on the conditions in an adjacent cell. This is a

simple representation o cell-to-cell transer o inormation with diusion through two

cell membranes.

Materials

Oneeight-inchbyfour-inchplasticdisposablestorageboxwithalid(clearor

translucent without color)

Fourpiecesofone-inchbyeight-inchdialysistubingthathavebeensoaked

overnight

1percentstarchsolution

DilutedLugolssolution(4mlper200mlofdistilledwater)

Stringordialysistubingclamps

Distilledwater

Procedure

Clamportieoffoneendofeachofthedialysistubing.

Placeenoughdistilledwaterintheplasticstorageboxtocoverthebottom.

Filltwopiecesofthedialysistubingwith1percentstarchsolutionandseal

the open ends.


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SPECIAL FOCuS: Cell-to-Cell CommunicationCell Signaling

4

FilltheremainingtwopiecesofdialysistubingwiththedilutedLugols

solution and seal the open ends.

Placethecompletedtubingintotheplasticstoragebox,alternatingrst

with Lugols-lled tubing and then a starched-lled tube, then another

Lugols-lled tube, and nally the last starch-lled tube. The tubes should t

snugly into the box so the sides o the tubing are in complete contact.

Placethelidontheplasticstorageboxtohelpkeepthetubingmoist,justas

cells are moist at all times.

Makeobservationseveryveminutestoobserveanychangesinthetubes.

Are there any color changes?

Analysis

1) Explain why it was important to keep the system moist.

2) Were there color changes in any o the tubes? I so, what do these changes

indicate?

3) Compare and contrast the dialysis tubing bags in contact with each other to

cells that are in contact with each other.

4) The dialysis tubing bags serve as a model or a community o living cells.

In what ways is the model an accurate portrayal o cell systems and in what

ways is it fawed?

5) Describetwospecicexamplesofcell-to-cellcommunication,namingthe

type o cell and what chemical message is passed.

Lab Questions Answer Key

Question 1:

The system must be kept moist or the solutions to diuse across the dialysis tubing

(membranes) just as the cell membranes are moist or the same deusing actions to

take place.

Question 2:

The starch tube will initially appear clear to milky white, depending on the amount o

starch; the iodine tube will initially be copper colored. The starch tube will turn dark


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Introductory Lab: Cell-to-Cell

5

as the iodine diuses into it. The iodine tube will become lighter in color as the iodine

leaves.

Question 3:

The dialysis tubes lying side by side are similar to cell membranes because they are

moist and they allow small particles to diuse. They are dierent because the only

method o material passage is diusion.

Question 4:

Cell membranes have protein channels and allow materials to be moved by

endocytosis and exocytosis, and they are moist to allow or diusion. The dialysis

tubing is a model or the diusion portion o the cell activity, and it also demonstrates

the need or the system to be moist.

Question 5:

Examples include neurotransmitters in the synapse, antigens triggering antibody

response, target cells responding to specic hormones, and many others.


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Cell Linkages: Integrins

Elizabeth A. Cowles, Ph.D.

Eastern Connecticut State University

Willimantic, Connecticut

Introduction

Communication is the name o the game, especially in cells; specialized receptors

called integrins provide vital communication links between the interior and exterior

o the cell. Integrins are transmembrane proteins that act as mechanotransducers

and signal conductors, providing a physical link between the extracellular matrix

(ECM) and the cells cytoskeleton. Although integrins do not have intrinsic enzymatic

activity, they can interact with enzymes such as kinases that have specic signaling

unctions. Integrins are involved in many cellular processes, such as dierentiation,

migration, prolieration, ECM protein expression, activation o growth actors,

apoptosis, and cell survival. Interestingly, integrins work rom either direction: Theycan bind to extracellular ligands, thus triggering intracellular signal cascades, or they

can be activated by actors rom within the cell to infuence the relationship o the cell

with its environment.

Integrins are heterodimers, meaning that they are composed o two distinct

subunits termed and . Humans produce 18 dierent alpha chains (the larger

subunitweighing120180kDa)and8differentbetas(smallersubunitsweighing

90110kDa),whichcombinetoformdifferentintegrins.Sofar,24humanintegrins

have been identied, each named or their two-component subunits (21, or

example). Studies o invertebrate species such asDrosophila melanogasterandCaenorhabditis elegans have revealed the presence o integrins (though there are

ewer varieties), and the basic heterodimer structure is highly conserved among all

animals. Proteins very similar to integrins are ound in plants, ungi, or prokaryotes;

these proteins may be important in touch (thigmo) responses in these organisms


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(Jae et al. 2001), in gravity perception in plants (Katembe et al. 1997), and in the

binding o a pathogenic ungus to bronectin (Kottom et al. 2008).

Integrins typically span the cells plasma membrane with the N- or amino-

terminus o both subunits extending into the extracellular matrix, providing potential

ligand binding sites. The subunits interact with each other and exist in either a

low-anity or a high-anity conormation depending on external and internal signals

(Humphries and Liddington 2002). The integrins are normally bent in the low-anity

state, but open like a switchblade upon activation via phosphorylation o the

subunits cytoplasmic end.

FIguRE 1

A model o integrin activation. Schematic

representation o a heterodimeric integrin

molecule in the bent, inactive conormation

(let) and the upright, active conormation(right). The switch in conormation is

triggered by the binding o a protein, in this

case talin, to the small cytoplasmic domain

o the subunit. The binding o talin induces

a separation o the two subunits and

conversion to the active conormation.

Activated integrins typically become

clustered as the result o interactions o their

cytoplasmic domains with the underlying

cytoskeleton. The extracellular ligand, in this

case a collagen fber, binds between the two

subunits in the head region o the activated

integrin dimer.

Figures 14 rom Cell and Molecular Biology: Concepts and Experiments by Gerald Karp. New York: John Wiley & Sons, Inc.,

2007. Used with permission o John Wiley & Sons, Inc.

This physical change modulates both the integrins anity or its ligand and

also the stability o the attachment. The relatively small 4070 amino acid subunit

ends that extend into the cytoplasm allow interactions with intracellular proteins;

the 4 cytoplasmic tail is so long, it can even bind to intermediate laments in the

cytoskeleton.

Fibronectin, which has important cell migration and wound healing unctions,

provides a good example o extracellular protein interaction with integrins.

FibronectincontainsanRGDorarginineglycineaspartatesequence,whichis

recognized by the integrin 51. The integrin simultaneously interacts with talin,

which provides a physical link to actin laments, thus allowing cells to migrate along

the bronectin.


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FIguRE 2

Focal adhesions are sites where cells adhere to

their substratum. This drawing o a ocal

adhesion shows the interactions o integrin

molecules with other proteins on both sides o

the lipid bilayer. The binding o extracellularligands, such as collagen and fbronectin, is

thought to induce conormational changes in

the cytoplasmic domains o the integrins that

cause the integrins to become linked to actin

flaments in the cytoskeleton. Linkages with the

cytoskeleton are mediated by various actin-

binding proteins, such as talin and a-actinin, that

bind to the subunit o the integrin. The

cytoplasmic domains o integrins are also

associated with protein kinases, such as FAK

(ocal adhesion kianse) and Src. The attachment

o the integrin to an extracellular ligand can

activate these protein kinases and start a chain

reaction that transmits signals throughout the cell. The association o myosin molecules with the actin

flaments can generate traction orces that are transmitted to sites o cellsubstrate attachment.

OtherproteinscontainingtheRGDsequenceincludevitronectin,bone

sialoprotein, von Willebrand actor, brillin, brinogen, thrombospondin, PECAM

(platelet endothelial cell adhesion molecule), tenascin, and LAP-TGF (latency

associated peptide transorming growth actor-).TheRGDmotifisalsousedfor

interactions between ECM proteins and integrins v1 and 81.Otherintegrinsuse

adifferenttripeptidesequence,leucine-aspartate-valine(LDV),torecognizeandbind

proteins important or intercellular adhesion, such as VCAM (vascular cell adhesion

molecule), ICAM (intercellular adhesion molecule), actor X, mucosal adhesion cell

adhesion molecule (MadCAM), and E-cadherin. Integrins containing the 1 and 2

subunits have an A domain, similar to von Willebrand actor, a blood glycoprotein

important in clotting. These subunits combine with 1 to orm receptors or collagen,

thrombospondin, and laminin.

Integrins and Cellular Signaling

Inactive integrins are dispersed over the cell surace. Upon binding to ECM proteins,

integrins migrate within the cell membrane to cluster and orm ocal adhesion sites in

a process called activation.

These sites may then include interactions with several additional proteins such

as ocal adhesion kinase (FAK), paxillin, talin, and tensin (Tadokoro et al. 2003; Lo

2006). Integrin interactions between talin, vinculin, -actinin, and paxillin provide a

physical linkage between the ECM and the actin cytoskeleton; these links are critical


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or cell anchorage and migration. Phosphorylation o the tail, in the cytoplasm,

disrupts the talinintegrin interaction, thus permitting cell movement.

Integrin activation via external actors can set o a cascade o events; this

is called outside-in signaling. These interactions can involve several proteins, in

whichtheintegrinhasacriticalmediatingrole.Outside-insignalingcanresult

in modication o the cytoskeleton, cause cellular prolieration or migration, and

determinecellsurvivalorapoptosis.OneexampleistheMAPK/ERK(mitogen-

activated protein kinase or extracellular signal-related kinase) signal pathway, which

is turned on by integrin-extracellular ligand interactions.

FIguRE 3

This pathway controls gene

expression by increasing the

stability o c-jun and

increasing transcription o

the protein c-os. C-jun and

c-os combine to orm AP-1

(activating protein-1), which

bindstospecicDNA

promoters; thereore,

integrins can control gene

transcription via the MAPK/

ERK signaling kinases. In

particular, AP-1 induces

expression o integrin 21

and its ligand, collagen.

Another example o integrin-mediated control o transcription involves activation o

the 51 integrin, which increases ERK; this ultimately up-regulates the transcription

o the protein Bcl-2, which is an anti-apoptotic signal. High Bcl-2 levels prevent

apoptosis, or programmed cell death. Temporary loss o integrin-substrate contact is

necessary or migration; however, loss o adhesion may trigger apoptosis. This balance

between integrin binding and apoptosis prevents inappropriate cell migration andadhesion; this equilibrium is oten aberrant in cancer cells.

Signaling via integrins is not always outside-in, nor is it always unidirectional.


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FIguRE 4

Blood clots orm when platelets adhere to one

another through fbrinogen bridges that bind to

platelet integrins. The presence o synthetic RGD

peptides can inhibit blood clot ormation by

competing with fbrinogen molecules or theRGD-binding sites on platelet III3 integrins.

Nonpeptide RDG analogs and anti-integrin

antibodies can act in a similar way to prevent clot

ormation in high-risk patients.

Recent research has ocused on the

intracellular Rho amily o GTPases.

Rho coordinates cell unctions such

as cell adhesion, cell migration, gene

expression, and the cell cycle. Integrins

activated by extracellular actorsregulate Rho through the MAPK/ERK

pathway.

Rho, however, increases integrin

avidity (stickiness) and the numbers

o stress bers, which in turn regulates

the ormation o integrin ocal adhesion

sites (Schwartz and Shattil 2000; Lo

2006). Thereore, an internal molecule

like Rho can modulate integrinECMinteractions by changing the integrin

conormation to the active orm.

The inside-out signaling is exemplied by the blood clotting system. Platelets

have inactive integrins, which prevent inappropriate adhesion to vessel walls

(Horowitz1997).Damagetoendothelialcellsexposesthrombin,whichactivates

platelets that come in direct contact by causing their IIb3 integrin to become more

adhesive and to bind brinogen. Platelets bind to the thrombin without the assistance

o integrins; the thrombinplatelet interaction elicits intracellular signals, which

change integrin adhesiveness.


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FIguRE 5

FromBiology, by Robert J. Brooker, Eric P. Widmaier, Linda Graham, and Peter Stiling. New York: McGraw-Hill Science, 2007.

Used with permission o The McGraw-Hill Companies.

The now-activated integrins on the platelet suraces capture circulating

von Willebrand actor and brinogen, which orm the blood clot. Glanzmanns

thrombasthenia is caused by a mutation in either the IIb or 3 integrin genes; the

disorder is characterized by abnormal bruising and bleeding and is oten mistaken

or hemophilia. Antagonists (inhibitors) oIIb3 integrin, such as abciximab and

xemiloban, are used to reduce clot ormation in patients at high risk or stroke or

heart attacks.

Leukocytes inltrate damaged tissues, but only do so when their M2 or

L2 integrins are activated by cytokines via inside-out signaling (Horowitz 1997).

Cytokines are small, secreted proteins which regulate immunity and infammation.

The integrins mediate attachment to vascular endothelial ICAMs (intercellular

adhesion molecules), and then the leukocyte migrates between the endothelial cells.

Leukocyteadhesiondeciency(LAD),averyrarehumandisorderinwhichpatients

lack 2 or make deective 2, occurs when phagocytes cannot attach to endothelial

cells.LADpatientsoftensuccumbtobacterialinfectionsearlyinlife.


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Many integrin signaling events are coupled with growth actor responses; this is

because cellular responses, such as migration and mitosis, require integrin-substrate

interactions or anchorage (Giancotti and Ruoslahti 1999).

Forexample,theplatelet-derivedgrowthfactor(PDGF)receptorresponds

maximally only when V3isboundtotheECMandPDGFincreasestheamountof

V3intheplasmamembrane.ThissynergisticactivitybetweenthePDGFreceptor

and the integrin increases cell migration and wound healing. The interactions

between the growth actor and integrin signaling pathways ne-tune the cells

response to its external environment and allow or coordinated regulation.

Integrins in Health and Disease

Angiogenesis, or the production o new blood vessels, is critical not only during

development but also during oncogenesis or cancer development; tumors need a ready

blood supply or survival. V3 integrin attachment to the ECM is regulated by the

vascular endothelial growth actor (VEGF) receptor; impairing the VEGF receptor

integrininteractionreducesangiogenesis(Mahabeleshwaretal.2006).Drugsthat

interere with integrin unction during angiogenesis are in clinical trials; Vitaxin, an

anti-V3 antibody, shrinks tumors by decreasing blood vessels and Avastin, an anti-

VEGF monoclonal antibody, is used or treating colorectal cancers.

Researchers have noted that certain breast cancers metastasized to bone. It

appears that V3 expression is elevated in breast cancer tissue, and this integrin

recognizes bone sialoprotein, a major bone matrix constituent. Cancer cells migrating

rom breast tumors bind to bone tissue through V3 and become established (Sloan

et al. 2006). Scientists are investigating whether V3 antagonists could prevent

metastases (Zhao et al. 2007). Unpublished data rom Barbara Susinis laboratory

(UniversityofCalifornia,SanDiego)indicatethatan 41 antagonist inhibits lymph

node blood vessel development; because breast cancer spreads via the lymphatic

system, such an antagonist may prevent breast cancer metastases.

Viral and bacterial pathogens take ull advantage o integrins. Bacterial

pathogens use integrins to maintain contact and prevent removal rom the host, and

then gain entry (Scibelli et al. 2007). Binding allows the bacteria to be phagocytosed,

to inject virulence actors, or to adhere indirectly through bronectin. The 51

integrin that binds bronectin is recognized by Shigella; several Shigella protein

antigens mediate bacterial-directed endocytosis. Staphlococcus aureus and

Streptococcus spp. express bronectin-binding proteins, and indirectly attach to cells

through the ECM.


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Viruses also employ integrins to bind and gain entry into cells (Stewart and

Nemerow 2007). Adenovirus is recognized by the V integrin. The herpes virus outer

envelope glycoprotein has a sequence that mimics a metalloprotease; this glycoprotein

binds to 1 and V3 integrins. Hantaviruses, which directly aect platelet and

endothelial cell unctions, have IIb3 and V3 as receptors. Binding not only allows

the virus access to the cells synthetic machinery but also to its signaling pathways.

Novel vaccines, therapeutic strategies, and antiviral drugs may be based upon

integrin antagonists.

A new area o integrin research is in nanoscale technology and material science

(Stevens and George 2005). Implants oten ail because cells do not attach and

reproduce on the oreign surace. Titanium implants are commonly used in dental

and joint replacements, but do not readily support osteogenesis. Implants coated with

matricesofcalciumcarbonate(hydroxylapatite)andRGD-containingproteins,such

as bronectin, collagen or related peptides, bond bone-orming osteoblasts better than

uncoated material (Reyes et al. 2007). These coatings promoted 21 binding, which

triggered the expression o osteoblast-specic genes, which resulted in increased cell

dierentiation and bone production.

Integrins are involved in many cellular and organismal processes, including

tissue remodeling, immunology, and prolieration. These biological activities require

coordination between the internal and external cellular environments; integrins

provide some o the critical communication links. Insights into these ascinating cell

surace receptors will help us design new therapies or cancer, infammation, and

pathogen-related diseases.

Bibliography

Giancotti, F. G., and E. Ruoslahti. Integrin Signaling. Science 285 (1999): 10281032.

Horowitz, A. F. Integrins and Health. Scientic American, May 1997; 6875.

Humphries,M.J.,andR.C.Liddington.MolecularBasisofIntegrin-DependentCell

Adhesion in Protein-Protein Recognition, InFrontiers in Molecular Biology:

Protein-Protein Recognition, edited by C. Kleanthous, 102125. New York:

OxfordUniversityPress,2000.


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Hynes,R.O.Integrins:Bidirectional,AllostericSignalingMachines. Cell110 (2002):

673687.

Jae, M. J., A. C. Leopold, and R. C. Staples. Thigmo Responses in Plants and Fungi.

American Journal o Botany89 (2002): 375382.

Katembe, W. J., L. J. Swatzell, C. A. Markaro, and J. Z. Kiss. Immunolocalization o

Integrin-Like Proteins inArabidopsis and Char.Physiologia Plantarum 99(1)

(1997), 714.

Kottom, T. J., C. C. Kennedy, and A. H. Limper. Pneumocystis PCINT1, a Molecule

withIntegrin-LikeFeaturesThatMediatesOrganismAdhesionto

Fibronectin.Molecular Microbiology(online early articles) (2008), 67: 747761.

Lo, S. H. Focal Adhesions: Whats New Inside.Developmental Biology294 (2006):280291.

Mahabeleshwar,G.H.,W.Feng,D.R.Phillips,andT.V.Boyzova.IntegrinSignaling

Is Critical or Pathological Angiogenesis. Journal o Experimental Medicine.

203(11) (2006): 2,4952,507.

Reyes,C.D.,T.A.Petrie,K.L.Burns,Z.Schwartz,andA.J.Garcia.Biomolecular

SurfaceCoatingtoEnhanceOrthopaedicTissueHealingandIntegration.

Biomaterials 28(21) (2007): 3,2283,238.

Schwartz, M. A., and A. J. Shattil. Signaling Networks Linking Integrins and Rho

Family GTPases. Trends in Biochemical Sciences 25 (2000): 388391.

Scibelli,A.,S.Roperto,L.Manna,L.M.Pavone,S.Tafuri,R.D.Morte,andN.Staiano.

Engagement o Integrins as a Route o Invasion by Bacterial Pathogens.

Veterinary Journal173 (2007): 482491.

Sloan,E.K.,N.Pouliot,K.L.Stanley,J.Chia,J.M.Mosley,D.K.Hards,andR.L.

Anderson. Tumor-Specic Expression oV3 Integrin Promotes Spontaneous

Metastasis o Breast Cancer to Bone.Breast Cancer Research 8 (2006): R20.

Stevens, M. M., and J. H. George. Exploring and Engineering the Cell Surace

Interace. Science 310 (2005): 11351138.


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Stewart, P. L., and G. R. Nemerow. Cell Integrins: Commonly Used Receptors or Viral

Pathogens. Trends in Microbiology15(11) (2007): 500507.

Tadokoro, S., S. J. Shattil, K. Eto, V. Tai, R. C. Liddington, J. M. de Pereda, M. H.

Ginsberg,andD.A.Calderwood.TalinBindingtoIntegrin Tails: A FinalCommon Step in Integrin Activation. Science 302 (2003): 103106.

Zhao,Y.,R.Bachelier,I.Treil leux,P.Pujuquet,O.Peyuchaud,R.Baron,P.Clment-

Lacroix,andP.Clzardin.TumorV3 Integrin is a Therapeutic Target or

Breast Cancer Metastases. Cancer Research 67(12) (2007): 5,8215,830.


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IntegrinDenitions

Adenovirus:Double-strandedDNAvirus;causesrespiratorytractinfections.

-actinin: Actin-crosslinking protein; ound in the cytoskeleton.

AP-1: Activator protein-1 transcription actor; dimeric complex o c-jun and c-os.

BindstoTPA(phorbolester)responsiveelementinDNA.

Bcl-2: Protein ound in mitochondrial, endoplasmic reticulum, and nuclear envelope

membranes. Helps protect cell rom apoptosis by inhibiting caspase (protease) activity.

Bone sialoprotein: Protein ound in mineralized tissue; may help in ormation o

hydroxylapatite.

c-os: Cellular proto-oncogene protein product oc-os gene; protein is produced

rapidly ater growth actor stimulation. Phosphorylation by MAPK stabilizes c-os.

c-jun: Cellular proto-oncogene protein product oc-jun gene; orms AP-1 with c-os.

c-src: Cellular proto-oncogene protein product oc-src gene; is a tyrosine kinase

important in transmitting integrin signals; these kinases phosphorylate tyrosine

residues. Protein is associated with cytoplasmic ace o plasma membrane. The src

amily o kinases includes Src, Lck, Hck, Fyn, Blk, Lyn, Fgr, Yes, and Yrk.

Cytokine: Small secreted proteins; important in mediating immune system and

infammation.

E-cadherin: Transmembrane protein used in epithelial cellcell adhesion. Found near

ocal adhesion sites.

Factor X: Thrombokinase; important in clotting (coagulation) cascade. Requires

vitamin K or synthesis.

FAK: Focal adhesion kinase; a protein tyrosine kinase. Localized at ocal adhesion

sites by C-terminal region; associates with and is phosphorylated by c-src.


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Fibrillin: ECM glycoprotein ound in microbrils; important in tissue elasticity.

Fibrinogen: Blood glycoprotein which is cleaved by thrombin to orm brin, which is

ound in blood clots.

Fibronectin: ECM glycoprotein; important in cell migration and wound healing.

Hantavirus: Negative-sense, single-stranded RNA virus in Bunyaviridae amily;

causes inectious respiratory disease.

Herpesvirus:Double-strandedDNAvirus(Herpesviridae);includesoralandgenital

herpes, and Epstein-Barr virus.

ICAM: Intercellular adhesion molecule with structure similar to immunoglobulins

(immunoglobulin super amily); dierent orms are tissue related.

Laminin: Basement membrane glycoprotein, which is a heterotrimer o-,

-, and

-polypeptides; orms a meshlike network.

LAP-TGF: Amino terminal latency associated protein (LAP) used with cytokine

transorming growth actor ; is secreted into ECM.

LDV region: Leucineaspartatevaline sequence ound in integrin ligands such as

VCAM.

MadCAM: Cell adhesion molecule ound in mucosal cells.

MAPK/ERK: Mitogen-activated protein kinase/extracellular signal-regulated kinase;

a amily o serine/threonine kinases, which are phosphorylated by other kinases or

ull activity. Important in gene transcription and regulation. Related proteins include

SAPK, JNK, and p38 MAPK.

Paxillin: Protein (signal transduction adaptor) that localizes to ocal adhesion sites.

Paxillin phosphorylation controls cell migration.

PDGF:Platelet-derivedgrowthfactor;adimericprotein.PDGFreceptoristyrosine

kinase.PDGFregulatescellgrowth,especiallyangiogenesis.

PECAM: Platelet/endothelial cell adhesion molecule; aids in leuckocyte migration

through endothelial cell intercellular junctions.

PKA: Protein kinase A or cyclic AMP-dependent protein kinase; is a serine/threonine

kinase. PKA activity is high when cAMP levels are high. Important in glycogen and

lipid metabolism.


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Rho: Family o GTP-binding proteins (GTPases); members include Rho, Rac, and

Cdc42. GTP-bound Rho regulated cell prolieration, actin polymerization, and

intercellular adhesion.

Shigella: Gram-negative, rod-shaped bacteria. Agent o shigellosis and dysentery,which are intestinal inections.

Staphlococcus aureus: Gram-positive, spherical bacteria that is ound on skin.

Agent o pneumonia, toxic-shock syndrome, impetigo, and septicemia.

Streptococcus: Gram-positive, spherical bacteria. Agent o strep throat, scarlet ever,

and rheumatic ever.

Talin: Protein ound in ocal adhesion sites; helps anchor actin to integrins and

activates integrin IIb3. Contains binding sites or vinculin.

Tenascin: ECM glycoprotein; ound in areas o cell prolieration and cell migration.

Tenascin levels are increased by TGF-.

Tensin: Actin-binding protein present in ocal adhesion sites.

Thrombospondin: Family o secreted glycoproteins. Thrombospondin-1 inhibits

angiogenesis.

VCAM: Vascular adhesion molecule; member o immunoglobulin super amily.

Mediates leukocyte-endothelial cell adhesion. Expressed on endothelial cells ater

cytokine stimulation.

VEGF: Vascular endothelial growth actor/vascular permeability actor; increases

endothelial cell prolieration and promotes angiogenesis.

Vinculin: Focal adhesion protein that binds to talin or -actinin.

Vitronectin: Also called S-protein; ound in ECM and blood. Interacts with collagen

and important in blood clotting.

Von Willebrand actor: Blood glycoprotein used in blood coagulation; binds to

platelets and to collagen.


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AP Biology Free-Response Questions

and Scoring Rubrics

Jlia Eichman


Joplin, Missouri

Question Topic: Plant Reproduction1985 Exam

Question

Seeds that are randomly positioned when planted in a pot o soil placed on a

windowsill produce seedlings with downward growing roots and upward growing

shoots.Aboveground,theshootsareorientedtowardlight.Describethephysiological

mechanisms that occur to produce:

a) the downward growth o the roots

b) the upward growth o the shoots

c) the bending o the shoots toward light

Readers Scoring Rubric

Standards: Not More Than 15 Total Points Were Given.

One Point or Each o the Following:

The hormone involved is auxin.

In vertical roots or stems, auxin is uniormly distributed.

In horizontally placed roots, auxin accumulates on the lower side.

The accumulation o auxin on the lower side in roots inhibits cell elongation

in the area.

In horizontally placed stems, auxin accumulates on the lower side.

Accumulation o auxin in stems is stimulatory.


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In a laterally illuminated stem, auxin accumulated on the shady side.

There is lateral transport o auxin rom the sunny to the shady side, or rom

top to bottom in horizontally placed stems and roots.

Two Points or Each o the Following:

Auxin is produced in the stem apex.

Auxin causes cell elongation in stems.

The optimum or root growth is an amount much less than or stem growth.

In high concentration, auxin is inhibitory in both stems and roots.

Lateral movement o auxin requires energy.

Auxin movement is too ast to be explained by diusion.

The perception o auxin in stem tips is light promoted (carotenes or

favenes).

Discussionoftheperceptionofgravity.

Evidence that the site o perception is the tip.

Five Points or the Following:

The downward growth o roots: The geotropic response o the root is dependent on the

production o a growth inhibitor or inhibitors produced in the root cap. The inhibitor(s)

move rom the cap through the apex to the elongating cells. I the root is horizontal, a

large part o the substance is transported laterally to the lower side. The dierence in

concentration produces unequal growth. [T]he lower side is more inhibited and the

root thereore turns down.

Question Topic: Plant Reproduction1984 Exam

Question

Denethefollowingplantresponsesandexplainthemechanismofcontrolforeach.

Cite experimental evidence as part o your discussion.

a) Phototropism

b) Photoperiodism


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AP Biology Free-Response Questions and Scoring Rubrics


Standards:

Phototropism:

Max. = 9 points i experimental evidence is given

Max. = 7 points i experimental evidence is lacking

Denition:Movementinresponsetolight(involvinggrowth)2points

Possibility o negative response

Mechanism

Auxins

Distribution(apex->stemorlateral)

Elongation o cells

Stem tip or coleoptile

Evidence (2 points or any o the ollowing)

Darwincoveredcoleoptiles

Paal cut coleoptiles agar, uneven placement

Boysen-Jensen mica

Went bioassay

Photoperiodism

Max. = 9 points i experimental evidence is given

Max. = 7 points i experimental evidence is lacking

Denitionresponsetolight/darkperiods

Flowering (or other response)

Mechanism

Categoriesofplants(LDP,SDP)

Receptor in lea

LDP(ifnightshorterthanminimum)

SDP(ifnightlongerthanminimum)

Night not day

Existence o phytochrome in two orms

PFR/PR interconvertible

PFR active orm

Ratio (PR/PFR) important

Possible hormonal involvement


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Evidence

Light fash in dark

Grating

Ratio o PR/PFR

Question Topic: Reproduction1985 Exam

Question

Describethestructureofabeanseedanddiscussitsgerminationtotheseedling

stage. Include in your essay hormonal controls, structural changes, and tissue

dierentiation.

Readers Scoring RubricStandards:

Structure: Max. = 8 points

Seed coat (protection)

Embryo (new plant)

Cotyledons (store ood)

Epicotyl (new shoot)

Hypocotyl (new stem/root)

Radicle (1st root)

Plumule (1st leaves) Hilum scar (attachment)

Micropyle (pollen tube entry)

Germination Discussion: Max. = 12 points

Imbibition o water (increases metabolism)

Correct temperature (enzymes)

Oxygen(forrespiration)

Radicle emerges rst (establishes root)

Subsequent shoot (photosynthesis when stored ood gone) Formation o hook/arch (pulls epicotyl)

Epigeal germination

a. Hormonal Control

Auxin in geotropism (+ or -)


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More auxin, lower 1/2 axis

Stem/root aected dierently

Gibberellins stimulate length growth

Cytokinins stimulate cell division

Abscisic acid inhibits root cell elongation

b. Structural Changes (Note: Some germination discussion is structural

change.)

Formation o root cap

Droppingspentcotyledons

Change, dark-to-light growth

Branch root production

Lea primordia

Two dierent oliage leaves

c. Tissue dierentiation

Cell division, elongation, maturation

Xylem, phloem (elaboration)

Apical meristem

Protoderm, ground meristem, procambium

Several vascular strands, stem; one, roots

Collenchyma, sclerenchyma

Mesophyll, epidermis, guard cells

Endodermis pericycle

Root hair ormation

Question Topic: Flight or Flight Response1992 Exam

Question

Survival depends on the ability o an organism to respond to changes in its

environment. Some plants fower in response to changes in day length. Some

mammals may run or ght when rightened. For both o these examples, describe the

physiological mechanisms involved in the response.


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Adaptive

Turn on needed systems/turn o those not needed; understanding o acute versus

chronic response, above and beyond statements in the question.

Mechanism

Descriptionofnervepathway(sensoryassociativemotor)

Sympathetic nervous system (autonomic) activation

Sympathetic system innervates adrenal medulla

Inhibition o parasympathetic by sympathetic

Parasympathetic counters sympathetic, return to normal homeostasis;

acetylcholine = neurotransmitter

Epinephrine adrenalin (cause and eect)

Norepinephrine noradrenalin (cause and eect)

Source adrenalin rom adrenal medulla (gland)

Source noradrenalin rom adrenal medulla and/or sympathetic nerve

endings

Receptor molecules on cell membranes

Use o cAMP (second messenger) to elicit intracellular response

Brie versus sustained contrasted (initial = sympathetic versus long =

adrenal)

Chemical structure o adrenalin/noradrenalin

Eect: Max. = 7 points

a. target tissues and eects (2 points)

b. pupillary muscles o eye dilates pupils

c. inhibits salivation

d. bronchi o lungs relaxes

e. increases respiratory rate

. heart muscle accelerates pulse, strengthens contraction

g. piloerection muscles attached to hair ollicles

h. liver breaks down glycogen, stimulates release o glucose

i. digestive tract decreases digestive activities peristalsis

j. stomach, small intestine, pancreas inhibits secretion o digestive

enzymes

k. stimulates release o atty acids rom at cells


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l. peripheral circulation vessels constrict

m. inhibit sex structures

n. relax bladder/bowels

o. decreased sensation o pain

p. superhuman

Question Topic: Biological Recognition1992 Exam

Question

Biological recognition is important in many processes at the molecular, cellular, and

organismal levels. Select three o the ollowing, and or each o the three that you have

chosen, explain how the process o recognition occurs and give an example.

a. Organismsrecognizeothersasmembersoftheirownspecies.

b. Neurotransmitters are recognized in the synapse.

c. Antigens trigger antibody responses.

d. Nucleic acids are complementary.

e. Target cells respond to specic hormones.


Standards:

Four points maximum or each o the ollowing

a. Organisms recognize others as members o their own species.

Denition(1point)

Importanceofspeciesrecognition/denitionofspecies/reproductive

isolation prezygotic (3 points)

Mechanisms(2points)

Visual/auditory/chemical/tactile/(multiple/ritual/behavioral)

Recognitionisinnateorlearned(imprinting)(1point)

Example (1 point)

Visualbirds, ruit fies

Auditorybirds, whales, rogs, insects

Chemicalmoths, voles

Tactileruit fies, octopods

Multiplealbatross, butterfies, ruit fies, people, dove

Imprintingducks, goats


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b. Neurotransmitters are recognized in the synapse.

Denition(1point)

Neurotransmitter is a chemical messenger

Synapse denition

Mechanisms(1pointeach)

Neurotransmitter binds to receptor on postsynaptic membrane

Receptor is a protein

Lock and Key Concept (3 points)

Enzymatic recognition and degradation o Neurotransmitter

Reabsorption o Neurotransmitter by presynaptic membrane

Presynaptic/Postsynaptic Events (1 point or any one)

Stimulus(impulse,depolarization,signal,actionpotential)travelsfrom

presynaptic membrane (axon terminus, synaptic knob)

Membrane channels opened (calcium channels, ion channels, calcium

goes in)

Neurotransmitter released rom presynaptic neuron (synaptic vesicle)

Neurotransmitter diuses across synapse/synaptic clet

Neurotransmitter binding alters permeability

Depolarizesand/orhyperpolarizespostsynapticmembrane(creates

EPSP [excitatory postsynaptic potential]/creates IPSP [inhibitory

postsynaptic potential])

Change membrane potential (toward or away rom threshold)

Openingionchannels

Alter metabolism inside postsynaptic cell (2nd messenger, cAMP)

Reversible binding o Neurotransmitter

Examples(1point)

Acetylcholine (ACh)Synapse Types

GABAAcetylcholinesterase (AChE)

NorepinephrineCatecholamines, L-dopa

DopamineandSerotoninBiogenicAmines Endorphins/EnkephalinsNeuropeptides

c. Antigens trigger antibody response

Denitions(1pointforeither)

Antigen (Ag)oreign substance/nonsel


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Antibody (Ab)deensive protein produced in response to Ag

structure (two heavy and two light polypeptide chains)

Processes (1 point or each)

Selection o B cell highly specic B cell surace Ab binds Ag to activate B cellplasma cell and memory

cell clones

Secondary response description

Ag-Ab complexamino acid sequence o light and heavy chains o

hypervariable regions at N-terminus

Specic site o Ag binding with Ab (Ab binding with Ag)

Receptors on B cells and capping

Free Ag with Ab

T-cell dependent activation o B cellsMacrophage (Ag presenting cell)

activates Interleukins to activate Helper T cells and B cells

Generation o Ab diversity

Examples o Antigens or Resultant Antibodies (1 point)

IgG,IgM,IgA,IgD,IgE

Bacterial cells, viruses, ungi, protozoa, allergens (pollen, dust, dander),

grats

(HLA), Heterologous Ag (RBCs), Sel Antigens

d. Nucleic acids are complementary.

Denitions(1point)

DNAandRNAarenucleicacids

Nucleic acids are polymers o nucleotides

Nucleotide = sugar (deoxyribose and ribose), phosphate, nitrogenous

base

Mechanisms(1pointforeach)

A with T or U, C with G or Chargas Rules

PyrimidinewithPurineorSingleringwithDoublering

2 Hydrogen Bonds with A+T/U and 3 Hydrogen Bonds with G+C or Hbonds

Antiparallel orientation 5'---3'/3'---5'

Template requirement or semiconservative replication mechanism

Primers


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DNA/RNApolymeraserequirements

Elongation/Initiation Factors

DivalentCations

Examples(1point) ReplicationofDNA(2strandsofdsDNAarecomplementary)

TranscriptionofDNAintomRNA,tRNA,rRNA

Translation - mRNA-tRNA (codon/anticodon complementarity)

Hybridization-DNA-DNA/DNA-RNA/Probes

e. Target cells respond to specic hormones.

Denition(1pointforeach)

Hormonechemical messenger released to travel to cause specic

biological response within organism, eective at low concentration

Protein hormone/receptor at cell surace (doesnt get in)

Steroid hormone/receptor inside cell (does get in)

Recognition o hormone is to specic receptor (specic proteins)

Protein hormone involves second messenger (cAMP, etc.)

Steroid hormone aects transcription

Examples(1pointeach)

Any hormone/target or eect (no pheromones, allomones, attractants)

Question Topic: Membranes1993 Exam

Question

Membranes are important structural eatures o cells.

(a)Describehowmembranestructureisrelatedtothetransportofmaterials

across a membrane.

(b)DescribetheroleofmembranesinthesynthesisofATPineitherrespiration

or photosynthesis.


Membranesservediversefunctionsineukaryoticandprokaryoticcells.Oneimportant

role is to regulate the movement o materials into and out o cells. The phospholipid

bilayer structure (fuid mosaic model) with specic membrane proteins accounts

or the selective permeability o the membrane and passive and active transport


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mechanisms. In addition, membranes in prokaryotes and in the mitochondria and

chloroplasts o eukaryotes acilitate the synthesis o ATP through chemiosmosis.

Part A. (6 Maximum)

Membrane Structure (3 Internal Maximum) Phospholipidstructurehydrophilic,hydrophobic,amphipathic

Phospholipidbilayer/uidmosaicdescription

Proteinsembeddedinthemembrane

Sterolsembeddedinthemembrane

Well-labeleddiagrammayreplaceoneoftheabove.

Membrane Transport (3 Internal Maximum)

Useofthetermselectivelypermeable,agooddenitionofselective

permeability, or an explanation o the role o phospholipids or proteins,

including nuclear pore proteins, in determining selective permeability.

Descriptionoftheeffectofsize,charge,polarity,lipidsolubilityon

membrane permeability.

Mechanisms + Description Related to Structure:

Passivetransport:diffusion/osmosis+referencetomembranegradient

Ionchannel:transportasamechanismforachangeinpermeability

Facilitateddiffusion:description(symport,antiport,uniport)

Activetransport:description

Exocytosis,endocytosis,phagocytosis,pinocytosis:description

(1 additional point) A good example o one o the above mechanisms

PART B. Role o the Membrane in the Production o ATP in Photosynthesis or

Respiration (6 Maximum)

Chemiosmosis:

Involvedmoleculesareembeddedinthemembrane.

Electroncarriersaresequentiallyorganized.

Theenergycomesfromtheowofelectrons.

H+/Proton/pHgradientestablished

Movement through the membrane generates ATP.

A specic protein makes ATP.


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RESPIRATIONor

Site is the mitochondrion

Inner mitochondrial membrane

(cristae) are involved in

ejkaryotes

Folded membrane present

Cell membrane is involved in

membranes prokaryotes

Correct direction o H+ fow

PHOTOSYNTHESIS

Site is the chloroplast

Thylakoid/grana are involved in

eukaryotes

Folded membrane present

Thylakoid/grana involved in

prokaryotes

Correct direction o H+ fow

Question Topic: Cellular Communication1999 Exam

Question

Communication occurs among the cells in a multicellular organism. Choose THREE o

the ollowing examples o cell-to-cell communication, and or each example, describe

the communication that occurs and the types o responses that result rom this

communication.

Communicationbetweentwoplantcells

Communicationbetweentwoimmune-systemcells

Communicationeither between a neuron and another neuron or between a

neuron and a muscle cell

Communicationbetweenaspecicendocrine-glandcellanditstargetcell


Overviewofpointdistribution:

Communication between two plant cells (Max. = 4 points)

Source(Max.=1point)

Hormone-producing cell (generic)

Plasmodesmata (elab. pt. or good description)

Signal(Max.=1point)

A specic plant hormone

Responses/Elab.(Max.=2points)

Various physiological changes

Ion movement; H20 movement; RNA movement


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Communication between two immune system cells (Max. = 4 points)

Source(Max.=1point)

Any two immune system cells interacting or

An immune system cell interacting with the product o another immunesystem cell

Signal(Max.=1point)

Tc/APC docking

Antibody

Histamine

Intereron

Responses/Elaboration(Max.=2points)

Dischargeofperform;phagocytosisofpathogen;inammatory

response; phagocyte activation; Ab secretion; clonal selection

Communication between two neurons or between a neuron and a muscle cell

(Max. = 4 points)

Source(Max.=1point)

Sending neuron

Signal(Max.=1point)

Neurotransmitter


Neuron-neuron: Chemical gating; depolarization o postsynaptic

membrane; EPSP, IPSP, or both

Neuron-muscle: Action potential to T tubules; Ca ++ release rom

sarcoplasmic reticulum; Ca ++ binding to troponin; cross-bridge

ormation

Communication between a specic endocrine-gland cell and its target cell

(Max. = 4 points)

Source(Max.=1point)

Specic gland (elaboration point or peptide vs. steroid hormone

pathways)

Signal(Max.=1point)

Specic hormone


Specic eect


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Question Topic: Proteins2001 Exam

Question

Proteinslarge complex moleculesare major building blocks o all living organisms.

Discussthefollowinginrelationtoproteins.

a. The chemical composition and levels o structure o proteins

b. TherolesofDNAandRNAinproteinsynthesis

c. The roles o proteins in membrane structure and transport o molecules

across the membrane


a. Chemical composition (Max. = 2 points)

Amino acids are the basic building blocks o proteins (Max. = 1 point)

Amino acids contain amino, carboxyl, and R groups or correct structural

ormula showing amino, carboxyl, and R group attached to central carbon or

proteins are composed o carbon, hydrogen, oxygen, and nitrogen

(Max. = 1 point)

R group determines the identity/properties o the amino acid

(Max. = 1 point)

Elaboration (Max. = 1 point)

Describeadditionoflipids,carbohydrates,and/orprostheticgroup

Levels o structure (Max. = 3 points)

(Note: To obtain any points, response must name level or list in correct order.)

Primary structure (Max. = 1 point)

sequence(chain,string)ofaminoacidsorthenumberandorderofamino

acids

aminoacidslinkedbypeptidebonds

aminoacidsbondedthroughdehydrationsynthesis

Secondary structure (Max. = 1 point)

helixand/orpleatedsheet

hydrogenbonds(betweencarboxylandaminogroups)


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Tertiary structure (Max. = 1 point)

singlepolypeptidechainformsglobularshape

hydrogen,ionic,disulde,andvanderWaalsbonds,and/orhydrophobic

interactions (i hydrogen must have more than one) interactionbetweenRgroups

Quaternary structure (Max. = 1 point)

morethanonepolypeptideorsubunit

hydrogen,ionic,disulde,andvanderWaalsbonds,and/orhydrophobic

interactions (i hydrogen must have more than one)

interactionbetweenRgroups


explanationofdomains

explanationofchaperones

(b) Global understanding o inormation fow (Max. = 1 point)

InformationinDNAistranscribedtomRNA,whichistranslatedinto

protein.

DNAcontainstheinformationthatultimatelydeterminesthesequence

o amino acids in the protein.

Roles

DNA(Max.=1point)

codesforRNA,mRNA,tRNA,orrRNA

mRNA (Max. = 1 point)

codesforaminoacidsequence

tRNA (Max. = 1 point)

bringsthecorrectaminoacidtotheribosome/mRNA

containsanticodoncomplementarytocodon

rRNA (Max. = 1 point)

formspartofribosome


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intronremovalbyRNA/snRNP/snRNA

alternativesplicingprovidesproteindiversity

actsasribozyme/involvedinformationofpeptidebond rRNAndsandbindsstartAUGofmRNA(inprokaryotes)

(c)Role in membrane structure (Max. = 2 points)

Descriptionofintegraland/orperipheralproteins

Membrane synthesis

Denesmembranesidedness

Membrane unction other than transport (Max. = 1 point)

Receptors

Enzymes

Cell-to-cellcommunication

Anchoringofcytoskeletonorextracellularmatrix

Spatialcongurationofreactionpathways(e.g.,electrontransportsystem)

Cellrecognition

Celljunctions

Role in transport (Max. = 3 points)

transportproteinsmaybespecic

processmayrequiredirectinputofenergy(e.g.,useofATP)

descriptionoftransportmechanisms(bindmolecule,conformational

change, release molecule) or description o how proteins orm channels and

move molecules through them


descriptionofaspecictransportsystem(e.g.,ATPsynthase,Na~/K~

pump, receptor-mediated endocytosis)

descriptionofchemiosmosis

morethanonemoleculetransported(e.g.,symport,antiport)

mayberegulatedbyelectricalorchemicalstimuli(gatedchannels)


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Question Topic: Immune Systems2005 Exam

Question

An important deense against diseases in vertebrate animals is the ability to

eliminate, inactivate, or destroy oreign substances and organisms.

Explain how the immune system achieves THREE o the ollowing:

Providesanimmediatenonspecicimmuneresponse

ActivatesTandBcellsinresponsetoaninfection

Respondstoalaterexposuretothesameinfectiousagent

Distinguishesselffromnonself


NOTE:Onepointisawardedforeachbulleteditem;maximumof4pointsforeach

section.

Provides an immediate nonspecic immune response (Max. = 4 points)

Physicalbarrier(e.g.,skinormucousmembranes[orbloodclot])with

explanation that barrier prevents pathogens and parasites rom entering the

body. Resident microfora prevents pathogen attachment. Saliva, mucus, or

tears wash away harmul entities; also, vomiting/diarrhea purge harmul

agents.

Chemicalbarriers(lowpH,salt,fattyacidsofskininhibitmicrobialgrowth,antimicrobial agents [e.g., lysozyme kills bacteria by digesting bacterial

wall]).

Inammatoryresponse:Bloodvesselsdilate(precapillaryarteriolesdilate

and postcapillary venules constrict), producing redness, edema, heat (ever),

pain, and leading to an increase in white blood cells and clotting actors.

Chemicalagents:

i. Intererons rom cells inected with viruses stimulate nearby cells to

producechemicalsthatinhibitviralreproduction,ORchemokines

activate monocytes to develop into macrophages.ii. Histamines cause increase in permeability o capillaries with an

increased blood fow that results in more clotting and more white blood

cells,ORhistaminessecretedbymastcells,ORprostaglandinsincrease

blood fow.


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iii. Pyrogens induce ever that inhibits pathogen.

Phagocytosis:ingestionbywhitebloodcells(e.g.,neutrophils,macrophages,

or monocytes)

Lysisofcells:Eosinophilsornaturalkillercells Complementsystem:leadstothelysisofmicrobes,oraidsinrecruitmentof

white blood cells

Elaborationofanyoneoftheabove(e.g.,asecondphysicalorchemical

barrier)

Activates T and B cells in response to an inection (primary immune response)

(Max. = 4 points)

Macrophages/whitebloodcellsengulfand/ordisplayantigens(maysay:

epitope) rom inection.

Antigen-presentingcellbindshelperTcellstoactivateorstimulatehelper

T cells.

Antigen-presentingcellactivatesorstimulatescytotoxicTcells.

AntigenbindingtoBcellactivatesBcell.

HelperTcellactivates/stimulatesBcelland/orcytotoxicTcell.

Interleukin1(frommacrophages)activateshelperTcells.

Interleukin2and/orcytokines(fromhelperTcells)activateBcellsor

cytotoxic T cells.

CD4onhelperTcellenhancesbindingofhelperTwithantigen-presenting

cell; leads to activated T cells.

CD8oncytotoxicTcellenhancesbindingandenhancesactivationof

cytotoxic T cell.

Elaborationpointforexplainingoneofthefollowing:

i. MHC in primary immune response.

ii. B (or plasma) cells produce/secrete antibody.

iii. Cytotoxic T cells destroy inected cells.

iv. Antibody mechanism o action (i.e., neutralization/agglutination/

precipitation).

Responds to a later exposure to the same inectious agent (secondary immune

response) (Max. = 4 points)

Mediatedbymemorycells(Tand/orB).

Memorycellsarespecicforthesameantigenencounteredpreviously.


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Memorycellsreceptors/antibodieshavegreaterafnityfortheantigen.

Productionofantibodies/responseisfasterand/ortoagreaterextent.

Originofmemorycells:

i. HelperTcell*MemoryHelperT~MemoryBandTcells

ii. Activated B cell * Memory B cell

iii. ActivatedCytotoxicTcell>MemoryTcell

Roleofmajorhistocompatibilitycomplex(MHC),cytokines,IL-I,orIL-2as

related to secondary immune response.

Memorycellsaremorenumerous(orantibodyconcentrationishigher).

Memorycellsarelonglived.

Elaborationofwhymeasles,mumps,orchickenpoxdonotrecur(vaccines),

or common cold/fu do recur.

Distinguishes sel rom nonsel (Max. = 4 points)

AllcellshaveuniqueIDtags(ags,markers,proteins,glycoproteins,MHC,

etc.).

Originofself-markersofMHCbymultiplealleles(polymorphicantigen

receptors).

Developmentalselectioninbonemarrowand/orthymuswhereantigen

receptors are tested (sel-antigen receptors are eliminated, or inactivated/

clonal selection).

Mechanismofrecognition(bindingelicitsimmuneresponse).

Illustrateself/nonselfincompatibilities(e.g.,autoimmunediseasesuchasMS, transplant incompatibility, blood types, and pathogens mimicking MHC

molecules, or cloaking with host cell membrane).

Elaborationof:

i. MHC (or human leukocyte antigens)

ii. DistinguishbetweenMHCIandII(e.g.,MHCIallnucleatedcells;

MHC JIdendritic cells, macrophages, B cells).


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Question Topic: Relationship o Structure to Function2006 Exam

Question

The relationship o structure to unction is one o the major themes in biology. For

three o the ollowing structure/unction pairs, describe the structure and then explain

how the unction is related to the structure.

a. Enzyme structure/catalysis

b. mRNA structure/protein synthesis

c. Cell membrane structure/signal transduction

d. Membrane protein structure/active transport or acilitated diusion


The relationship o structure to unction is one o the major themes in biology. For

three o the ollowing structure/unction pairs, describe the structure and then explain

how the unction is related to the structure.

a. Enzyme structure/catalysis (Max. = 4 points)

Description(2points)

3-Dshapethatresultsfromfoldingofpolypeptidechains

Foldingproducesapocketinwhichsubstratemaybind

Levelsofproteinstructure(primary,secondary,tertiary)

Explanation (2 points)

Complementary3-Dshapeofenzymeandsubstratearerequiredfor

proper interaction and catalysis in active sitereduction o activation

energy; induced t

Allostericmodulation,effectofpH,temperature(orotherenvironmental

actors) on enzyme shape

Elaborationpoints:competitive/noncompetitiveinhibitioneffecton

enzyme action; amino acid side groups in active site interact with

substrate to stress bonds in substrate and reduce activation energy o

reaction

b. mRNA structure/protein synthesis (Max. = 4 points)


LinearsequenceofRNAnucleotides

Details:5cap;poly-Atail;introns


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Descriptionoforiginand/orfateofmRNA(transcription,processing,and

translation)

FinedetailsofRNAnucleotidestructure

Explanation (2 points) ThelinearsequenceofRNAnucleotides,readascodons(threeatatime;

contiguous; nonoverlapping)

specifythesequenceofaminoacidsincorporatedinanewproteinbeing

constructed at a ribosome

startcodonand/orstopcodonroles

c. Cell membrane structure/signal transduction (Max. = 4 points)


Aphospholipidbilayerthatincorporatesmalleable(and,often,mobile)

integral or membrane-associated proteins

Membrane-embeddedreceptormoleculeswithtransmembranedomains

Explanation (2 points)

Receptorproteinsundergoshapechangeswhenproperstimulusis

presentsignal is communicated through membrane by allosteric shape

change.

Thealteredproteinsmaytheninuenceothercellulareventsorstates:

activation o G-proteins and/or tyrosine-kinase receptor protein auto-

and heterophosphorylations leading to cellular response.

Question Topic: Membranes2007 Exam

Question

Membranes are essential components o all cells.

a. Identiy THREE macromolecules that are components o the plasma

membrane in a eukaryotic cell and discuss the structure and unction o

each.b. Explain how membranes participate in THREE o the ollowing biological

processes:

Musclecontraction

Fertilizationofanegg


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ChemiosmoticproductionofATP

Intercellularsignaling


Membranes are essential components o all cells.

a. Identiy THREE macromolecules that are components o the plasma

membrane in a eukaryotic cell and discuss the structure and unction o

each. (Max. = 6 points; 1 point or each macromolecule + structure, 1 point

or each macromolecule + unction)

NOTE:Onlytherstthreemoleculesmentionedwillbescored.

Macromolecle Strctre

Fnction (mst match

selected macromolecle)

Phospholipids OR Lipid withphosphate

Glycerol,twofattyacids,and polar head group w/

phosphate

Amphipathic

Hydrophilicorpolar(head)

and hydrophobic or

nonpolar (tails)

Formsalipidbilayer

Selectivelypermeable Fluidity

Createscompartment!

separates cell rom

environment; barrier

Signals,inositolpathway

(1P3) diacylglycerol (IJAG)

Cholesterol Ringstructure

Steroid

Amphipathic

Embeddedinbilayer

Moderatesuidity

Stabilizesmembrane

ProteinsIntegral

Peripheral

Pump

Receptor

Transport

Recognition

Tight junction

Desmosomes

Gap junctions

IntegrinsEnzyme

Channel

General Structure Polypeptides;aminoacids

2,30,40structure

description

Specifc Structure

Integral,transmembrane,

embedded; orms a channel

Peripheral,onsurface

Structurettosubstrateor

ligand

Transport Enzyme,catalysis

Signaltransduction

Attachment:extracellular

matrix (ECM)

cytoskeleton

Recognition

Celljunction

GlycolipidGlycoprotein Carbohydrate(chains)linked

to lipid protein

Cellrecognition

Attachmenttoexternal

molecule or another cell


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b. Explain how membranes participate in THREE o the ollowing biological

processes: (Max. = 6 points; 2 points per section)

Muscle contraction

Motorneuronoraxonterminalreleasesneurotransmitteroracetylcholine

(ACh).

AChbindstoreceptors

Depolarization,orNa+movesinthroughmembranechannels,ormembrane

depolarizes

Actionpotentialpropagatesalongcellmembrane(sarcolemma)orTtubules

Depolarizationchangespermeabilityofsarcoplasmicreticulum(SR)orCa2~

released rom SR

Ca2+ active transport into SR (reuptake o Ca2~)

Repolarizationormaintenanceofmembranepotential(Na~/K+pump)

Smoothorcardiacmusclegapfunctionsdirectlytransfermembrane

potential between cells

Fertilization o an egg

Partoftheacrosomalreactionorspermacrosomereleaseshydrolytic

enzymes (by exocytosis)

Spermbindstoreceptorsonegg

Fusionofspermandeggplasmamembranes

Changeinmembraneelectricalchargeorfastblock(depolarization)to

prevent urther ertilization (polyspermy)

Corticalreactionorslowblockbyexocytosis(preventspolyspermy)or

hardening o membrane

Separationoffertilizationmembrane(envelope)

Fusionofeggandspermnuclearmembranesornuclei

Chemiosmotic production o ATP

Electrontransportchain(ETC)inmembranepumpsH+acrossmembrane

H+gradientestablishedacrossmembrane

H+movethroughATPsynthaseembeddedinmembranetoproduceATP

Membraneinfoldingincreasessurfacearea


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Intercellular signaling

Releaseofchemicalsignalsbyexocytosis

Receptorsinmembranebindligandsorchemicalsignalsorchemicalsignals

pass through the membrane (examples: neurotransmitters, hormones,pheromones)

Ligand-gatedionchannelsopening/closing

Cascadeofcellularevents,includingenzymaticreactionsandsecond

messengers (examples: G-proteins, cAMP, I P3, Ca2~)

Antibodiesactivateimmunefunction

Descriptionsofgapjunctions,plasmodesmata(communicatingjunctions)

Question Topic: Immune Systems2007 Exam

Question

The deenses o the human body to the entry and establishment o a pathogen

(disease-causing organism) can be divided into nonspecic responses and specic

responses.

a. Explain how three types o nonspecic deenses can prevent the entry and/

or establishment o a pathogen in a persons body.

b. Discusshowtheimmunesystemrespondstoaninitialpathogenic

exposure, and how this initial exposure can lead to a quicker responseollowing a second exposure to the same pathogen.

c. Explain the biological mechanisms that lead to the rejection o transplanted

organs.


The deenses o the human body to the entry and establishment o a pathogen

(disease-causing organism) can be divided into nonspecic responses and specic

responses.

a. Explain how three types o nonspecic deenses can prevent the entry and/

or establishment o a pathogen in a persons body.

One point or each o the ollowing explanations/identications:

Barrier (skin)

Traps (mucous membranes, cilia, hair, ear wax)


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Phagocytosis (white blood cells)

Elimination (coughing, sneezing, urination)

Unavorable pH (stomach acid, sweat, saliva, urine)

Unavorable environment (normal fora, atty acids, enzymes)

Cell destruction (complement, natural killer cells)

Intererence with viral replication (intereron)

Lysozyme action (tears, sweat)

Infammatory response (increase in body temperature, capillary

permeability, attraction o macrophages, histamine release, vasodilation)

b. Discuss how the immune system responds to an initial pathogenic

exposure, and how this initial exposure can lead to a quicker response

ollowing a second exposure to the same pathogen.


APCs (macrophages, dendritic cells, B cells) present antigen

B cells/plasma cells produce/secrete antibodies

Helper T cells activate B cells, cytotoxic T cells, and/or macrophages

Cytotoxic T cells cause cell death (apoptosis)

Ag presented on MI-IC

Explanation o how antibodies destroy the pathogen

Secretion o cytokines (or interleukins) to signal or activate

Memory cells produced in primary response speed up secondary

response

c. Explain the biological mechanisms that lead to the rejection o transplanted

organs.


Cell-mediatedresponseorexplanationofcytotoxicT,CD8,killerTcells,

or natural killer cells

Concept o nonsel (oreign) or MHC incompatibility

Explanation o the role o cell death or apoptosis or cell lysis

Note: To obtain a score o 10, the student must earn the memory cell point in part b.


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Additional Web Resources

Compiled by Carolyn Schofeld Bronston

http://bama.ua.edu/~hsmithso/class/bsc_495/signal/signal_web.html:Alistingof

many cell signaling links, including most o these below.

http://www.signaling-gateway.org/: From the Nature Publishing Group, the Signaling

Gateway links to the most recent articles about new signaling ndings.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellSignaling.html: From

John W. Kimballs online biology textbook, a short introduction to cell signaling.

http://www.biology.arizona.edu/Cell_BIO/problem_sets/signaling/Index.html:From

the University o Arizona, a 12-part Cell Signaling Problem Set that covers basic

signaling topics with multiple-choice questions and tutorials or students needing

more inormation.

http://www.celanphy.science.ru.nl/Bruce%20web/Flash%20Movies.htm: Twenty-one

dierent animated overviews o cell signaling, rom G proteins to cAMP to the eects

o toxins on some systems.

http://mama.uchsc.edu/vc/cancer/signal/p3.cm: Animation rom the Biology o

Cancer site, which shows how cell divison could be activated.

http://cgmp.blauplanet.com/transd.html: Several animations on general signal

transduction.

http://student.ccbcmd.edu/courses/bio141/lecguide/unit4/innate/lpssignal_ash.html:

Animation on signaling that produces proinfammatory cytokines.


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http://dkc.jhu.edu/~teal/gprotein.html:Twoanimationsshowingcomplexsignaling

cascades.

http://entochem.tamu.edu/G-Protein/index.html: Texas A&M Protein Hormone Signal

Transduction with sound eects.

http://www.grossmont.edu/cmilgrim/Bio220/Outline/ECB2Animations/16.3-cAMP_

signaling.mov: QuickTime movie about adenyl cyclase that shows signaling pathway.

http://edissertations.library.swmed.edu/pd/WableL123004/maps/calcium7.html: Web

site on calcium signaling, showing various cell organelles that play a part.

http://www.learner.org/channel/courses/biology/archive/animations/hires/a_

cancer1_h.html:Signaltransductionvideothatusesfallingdominostoillustratethe

multiplicative eect o signal cascades.

http://www.bio.davidson.edu/courses/Immunology/Flash/MAPK.html: Kinase

signal transduction with sound eects showing pinball animation and nal mRNA

transcription.

http://student.ccbcmd.edu/courses/bio141/lecguide/unit4/innate/lpssignal_ash.html:

GreatmoviefromDolanDNALearningCenter(ColdSpringHarbor)showingthe

complex signaling that occurs ater an injury. The site takes a tour into a cell and has

beautiul graphics.

http://www.cellsignallingbiology.org/: Source or a ew excellent PowerPoint slide

rames that outline the idea o cell signaling.

http://www.accessexcellence.org/RC/VL/GG/ecb/forms_of_cell_signaling.html:From

Access Excellence, a slide showing the our major types o signaling.

http://employees.csbsju.edu/hjakubowski/classes/ch331/signaltrans/olsignalkinases.

html: Slide showing ve major protein kinases.

http://www.sigmaaldrich.com/Area_of_Interest/Life_Science/PathFinder.html

http://www.genscript.com/phospho_specic_antibody.html?src=google&gclid=CKTa

w421yZACFRcdsgodaAIWYA


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Additional Web Resources

http://www.cellsignal.com/; http://www.biocarta.com/genes/CellSignaling.asp:

Companies selling research materials (Sigma, GenScript, Cell Signaling Technology,

and BioCarta) show diagrams o complicated signal transduction pathways.


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About the Editor

Julia Kay Christensen Eichman taught high school advanced and AP

Biology or 20 years and has been active in AP workshop presentations and

AP Biology Exam Readings. Presently she is a student at the University oArkansas,wheresheispursuingaPh.D.,andanadjunctfacultymemberat

Missouri Southern State University.

About the Authors

Elizabeth A. Cowles did two postdoctoral stints. The rst was in the

entomology department at the University o Caliornia, Riverside (19901994),

where she isolated and characterized the Bacillus thuringiensis (Bt) toxin

receptors rom insect midguts. The second was in the orthopedic surgery

department at the University o Connecticut Health Center, where sheresearched integrin unction and signaling in bone cells (19941997).

Liz has been at Eastern Connecticut State University since 1997. She teaches

reshman biology, entomology, and biochemistry. She is an AP Biology

consultant and has done workshops around New England and at Rice

University. Liz has been an AP Biology Reader, Table Leader, and Question

Leader or the AP Biology Exam.

Carolyn Schofeld Bronston has taught at Memorial High School in Spring

Branch, Texas, and Robert E. Lee High School in Tyler, Texas. Traveling as a

consultant or the College Board since 1979, she also reads the AP Exam each June,

authored the Teachers Guide AP Biology, created the AP Teachers Corner, is a

memberoftheBiologyDevelopmentCommittee,andservesastheCollegeBoards

AP Biology Advisor. She is a winner o the Presidential Award or Excellence, the

OutstandingBiologyTeacherAward(OBTA)forTexas,theTandyAward,andthe

Texas Excellence Award.


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Documents

AP Sf Bio Cell to Cell Communication