NVC Biol 120 11 Communication - Napa Valley College 120 Lectures/NVC... · 10/15/2011 1 Chapter 11 – Cell Communication Outline I. Cell Signaling II. Forms of cell signaling III

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Chapter 11 – Cell Communication Outline

I. Cell SignalingII. Forms of cell signalingIII. Quick review of cell membraneIV. Cell Surface Receptors

I. G-protein Coupled ReceptorsII. Tyrosine Kinase ReceptorsIII. Ligand-Gated Ion Channels

V. Intracellular ReceptorsI. Down regulationII. Apoptosis

Overview: Cellular Messaging

Cell-to-cell communication is essential for both multicellular and unicellular organisms

Biologists have discovered some universal mechanisms of cellular regulation

Cells most often communicate with each other via chemical signals

For example, the fight-or-flight response is triggered by a signaling molecule called epinephrine

© 2011 Pearson Education, Inc.

Figure 11.1

Evolution

Fossil record indicate that one celled bacteria were present on earth 3.5 billion years ago

But it took another 2.5 billions years for multicellular organisms to appear in the fossil record

What took so long for multicellular life to evolve?

Pathway similarities suggest that ancestral signaling molecules evolved in prokaryotes and were modified later in eukaryotes

The concentration of signaling molecules allows bacteria to sense local population density


Evolution of Signaling

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Local and Long-Distance Signaling

Cells in a multicellular organism communicate by chemical messengers

Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells

In local signaling, animal cells may communicate by direct contact, or cell-cell recognition


Figure 11.4 Plasma membranes

Gap junctionsbetween animal cells

Plasmodesmatabetween plant cells

(a) Cell junctions

(b) Cell-cell recognition

Local and Long-Distance Signaling

In many other cases, animal cells communicate using local regulators, messenger molecules that travel only short distances

In long-distance signaling, plants and animals use chemicals called hormones

The ability of a cell to respond to a signal depends on whether or not it has a receptor specific to that signal


Forms of Signaling

1. Gap Junctions2. Autocrine A cell secretes a molecule that binds back onto

its own receptor 3. Paracrine Local mediators

4. Synaptic – Nerve cell signal transmission Neurotransmitters, released into synaptic cleft

5. Endocrine Hormones, secreted into the bloodstream

Figure 11.5a

Local signaling

Target cell

Secretingcell

Secretoryvesicle

Local regulatordiffuses throughextracellular fluid.

(a) Paracrine signaling (b) Synaptic signaling

Electrical signalalong nerve celltriggers release ofneurotransmitter.

Neurotransmitterdiffuses across

synapse.

Target cellis stimulated.

Figure 11.5bLong-distance signaling

Endocrine cell Bloodvessel

Hormone travelsin bloodstream.

Target cellspecificallybinds hormone.

(c) Endocrine (hormonal) signaling

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The Three Stages of Cell Signaling

Earl W. Sutherland discovered how the hormone epinephrine acts on cells

Sutherland suggested that cells receiving signals went through three processes Reception Transduction Response

© 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc.

Animation: Overview of Cell Signaling Right-click slide / select “Play”

Figure 11.6-1

Plasma membraneEXTRACELLULARFLUID

CYTOPLASM

Reception

Receptor

Signalingmolecule

1

Figure 11.6-2


CYTOPLASM

Reception Transduction

Receptor

Signalingmolecule

Relay molecules in a signal transductionpathway

21

Figure 11.6-3


CYTOPLASM

Reception Transduction Response

Receptor

Signalingmolecule

Activationof cellularresponse

Relay molecules in a signal transductionpathway

321

Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell

Signal transduction usually involves multiple steps

Multistep pathways can amplify a signal: A few molecules can produce a large cellular response

Multistep pathways provide more opportunities for coordination and regulation of the cellular response


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Fig. 9.8.b

Signal Transduction Pathways

The molecules that relay a signal from receptor to response are mostly proteins

Like falling dominoes, the receptor activates another protein, which activates another, and so on, until the protein producing the response is activated

At each step, the signal is transduced into a different form, usually a shape change in a protein


Protein Phosphorylation

In many pathways, the signal is transmitted by a cascade of protein phosphorylations

Protein kinases transfer phosphates from ATP to protein, a process called phosphorylation


Protein phosphatases remove the phosphates from proteins, a process called dephosphorylation

This phosphorylation and dephosphorylationsystem acts as a molecular switch, turning activities on and off or up or down, as required


Protein Dephosphorylation

Receptor

Signaling molecule

Activated relaymolecule

Inactiveprotein kinase

1 Activeprotein kinase

1

Activeprotein kinase

2


3


2


3

Inactiveprotein

Activeprotein

Cellularresponse

ATPADP

ATPADP

ATPADP

PP

PP

PP

P

P

P

P i

P i

P i

Figure 11.10

Activated relaymolecule


1 Activeprotein kinase

1


2


3


2


3

Inactiveprotein

Activeprotein

ATPADP

ATPADP

ATPADP

PP

PP

PP

P

P

P i

P i

P i

P

Figure 11.10a

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Fig. 9.3

Copyright © 2009 Pearson Education, Inc.

Which type of ligand would bind to a receptor in the plasma membrane

1 2

50%50%1. Water soluble2. Lipid soluble

Copyright © 2009 Pearson Education, Inc.

The following can freely pass through a membrane:

1 2 3 4

25% 25%25%25%1. Ions2. Hydrophobic

molecules3. hydrophillic

molecules4. Ions and

hydrophilic molecules

Fig. 9.1

Reception: A signaling molecule binds to a receptor protein, causing it to change shape

The binding between a signal molecule (ligand) and receptor is highly specific

A shape change in a receptor is often the initial transduction of the signal

Most signal receptors are plasma membrane proteins


Receptors in the Plasma Membrane

Most water-soluble signal molecules bind to specific sites on receptor proteins that span the plasma membrane = cell surface receptors

There are three main types of membrane receptors G protein-coupled receptors Receptor tyrosine kinases Ion channel receptors


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G protein-coupled receptors (GPCRs) are the largest family of cell-surface receptors

A GPCR is a plasma membrane receptor that works with the help of a G protein


Receptors in the Plasma Membrane - GPCRs Figure 11.7a

G protein-coupled receptor

Signaling molecule binding site

Segment thatinteracts with G proteins

G-Coupled Receptor G Proteins

Trimeric GTP-binding protein = G Proteins

G Proteins are either in the active or inactive state

Active state has GTP bound

When the ligand binds the G-protein Coupled Receptor, this causes a change in shape, that activates the G Protein

This starts a chain of events that involve intracellular mediators = secondary messengers

Figure 11.7b

G protein-coupledreceptor

21

3 4

Plasmamembrane

G protein(inactive)

CYTOPLASM Enzyme

Activatedreceptor

Signalingmolecule

Inactiveenzyme

Activatedenzyme

Cellular response

GDPGTP

GDPGTP

GTP

P i

GDP

GDP

Trimeric G Proteins

G Proteins are composed of three proteins: α and β and γ subunits

When the G Protein is activated (GTP is bound) the α subunit (with GTP) goes one way and the β and γ go together another way.

β and γ are active when they are not attached to the α subunit

the α subunit has GTPase activity

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GTPase activity in G proteins

The G protein is active only when it has GTP bound to it.

The G protein has GTPase activity, which means it will automatically hydrolyze a phosphate and have GDP bound.

This way it inactivates itself automatically

This GTPase activity is enhanced by GTPase Activating Proteins (GAPs)

Fig. 9.11

GPCR video

http://youtu.be/V_0EcUr_txk

Small Molecules and Ions as Second Messengers

The extracellular signal molecule (ligand) that binds to the receptor is a pathway’s “first messenger”

Second messengers are small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion

Second messengers participate in pathways initiated by GPCRs and RTKs

Cyclic AMP and calcium ions are common second messengers


Cyclic AMP

• Cyclic AMP (cAMP) is one of the most widely used second messengers

• Adenylyl cyclase, an enzyme in the plasma membrane, converts ATP to cAMP in response to an extracellular signal


Figure 11.11a

Adenylyl cyclase

Pyrophosphate

ATP

P iP

cAMP

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Figure 11.11b

Phosphodiesterase

AMP

H2O

cAMP

H2O

Figure 11.12

G protein

First messenger(signaling moleculesuch as epinephrine)

G protein-coupledreceptor

Adenylylcyclase

Second messenger

Cellular responses

Proteinkinase A

GTP

ATPcAMP

cAMP Pathway

1. A ligand binds to the G-protein Coupled Receptor (GPCR).

2. The binding of the ligand (hormone) activates the GPCR.

3. The active GPCR is able to bind the G-protein

4. The G-protein ejects a GDP and accepts a GTP molecule. The G-protein is now active

5. The α subunit of the G-protein with the GTP disassociates from the β and γ subunits

6. The α subunit of the G-protein with the GTP goes to adenylyl cyclase and activates it

7. The active adenylyl cyclase transforms ATP into cAMP

8. cAMP activates a protein kinase A (PKA)9. cAMP is inactivated by phosphodiesterases10. The PKA phosphorylates proteins11. The phosphorylated proteins are now active

and can change the cell activity12. The g-protein with GTP bound will hydrolyze

the phosphate from GTP, now has GDP bound and is inactive. It will reform with the βand γ subunits and this inactivates them

Fig. 9.13 Fig. 9.16

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Figure 11.16Reception

Transduction

Response

Binding of epinephrine to G protein-coupled receptor (1 molecule)

Inactive G proteinActive G protein (102 molecules)

Inactive adenylyl cyclaseActive adenylyl cyclase (102)

ATPCyclic AMP (104)

Inactive protein kinase AActive protein kinase A (104)

Inactive phosphorylase kinaseActive phosphorylase kinase (105)

Inactive glycogen phosphorylaseActive glycogen phosphorylase (106)

GlycogenGlucose 1-phosphate

(108 molecules)

Gene transcription by cAMP

The cAMP pathway can also activate the transcription of specific genes

The protein kinase A (PKA) activated by cAMP can turn on transcription of DNA using a CRE-binding protein (cAMP response element)

Examples of Hormone induced responses mediated by cAMP

Target Tissue Hormone Major ResponseAdrenal Cortex ACTH Cortisol Secretion

Ovary LH Progesterone secretionMuscle Adrenaline Glycogen breakdownBone Parathyroid

hormone (PTH) Bone reabsorption

Heart Adrenaline Increase heart rateLiver Glucagon Glycogen breakdown

Kidney Vasopressin Water reabsorptionFat Adrenaline,

ACTH, glucagonTriglyceride breakdown © 2011 Pearson Education, Inc.

Animation: Signal Transduction Pathways Right-click slide / select “Play”

Calcium Ions and Inositol Triphosphate (IP3)

Calcium ions (Ca2+) act as a second messenger in many pathways

Calcium is an important second messenger because cells can regulate its concentration


Figure 11.13

Mitochondrion

EXTRACELLULARFLUID

Plasmamembrane

Ca2

pump

Nucleus

CYTOSOL

Ca2

pump

Ca2

pump

Endoplasmicreticulum(ER)

ATP

ATP

Low [Ca2 ]High [Ca2 ]Key

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A signal relayed by a signal transduction pathway may trigger an increase in calcium in the cytosol

Pathways leading to the release of calcium involve inositol triphosphate (IP3) and diacylglycerol (DAG) as additional second messengers


Calcium Ions IP3 and DAG IP3/DAG Pathway

Remember that the plasma membrane is a double layer of phospholipids. It is a mixture of different phospholipids.

One of the phospholipids in the membrane is PIP2in the membrane.

G protein

EXTRA-CELLULARFLUID

Signaling molecule(first messenger)

G protein-coupledreceptor Phospholipase C

DAG

PIP2

IP3 (second messenger)

IP3-gatedcalcium channel

Endoplasmicreticulum (ER)

CYTOSOL

Ca2

GTP

Figure 11.14-1

Figure 11.14-2

G protein

EXTRA-CELLULARFLUID



DAG

PIP2




CYTOSOL

Ca2

(secondmessenger)

Ca2

GTP

Figure 11.14-3

G protein

EXTRA-CELLULARFLUID



DAG

PIP2




CYTOSOL

Variousproteinsactivated

Cellularresponses

Ca2

(secondmessenger)

Ca2

GTP

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Fig. 9.14

Ca2+ Ca2+ Ca2+

Inactiveprotein

Activeprotein

Calmodulin

Calmodulin

a. b.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

IP3 and DAG Pathway

1. A ligand binds to the G-protein Coupled Receptor (GPCR).

2. The binding of the ligand (hormone) activates the GPCR.

3. The active GPCR is able to bind the G-protein

4. The G-protein ejects a GDP and accepts a GTP molecule. The G-protein is now active

5. The α subunit of the G-protein with the GTP disassociates from the β and γ subunits

6. The α subunit of the G-protein with the GTP bound goes to phospholipase C (PLC) and activates it

7. The active PLC splits the phospholipid PIP2into two parts: IP3 and DAG.

8. IP3 causes the endoplasmic reticulum to release Ca++

9. Ca ++ binds to proteins like calmodulin 10. Calmodulin with Ca ++ bound activates other

proteins

11. DAG activates protein kinase C (PKC), Ca++

is needed for the activation12. Active PKC phosphorylates proteins13. Phosphorylated proteins are active and alter

cell activity14. The g-protein with GTP bound will hydrolyze

the phosphate from GTP, now has GDP bound and is inactive. It will reform with the β and γ subunits and this inactivates them

15. The cell stores Ca++ in organelles and pumps it out of the cell

Target Tissue Signaling Molecule

Major Response

Liver Vasopressin Glycogen Breakdown

Pancreas Acetylcholine Amylase secretion

Smooth Muscle Acetylcholine Contraction

Mast cells Antigen Histamine Secretion

Blood Platelets Thrombin Aggregation

Cellular responses mediated by IP3

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Enzyme-Linked Cell Surface Receptors

Receptor tyrosine kinases (RTK) Phosphorylates tyrosine amino acids on

signaling proteins

Receptor Serine/threonine kinases Phosphorylates serine or threonine amino

acids on signaling proteins

Receptor tyrosine kinases (RTKs)

Receptor tyrosine kinases (RTKs) are membrane receptors that attach phosphates to tyrosines

A receptor tyrosine kinase can trigger multiple signal transduction pathways at once

Abnormal functioning of RTKs is associated with many types of cancers


Receptor Tyrosine Kinase

These receptors just cross the plasma membrane once – single transmembrane proteins

RTKs are dimers – it takes two RTKs to function

Binding of the ligand causes two RTKs to come together and link to form a dimer = dimerize

Receptor Tyrosine Kinase

When the two receptors link together, they now have enzyme activity

They phosphorylate tyrosine residues on each other = autophosphorylation

This requires ATP

Receptor Tyrosine Kinase Ligands

Examples of ligands for receptor tyrosine kinases: Insulin Growth hormone Erythropoietin

Figure 11.7c

Signalingmolecule (ligand)

21

3 4

Ligand-binding site

helix in themembrane

Tyrosines

CYTOPLASM Receptor tyrosinekinase proteins(inactive monomers)

Signalingmolecule

Dimer

TyrTyr

Tyr

TyrTyrTyr

TyrTyrTyr

Tyr

TyrTyr

TyrTyrTyr

TyrTyrTyr

TyrTyrTyr

TyrTyrTyr

TyrTyrTyr

TyrTyr

Tyr

TyrTyrTyr

TyrTyr

Tyr

P

PP

PPP

P

PP

P

PP

Activated tyrosinekinase regions(unphosphorylateddimer)

Fully activatedreceptor tyrosinekinase(phosphorylateddimer)

Activated relayproteins

Cellularresponse 1

Cellularresponse 2

Inactiverelay proteins

6 ATP 6 ADP

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Fig. 9.7

MAP Cascades

Mitogen-activated protein kinases (MAP)

Mitogens are important in normal cell division

MAP kinases are a series of protein kinases that phosphorylate other protein kinases

Ending in a cellular response including gene transcription

These cascades amplify the response

MAP Cascades

The process starts with a growth factor binding to a RTK

RTK dimerizes and autophorylates

The activated RTK bind activator proteins

The activator proteins (GRB2 and SOS) activate a GTP-binding proteins (G protein) called Ras

When Ras is activated, it releases GDP and accepts GTP

Ras activates MKKK, which activates MKK……

Fig. 9.8.a

Fig. 9.8.b

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Fig. 9.10

Figure 11.15Growth factor

ReceptorReception

Transduction

CYTOPLASM

Response

Inactivetranscriptionfactor

Activetranscriptionfactor

DNA

NUCLEUS mRNA

Gene

Phosphorylationcascade

P

Summary of RTK/Ras/MAP Pathway1. Two ligands binds to two RTKs (one ligand/receptor)

2. The two RTK dimerize and phosphorylate each other, activating each other

3. The active RTKs activate a protein that stimulates Ras to eject GDP and accept GTP

4. The now active Ras activates the MAP kinase cascade until the MAP kinase is activated

5. The MAP kinase activates proteins which leads to cellular activity.

6. Ras will automatically inactivate by dephosphorylating the GTP to GDP

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Ligand-gated ion channel

A ligand-gated ion channel receptor acts as a gate when the receptor changes shape

When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor


Figure 11.7d

Signalingmolecule (ligand)

21 3

Gate closed Ions

Ligand-gatedion channel receptor

Plasmamembrane

Gate open

Cellularresponse

Gate closed

Intracellular Receptors

Intracellular receptor proteins are found in the cytosol or nucleus of target cells

Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors

Examples of hydrophobic messengers are the steroid and thyroid hormones of animals

An activated hormone-receptor complex can act as a transcription factor, turning on specific genes



Lipid soluble and small signaling molecules bind to receptors located inside the cell.

Intracellular receptors are located in the cytosol or the nucleus

The intracellular receptors in the cytosol will bind with the ligand, the binding will cause the receptor/ligand complex to travel to the nucleus.

Examples of Intracellular Receptors

Steroid hormones Estrogen, testosterone, cortisol Effects gene expression

Nitric Oxide (gas) Binds to receptor that is an enzyme = guanylyl

cyclase

Steroid Hormone Intracellular Receptors

These hormones cross the plasma membrane and bind to an intracellular receptor in the cytosol

The binding of the ligand to the receptor causes the ligand/receptor to go to the nucleus

The ligand/receptor regulates gene expression

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Intracellular receptors have three regions:

Ligand binding domain DNA binding domain Transcription activating domain


Prior to the ligand binding, the receptor may have proteins that block the DNA binding domain.

The binding of the ligand signals the receptor to go the nucleus and allow the receptor to bind to the DNA

Fig. 9.5 Figure 11.9-1Hormone(testosterone)

Receptorprotein

Plasmamembrane

DNA

NUCLEUS

CYTOPLASM

EXTRACELLULARFLUID

Figure 11.9-2Hormone(testosterone)

Receptorprotein

Plasmamembrane

Hormone-receptorcomplex

DNA

NUCLEUS

CYTOPLASM

EXTRACELLULARFLUID


Receptorprotein

Plasmamembrane


DNA

NUCLEUS

CYTOPLASM

EXTRACELLULARFLUID

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Receptorprotein

Plasmamembrane


DNA

mRNA

NUCLEUS

CYTOPLASM

EXTRACELLULARFLUID


Receptorprotein

Plasmamembrane

EXTRACELLULARFLUID


DNA

mRNA

NUCLEUS

CYTOPLASM

New protein

Nuclear and Cytoplasmic Responses

Ultimately, a signal transduction pathway leads to regulation of one or more cellular activities

The response may occur in the cytoplasm or in the nucleus

Many signaling pathways regulate the synthesis of enzymes or other proteins, usually by turning genes on or off in the nucleus

The final activated molecule in the signaling pathway may function as a transcription factor


Wild type (with shmoos) Fus3 formin

Matingfactoractivatesreceptor.

Matingfactor G protein-coupled

receptor

Shmoo projectionforming

Formin

G protein binds GTPand becomes activated.

2

1

3

4

5

P

P

P

PForminFormin

Fus3

Fus3Fus3

GDP GTPPhosphory-

lationcascade

Microfilament

Actinsubunit

Phosphorylation cascadeactivates Fus3, which movesto plasma membrane.

Fus3 phos-phorylatesformin,activating it.

Formin initiates growth ofmicrofilaments that formthe shmoo projections.

RESULTS

CONCLUSION

Figure 11.17

Fine-Tuning of the Response

There are four aspects of fine-tuning to consider Amplification of the signal (and thus the

response) Specificity of the response Overall efficiency of response, enhanced by

scaffolding proteins Termination of the signal


Signal Amplification

Enzyme cascades amplify the cell’s response

At each step, the number of activated products is much greater than in the preceding step


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The Specificity of Cell Signaling and Coordination of the Response

Different kinds of cells have different collections of proteins

These different proteins allow cells to detect and respond to different signals

Even the same signal can have different effects in cells with different proteins and pathways

Pathway branching and “cross-talk” further help the cell coordinate incoming signals


Figure 11.18

Signalingmolecule

Receptor

Relay molecules

Response 1

Cell A. Pathway leadsto a single response.

Response 2 Response 3 Response 4 Response 5

Activationor inhibition

Cell B. Pathway branches,leading to two responses.

Cell C. Cross-talk occursbetween two pathways.

Cell D. Different receptorleads to a differentresponse.

Signaling Efficiency: Scaffolding Proteins and Signaling Complexes

Scaffolding proteins are large relay proteins to which other relay proteins are attached

Scaffolding proteins can increase the signal transduction efficiency by grouping together different proteins involved in the same pathway

In some cases, scaffolding proteins may also help activate some of the relay proteins


Figure 11.19

Signalingmolecule

Receptor

Plasmamembrane

Scaffoldingprotein

Threedifferentproteinkinases

Termination of the Signal

Inactivation mechanisms are an essential aspect of cell signaling

If ligand concentration falls, fewer receptors will be bound

Unbound receptors revert to an inactive state


Receptor Internalization

One way this pathway is inactivated is through Ras GTPase activity

Another way this pathway is down-regulated is internalization of the receptors

We will come back to this at the end of the lecture

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Controlling Cell Signaling

To control cell signaling:

1. The G-proteins have GTPase activity2. Ligand levels fall3. Ca++ is sequestered4. There are phosphatases that inactivate the

proteins that were activated by phosphorylation

5. Phosphodiesterases6. Receptors are internalized

http://biochemistry.utoronto.ca/brown/mgy425/egan_tk_ras_2009.ppt#68

Apoptosis integrates multiple cell-signaling pathways

Apoptosis is programmed or controlled cell suicide

Components of the cell are chopped up and packaged into vesicles that are digested by scavenger cells

Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells

Figure 11.20

2 m

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Apoptotic Pathways and the Signals That Trigger Them

Mitochondria release cytochrome C

Caspases are the main proteases (enzymes that cut up proteins) that carry out apoptosis

Apoptosis can be triggered by An extracellular death-signaling ligand DNA damage in the nucleus Protein misfolding in the endoplasmic reticulum


Apoptosis evolved early in animal evolution and is essential for the development and maintenance of all animals

Apoptosis may be involved in some diseases (for example, Parkinson’s and Alzheimer’s); interference with apoptosis may contribute to some cancers


Apoptotic Pathways

Figure 11.22

Interdigital tissueCells undergoing

apoptosisSpace between

digits1 mm

Apoptosis video

Florescent labeled Death ligand

Important Concepts Know the vocabulary covered in this lecture

Know examples of signaling molecules

Know the forms of cell signaling

Know the main classifications of signaling receptors, what are the main differences and what type of ligands generally bind these receptors

Understand how intracellular receptors work, what are the steps from the binding of a ligand to the cellular activity and what type of activity is regulated by intracellular receptors.

Important Concepts Know the three domains of intracellular

receptors

Know the classes of Cell Surface Receptor Proteins

Understand how protein kinases work, what do they do?

Know the properties of RTKs. Be able to describe the steps of how the receptors regulate cellular activity

What is the benefit of having kinase cascades?

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Important Concepts Know the examples of ligands for the receptors

Be able to describe how cellular activity is regulated by the cAMP pathway, starting with the binding of a ligand to the GCPR, including how the g-protein is inactivated

Know examples of a cellular response mediated by cAMP

Understand the apoptotic pathways and how they are triggered

Important Concepts

Be able to describe the steps of how cellular activity is effected by the IP3 and DAG pathway, starting with the binding of a ligand to the GCPR, including how the g-protein is inactivated

Know examples of cellular responses mediated by IP3

How are cell signaling pathways controlled

What are differences and similarities between G-protein couple receptors, enzyme linked receptors (like RTK) and intracellular receptors

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NVC Biol 120 11 Communication - Napa Valley College 120 Lectures/NVC... · 10/15/2011 1 Chapter 11 – Cell Communication Outline I. Cell Signaling II. Forms of cell signaling III