Copyright 2010, John Wiley & Sons, Inc. Chapter 3 Cells

Copyright 2010, John Wiley & Sons, Inc.

Chapter 3

Cells


Cell Structure

Plasma membrane Cytoplasm: cytosol + organelles Nucleus


Generalized View of Cell Structure


Cell Membrane

Phospholipid bilayer Cholesterol Proteins (integral and peripheral) Attached carbohydrates (glycolipids and

gycoproteins)


Plasma Membrane: Chemistry and Structure


Membrane Function

Barrier between inside and outside of cell Controls entry of materials: transport Receives chemical and mechanical signals Transmits signals between intra- and extra-

cellular spaces Note variety of proteins in Figure 3-2.


Terminology: Body Fluid Pools Intracellular (ICF)

Within cells: 2/3 of total Extracellular (ECF):

Between cells = Interstitial In blood vessels = Plasma In lymphatic vessels = Lymphatic


Terminology: Solutions

Solvent: the liquid doing the dissolving Usually water

Solute: the dissolved material (particles or gas)

Concentration Amount of solute in a given amount of solvent

Concentration gradient Difference in concentration between 2 areas of

solution


Principle of Diffusion


Passive Transport: Simple Diffusion Requirements for simple diffusion

Concentration gradient of solute present Solute can diffuse across a membrane if

membrane is present Pathways of simple diffusion:

Pass across lipid bilayer if lipid-soluble (O2, CO2, N2, fatty acids, steroids, fat-soluble vitamins), or if polar molecules (H2O, urea)

Pass through ion channels (which may be gated: gates open and close) if ions such as K+, Ca2+, Cl–


Simple Diffusion


Facilitated Diffusion Requires a carrier in membrane but not

ATP Solute goes down concentration gradient Maximum transport speed depends on

number of carriers insulin increases number of carriers for

glucose in plasma membrane


Facilitated Diffusion


Facilitated Diffusion


Osmosis Diffusion of water across selectively

permeable membrane: Permeable to solvent Impermeable to solute

Types of solutions surrounding human RBCs Isotonic: solution outside RBC has same

concentration of solute as RBC: 0.9% NaCl Hypotonic: solution outside of RBC has lower

concentration: 0% NaCl hemolysis Hypertonic: solution outside of RBC has higher

concentration: 4% NaCl crenation


Osmosis


Osmosis


Active Transport Requires a carrier (called a pump) Requires energy (ATP) Can transport up a concentration gradient Critical for moving important ions Major active transport in most cells is

sodium-potassium (Na+/K+) pump


Copyright 2009 John Wiley & Sons, Inc. 19

Active TransportSolutes are transported across plasma membranes with the use of

energy, from an area of lower concentration to an area of higher concentration

Example: Sodium-potassium pump

1

3 Na+

K+

gradient

Cytosol

1

3 Na+ expelled

3 Na+

ADPP

P

2 K+

imported

K+

gradient

Na+

gradientNa+/K+ ATPase

Extracellular fluid

Cytosol

2K+

ATP2 3 4


Transport in Vesicles

Requires energy (ATP) Involves small membrane sac Endocytosis: importing materials into cell

Phagocytosis: ingestion of particles such as bacteria into white blood cells (WBCs)

Pinocytosis: ingestion of fluid Exocytosis: exporting materials


Transport Across the Plasma Membrane

Transport Across the Plasma MembraneInteractions Animation

You must be connected to the internet to run this animation.


Cell Organelles: Table 3.2

Cytoskeleton Flagella, cilia & centrioles Endoplasmic reticulum Golgi apparatus Mitochondrion Nucleus, nucleolus, nuclear envelope Vesicles, e.g. lysosome


Cytoplasm Cell contents Includes organelles and cytosol Excludes nucleus


Cytoskeleton

Maintains shape of cell

Positions organelles Changes cell shape Includes:

microfilments, intermediate filaments, microtubules


Centrosome

Structure: Two centrioles arranged perpendicular to each

other Composed of microtubules: 9 clusters of 3 (triplets)

Pericentriolar material Composed of tubulin that grows the mitotic spindle

Function: moves chromosomes to ends of cell during cell division


Centrosome


Cilia and Flagella

Specialized for motion Flagellum: single tail like structure on sperm

Propels sperm forward in reproductive tract Cilia: in groups

Found in respiratory system: move mucus


Ribosomes Made within the nucleus (in nucleolus) Sites of protein synthesis (on E.R. or freely

within cytoplasm) Consist of ribosomal RNA (rRNA) + proteins Contain large and small subunits Can be attached to endoplasmic reticulum or

free in cytosol


Endoplasmic Reticulum (E.R.) Structure: network of folded membranes Functions: synthesis, intracellular transport Types of E.R.

Rough E.R.: studded with ribosomes (sites of protein synthesis)

Smooth E.R. lacks ribosomes. Functions: lipid synthesis release of glucose in liver cells into bloodstream drug detoxification (especially in liver cells) storage and release of Ca2+ in muscle cells (where

smooth E.R. is known as sarcoplasmic reticulum or SR)


Endoplasmic Reticulum (E.R.)


Structure: Flattened membranes (cisterns) with bulging

edges (like stacks of pita bread) Functions:

Modify proteins glycoproteins and lipoproteins that:

Become parts of plasma membranes Are stored in lysosomes, or Are exported by exocytosis

Golgi Complex


Golgi Complex


Small Bodies Lysosomes: contain digestive enzymes

Help in final processes of digestion within cells Carry out autophagy (destruction of worn out parts of

cell) and death of old cells (autolysis) Tay-Sachs: hereditary disorder; one missing

lysosomal enzyme leads to nerve destruction Peroxisomes: detoxify; abundant in liver Proteasomes: digest unneeded or faulty

proteins Faulty proteins accumulate in brain cells in persons

with Parkinson or Alzheimer disease.


Mitochondria Structure:

Sausage-shaped with many folded membranes (cristae) and liquid matrix containing enzymes

Have some DNA, ribosomes (can make proteins) Function:

Nutrient energy is released and trapped in ATP; so known as “power houses of cell”

Chemical reactions require oxygen Abundant in muscle, liver, and kidney cells

These cells require much ATP


Mitochondria


Nucleus Round or oval structure surrounded by nuclear

envelope with nuclear pores Contains nucleolus: makes ribosomes that pass

into cytoplasm through nuclear pores Store genetic material (DNA) in genes arranged

in 46 chromosomes (the human genome containing 30,000 genes!)

DNA contains information for directing protein synthesis: In this cell In new cells (formed by cell reproduction)


Nucleus


Protein Synthesis 2 steps:

Nuclear = transcription Cytoplasmic = translation


Protein Synthesis: Transcription


Protein Synthesis: Transcription


Transcription In nucleus RNA polymerase (enzyme) transcribes DNA into

RNA; complementary base pairs C-G, G-C, T-A, A-U

Types of RNA formed: 1. Messenger RNA (mRNA)

Directs synthesis of polypeptide

2. Ribosomal RNA Component of ribosomes

3. Transfer RNA (tRNA) Carries amino acids to ribosome for reaction


Translation

Requires 3 different RNAs Messenger RNA- from nucleus (mRNA)

direct sequencing of amino acids Ribosomes contain ribosomal RNA (rRNA)

and are the sites of translation Transfer RNA- carry amino acids (tRNA) to

sites on mRNA


1

Key:

Initiator tRNA attaches to astart codon.

Amino acid(methionine)

AnticodonmRNA

mRNAbindingsite

Initiator tRNA

Start codon

Smallsubunit

= Adenine

= Guanine

= Cytosine

= Uracil

UUU G GGG G GAAAAA

U A CC UCUA

ACUC

1

Key:


Large and small ribosomalsubunits join to form a functionalribosome and initiator tRNAfits into P site.Amino acid

(methionine)

AnticodonmRNA

mRNAbindingsite

Initiator tRNA

Start codon

Smallsubunit

Initiator tRNA

Smallsubunit

LargesubunitP site

A site

= Adenine

= Guanine

= Cytosine

= Uracil

UUU G GGG G GAAAAA

U A CC UCUA

ACUC

GAUUU GG AAAAACC G GUCU ACU

U A CG

2

1

Key:



(methionine)

Amino acid

Anticodon

Anticodon

Codons

mRNA

mRNA

mRNAbindingsite

Initiator tRNA

tRNA

Start codon

Smallsubunit

Initiator tRNA

Smallsubunit

LargesubunitP site

A site

Anticodon of incoming tRNA pairswith next mRNA codon at A site.

P site

A site

= Adenine

= Guanine

= Cytosine

= Uracil

UUU G GGG G GAAAAA

U A CC UCUA

ACUC


U A CG

A UC

UUU GGG G GAAAAAC UCU

ACU

C

U A CGA2

3

1

Key:



(methionine)

Amino acid

Anticodon

Anticodon

Codons

mRNA

mRNA

mRNAbindingsite

Initiator tRNA

tRNA

Start codon

Smallsubunit

Initiator tRNA

Smallsubunit

LargesubunitP site

A site


Amino acid on tRNA at P siteforms a peptide bond withamino acid at A site.

P site

A site

= Adenine

= Guanine

= Cytosine

= Uracil

UUU G GGG G GAAAAA

U A CC UCUA

ACUC


U A CG

A UC


ACU

C

U A CGA

CGAUUUU GGG G GAAAAA

C UCU AC

U A C A UC

2

3

4

1

Key:



(methionine)

Amino acid

Anticodon

Anticodon

Codons

mRNA

mRNA

mRNAmovement

mRNAbindingsite

Initiator tRNA

tRNA

Start codon

Smallsubunit

Initiator tRNA

Smallsubunit

LargesubunitP site

A site


tRNA at P site leaves ribosome,ribosome shifts by one codon;tRNA previously at A site is nowat the P site.

Newpeptidebond Amino acid on tRNA at P site

forms a peptide bond withamino acid at A site.

P site

A site

= Adenine

= Guanine

= Cytosine

= Uracil

UUU G GGG G GAAAAA

U A CC UCUA

ACUC


U A CG

A UC


ACU

C

U A CGA


C UCU AC

U A C A UC

CGAUUUU

GGG G GAAAAAC UCU

AC

C

U A C A U

2

3

4

5

1

Key:



(methionine)

Amino acid

Anticodon

Anticodon

Codons

Stop codon

mRNA

mRNA

mRNAmovement

mRNAbindingsite

Initiator tRNA

tRNA

Start codon

Smallsubunit

Initiator tRNA

Smallsubunit

LargesubunitP site

A site


Protein synthesis stops whenthe ribosome reaches stopcodon on mRNA.

tRNA at P site leaves ribosome,ribosome shifts by one codon;tRNA previously at A site is nowat the P site.

Newpeptidebond Amino acid on tRNA at P site

forms a peptide bond withamino acid at A site.

P site

A site

Summary of movement of ribosome along mRNA

mRNA

tRNA

Complete proteinGrowingprotein= Adenine

= Guanine

= Cytosine

= Uracil

UUU G GGG G GAAAAA

U A CC UCUA

ACUC


U A CG

A UC


ACU

C

U A CGA


C UCU AC

U A C A UC

CGAUUUU

GGG G GAAAAAC UCU

AC

C

U A C A U

CUU G GGG G GAA C UCUA ACU

A U

2

3

4

56

Translation


Translation


Translation


Translation


Translation


Translation


Translation


Somatic Cell Division In all body cells except gametes Interphase

Period of growth and development of cell Preparation for reproduction: DNA synthesis

Mitotic Phase = division of nucleus 4 phases

Cytokinesis= division of cytoplasm


1

Pericentriolar material

NucleolusNuclear envelopeChromatinPlasma membraneCytosol

(a) INTERPHASE

CentriolesCentrosome:

all at 700xLM

1

LateEarly



Chromosome(two chromatidsjoined atcentromere

(a) INTERPHASE

(b) PROPHASE


Fragments ofnuclear envelope

Mitotic spindle(microtubules)

Kinetochore

2

all at 700xLM

Centromere

1



Metaphase plate

(a) INTERPHASE


(c) METAPHASE

2

3

LateEarly (b) PROPHASE



Kinetochore

all at 700xLM


Centromere

1

EarlyLate(d) ANAPHASE



Chromosome

(a) INTERPHASE


(c) METAPHASE

2

3

4

Cleavage furrow




Kinetochore

Metaphase plate

all at 700xLM


Centromere

1




(a) INTERPHASE


Cleavage furrow

(e) TELOPHASE

(c) METAPHASE

2

3

4

5

Cleavage furrow




Kinetochore

Metaphase plate

Chromosome

all at 700xLM


Centromere

1




(a) INTERPHASE


(f) IDENTICAL CELLS IN INTERPHASE

Cleavage furrow

(e) TELOPHASE

(c) METAPHASE

Cleavage furrow

2

3

4

5

6




Kinetochore

Metaphase plate

Chromosome

all at 700xLM

Centromere


Mitosis


Prophase Chromatin condenses into pairs of

chromatids connected at centromeres Centrosomes form the mitotic spindle

(composed of microtubules) that extends from pole to pole of the cell Some chemotherapy drugs fight cancer cells by

inhibiting formation of the mitotic spindle Nuclear envelope and nucleolus break down


Prophase


Metaphase

Centromeres of chromatid pairs are aligned along microtubules at the center (“equator”) of the metaphase plate


Metaphase


Anaphase

Centromeres split, separating “sister chromatids” (chromosomes)

Chromosomes are pulled to opposite ends of spindle by microtubules of the mitotic spindle

Cytokinesis (division of cytoplasm) begins by the formation of a cleavage furrow


Anaphase


Telophase

Chromosomes revert to threadlike chromatin Nuclear envelope and nucleolus reappear Mitotic spindle breaks up Cytokinesis is completed


Cellular Diversity Because structure determines function, cells

differ in structure related to their functions. Nerve cells may reach several feet in length to

carry nerve impulses from spinal cord to toe Muscle cells can produce effective contractions

because they are cylindrical or spindle-shaped Microvilli increase surface area of intestinal cells

to maximize absorptive ability Most cells are microscopic; the diameter of

the largest human cell (an oocyte) can barely be seen with the unaided eye.


Aging A number of factors contribute to aging:

May be programmed genetically Decreased rate of mitosis; nerve cells and skeletal

muscle cells cannot be replaced Telomeres (DNA at tips of chromosomes)

Telomeres shorten with aging Progeria (rapid aging): profound telomere shortening

Protein damage by glucose cross-links Free radicals damage. (See Focus on Wellness:

action of antioxidants to reduce effects of free radicals.)

Autoimmune responses


End of Chapter 3

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Copyright 2010, John Wiley & Sons, Inc. Chapter 3 Cells