chapter 3 the cellular level of...

Copyright 2009 John Wiley & Sons, Inc.

Chapter 3The Cellular Level of Organization


A Generalized Cell

1. Plasma membrane- forms the cell’s outer boundary- separates the cell’s internal environment

from the outside environment- is a selective barrier- plays a role in cellular communication


A Generalized Cell

2. Cytoplasm- all the cellular contents between the plasma membrane and the nucleus- cytosol - the fluid portion, mostly water- organelles - subcellular structures having characteristic shapes and specific functions


A Generalized Cell

3. Nucleus- large organelle that contains DNA- contains chromosomes, each of which consists of a single molecule of DNA and associated proteins

- a chromosome contains thousands of hereditary units called genes


Fig. 3.1 Generalized Body Cell


Plasma Membrane

Flexible yet sturdy barrier The fluid mosaic model - the arrangement of

molecules within the membrane resembles a sea of lipids containing many types of proteins

The lipids act as a barrier to certain substances

The proteins act as “gatekeepers” to certain molecules and ions


Structure of a Membrane

Consists of a lipid bilayer - made up of phospholipids, cholesterol and glycolipids

Integral proteins - extend into or through the lipid bilayer

Transmembrane proteins - most integral proteins, span the entire lipid bilayer

Peripheral proteins - attached to the inner or outer surface of the membrane, do not extend through it


Structure of the Plasma Membrane


Structure of a Membrane

Glycoproteins - membrane proteins with a carbohydrate group attached that protrudes into the extracellular fluid

Glycocalyx - the “sugary coating” surrounding the membrane made up of the carbohydrate portions of the glycolipids and glycoproteins


Functions of Membrane Proteins

Some integral proteins are ion channels Transporters - selectively move substances

through the membrane Receptors - for cellular recognition; a ligand

is a molecule that binds with a receptor Enzymes - catalyze chemical reactions Others act as cell-identity markers


Figure 3.3


Membrane Permeability

The cell is either permeable or impermeable to certain substances

The lipid bilayer is permeable to oxygen, carbon dioxide, water and steroids, but impermeable to glucose

Transmembrane proteins act as channels and transporters to assist the entrance of certain substances, for example, glucose and ions


Passive vs. Active Processes

Passive processes - substances move across cell membranes without the input of any energy; use the kinetic energy of individual molecules or ions

Active processes - a cell uses energy, primarily from the breakdown of ATP, to move a substance across the membrane, i.e.,against a concentration gradient


Diffusion

Steepness of concentration

gradient Temperature Mass of diffusing

substance Surface area Diffusion

distance


Simple Diffusion, Channel-mediated Facilitated Diffusion, and Carrier-mediated Facilitated Diffusion


Channel-mediated Facilitated Diffusion of Potassium ions through a Gated K + Channel


Carrier-mediated Facilitated Diffusion of Glucose across a Plasma Membrane

Glucosetransporter

Glucosegradient

Glucose

Extracellular fluid Plasma membrane Cytosol

1

Glucosetransporter

Glucosegradient

Glucose


1

2

Glucosetransporter

Glucosegradient

Glucose

Glucose


1

2

3


Osmosis

Net movement of water through a selectively permeable membrane from an area of high concentration of water (lower concentration of solutes) to one of lower concentration of water

Water can pass through plasma membrane in 2 ways:

1. through lipid bilayer by simple diffusion2. through aquaporins, integral membrane

proteins


Tonicity and its effect on RBCS


Active TransportSolutes are transported across plasma membranes with the use of energy, from an area

of lower concentration to an area of higher Concentration Sodium-potassium pump

1

3 Na+

K+

gradient

Na+

gradientNa+/K+ ATPase

Extracellular fluid

Cytosol

1

3 Na+ expelled

3 Na+

ADP

P

K+

gradient

Na+


Extracellular fluid

CytosolATP

21

3 Na+ expelled

3 Na+

ADP P

P

K+

gradient

Na+


Extracellular fluid

Cytosol

2K+

ATP2 31

3 Na+ expelled

3 Na+

ADP P

P

2 K+

importedK+

gradient

Na+


Extracellular fluid

Cytosol

2K+

ATP2 3 4


Transport in Vesicles

Vesicle - a small spherical sac formed by budding off from a membrane

Endocytosis - materials move into a cell in a vesicleformed from the plasma membrane

three types: receptor-mediated endocytosis phagocytosisbulk-phase endocytosis (pinocytosis)

Exocytosis - vesicles fuse with the plasma membrane, releasing their contents into the extracellular fluid

Transcytosis - a combination of endocytosis and exocytosis


Receptor-Mediated Endocytosis

1

Clathrin-coatedpit

Binding

Receptor

Receptor-LDLcomplex LDL particle Plasma

membrane

Invaginated plasmamembrane

1

Clathrin-coatedvesicle

Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex LDL particle Plasma

membrane


2

1


Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex

Uncoated vesicle

Uncoating

LDL particle Plasmamembrane


2

3

1


Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex

Uncoated vesicle

Fusion withendosome

Uncoating



Endosome

2

3

4

Transportvesicle

1


Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex

Uncoated vesicleTransportvesicle

Fusion withendosome

Recyclingof receptorsto plasmamembrane

Uncoating



Endosome

2

3

4

5

Transportvesicle

1


Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex

Uncoated vesicle

Degradationin lysosome

Lysosome

Transportvesicle

Transportvesicle

Fusion withendosome

Recyclingof receptorsto plasmamembrane

Uncoating



Endosome

Digestiveenzymes

2

3

4

5

6


Phagocytosis


Bulk-phase Endocytosis


Cytoplasm - 2 components

1. Cytosol - intracellular fluid, surrounds the organelles- the site of many chemical reactions- energy is usually released by these reactions- reactions provide the building blocks for cell maintenance, structure, function and growth

2. OrganellesSpecialized structures within the cellThe cytoskeleton - network of protein filaments throughout the cytosol-provides structural support for the cell-three types according to increasing size: microfilaments, intermediate filaments, and microtubules


The Cytoskeleton


Organelles

Centrosome - located near the nucleus, consists of two centrioles and pericentriolar material (Fig. 2.7)

Cilia - short, hair-like projections from the cell surface, move fluids along a cell surface

Flagella - longer than cilia, move an entire cell; only example is the sperm cell’s tail (Fig. 2.8)


The Centrosome


Cilia and Flagella


Organelles

Ribosomes - sites of protein synthesis Endoplasmic reticulum - network of membranes in

the shape of flattened sacs or tubules- Rough ER - connected to the nuclear envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins-Smooth ER - a network of membrane tubules, does not have ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs


Ribosomes


Endoplasmic Reticulum


Organelles

Golgi complex - consists of 3-20 flattened, membranous sacs called cisternae

- modify, sort, and package proteins for transport to different destinations- proteins are transported by various vesicles

Lysosomes - vesicles that form from the Golgi complex, contain powerful digestive enzymes


Golgi Complex


Processing and Packaging

Transport vesicleRibosomeSynthesizedprotein 1

Rough ER

Transport vesicleRibosomeSynthesizedprotein

Rough ER

21 Transport vesicleRibosome

Entry face cisterna

Exit face cisterna

Medial cisterna

Synthesizedprotein

Rough ER

3

21 Transport vesicleRibosome

Entry face cisterna

Exit face cisterna

Medial cisterna

Synthesizedprotein

Transfer vesicle

Rough ER

Transfer vesicle

4

3

21

4

Transport vesicleRibosomeEntry face cisterna

Exit face cisterna

Medial cisterna

Synthesizedprotein

Transfer vesicle

Rough ER

Transfer vesicle

54

3

21

4


Exit face cisterna

Medial cisterna

Synthesizedprotein

Transfer vesicle

Rough ER

Transfer vesicle

6

54

3

21

4


Exit face cisterna

Medial cisterna

Synthesizedprotein

Transfer vesicle

Rough ER

Transfer vesicleSecretoryvesicle

7

6

54

3

21

4

Proteins exportedfrom cell by exocytosis

Plasmamembrane

Proteins in vesiclemembrane mergewith plasmamembrane


Plasmamembrane


Exit face cisterna

Medial cisterna

Synthesizedprotein

Transfer vesicle

Rough ER

Transfer vesicle

Membranevesicle

Secretoryvesicle

8

7

6

54

3

21

4

Proteins in vesiclemembrane mergewith plasmamembrane


Plasmamembrane


Exit face cisterna

Medial cisterna

Synthesizedprotein

Transport vesicle(to lysosome)

Transfer vesicle

Rough ER

Transfer vesicle

Membranevesicle

Secretoryvesicle

9

8

7

6

54

3

21

4


Lysosomes


Organelles

Peroxisomes - smaller than lysosomes, detoxify several toxic substances such as alcohol, abundant in the liver

Proteasomes - continuously destroy unneeded, damaged, or faulty proteins, found in the cytosol and the nucleus


Organelles

Mitochondria - the “powerhouses” of the cell Generate ATP More prevalent in physiologically active cells: muscles, liver

and kidneys Inner and outer mitochondrial membranes Cristae - the series of folds of the inner membrane Matrix - the large central fluid-filled cavity Self-replicate during times of increased cellular demand or

before cell division


Mitochondria


Organelles - Nucleus Spherical or oval shaped structure Usually most prominent feature of a cell Nuclear envelope - a double membrane that

separates the nucleus from the cytoplasm Nuclear pores - numerous openings in the nuclear

envelope, control movement of substances between nucleus and cytoplasm

Nucleolus - spherical body that produces ribosomes Genes - are the cell’s hereditary units, control

activities and structure of the cell Chromosomes - long molecules of DNA combined

with protein molecules


Packing of DNA into a Chromosome of a Dividing Cell


Overview of Gene Expression


Transcription


Translation

1

Key:

Initiator tRNA attaches to astart codon.

Amino acid(methionine)

AnticodonmRNA

mRNAbindingsite

Initiator tRNA

Start codon

Smallsubunit

= Adenine

= Guanine

= Cytosine

= Uracil

U GGG AU A C

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

U GGG AU A C

UGG AU A C

G

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

U GGG AU A C

UGG AU A C

G C

U GGG AU A C

2

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

U GGG AU A C

UGG AU A C

G C

U GGG AU A C

GAUU GGG AU A C U

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

U GGG AU A C

UGG AU A C

G C

U GGG AU A C

GAUU GGG AU A C U

GUU GGG A CU

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

mRNAtRNA

Complete proteinGrowingprotein= Adenine

= Guanine

= Cytosine

= Uracil

U GGG AU A C

UGG AU A C

G C

U GGG AU A C

GAUU GGG AU A C U

GUU GGG A CU

C

2

3

4

56


Somatic Cell Division - Mitosis

The cell cycle is a sequence of events in which a body cell duplicates its contents and divides in two

Human somatic cells contain 23 pairs of chromosomes (total = 46)

The two chromosomes that make up each pair are called homologous chromosomes (homologs)

Somatic cells contain two sets of chromosomes and are called diploid cells


Cell Division

Interphase - the cell is not dividing- the cell replicates its DNA - consists of three phases, G1, S, and G2,

replication of DNA occurs in the S phase Mitotic phase - consists of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells


The Cell Cycle


DNA Replication


Nuclear Division: Mitosis

Prophase - the chromatin fibers change into chromosomes

Metaphase - microtubules align the centromeres of the chromatid pairs at the metaphase plate

Anaphase - the chromatid pairs split at the centromere and move to opposite poles of the cell;the chromatids are now called chromosomes

Telophase - two identical nuclei are formed around the identical sets of chromosomes now in their chromatin form


Cytoplasmic Division: Cytokinesis

Division of a cell’s cytoplasm to form two identical cells

Usually begins in late anaphase The plasma membrane constricts at its

middle forming a cleavage furrow The cell eventually splits into two daughter

cells Interphase begins when cytokinesis is

complete

1

Pericentriolar materialNucleolusNuclear 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



Reproductive Cell Division

During sexual reproduction each new organism is the result of the union of two gametes (fertilization), one from each parent

Meiosis - reproductive cell division that occurs in the gonads (ovaries and testes) that produces gametes with half the number of chromosomes

Haploid cells - gametes contain a single set of 23 chromosomes

Fertilization restores the diploid number of chromosomes (46)


Reproductive Cell Division Meiosis occurs in two successive stages:

meiosis I and meiosis II Each of these two stages has 4 phases:

prophase, metaphase, anaphase, and telophase

Summary - Meiosis I begins with a diploid cell and ends with two cells having the haploid number of chromosomes; in Meiosis II, each of the two haploid cells divides, the net result is four haploid gametes that are genetically different from the original diploid starting cell


Cellular Diversity

The average adult has nearly 100 trillion cells

There are about 200 different types of cells

Cells come in a variety of shapes and sizes

Cellular diversity permits organization of cells into more complex tissues and organs


End of Chapter 3

Copyright 2009 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.

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