Organization of the CellOrganization of the Cell

Chapter 4

Learning Objective 1Learning Objective 1

• What is cell theory?

• How does cell theory relate to the evolution of life?

Cell TheoryCell Theory

(1) Cells are basic units of organization and function in all living organisms

(2) All cells come from other cells

All living cells have evolved from a common ancestor

Learning Objective 2Learning Objective 2

• What is the relationship between cell organization and homeostasis?

HomeostasisHomeostasis

• Cells have many organelles, internal structures that carry out specific functions, that help maintain homeostasis

KEY CONCEPTSKEY CONCEPTS

• Cell organization and size are critical in maintaining homeostasis

Plasma MembranePlasma Membrane

• Plasma membrane • surrounds the cell• separates cell from external environment• maintains internal conditions • allows the cell to exchange materials with

outer environment

KEY CONCEPTSKEY CONCEPTS

• Eukaryotic cells are divided into compartments by internal membranes

• Membranes provide separate, small areas for specialized activities

Learning Objective 3Learning Objective 3

• What is the relationship between cell size and homeostasis?

Biological SizeBiological Size

Fig. 4-1, p. 75

1 μm

Atom

Aminoacids

Protein

Ribosomes

Virus

Mitochondrion

0.1 nm

Smallestbacteria

1 nm 10 nm 100 nm 10 μm

Chloroplast

Nucleus

10 m1 m100 mm

Electron microscopeLight microscope

10 mm

Typicalbacteria

Red bloodcells

Epithelialcell

Humanegg

Frog egg

Chickenegg

Somenerve cells

Adulthuman

1 mm100 μm

Measurements1 meter = 1000 millimeters (mm)1 millimeter = 1000 micrometers (μm)1 micrometer = 1000 nanometers (nm)

Human eye

Surface to Volume RatioSurface to Volume Ratio

• SVR• ratio of plasma membrane (surface area)

to cell’s volume• regulates passage of materials into and out

of the cell

• Critical factor in determining cell size

SVRSVR

Fig. 4-2, p. 76

24Surface area =height width number of sides number of cubes

Volume =height width length number of cubes

Surface area/volume

Surface Area/Volume Ratio

Volume(mm3)

(24 :8)3

(48 :8)6

(2 2 2 1) (1 1 1 8)

88

Surface Area(mm2)

(1 1 6 8)(2 2 6 1)

48

1 mm

2 mm

2 mm

1 mm

Learning Objective 4Learning Objective 4

• What methods do biologists use to study cells?

• How are microscopy and cell fractionation used?

MicroscopesMicroscopes

• Light microscopes

• Electron microscopes• superior resolving power

MicroscopesMicroscopes

Fig. 4-4a, p. 79

Light source

Lightmicroscope Light beam

Ocular lens

Objective lensSpecimen

Condenser lens

(a) A phase contrast light microscope can be used to view stained or living cells, but at relatively low resolution.

100 μm

Fig. 4-4b, p. 79

Projector lens(electromagnetic)

Transmissionelectron

microscope

Electron gun

Electron beam

First condenser lens(electromagnet)

Specimen

Film or screen

(b) The transmission electron microscope(TEM) produces a high-resolution imagethat can be greatly magnified. A smallpart of a thin slice through theParamecium is shown. 1 μm

Fig. 4-4c, p. 79

Electron gun

Electron beam

First condenser lens(electromagnet)

Secondaryelectrons

Scanningelectronmicroscope

Second condenserlens

Scanning coil

Final (objective)lens

Cathode ray tubesynchronized withscanning coil

Electrondetector

Specimen

100 μm

(c) The scanning electron microscope(SEM) provides a clear view of surfacefeatures.

Cell FractionationCell Fractionation

• Cell fractionation• purifies organelles• to study function of cell structures

Cell FractionationCell Fractionation

Fig. 4-5a, p. 80

Centrifugal force

(a) Centrifugation. Due to centrifugal force, large or very dense particles move toward the bottom of a tube and form a pellet.

Centrifuge rotor

Hinged bucketcontaining tube

Centrifugal force

Fig. 4-5b, p. 80

Plasmamembrane

Golgi

ER

Layeredmicrosomalsuspension

sucroseconcentration

High

100,000 x G

Centrifugesupernatant100,000 x G

90 minutes

Disrupt cells inbuffered solution

Centrifuge600 x G

10 minutes

Nuclei inpellet

Mitochondria,chloroplastsin pellet

30 minutes

Centrifugesupernatant20,000 x G

Resuspendpellet layeron top ofsucrosegradient

Densitygradientcentrifugation

Low sucroseconcentration

Su

cro

se d

ensi

ty

gra

die

nt

Microsomal pellet(contains ER, Golgi,plasma membrane)

(b) Differential centrifugation. Cell structures can be separated into various fractions by spinning the suspension at increasing revolutions per minute. Membranes and organelles from the re-suspended pellets can then be further purified by density gradient centrifugation (shown as last step). G is the force of gravity. ER is the endoplasmic reticulum.

Stepped Art

Fig. 4-5b, p. 80

Disrupt cells inbuffered solution

Centrifuge600 x G

10 minutes

Nuclei inpellet

Mitochondria,chloroplastsin pellet

Centrifugesupernatant20,000 x G

30 minutes

Microsomal pellet(contains ER, Golgi,plasma membrane)

90 minutes

Centrifugesupernatant100,000 x G

Low sucroseconcentration

Su

cro

se d

ensi

ty

gra

die

nt

Layeredmicrosomalsuspension

Resuspendpellet layeron top ofsucrosegradient

High sucroseconcentration

Plasmamembrane

Golgi

ER

Densitygradientcentrifugation

100,000 x G

Learning Objective 5Learning Objective 5

• How do the general characteristics of prokaryotic and eukaryotic cells differ?

• How are plant and animal cells different?

ProkaryotesProkaryotes

• Prokaryotic cells• No internal membrane organization• nuclear area (not nucleus)• cell wall• ribosomes• flagella

ProkaryotesProkaryotes

Fig. 4-6, p. 81

Plasmamembrane

0.5 μm

Pili

Storage granule

FlagellumRibosome

Cell wall

CapsuleNucleararea

DNA

EukaryotesEukaryotes

• Eukaryotic cells • membrane-enclosed nucleus• cytoplasm contains organelles• cytosol (fluid component)

Animal CellsAnimal Cells

Fig. 4-8, p. 83

Lysosome

Ribosomes

RoughER

Smooth ERCentrioles Mitochondrion

Rough and smoothendoplastic reticulum (ER)

Nuclearenvelope

Nucleolus

Nucleus

Chromatin

Nuclearpores

Nuclearenvelope

Membranoussacs ofGolgi

Golgi complex

Plasmamembrane

Cristae

Plant CellsPlant Cells

• Plant cells• rigid cell walls• plastids• large vacuoles• no centrioles

Plant CellsPlant Cells

Fig. 4-7, p. 82

Ribosomes

Chloroplast

Granum

Stroma

Smooth ER

Rough and smooth endoplasmic reticulum (ER)

Chromatin

Nuclear pores

Nuclear envelope

Nucleolus

Nucleus

Rough ER

Mitochondrion

VacuolePlasma membraneCell wall

Membranoussacs

Golgi complex

Cristae

Learning Objective 6Learning Objective 6

• What are the three functions of cell membranes?

Cell MembranesCell Membranes

• Divide cell into compartments

• Vesicles transport materials between compartments

• Important in energy storage and conversion

• Endomembrane system

Learning Objective 7Learning Objective 7

• What are the structures and functions of the nucleus?

The NucleusThe Nucleus

• Control center of cell• genetic information coded in DNA

• Nuclear envelope• double membrane

• Nuclear pores• communicate with cytoplasm

Nuclear StructuresNuclear Structures

• Chromatin• DNA and protein

• Chromosomes• DNA condensed for cell division

• Nucleolus• ribosomal RNA synthesis• ribosome assembly

The NucleusThe Nucleus

Fig. 4-11, p. 88(c)

0.25 μm

ER continuouswith outer membraneof nuclear envelope

Outernuclearenvelope Nuclear pore

Inner nuclearenvelope

Nuclearporeproteins

Nucleoplasm

2 μm

Nuclearpore

Chromatin

Nucleolus

Rough ER

Nuclearpores

Nuclearenvelope

(a)

(b)

KEY CONCEPTSKEY CONCEPTS

• Eukaryotic cells have nuclei containing genetic information coded in DNA

Learning Objective 8Learning Objective 8

• What are the structural and functional differences between smooth ER and rough ER?

EEndoplasmic Reticulum (ER)ndoplasmic Reticulum (ER)

• Network of folded membranes• in cytosol

• Smooth ER• lipid synthesis• calcium ion storage• detoxifying enzymes

• Rough ER • ribosomes on outer surface• assembles proteins

ERER

Fig. 4-12, p. 90

1 μm

ER lumenMitochondrion

Ribosomes

RoughER

Smooth ER

Learning Objective 9Learning Objective 9

• Trace the path of protein synthesis:• synthesis in the rough ER• processing, modification, and sorting by

the Golgi complex• transportation to specific destinations

The Golgi ComplexThe Golgi Complex

• Processes proteins synthesized by ER

• Manufactures lysosomes

• Cisternae • stacks of flattened membranous sacs

Transport VesiclesTransport Vesicles

• Formed by membrane budding

• Move glycoproteins • from ER to cis face of Golgi complex• Carry modified proteins from trans face to

specific destination

Protein SynthesisProtein Synthesis

Fig. 4-14, p. 92

transface

Plasmamembrane

Glycoprotein

Rough ER

Ribosomes

Polypeptides synthesizedon ribosomes are insertedinto ER lumen.

Sugars are added, forming glycoproteins.

Transport vesicles deliver glycoproteins to cis face of Golgi.

Glycoproteins modifiedfurther in Golgi.

Glycoproteins move to transface where they are packagedin transport vesicles.

Glycoproteins transported toplasma membrane (or otherorganelle).

Contents of transport vesiclereleased from cell.

Golgi complex

cisface

KEY CONCEPTSKEY CONCEPTS

• Proteins are • synthesized on ribosomes• processed in the endoplasmic reticulum• processed by the Golgi complex• transported by vesicles

Learning Objective 10Learning Objective 10

• What are the functions of lysosomes, vacuoles, and peroxisomes?

Other OrganellesOther Organelles

• Lysosomes• enzymes break down structures

• Vacuoles • store materials in plant cells

• Peroxisomes• produce and degrade hydrogen peroxide

(catalase)

Learning Objective 11Learning Objective 11

• Compare the functions of mitochondria and chloroplasts

• How is ATP synthesized by each of these organelles?

MitochondriaMitochondria

• Site of aerobic respiration

• Double membrane• inner membrane folded (cristae)• matrix (cristae and inner compartment)

• Important in apoptosis• programmed cell death

MitochondriaMitochondria

Fig. 4-19, p. 95

Cristae

0.25 μm

Outermitochondrialmembrane

Innermitochondrialmembrane

Matrix

Aerobic RespirationAerobic Respiration

• Breaks down nutrients using oxygen

• Energy from nutrients packaged in ATP

• CO2, H2O produced as by-products

PlastidsPlastids

• Plastids• organelles that produce and store food• in cells of plants and algae

• Chloroplasts• plastids that carry out photosynthesis

Chloroplast StructureChloroplast Structure

• Stroma• fluid-filled space enclosed by inner

membrane of chloroplast

• Grana• stacks of membranous sacs (thylakoids)• suspended in stroma

ChloroplastsChloroplasts

Fig. 4-20, p. 96

1 μm

Granum(stack ofthylakoids)

StromaInnermembrane

Outermembrane

Intermembranespace

Thylakoidmembrane

Thylakoidlumen

PhotosynthesisPhotosynthesis

• Chlorophyll• green pigment in thylakoid membranes• traps light energy

• Light energy converted to chemical energy in ATP• used to synthesize carbohydrates from

carbon dioxide and water

Mitochondria and Mitochondria and ChloroplastsChloroplasts

Fig. 4-18, p. 95

Light

Aerobic respirationMitochondria (most eukaryotic cells)

PhotosynthesisChloroplasts (some plant and

algal cells)

Glucose Glucose

KEY CONCEPTSKEY CONCEPTS

• Mitochondria and chloroplasts convert energy from one form to another

Learning Objective 12Learning Objective 12

• What are the structures and functions of the cytoskeleton?

The CytoskeletonThe Cytoskeleton

• Microtubules• hollow tubulin cylinders• MTOCs and MAPs

• Microfilaments• actin filaments• important in cell movement

• Intermediate filaments• strengthen cytoskeleton• stabilize cell shape

MicrotubulesMicrotubules

Fig. 4-22a, p. 98

Dimer on

(a) Microtubules are manufactured in the cell by adding dimers of α-tubulin and β-tubulin to an end of the hollow cylinder. Notice that the cylinder has polarity. The end shown at the top of the figure is the fast-growing, or plus,end; the opposite end is the minus end. Each turn of the spiral requires 13 dimers.

α-Tubulin

β-Tubulin

Dimersoff

Minus end

Plus end

Intermediate FilamentsIntermediate Filaments

Fig. 4-27a, p. 101

Protofilament

(a) Intermediate filaments are flexible rods about10 nm in diameter. Each intermediate filamentconsists of components, called protofilaments,composed of coiled protein subunits.

Protein subunits

Intermediate filament

Fig. 4-27b, p. 101

(b) Intermediate filaments are stained green inthis human cell isolated from a tissue culture.

100 μm

MicrofilamentsMicrofilaments

Fig. 4-26a, p. 101

(a) A microfilament consists of two intertwined strings of beadlikeactin molecules.

Fig. 4-26b, p. 101

(b) Many bundles of microfilaments (green) are evident in thisfluorescent LM of fibroblasts, cells found in connective tissue.

100 μm

CytoskeletonCytoskeleton

Fig. 4-21, p. 97

Microtubule

Plasmamembrane

Microfilament

Intermediatefilament

CentrosomeCentrosome

• Main MTOC of animal cells

• Usually contains two centrioles

• Each centriole has 9 x 3 arrangement of microtubules

CentriolesCentrioles

Fig. 4-24a, p. 99

0.25 μm

(a) In the TEM, the centrioles are positioned atright angles to each other, near the nucleus ofa nondividing animal cell.

Centrioles

MTOC

Fig. 4-24b, p. 99

(b) Note the 9 x 3 arrangement of microtubules.The centriole on the right has been cut transversely.

A Kinesin MotorA Kinesin Motor

Fig. 4-23, p. 98

ATP

Microtubule does not move

Plusend

Minusend

Vesicle

Kinesinreceptor

Kinesin

ATP

KEY CONCEPTSKEY CONCEPTS

• The cytoskeleton is a dynamic internal framework that functions in various types of cell movement

Learning Objective 13Learning Objective 13

• How do cilia and flagella differ in structure and function?

Cilia and FlagellaCilia and Flagella

• Cilia and flagella• thin, movable structures• project from cell surface• function in movement

• Cilia are short, flagella are long

CiliaCilia

Fig. 4-25a, p. 100

(a) TEM of a longitudinal section through cilia and basal bodies of the freshwaterprotist Paramecium multimicronucleatum.Some of the interior microtubules are visible.

0.5 μm

Fig. 4-25b, p. 100

(b) TEM of cross sectionsthrough cilia showing9 + 2 arrangement ofmicrotubules.

0.5 μm

Fig. 4-25c, p. 100

0.5 μm

(c) TEM of cross sectionthrough basal bodyshowing 9 x 3 structure.

Fig. 4-25d, p. 100

Central microtubules

(d) This 3-D representation showsnine attached microtubule pairs(doublets) arranged in a cylinder,with two unattached microtubulesin the center. The dynein “arms,”shown widely spaced for clarity,are actually much closer togetheralong the longitudinal axis.

Outer pair of microtubules

Dynein

Plasma membrane

Fig. 4-25e, p. 100

Microtubularbend

(e) The dynein arms move the microtubules by forming and breaking cross bridges on theadjacent microtubules, so that one microtubule “walks” along its neighbor. Flexible linkingproteins between microtubule pairs prevent microtubules from sliding very far. Instead, the motor action causes the microtubules to bend, resulting in a beating motion.

Pair ofmicrotubules

Dynein

Linkingproteins

Learning Objective14Learning Objective14

• Describe the glycocalyx, extracellular matrix, and cell wall

Cell CoatCell Coat

• Glycocalyx (cell coat)• Surrounds cell• Polysaccharides extend from plasma

membrane

ECMECM

• Extracellular matrix (ECM) • Surrounds many animal cell• Carbohydrates and protein

• Fibronectins • glycoproteins of ECM• bind to integrins

• Integrins• receptor proteins in plasma membrane

ECMECM

Fig. 4-28, p. 102

Plasmamembrane

Collagen

Fibronectins

Integrin

Intermediatefilament

Microfilaments

Extracellularmatrix

Cytosol

Cell WallCell Wall

• Cellulose & other polysaccharides• form rigid cell walls• in bacteria, fungi, and plant cells

Fig. 4-29, p. 102

2.5 μm

Cell 1

Middlelamella

Primary cell wall

Multiple layers ofsecondary cell wall

Cell 2

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Typical Prokaryotic CellTypical Prokaryotic Cell

Plant Cell WallsPlant Cell Walls

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Cytoskeletal ComponentsCytoskeletal Components

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Common Eukaryotic Common Eukaryotic OrganellesOrganelles

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Flagella StructureFlagella Structure

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Motor ProteinsMotor Proteins

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The Endomembrane SystemThe Endomembrane System

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