Chapter 3:Cells

(The Living Units)

Camillo Golgi (1843-1926)Identified the cell organelle now named the “Golgi Body” and he worked extensively in

research helping to define the field of neurobiology. Dr. Golgi received Nobel Prize in

1906.

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Figure 3.2 Structure of the generalized cell.

Secretion beingreleased from cellby exocytosis

Peroxisome

Ribosomes

Roughendoplasmicreticulum

Nucleus

Nuclear envelopeChromatin

Golgi apparatus

NucleolusSmooth endoplasmicreticulum

Cytosol

Lysosome

Mitochondrion

CentriolesCentrosomematrix

Cytoskeletalelements• Microtubule• Intermediate filaments

Plasmamembrane

Figure 3.1 Cell diversity.

Fibroblasts

Erythrocytes

Epithelial cells

(d) Cell that fights disease

Nerve cell

Fat cell

Sperm

(a) Cells that connect body parts, form linings, or transport gases

(c) Cell that storesnutrients

(b) Cells that move organs and body parts

(e) Cell that gathers information and control body functions

(f) Cell of reproduction

SkeletalMusclecell

Smoothmuscle cells

Macrophage

Figure 3.3 Structure of the plasma membrane according to the fluid mosaic model.

Integralproteins

Extracellular fluid(watery environment)

Cytoplasm(watery environment)

Polar head ofphospholipid molecule

Glycolipid

Cholesterol

Peripheralproteins

Bimolecularlipid layercontainingproteins

Inward-facinglayer ofphospholipids

Outward-facinglayer ofphospholipids

Carbohydrate of glycocalyx

Glycoprotein

Filament of cytoskeleton

Nonpolar tail of phospholipid molecule

Figure 3.4a Membrane proteins perform many tasks.

A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane.

(a) Transport

Figure 3.4b Membrane proteins perform many tasks.

A membrane protein exposed to the outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external signal may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell.

(b) Receptors for signal transductionSignal

Receptor

Figure 3.4c Membrane proteins perform many tasks.

Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together.

(c) Attachment to the cytoskeleton and extracellular matrix (ECM)

Figure 3.4d Membrane proteins perform many tasks.

A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic pathway as indicated (left to right) here.

(d) Enzymatic activity

Enzymes

Figure 3.4e Membrane proteins perform many tasks.

Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions.

CAMs

(e) Intercellular joining

Figure 3.4f Membrane proteins perform many tasks.

Some glycoproteins (proteins bonded to short chains of sugars) serve as identification tags that are specifically recognized by other cells.

(f) Cell-cell recognition

Glycoprotein

Figure 3.5 Cell junctions.

Interlockingjunctionalproteins

Intercellularspace

Intercellularspace

Plasma membranesof adjacent cells

Microvilli

Intercellularspace

Basement membrane

Plaque

Linkerglycoproteins(cadherins)

Intermediatefilament(keratin)

Intercellularspace

Channelbetween cells(connexon)

(a) Tight junctions: Impermeable junctions prevent molecules from passing through the intercellular space.

(b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers.

(c) Gap junctions: Communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication.

Figure 3.6 Diffusion.

Figure 3.7 Diffusion through the plasma membrane.

Extracellular fluid

Lipid-solublesolutes

Cytoplasm

Lipid-insoluble solutes (such as sugars or amino acids)

Small lipid-insoluble solutes

Watermolecules

Lipidbillayer

Aquaporin

(a) Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer

(b) Carrier-mediated facilitated diffusion via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein

(c) Channel-mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge

(d) Osmosis, diffusion of a solvent such as water through a specific channel protein (aquaporin) or through the lipid bilayer

(a) Membrane permeable to both solutes and water

Solute and water molecules move down their concentration gradientsin opposite directions. Fluid volume remains the same in both compartments.

Leftcompartment:Solution withlower osmolarity

Rightcompartment:Solution with greater osmolarity

Membrane

H2O

Solute

Solutemolecules(sugar)

Both solutions have thesame osmolarity: volumeunchanged

Figure 3.8a Influence of membrane permeability on diffusion and osmosis.

(b) Membrane permeable to water, impermeable to solutes

Both solutions have identicalosmolarity, but volume of thesolution on the right is greaterbecause only water is free to move

Solute molecules are prevented from moving but water moves by osmosis.Volume increases in the compartment with the higher osmolarity.

Leftcompartment

Rightcompartment

Membrane

Solutemolecules(sugar)

H2O

Figure 3.8b Influence of membrane permeability on diffusion and osmosis.

Figure 3.9 The effect of solutions of varying tonicities on living red blood cells.

Cells retain their normal size andshape in isotonic solutions (same

solute/water concentration as insidecells; water moves in and out).

Cells lose water by osmosis and shrink in a hypertonic solution

(contains a higher concentration of solutes than are present inside

the cells).

(a) Isotonic solutions (b) Hypertonic solutions (c) Hypotonic solutions

Cells take on water by osmosis untilthey become bloated and burst (lyse)

in a hypotonic solution (contains alower concentration of solutes than

are present in cells).

Figure 3.10 Primary Active Transport: The Na+-K+ Pump

Extracellular fluid

6 K+ is released from the pump proteinand Na+ sites are ready to bind Na+ again.The cycle repeats.

2 Binding of Na+ promotes phosphorylation of the protein by ATP.

1 Cytoplasmic Na+ binds to pump protein.

Na+

K+ released

ATP-binding siteNa+ bound

Cytoplasm

ATPADP

P

K+

5 K+ binding triggers release of the phosphate. Pump protein returns to its original conformation.

3 Phosphorylation causes the protein to change shape, expelling Na+ to the outside.

4 Extracellular K+ binds to pump protein.

Na+ released

P

K+

PPi

Na+–K+ pump

K+ bound

Figure 3.12 Events of endocytosis mediated by protein-coated pits.

Coated pit ingestssubstance.

Protein-coated vesicle detaches.

Coat proteins detachand are recycled to plasma membrane.

Uncoated vesicle fuseswith a sorting vesicle called an endosome.

Transport vesicle containing

membrane components moves to the plasma

membrane for recycling.Fused vesicle may (a) fusewith lysosome for digestion of its contents, or (b) deliver its contents to the plasmamembrane on the opposite side of the cell (transcytosis).

Protein coat(typically clathrin)

Extracellular fluid Plasmamembrane

Endosome

Lysosome

Transportvesicle

(b)(a)

Uncoatedendocytic vesicle

Cytoplasm

1

2

3

4

5

6

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Overview of Endocytosis (This diagram is not in your textbook.)

Recycling ofmembrane andreceptors (if present)to plasma membrane

CytoplasmExtracellular fluid

Extracellularfluid

Plasmamembrane

Detachmentof clathrin-coatedvesicle

Clathrin-coatedvesicle

Uncoating

Uncoatedvesicle

Uncoatedvesiclefusing withendosome

To lysosomefor digestionand releaseof contents

Transcytosis

Endosome

Exocytosisof vesiclecontents

Clathrin-coatedpit

Plasmamembrane

Ingestedsubstance

Clathrinprotein

(c) Receptor-mediated endocytosis

Extracellularfluid

Cytoplasm

Bacteriumor otherparticle

Pseudopod

Clathrinprotein

(b) Phagocytosis

Clathrinprotein

Membranereceptor

(a) Clathrin-mediated endocytosis

1

3

2

Phagosome

(a) PhagocytosisThe cell engulfs a large particle by forming pro-jecting pseudopods (“false feet”) around it and en-closing it within a membrane sac called a phagosome. The phagosome is combined with a lysosome. Undigested contents remain in the vesicle (now called a residual body) or are ejected by exocytosis. Vesicle may or may not be protein-coated but has receptors capable of binding to microorganisms or solid particles.

Figure 3.13a Comparison of three types of endocytosis.

Figure 3.13b Comparison of three types of endocytosis.

Vesicle

(b) PinocytosisThe cell “gulps” drops of extracellular fluid containing solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated.

Figure 3.13c Comparison of three types of endocytosis.

Vesicle

Receptor recycledto plasma membrane

(c) Receptor-mediatedendocytosisExtracellular substances bind to specific receptor proteins in regions of coated pits, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles. Ligands may simply be released inside the cell, or combined with a lysosome to digest contents. Receptors are recycled to the plasma membrane in vesicles.

Copyright © 2010 Pearson Education, Inc.

The Process of Exocytosis (This is not in your textbook).

Extracellularfluid

Cytoplasm

Molecules tobe secreted

VesicleSNARE

Plasma membraneSNARE

Secretory vesicle

(a)

(b)

i>Clicker Question #1:

Which of the following would be considered true for facilitated diffusion?

a.The movement of materials is along (or with) the concentration gradient.

b. The process may use a channel protein.

c. An example of facilitated diffusion is seen in the sodium-potassium pump.

d.Two of the above are correct.

e.All of the above are correct.

Figure 3.14a Exocytosis.

1 The membrane-bound vesicle migrates to the plasma membrane.

2 There, proteinsat the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins).

(a) The process of exocytosisExtracellular

fluid

Plasma membraneSNARE (t-SNARE)

Secretoryvesicle

VesicleSNARE(v-SNARE)

Molecule tobe secreted

Cytoplasm

Fusedv- and

t-SNAREs

3 The vesicleand plasma membrane fuse and a pore opens up.

4 Vesiclecontents are released to the cell exterior.

Fusion pore formed

Figure 3.14b Exocytosis.

Figure 3.17 Mitochondrion.

Enzymes

Matrix

Cristae

Mitochondrial DNA

Ribosome

Outer mitochondrial membrane

Inner mitochondrial membrane

(b)

(a)

(c)

Figure 3.18 The endoplasmic reticulum.

Nuclearenvelope

Ribosomes

Rough ER

Smooth ER

(a) Diagrammatic view of smooth and rough ER

(b) Electron micrograph of smooth and rough ER (10,000x)

Figure 3.19 Golgi apparatus.

Cis face—“receiving” side of Golgi apparatus

Secretoryvesicle

(a) Many vesicles in the process of pinching off from the membranous Golgi apparatus.

(b) Electron micrograph of the Golgi apparatus (90,000x)

Transport vesiclefrom the Golgi apparatus

Transportvesiclefromtrans face

Trans face—“shipping” side ofGolgi apparatus

New vesiclesforming

New vesicles forming

Cisternae

Transport vesiclefrom rough ER

Golgi apparatus

Figure 3.20 The sequence of events from protein synthesis on the rough ER to the final distribution of those proteins.

Protein-containing vesicles pinch off rough ERand migrate to fuse with membranes ofGolgiapparatus.

Proteins aremodified withinthe Golgi compartments.

Proteins arethen packagedwithin differentvesicle types, depending ontheir ultimatedestination.

Plasmamem-brane

Secretion byexocytosis

Vesicle becomeslysosome

Golgiapparatus

Rough ER ERmembrane

Phagosome

Proteins incisterna

Pathway B:Vesicle membraneto be incorporatedinto plasmamembrane

Pathway A:Vesicle contentsdestined for exocytosis Extracellular fluid

Secretoryvesicle

Pathway C:Lysosome containing acid hydrolaseenzymes

1

3

2

Figure 3.21 Electron micrograph of a cell containing lysosomes (12,000x).

Lysosomes

Light areas are regions wherematerials are being digested.

Figure 3.22 The endomembrane system.

Golgiapparatus

Transportvesicle

Plasmamembrane

Vesicle

Smooth ER

Rough ER

Nuclear envelope

Lysosome

Nucleus

Figure 3.23 Cytoskeletal elements support the cell and help to generate movement.

Strands made of spherical proteinsubunits called actins

Tough, insoluble protein fibersconstructed like woven ropes

(a) Microfilaments (b) Intermediate filaments (c) Microtubules

Hollow tubes of spherical proteinsubunits called tubulins

Actin subunit

7 nm 10 nm 25 nm

Fibrous subunits

Tubulin subunits

Microfilaments form the blue networksurrounding the pink nucleus in this photo.

Intermediate filaments form the purplebatlike network in this photo.

Microtubules appear as gold networks surrounding the cells’ pink nuclei in this photo.

Figure 3.25 Centrioles.

Centrosome matrix

(b)

(a)

Centrioles

Microtubules

Figure 3.26 Structure of a cilium.

Plasmamembrane

Outer microtubuledoublet

Dynein arms

Centralmicrotubule

Radial spoke

Radial spoke

TEM

TEM

Triplet

Basal body(centriole)

Cilium

Microtubules

Plasmamembrane

Basal body

Cross-linkingproteins insideouter doublets

Cross-linkingproteins insideouter doublets

A longitudinal section of acilium shows microtubules running the length of thestructure.

The doubletsalso have attached motor proteins, the dynein arms.

The outermicrotubule doublets and the two central microtubules are held together by cross-linking proteins and radial spokes.

A cross section through thebasal body. The nine outer doublets of a cilium extend into a basal body where each doublet joins another microtubule to form a ring of nine triplets.

A cross section through thecilium shows the “9 + 2”arrangement of microtubules.

TEM

Figure 3.27 Ciliary function.

(a) Phases of ciliary motion.

(b) Traveling wave created by the activity ofmany cilia acting together propels mucusacross cell surfaces.

Power, orpropulsive,stroke

Layer of mucus

Cell surface

Recovery stroke, whencilium is returning to itsinitial position

1 2 3 4 5 6 7

Figure 3.29 The nucleus.

Chromatin (condensed)

Nuclear envelope

Nucleus

Nuclear pores

Fracture line of outermembrane

Nuclear porecomplexes. Each pore is ringed by protein particles.

Surface of nuclear envelope.

Nuclear lamina. The netlike lamina composed of intermediate filaments formed by lamins lines the inner surface of the nuclear envelope.

Nucleolus

Cisternae of rough ER

(a)

(b)

Figure 3.30 Chromatin and chromosome structure.

Metaphasechromosome(at midpointof cell division)

Nucleosome (10-nm diameter; eight histone proteins wrapped by two winds of the DNA double helix)

Linker DNA

Histones

(a)

(b)

1 DNA doublehelix (2-nm diameter)

2 Chromatin(“beads on a string”) structurewith nucleosomes

3 Tight helical fiber(30-nm diameter)

5 Chromatid(700-nm diameter)

4 Looped domain structure (300-nm diameter)

Figure 3.31 The cell cycle.

G1

Growth

SGrowth and DNA

synthesis G2

Growth and finalpreparations for

divisionM

G2 checkpoint

G1 checkpoint(restriction point)

Figure 3.33 Mitosis (1 of 2)

Centrosomes (each has 2 centrioles)

Earlymitoticspindle

Spindle pole

Kinetochore Kinetochoremicrotubule

Polar microtubule

Nucleolus

Interphase Early Prophase Late Prophase

Centromere

Plasmamembrane Fragments

of nuclearenvelope

Aster

Nuclearenvelope

Chromosomeconsisting of twosister chromatids

Chromatin

Interphase Early Prophase Late Prophase

Figure 3.33 Mitosis (2 of 2)

Contractilering at

cleavagefurrow

Nuclearenvelopeforming

Nucleolus forming

Spindle

Metaphaseplate

Metaphase Anaphase Telophase

Daughterchromosomes

Metaphase Anaphase Telophase andCytokinesis

Cell Metabolism Characteristics

•Cofactors & coenzymes

Cell Metabolism Characteristics

•Aerobic & Anaerobic Respiration

Cell Metabolism Characteristics

•Pathways used in breakdown of Carbohydrates, Lipids, Fats