Chapter 6

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 6Chapter 6

A Tour of the Cell

Eukaryotic cells have internal membranes that compartmentalize their functions

• Basic features of all cells: plasma membrane, cytosol, chromosomes, ribosomes

• Prokaryotic vs Eukaryotic cells

– prokaryotic cells Bacteria and Archaea

• No nucleus

• DNA in an unbound region called the nucleoid

• No membrane-bound organelles

• Cytoplasm bound by the plasma membrane

– eukaryotic cells Protists, fungi, animals and plants

• DNA in a nucleus bounded by nuclear envelope

• Membrane-bound organelles

• Cytoplasm in the region between the plasma membrane and nucleus


Fig. 6-6

Fimbriae

Nucleoid

Ribosomes

Plasma membrane

Cell wall

Capsule

Flagella

Bacterialchromosome

0.5 µm

Prokaryotic cell

Fig. 6-9a

ENDOPLASMIC RETICULUM (ER)

Smooth ERRough ERFlagellum***(not in plants)

Centrosome

CYTOSKELETON:

Microfilaments

Intermediatefilaments

Microtubules

Microvilli

Peroxisome

MitochondrionLysosome***(not in plants/prokaryotes)

Golgiapparatus

Ribosomes

Plasma membrane

Nuclearenvelope

Nucleolus

Chromatin

NUCLEUS

Eukaryotic Animal Cell

Fig. 6-9b

NUCLEUS

Nuclear envelopeNucleolusChromatin

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Ribosomes

Central vacuole***

MicrofilamentsIntermediate filamentsMicrotubules

CYTO-SKELETON

Chloroplast***

Plasmodesmata***Wall of adjacent cell

Cell wall***

Plasma membrane

Peroxisome

Mitochondrion

Golgiapparatus

Eukaryotic Plant Cell

***specific to plants

Organelles to know

• Nucleus – Genetic information

• Ribosomes – protein factories

• Endoplasmic Reticulum – protein trafficking and metabolic functions

• Golgi Apparatus – shipping and receiving center

• Lysosomes – digestive compartments

• Vacuoles – maintenance compatments

• Mitochondria – chemical energy conversion (site of cellular respiration)

• Chloroplasts – light energy conversion (site of photosynthesis)

• Peroxisomes - oxidation

• Cytoskeleton – support, motility and regulation

• Extracellular Matrix – support, adhesion, movement, regulation

• Intercellular Junctions – facilitate contact between cells

Nucleus: Information Central

– nuclear envelope encloses the nucleus, separating it from the cytoplasm

– nuclear membrane is a double membrane; each membrane consists of a lipid bilayer

– Pores regulate the entry and exit of molecules from the nucleus

– The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein

– In the nucleus, DNA and proteins form genetic material called chromatin

– Chromatin condenses to form discrete chromosomes

– The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis


Fig. 6-10

NucleolusNucleus

Nuclear lamina

Close-up of nuclear envelope

1 µm

1 µm

0.25 µm

Ribosome

Pore complex

Nuclear pore

Nuclear envelope

Chromatin

Surface ofnuclear envelope

Pore complexes

Ribosomes: Protein factories

– particles made of ribosomal RNA and protein

– Protein synthesis occurs here

• Free ribosomes are localized to the cytosol

• Bound ribosomes are on the ER or the nuclear envelope

Fig. 6-11

Cytosol

Endoplasmic reticulum (ER)

Free ribosomes

Bound ribosomes

Large subunit

Small subunit

Diagram of a ribosome

Endoplasmic Reticulum (ER): Protein Trafficking

– The ER membrane is attached to the nuclear envelope

– There are two distinct regions of ER:

• Smooth ER lacks ribosomes

– Synthesizes lipids

– Metabolizes carbohydrates

– Detoxifies poison

– Stores calcium

• Rough ER with ribosomes

– Secretes glycoproteins (proteins covalently bonded to carbohydrates)

– Distributes transport vesicles, proteins surrounded by membranes

– membrane factory for the cell


Fig. 6-12Smooth ER

Rough ER Nuclear envelope

Rough ERSmooth ER

Transport vesicle

Ribosomes

Golgi apparatus: Shipping and Receiving Center

– shipping and receiving center

– consists of flattened membranous sacs called cisternae

– Functions:

• Modifies products of the ER

• Manufactures certain macromolecules

• Sorts and packages materials into transport vesicles


Cisternae

Lysosome: Digestive Compartment

– a membranous sac of hydrolytic enzymes that can digest macromolecules

– Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids

• After phagocytosis (engulfing of another cell) lysosomes fuse with the food vacuole and digests the molecules

• Autophagy uses enzymes to recycle the cell’s own organelles and macromolecules


Digestiveenzymes

Lysosome

Plasmamembrane

Food vacuole

Digestion

Peroxisome

Vesicle

Lysosome

Mitochondrion Digestion

(a) Phagocytosis (b) Autophagy

– Diverse Maintenance Compartments

– Food vacuoles are formed by phagocytosis

– Contractile vacuoles pump excess water out of cells

– Central vacuoles (in many mature plant cells) hold organic compounds and water


Fig. 6-15

Central vacuole

Cytosol

Central vacuole

Nucleus

Cell wall

Chloroplast

Vacuoles: Maintenance Compartment

The Endomembrane System: A Review

• The endomembrane system is a complex and dynamic player in the cell’s compartmental organization

– Nuclear envelope

– ER

– Golgi apparatus

– Lysosomes

– Vacuoles

– Plasma membrane


Fig. 6-16-3

Smooth ER

Nucleus

Rough ER

Plasma membrane

Golgi

•Nuclear envelope is connected to rough ER•Proteins produced by the ER flow in transport vessicles to the Golgi•Golgi pinches off vessicles that give rise to lysosomes, vessicles and vacuoles•Lysosomes can fuse with another vessicle for digestion•Transport vessicle carries proteins to plasma membrane for secretion•Plasma membrane expands by fusion of vessicles; proteins are secreted from the cell

Transport vessicle

Transport vessicle

Lysosome

Mitochondria: Chemical Energy Conversion

– sites of cellular respiration, a metabolic process that generates ATP

– Have a double membrane

– Contain their own DNA

– Mitochondria are in nearly all eukaryotic cells

– They have a smooth outer membrane and an inner membrane folded into cristae

• Cristae present a large surface area for enzymes that synthesize ATP

– The inner membrane creates two compartments: intermembrane space and mitochondrial matrix

• Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix


Fig. 6-17

Free ribosomesin the mitochondrial matrix

Intermembrane space

Outer membrane

Inner membraneCristae

Matrix

0.1 µm

Chloroplasts: Light Energy Conversion

– Capture light energy, are the sites of photosynthesis

– found in plants and algae

– Have a double membrane (similar to mitochondria)

– Contain their own DNA (similar to mitochondria)

– contain chlorophyll and other molecules that function in photosynthesis

– found in leaves and other green organs of plants and in algae


Ribosomes

Thylakoid

Stroma

Granum

Inner and outer membranes

1 µm

– oxidative organelles

– specialized metabolic compartments bounded by a single membrane

– produce hydrogen peroxide and convert it to water

– Oxygen is used to break down different types of molecules


1 µm

ChloroplastPeroxisome

Mitochondrion

Peroxisome: Oxidation

Cytoskeleton: Support, Motility and Regulation

– a network of fibers extending throughout the cytoplasm

– organizes the cell’s structures and activities, anchoring many organelles

– composed of three types of molecular structures:

• Microtubules are the thickest of the three components

• Microfilaments, also called actin filaments, are the thinnest components

• Intermediate filaments are fibers with diameters in a middle range

– helps to support the cell and maintain its shape

– interacts with motor proteins to produce motility


• Functions

– Shaping the cell

– Guiding movement of organelles

– Separating chromosomes during cell division

• Centrosomes

– The centrosome is a “microtubule-organizing center”

– microtubules grow out from a centrosome near the nucleus and attach to chromosomes during mitosis

• Cilia and Flagella

– Microtubules control the beating of cilia and flagella

– A core of microtubules sheathed by the plasma membrane


Microtubules

Fig. 6-22

Centrosome

Microtubule

centrosome

microtubules

Microtubules separate chromosomes during mitosis

Fig. 6-23

(a) EX: Motion of flagella in sperm (b) EX: Motion of cilia in aquatic life

Microtubules assist in motility

Fig. 6-24

(c) Cross section of basal body

(a) Longitudinal section of cilium

Plasma membrane

Basal body

Microtubules

(b) Cross section of cilium

Plasma membrane

Microtubule structure in cilia

Microfilaments (Actin Filaments)

• Microfilaments are solid rods built as a twisted double chain of actin subunits

• The structural role: bear tension and resist pulling forces within the cell

• Cellular function: cellular motility

– Myosin and actin contribute to this

• Examples

– Muscle contraction

– Ameoboid movement occurs through Pseudopodia

– Cytoplasmic streaming


Microvillus

Microfilaments (actin filaments)

Intermediate filaments

Intermediate Filaments

• They support cell shape and fix organelles in place

• more permanent cytoskeleton fixtures than the other two classes


Cell Walls of Plants

• Prokaryotes, fungi, and some protists also have cell walls

• Functions: protects the plant cell, maintains its shape, prevents excessive uptake of water

• made of cellulose fibers

• Plant cell walls may have multiple layers:

– Primary cell wall: relatively thin and flexible

– Middle lamella: thin layer between primary walls of adjacent cells

– Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall


Fig. 6-28

Secondary cell wall

Primary cell wall

Middle lamella

Central vacuoleCytosol

Plasma membrane

Plant cell walls

Plasmodesmata

1 µm

The Extracellular Matrix (ECM) of Animal Cells

• Functions

– Support

– Adhesion

– Movement

– Regulation

• made up of glycoproteins (collagen, proteoglycans, and fibronectin)

• ECM proteins bind to receptor proteins in the plasma membrane called integrins


EXTRACELLULAR MATRIXCollagen

Fibronectin

Micro-filaments

CYTOPLASM

Integrins

Proteoglycancomplex

Intercellular Junctions

• Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact

• Intercellular junctions facilitate this contact

• There are several types of intercellular junctions

– Plasmodesmata – channels that perforate cell walls

– Tight junctions - membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid

– Desmosomes (anchoring junctions) fasten cells together into strong sheets

– Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells


Fig. 6-32

Tight junction

0.5 µm

Desmosome

Gap junction

Extracellularmatrix

0.1 µm

Plasma membranesof adjacent cells

Spacebetweencells

Gapjunctions

Desmosome

Intermediatefilaments

Tight junction

Tight junctions preventfluid from movingacross a layer of cells

Desmosomes fasten cells together in sheets

Gap junctions all cells to communicate with one another via cytoplasmic channels

Fig. 6-UN1Cell Component Structure Function

Houses chromosomes, made ofchromatin (DNA, the geneticmaterial, and proteins); containsnucleoli, where ribosomalsubunits are made. Poresregulate entry and exit ofmaterials.

Nucleus

(ER)

Concept 6.3 The eukaryotic cell’s geneticinstructions are housed inthe nucleus and carried outby the ribosomes

Ribosome

Concept 6.4 Endoplasmic reticulum The endomembrane systemregulates protein traffic andperforms metabolic functionsin the cell

(Nuclearenvelope)

Concept 6.5 Mitochondria and chloro-plasts change energy fromone form to another

Golgi apparatus

Lysosome

Vacuole

Mitochondrion

Chloroplast

Peroxisome

Two subunits made of ribo-somal RNA and proteins; can befree in cytosol or bound to ER

Extensive network ofmembrane-bound tubules andsacs; membrane separateslumen from cytosol;continuous withthe nuclear envelope.

Membranous sac of hydrolyticenzymes (in animal cells)

Large membrane-boundedvesicle in plants

Bounded by doublemembrane;inner membrane hasinfoldings (cristae)

Typically two membranesaround fluid stroma, whichcontains membranous thylakoidsstacked into grana (in plants)

Specialized metaboliccompartment bounded by asingle membrane

Protein synthesis

Smooth ER: synthesis oflipids, metabolism of carbohy-drates, Ca2+ storage, detoxifica-tion of drugs and poisons

Rough ER: Aids in synthesis ofsecretory and other proteins frombound ribosomes; addscarbohydrates to glycoproteins;produces new membrane

Modification of proteins, carbo-hydrates on proteins, and phos-pholipids; synthesis of manypolysaccharides; sorting of Golgiproducts, which are then released in vesicles.

Breakdown of ingested substances,cell macromolecules, and damagedorganelles for recycling

Digestion, storage, wastedisposal, water balance, cellgrowth, and protection

Cellular respiration

Photosynthesis

Contains enzymes that transferhydrogen to water, producinghydrogen peroxide (H2O2) as aby-product, which is convertedto water by other enzymesin the peroxisome

Stacks of flattenedmembranoussacs; has polarity(cis and transfaces)

Surrounded by nuclearenvelope (double membrane)perforated by nuclear pores.The nuclear envelope iscontinuous with theendoplasmic reticulum (ER).