Chapter 2 Cell Structure & Function

© 2012 Pearson Education Inc.

Lecture prepared by Mindy Miller-KittrellNorth Carolina State University

Chapter 3

Cell Structure and Function

Processes of Life

• Growth• Reproduction• Responsiveness• Metabolism


Figure 3.1 Examples of types of cells-overview

• Prokaryotes– Lack nucleus

– Lack various internal structures bound with phospholipid membranes

– Are small (~1.0 µm in diameter)

– Have a simple structure

– Include bacteria and archaea


Prokaryotic and Eukaryotic Cells: An Overview

Figure 3.2 Typical prokaryotic cell

Ribosome

Cytoplasm

Nucleoid

GlycocalyxCell wall Cytoplasmic membrane

Inclusions

Flagellum

• Eukaryotes– Have nucleus

– Have internal membrane-bound organelles

– Are larger (10–100 µm in diameter)

– Have more complex structure

– Include algae, protozoa, fungi, animals, and plants


Prokaryotic and Eukaryotic Cells: An Overview

Figure 3.3 Typical eukaryotic cell

Nucleolus

Cilium

Ribosomes

Nuclear envelope

Nuclear pore

Lysosome

Mitochondrion

Centriole

Secretory vesicle

Golgi body

Transport vesicles

Rough endoplasmicreticulum

Smooth endoplasmicreticulum

Cytoplasmicmembrane

Cytoskeleton

Figure 3.4 Approximate size of various types of cells

Chicken egg4.7 cm diameter

(47,000 m)*

VirusOrthopoxvirus

0.3 m diameter

BacteriumStaphylococcus1 m diameter

Parasitic protozoanGiardia

14 m length

*Actually, the inset box on the egg would be too small to be visible. (Width of box would be about 0.002 mm.)

External Structures of Bacterial Cells

• Glycocalyces

– Gelatinous, sticky substance surrounding the outside of the cell

– Composed of polysaccharides, polypeptides, or both



• Two Types of Glycocalyces– Capsule

– Composed of organized repeating units of organic chemicals

– Firmly attached to cell surface– May prevent bacteria from being recognized by host

– Slime layer– Loosely attached to cell surface– Water soluble– Sticky layer allows prokaryotes to attach to surfaces


Figure 3.5 Glycocalyces-overview

Glycocalyx(capsule)

Glycocalyx(slime layer)


ANIMATION Motility



• Flagella– Are responsible for movement

– Have long structures that extend beyond cell surface

– Are not present on all bacteria



• Flagella– Structure

– Composed of filament, hook, and basal body– Basal body anchors filament and hook to cell wall

by a rod and a series of either two or four rings of integral proteins




ANIMATION Flagella: Structure

Figure 3.6 Proximal structure of bacterial flagella-overview

Filament

Directionof rotationduring run

Peptidoglycanlayer (cell wall)

Cytoplasmicmembrane

Cytoplasm

Rod

Protein rings

Gram Gram

Filament

Outerproteinrings

Rod

Integral protein

Innerproteinrings

Integralprotein

Basalbody

Cytoplasm

Outer membrane

Peptidoglycanlayer

Cytoplasmicmembrane

Cellwall

Ho

o

k

Ho

o

k

Figure 3.7 Micrographs of basic arrangements of bacterial flagella-overview



ANIMATION Flagella: Arrangement

ANIMATION Flagella: Spirochetes

Figure 3.8 Axial filament-overview

Axial filament

Endoflagellarotate Axial filament

rotates aroundcell

Outermembrane

Cytoplasmicmembrane

Axial filamentSpirochetecorkscrewsand movesforward


• Flagella– Function

– Rotation propels bacterium through environment– Rotation reversible; can be counterclockwise or

clockwise– Bacteria move in response to stimuli (taxis)

– Runs – Tumbles


Figure 3.9 Motion of a peritrichous bacterium

Tumble

Run

Tumble

Attractant

Run



ANIMATION Flagella: Movement


• Fimbriae and Pili– Rodlike proteinaceous extensions




• Fimbriae– Sticky, bristlelike projections– Used by bacteria to adhere to one another, to

hosts, and to substances in environment– Shorter than flagella– Serve an important function in biofilms

Figure 3.10 Fimbriae

Flagellum Fimbria


• Pili– Special type of fimbria

– Also known as conjugation pili

– Longer than other fimbriae but shorter than flagella

– Bacteria typically have only one or two per cell

– Mediate the transfer of DNA from one cell to another (conjugation)


Figure 3.11 Pili

Conjugation pilus

Bacterial Cell Walls

• Bacterial Cell Walls– Provide structure and shape and protect cell from

osmotic forces– Assist some cells in attaching to other cells or in

resisting antimicrobial drugs– Can target cell wall of bacteria with antibiotics– Give bacterial cells characteristic shapes– Composed of peptidoglycan– Scientists describe two basic types of bacterial cell

walls, Gram-positive and Gram-negative


Figure 3.12 Bacterial shapes and arrangements-overview

Figure 3.13 Comparison of the structures of glucose, NAG, and NAM-overview

Glucose N-acetylglucosamineNAG

N-acetylmuramic acidNAM


• Gram-Positive Bacterial Cell Walls– Relatively thick layer of peptidoglycan

– Contain unique polyalcohols called teichoic acids

– Appear purple following Gram staining procedure

– Up to 60% mycolic acid in acid-fast bacteria helps cells survive desiccation


Figure 3.15a Comparison of cell walls of Gram-positive and Gram-negative bacteria

Gram-positive cell wall

Peptidoglycan layer(cell wall)

Cytoplasmic membrane

Teichoic acid

Lipoteichoic acid

Integralprotein


• Gram-Negative Bacterial Cell Walls– Have only a thin layer of peptidoglycan

– Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)

– May be impediment to the treatment of disease

– Appear pink following Gram staining procedure


Figure 3.15b Comparison of cell walls of Gram-positive and Gram-negative bacteria

Gram-negative cell wall

Outermembraneof cell wall

Peptidoglycanlayer of cell wall

Cytoplasmicmembrane

Lipopolysaccharide(LPS)

Porin

Porin(sectioned)

Periplasmic space

Phospholipid layers

Integralproteins

n

Corepolysaccharide

O side chain(varies Inlength andcomposition)

Lipid A(embeddedin outermembrane)

Fatty acid

Bacterial Cytoplasmic Membranes

• Structure– Referred to as phospholipid bilayer

– Composed of lipids and associated proteins– Fluid mosaic model describes current

understanding of membrane structure


Figure 3.16 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer

Head, whichcontains phosphate(hydrophilic)

Tail(hydrophobic)

Phospholipid

Phospholipidbilayer

Integral proteinPeripheral protein

Integralprotein

Cytoplasm

Integralproteins


• Function– Energy storage– Harvest light energy in photosynthetic bacteria– Selectively permeable– Naturally impermeable to most substances– Proteins allow substances to cross membrane– Maintain concentration and electrical gradient


Figure 3.17 Electrical potential of a cytoplasmic membrane

Cell exterior (extracellular fluid)

Cell interior (cytoplasm)


Integralprotein

Protein

Protein

DNA


• Function– Passive processes

– Diffusion– Facilitated diffusion – Osmosis


Figure 3.18 Passive processes of movement across a cytoplasmic membrane-overview

Extracellular fluid

Cytoplasm

Diffusionthrough thephospholipidbilayer

Facilitateddiffusionthrough anonspecificchannelprotein

Facilitated diffusionthrough a permeasespecific for one chemical;binding of substratecauses shape change inthe channel protein

Osmosis,the diffusion ofwater through aspecific channelprotein or throughthe phospholipidbilayer

Figure 3.19 Osmosis, the diffusion of water across a selectively permeable membrane-overview

Solutes Semipermeablemembrane allowsmovement of H2O,but not of solutes

Figure 3.20 Effects of isotonic, hypertonic, and hypotonic solutions on cells-overview

Isotonic solution Hypertonic solution Hypotonic solution

Cells without a wall(e.g., mycoplasmas,animal cells)

Cells with a wall(e.g., plants, fungaland bacterial cells)

Cell wall Cell wall

Cell membrane Cell membrane

H2O H2O

H2O

H2O H2O H2O


• Function– Active processes

– Active transport

– Group translocation– Substance chemically modified during transport


Figure 3.21 Mechanisms of active transport-overview

Extracellular fluidUniport

Cytoplasmicmembrane

Symport

Cytoplasm

Uniport Antiport Coupled transport:uniport and symport



ANIMATION Active Transport: Overview

ANIMATION Active Transport: Types

Figure 3.22 Group translocation

Extracellular fluid

Glucose

Cytoplasm

Glucose 6-PO4

Cytoplasm of Bacteria

• Cytosol – Liquid portion of cytoplasm• Inclusions – May include reserve deposits of

chemicals• Endospores – Unique structures produced by

some bacteria that are a defensive strategy against unfavorable conditions


Figure 3.23 Granules of PHB in the bacterium Azotobacter chroococcum

Polyhydroxybutyrate

Figure 3.24 The formation of an endospore-overview

DNA is replicated.

DNA aligns alongthe cell’s long axis.

Cytoplasmic membraneinvaginates to formforespore.

Cytoplasmic membranegrows and engulfsforespore within a second membrane.Vegetative cell’s DNAdisintegrates.

Cell wallCytoplasmicmembrane

DNA

Vegetative cell

Forespore

Firstmembrane

Second membrane

A cortex of calcium anddipicolinic acid isdeposited betweenthe membranes.

Spore coat formsaround endospore.

Endospore matures:completion of spore coatand increase in resistanceto heat and chemicals byunknown process.

Endospore is released fromoriginal cell.

Cortex

Spore coat

Outerspore coat

Endospore

Outerspore coat

Cytoplasm of Bacteria

• Nonmembranous Organelles

– Ribosomes – Sites of protein synthesis

– Cytoskeleton – Plays a role in forming the cell’s basic shape


Figure 3.25 A simple helical cytoskeleton

External Structures of Archaea

• Glycocalyces– Function in the formation of biofilms– Adhere cells to one another and inanimate objects

• Flagella– Consist of basal body, hook, and filament – Numerous differences with bacterial flagella

• Fimbriae and Hami– Many archaea have fimbriae– Some make fimbriae-like structures called hami

– Function to attach archaea to surfaces


Figure 3.26 Archaeal hami

Hamus

Grapplinghook

Prickles

Archaeal Cell Walls and Cytoplasmic Membrane

– Most archaea have cell walls– Do not have peptidoglycan – Contain variety of specialized polysaccharides

and proteins

– All archaea have cytoplasmic membranes– Maintain electrical and chemical gradients– Control import and export of substances from the

cell


Figure 3.27 Representative shapes of archaea-overview

Cytoplasm of Archaea

– Archaeal cytoplasm similar to bacterial cytoplasm– Have 70S ribosomes – Fibrous cytoskeleton– Circular DNA

– Archaeal cytoplasm also differs from bacterial cytoplasm– Different ribosomal proteins– Different metabolic enzymes to make RNA– Genetic code more similar to eukaryotes


External Structure of Eukaryotic Cells

• Glycocalyces – Never as organized as prokaryotic capsules

– Help anchor animal cells to each other

– Strengthen cell surface

– Provide protection against dehydration

– Function in cell-to-cell recognition and communication


Eukaryotic Cell Walls

– Fungi, algae, plants, and some protozoa have cell walls

– Composed of various polysaccharides– Plant cell walls composed of cellulose– Fungal cell walls composed of cellulose, chitin,

and/or glucomannan– Algal cell walls composed of a variety of

polysaccharides


Figure 3.28 A eukaryotic cell wall

Cell wall Cytoplasmic membrane

Eukaryotic Cytoplasmic Membranes

– All eukaryotic cells have cytoplasmic membrane– Are a fluid mosaic of phospholipids and proteins– Contain steroid lipids to help maintain fluidity– Contain regions of lipids and proteins called

membrane rafts– Control movement into and out of cell


Figure 3.29 Eukaryotic cytoplasmic membrane

Cytoplasmicmembrane

Intercellularmatrix

Cytoplasmicmembrane

Figure 3.30 Endocytosis-overview

Pseudopodium

Cytoplasm of Eukaryotes

• Flagella– Structure and arrangement

– Differ structurally and functionally from prokaryotic flagella

– Within the cytoplasmic membrane– Shaft composed of tubulin arranged to form

microtubules– Filaments anchored to cell by basal body– May be single or multiple

– Function– Do not rotate but undulate rhythmically


Figure 3.31a Eukaryotic flagella and cilia

Flagellum

Figure 3.31b Eukaryotic flagella and cilia

Cilia

Figure 3.32 Movement of eukaryotic flagella and cilia-overview

Direction of motion

Direction of motion

Flagella

Cilia


• Cilia– Shorter and more numerous than flagella

– Coordinated beating propels cells through their environment

– Also used to move substances past the surface of the cell


Figure 3.31c Eukaryotic flagella and cilia


Cytosol

Central pairmicrotubules

Microtubules(doublet)

“9 2”arrangement

Cytoplasmicmembrane

Basal body

Microtubules(triplet) “9 0”

arrangement

Portioncut away to showtransition areafrom doubletsto triplets andthe end ofcentralmicrotubules. ..


• Other Nonmembranous Organelles– Ribosomes

– Larger than prokaryotic ribosomes (80S versus 70S)– Composed of 60S and 40S subunits

– Cytoskeleton– Extensive network of fibers and tubules– Anchors organelles– Produces basic shape of the cell– Made up of tubulin microtubules, actin

microfilaments, and intermediate filaments


Figure 3.33 Eukaryotic cytoskeleton-overview

Microtubule Microfilament

Intermediate filament

Tubulin

Actinsubunit

Proteinsubunits


• Other Nonmembranous Organelles– Centrioles and centrosome

– Centrioles play a role in mitosis, cytokinesis, and formation of flagella and cilia

– Centrosome is region of cytoplasm where centrioles are found


Figure 3.34 Centrosome-overview Centrosome (made up of two centrioles)

Microtubules

Triplet


• Membranous Organelles– Nucleus

– Often largest organelle in cell– Contains most of the cell’s DNA– Nucleoplasm

– Contains chromatin– Nucleoli present in nucleoplasm; RNA

synthesized in nucleoli– Surrounded by nuclear envelope


Figure 3.35 Eukaryotic nucleus

Nucleolus

Nucleoplasm

Chromatin

Nuclear envelope

Two phospholipidbilayers

Nuclear pores

Rough ER


• Membranous Organelles– Endoplasmic reticulum

– Netlike arrangement of flattened, hollow tubules continuous with nuclear envelope

– Functions as transport system– Two forms

– Smooth endoplasmic reticulum (SER) – Rough endoplasmic reticulum (RER)


Figure 3.36 Endoplasmic reticulum

Membrane-boundribosomes

Mitochondrion

Free ribosome

Smooth endoplasmic reticulum (SER)

Rough endoplasmicreticulum (RER)


• Membranous Organelles– Golgi body

– Flattened hollow sacs surrounded by phospholipid bilayer

– Receives, processes, and packages large molecules for export from cell

– Packages molecules in secretory vesicles– Not in all eukaryotic cells


Secretory vesicles

Vesiclesarrivingfrom ER

Figure 3.37 Golgi body


• Membranous Organelles– Lysosomes, peroxisomes, vacuoles, and vesicles

– Store and transfer chemicals within cells– May store nutrients in cell– Lysosomes contain catabolic enzymes – Peroxisomes contain enzymes that degrade

poisonous wastes


Figure 3.38 Vacuole

Cell wall

Nucleus

Central vacuole

Cytoplasm

Bacterium

Phagosome(food vesicle)

Vesicle fuses with a lysosome

Smoothendoplasmicreticulum(SER)

Transportvesicle

Lysosome

Phagolysosome

Golgi body

Secretoryvesicle

Endocytosis(phagocytosis)

Exocytosis(elimination, secretion)

Figure 3.39 The roles of vesicles in the destruction of a phagocytized pathogen within a white blood cell


• Membranous Organelles– Mitochondria

– Have two membranes composed of phospholipid bilayer

– Produce most of cell’s ATP– Interior matrix contains 70S ribosomes and

molecule of DNA


Figure 3.40 Mitochondrion

Outer membrane

Inner membrane

Crista

Matrix

Ribosomes


• Membranous Organelles– Chloroplasts

– Light-harvesting structures found in photosynthetic eukaryotes

– Have two phospholipid bilayer membranes and DNA

– Have 70S ribosomes


Figure 3.41 Chloroplast

Granum

Thylakoidspace

Stroma

Thylakoid

Inner bilayermembrane

Outer bilayermembrane


• Endosymbiotic Theory– Eukaryotes formed from union of small aerobic

prokaryotes with larger anaerobic prokaryotes– Smaller prokaryotes became internal parasites

– Parasites lost ability to exist independently– Larger cell became dependent on parasites for

aerobic ATP production– Aerobic prokaryotes evolved into mitochondria– Similar scenario for origin of chloroplasts

– Not universally accepted


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Chapter 2 Cell Structure & Function