lecture presentations prepared by mindy miller-kittrell

PowerPoint® Lecture

Presentations prepared by

Mindy Miller-Kittrell,

North Carolina

State University

C H A P T E R

Cell Structure

and Function

Processes of Life

• Growth

• Reproduction

• Responsiveness

• Metabolism

LIFE - hard to define but easier to describe

Microbiology – study of small living things

Figure 3.1 Examples of types of cells.

Prokaryotic and Eukaryotic Cells: An Overview

• Prokaryotes (before nucleus)

• Composed of bacteria and archaea

• Lack nucleus

• Lack various internal structures bound with phospholipid

membranes

• Are typically 1.0 µm in diameter or smaller

• Have a simple structure

Figure 3.2 Typical prokaryotic cell.

Ribosome

CytoplasmNucleoid

GlycocalyxCell wall

Cytoplasmic membrane

Flagellum

Inclusions

Prokaryotic and Eukaryotic Cells: An Overview

• Eukaryotes (true nucleus)

• Have nucleus

• Have internal membrane-bound organelles

• Are larger: 10–100 µm in diameter

• Have more complex structure

• Composed of algae, protozoa, fungi, animals, and

plants

External Structures of Bacterial Cells

• Glycocalyces

• Gelatinous, sticky substance surrounding the outside of

the cell

• Composed of polysaccharides, polypeptides, or both

• Function – avoid dessication, adhesion, protect from

host defense

External Structures of Bacterial Cells• 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 –

- forms e.g. Dental plaques

• Also check page 63 for highlight

BIOFILMS

• Flagella

• Are responsible for movement

• Have long structures that extend beyond cell surface

• Are not present on all bacteria

• Flagella

• Structure

• Composed of 3 units - filament, hook, and basal body

• Basal body anchors the filament and hook to cell wall

Filament

Protein rings

Directionof rotationduring run

Peptidoglycanlayer (cell wall)

Cytoplasmicmembrane

Cytoplasm

Gram + Gram –

Filament

Outermembrane

Peptidoglycanlayer

Cellwall

Cytoplasmicmembrane

Cytoplasm

Outerproteinrings

Integralprotein

Innerproteinrings

Integralprotein

Basalbody

Figure 3.6 Proximal structure of bacterial flagella.

Filament = flagellin

Figure 3.7 Micrographs of basic arrangements of bacterial flagella.

Different

Arrangement

of flagella

Axial filament

Spirochete

corkscrews

and moves

forward

Axial filament

Cytoplasmic

membrane

Axial filament

rotates around

Endoflagella

rotate

Figure 3.8 Axial filament.

Endoflagella

• 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.

100,000 rpm = 670 miles per hour

Positive/Negative taxis

Chemo/Photo

Movement in response to stimulus = taxis

• Fimbriae and Pili

• Fimbriae

• Nonmotile, rodlike, Sticky, bristlelike projections

• Used by bacteria to adhere to one another and to

substances in environment

• Shorter than flagella

• Serve an important function in biofilms

Flagellum FimbriaFigure 3.10 Fimbriae.

External Structures of Prokaryotic Cells

• Pili

• Special type of fimbria

• Also known as conjugation pili

• Longer than fimbriae but shorter than flagella

• Bacteria typically only have one or two per cell

• Hollow tubes- transfer DNA from one cell to another

(conjugation)

pili or fimbriae ?

What’s the difference ?

PilusFigure 3.11 Pili.

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 - penicillin

• Scientists describe two basic types of bacterial cell walls

• Gram-positive and Gram-negative

Figure 3.12 Bacterial shapes and arrangements.

coccibacilli

sarcinae

Give bacterial cells characteristic shapes

Sugarbackbone

Tetrapeptide(amino acid)crossbridge

Connecting chainof amino acids

Figure 3.13 Possible structure of peptidoglycan.

Composed of peptidoglycan

Bacterial Cell Walls

• 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 (waxy lipids) in acid-fast gram

positive bacteria helps cells survive desiccation – M.

leprae and M.tuberculosis

Figure 3.14a Comparison of cell walls of Gram-positive and Gram-negative bacteria.

Peptidoglycan layer

(cell wall)

Gram-positive cell wall

Cytoplasmic

membrane

Teichoic acid

Lipoteichoic acid

Integral

protein

Prokaryotic Cell Walls

• Gram-Negative Bacterial Cell Walls

• Have only a thin layer of peptidoglycan

• Bilayer membrane outside the peptidoglycan contains

phospholipids, proteins, and lipopolysaccharide (LPS)

• Lipid A portion of LPS can cause fever, vasodilation,

inflammation, shock, and blood clotting

• May impede the treatment of disease (OM is protective)

• Appear pink following Gram staining procedure

Figure 3.14b Comparison of cell walls of Gram-positive and Gram-negative bacteria.

Integral

proteins

membrane

of cell wall

Gram-negative cell wall

Peptidoglycan

layer of cell wall

Cytoplasmic

membrane

Lipopolysaccharide

(LPS) layer, containing

lipid A

(sectioned)

Periplasmic space

Phospholipid layers

Prokaryotic Cell Walls

• Bacteria Without Cell Walls

• A few bacteria lack cell walls – Mycoplasma pneumoniae

• Often mistaken for viruses due to small size and lack of

cell wall

• Have other features of prokaryotic cells such as

ribosomes

Bacterial Cytoplasmic Membranes

• Structure

• Referred to as phospholipid bilayer

• Composed of lipids and associated proteins

• Integral proteins

• Peripheral proteins

• Fluid mosaic model describes current understanding of

membrane structure

Figure 3.15 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer.

Phospholipid

Head, which

contains phosphate

(hydrophilic)

(hydrophobic)

Phospholipidbilayer

Integral protein

Peripheral protein

Integral

protein

Cytoplasm

Integral

proteins

• 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

Cell exterior (extracellular fluid)

Integralprotein

Protein

Cell interior (cytoplasm)

Protein

Figure 3.16 Electrical potential of a cytoplasmic membrane.

Concentration gradient

chemical gradient

electrical gradient

• Function

• Passive processes

• Diffusion

• Facilitated diffusion

• Osmosis

Figure 3.17 Passive processes of movement across a cytoplasmic membrane.

Gases/alcohol

permease

Semi-permeable

Figure 3.18 Osmosis, the diffusion of water across a semipermeable membrane.

Water moves from high to low

hypotonic

Figure 3.19 Effects of isotonic, hypertonic, and hypotonic solutions on cells.

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

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

Cell wallCell wall

Cell membrane Cell membrane

Isotonic

solution

Hypertonic

solution

Hypotonic

solution

H2OH2OH2O

Prokaryotic Cytoplasmic Membranes

• Function

• Active processes

• Active transport

• Group translocation

• Substance is chemically modified during transport

Figure 3.20 Mechanisms of active transport.

Extracellular fluid

Cytoplasmicmembrane

Cytoplasm

Uniport

Antiport Coupled transport:

uniport and symport

Symport

Uniport

Against gradient

Gated Channels or Ports

Figure 3.21 Group translocation.

Extracellularfluid

Cytoplasm

Glucose

Glucose 6-PO4

Substance chemically changed

Very efficient – 1 ppm

Cytoplasm of Bacteria

• Cytosol

• Liquid portion of cytoplasm

• Mostly water

• Contains cell's DNA in region called the nucleoid

• Inclusions

• May include reserve deposits of chemicals

• Magnetospirillum magnetotacticum

Cytoplasm of Bacteria

• Endospores

• Unique structures produced by some bacteria

• Defensive strategy against unfavorable conditions

• Vegetative cells transform into endospores when

multiple nutrients are limited

• Resistant to extreme conditions such as heat, radiation,

chemicals

Figure 3.23 The formation of an endospore.

Steps in Endospore Formation

DNA is replicated.

DNA aligns along

the cell’s long axis.

invaginates to form

forespore.

grows and engulfs

forespore within a

second membrane.

Vegetative cell’s DNA

disintegrates.

Cell wallCytoplasmic

membrane

Vegetative cell

A cortex of peptidoglycan

is deposited between the

membranes; meanwhile,

dipicolinic acid and

calcium ions accumulate

within the center of the

endospore.

Spore coat forms

around endospore.

Forespore

membrane

Second

membrane

Endospore matures:

completion of spore coat

and increase in resistance

to heat and chemicals by

unknown process.

Endospore is released from

original cell.

Cortex

Spore coat

spore coat

Endospore

reproductive structure ?

Also make endotoxins

Cause anthrax, tetanus, gangrene

Cytoplasm of Prokaryotes

• Nonmembranous Organelles

• Ribosomes

• Sites of protein synthesis

• Composed of polypeptides and ribosomal RNA

• Cytoskeleton

• Composed of three or four types of protein fibers

• Can play different roles in the cell

• Cell division

• Cell shape

• Segregate DNA molecules

• Move through the environment

Figure 3.26 Representative shapes of archaea.

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 – analogous structures

• Fimbriae and hami

• Many archaea have fimbriae

• Some make fimbria-like structures called hami

• Function to attach archaea to surfaces

Grapplinghook

Prickles

HamusFigure 3.25 Archaeal hami.

Archaeal Cell Walls and Cytoplasmic

Membranes

• 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

Cytoplasm of Archaea

• Archaeal cytoplasm similar to bacterial cytoplasm

• 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

Clear-cut differences ?

Nucleolus

Cilium

Ribosomes

Cytoskeleton

Cytoplasmic

membrane

Smooth endoplasmicreticulum

Rough endoplasmicreticulum

Transport vesicles

Golgi body

Secretory vesicle

Centriole

Mitochondrion

Lysosome

Nuclear pore

Nuclear envelope

Figure 3.3 Typical eukaryotic cell.

Eukaryotic Cell Walls and Cytoplasmic

Membranes

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

• But no glycocalyx and no peptidoglycan

• Composed of various polysaccharides

• Cellulose found in plant cell walls

• Fungal cell walls composed of cellulose, chitin, and/or

glucomannan

• Algal cell walls composed of a variety of polysaccharides

Membranes

• All eukaryotic cells have cytoplasmic membrane

Attach sugars to lipids and protein within the 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 ?

Membranes

• Control movement into and out of cell

• Do not perform group translocation but

endocytosis – unique to eukaryotes

Endocytosis

(phagocytosis)

Smoothendoplasmicreticulum(SER)

Transportvesicle

Lysosome

Phagolysosome

Golgi body

Secretoryvesicle

Exocytosis

(elimination, secretion)

Phagosome(food vesicle)

Vesiclefuses with alysosome

Bacterium

Figure 3.38 The roles of vesicles in endocytosis and exocytosis.

PseudopodiumFigure 3.29 Endocytosis. https://www.youtube.com/watch?v=7pR7TNzJ_pA&list=P

LJYr_JA9Jjd6zhzlkN4OOldkc7gCft9Pa

Phagocytosis ?

Pinocytosis ?

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; no hook

• May be single or multiple; generally found at one pole of cell

• Function

• Do not rotate but undulate rhythmically

Flagellum

Figure 3.30a-b Eukaryotic flagella and 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

Cytoplasmicmembrane

Cytosol

Central pair

microtubules

“9 + 2”arrangementMicrotubules

(doublet)

Portioncut away to showtransition areafrom doubletsto triplets andthe end ofcentralmicrotubules

“9 + 0”arrangement

Microtubules

(triplet)

Basal body

Figure 3.30c Eukaryotic flagella and cilia.

Microtubule

Tubulin

Figure 3.31 Movement of eukaryotic flagella and cilia.

https://www.youtube.com/watch?v=BbI47l2nbDQ

• 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

Eukaryotic ribosome (80S) larger

than prokaryotic ribosomes (70S)

• 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

• Theory is not universally accepted

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