lecture presentations prepared by mindy miller-kittrell
TRANSCRIPT
PowerPoint® Lecture
Presentations prepared by
Mindy Miller-Kittrell,
North Carolina
State University
C H A P T E R
© 2014 Pearson Education, Inc.
Cell Structure
and Function
3
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Processes of Life
• Growth
• Reproduction
• Responsiveness
• Metabolism
LIFE - hard to define but easier to describe
Microbiology – study of small living things
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Figure 3.1 Examples of types of cells.
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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
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Figure 3.2 Typical prokaryotic cell.
Ribosome
CytoplasmNucleoid
GlycocalyxCell wall
Cytoplasmic membrane
Flagellum
Inclusions
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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
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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
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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
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External Structures of Bacterial Cells
• Flagella
• Are responsible for movement
• Have long structures that extend beyond cell surface
• Are not present on all bacteria
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External Structures of Bacterial Cells
• Flagella
• Structure
• Composed of 3 units - filament, hook, and basal body
• Basal body anchors the filament and hook to cell wall
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Filament
Rod
Protein rings
Directionof rotationduring run
Peptidoglycanlayer (cell wall)
Cytoplasmicmembrane
Cytoplasm
Gram + Gram –
Filament
Outermembrane
Peptidoglycanlayer
Cellwall
Cytoplasmicmembrane
Cytoplasm
Outerproteinrings
Rod
Integralprotein
Innerproteinrings
Integralprotein
Basalbody
Figure 3.6 Proximal structure of bacterial flagella.
Filament = flagellin
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Figure 3.7 Micrographs of basic arrangements of bacterial flagella.
Different
Arrangement
of flagella
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Axial filament
Spirochete
corkscrews
and moves
forward
Axial filament
Cytoplasmic
membrane
Outer
membrane
Axial filament
rotates around
cell
Endoflagella
rotate
Figure 3.8 Axial filament.
Endoflagella
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External Structures of Bacterial Cells
• Flagella
• Function
• Rotation propels bacterium through environment
• Rotation reversible; can be counterclockwise or clockwise
• Bacteria move in response to stimuli (taxis)
• Runs
• Tumbles
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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
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External Structures of Bacterial Cells
• 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
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Flagellum FimbriaFigure 3.10 Fimbriae.
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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 ?
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PilusFigure 3.11 Pili.
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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
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Figure 3.12 Bacterial shapes and arrangements.
strep
staph
coccibacilli
sarcinae
Give bacterial cells characteristic shapes
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Sugarbackbone
Tetrapeptide(amino acid)crossbridge
Connecting chainof amino acids
Figure 3.13 Possible structure of peptidoglycan.
Composed of peptidoglycan
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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
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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
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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
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Figure 3.14b Comparison of cell walls of Gram-positive and Gram-negative bacteria.
Integral
proteins
Outer
membrane
of cell wall
Gram-negative cell wall
Peptidoglycan
layer of cell wall
Cytoplasmic
membrane
Lipopolysaccharide
(LPS) layer, containing
lipid A
Porin
Porin
(sectioned)
Periplasmic space
Phospholipid layers
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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
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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
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Figure 3.15 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer.
Phospholipid
Head, which
contains phosphate
(hydrophilic)
Tail
(hydrophobic)
Phospholipidbilayer
Integral protein
Peripheral protein
Integral
protein
Cytoplasm
Integral
proteins
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Bacterial Cytoplasmic Membranes
• 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
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Cell exterior (extracellular fluid)
Integralprotein
Protein
Cell interior (cytoplasm)
Cytoplasmic membrane
Protein
DNA
mV
Na+
Cl–
–30
Figure 3.16 Electrical potential of a cytoplasmic membrane.
Concentration gradient
chemical gradient
electrical gradient
-
+
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Bacterial Cytoplasmic Membranes
• Function
• Passive processes
• Diffusion
• Facilitated diffusion
• Osmosis
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Figure 3.17 Passive processes of movement across a cytoplasmic membrane.
Gases/alcohol
permease
Semi-permeable
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Figure 3.18 Osmosis, the diffusion of water across a semipermeable membrane.
Water moves from high to low
cell
hypotonic
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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)
H2O
Cell wallCell wall
Cell membrane Cell membrane
Isotonic
solution
Hypertonic
solution
Hypotonic
solution
H2O
H2O
H2OH2OH2O
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Prokaryotic Cytoplasmic Membranes
• Function
• Active processes
• Active transport
• Group translocation
• Substance is chemically modified during transport
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Figure 3.20 Mechanisms of active transport.
Extracellular fluid
Cytoplasmicmembrane
ATP
ADP
Cytoplasm
Uniport
Antiport Coupled transport:
uniport and symport
Symport
Uniport
ATP
ADP P
P
Against gradient
Gated Channels or Ports
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Figure 3.21 Group translocation.
Extracellularfluid
Cytoplasm
Glucose
Glucose 6-PO4
PO4
Substance chemically changed
Very efficient – 1 ppm
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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
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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
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Figure 3.23 The formation of an endospore.
1
Steps in Endospore Formation
DNA is replicated.
DNA aligns along
the cell’s long axis.
Cytoplasmic membrane
invaginates to form
forespore.
Cytoplasmic membrane
grows and engulfs
forespore within a
second membrane.
Vegetative cell’s DNA
disintegrates.
Cell wallCytoplasmic
membrane
DNA
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
First
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
Outer
spore coat
Endospore
2
3
4 8
7
6
5
reproductive structure ?
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Also make endotoxins
Cause anthrax, tetanus, gangrene
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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
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Figure 3.26 Representative shapes of archaea.
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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
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Grapplinghook
Prickles
HamusFigure 3.25 Archaeal hami.
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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
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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
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Clear-cut differences ?
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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.
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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
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Eukaryotic Cell Walls and Cytoplasmic
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 ?
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Eukaryotic Cell Walls and Cytoplasmic
Membranes
• Control movement into and out of cell
• Do not perform group translocation but
endocytosis – unique to eukaryotes
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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.
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PseudopodiumFigure 3.29 Endocytosis. https://www.youtube.com/watch?v=7pR7TNzJ_pA&list=P
LJYr_JA9Jjd6zhzlkN4OOldkc7gCft9Pa
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Phagocytosis ?
Pinocytosis ?
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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
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Flagellum
Cilia
Figure 3.30a-b Eukaryotic flagella and cilia.
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Cytoplasm of Eukaryotes
• 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
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Cytoplasmicmembrane
Cytosol
Central pair
microtubules
“9 + 2”arrangementMicrotubules
(doublet)
Cytoplasmic membrane
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
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Figure 3.31 Movement of eukaryotic flagella and cilia.
https://www.youtube.com/watch?v=BbI47l2nbDQ
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Cytoplasm of Eukaryotes
• 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
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Eukaryotic ribosome (80S) larger
than prokaryotic ribosomes (70S)
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Cytoplasm of Eukaryotes
• 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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