Download Prokaryotic Cells

MICROBIOLOGY
WITH DISEASES BY TAXONOMY, THIRD EDITION
Chapter 3
Cell Structure and Function
Lecture prepared by Mindy Miller-Kittrell, University of Tennessee, Knoxville
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Prokaryotic and Eukaryotic Cells
Cell: the structural and functional unit of all living organisms (Cell
theory by Schleiden and Schwann)
• Two Types of Cells:
– Prokaryote (comes from the Greek words for “before nucleus”)
– Lack a membrane around their DNA – No nucleus
– Eukaryote (comes from the Greek words for “true nucleus”)
– Have a membrane surrounding DNA – Nucleus
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Prokaryote
Fimbria
Eukaryote
Inclusion body
Cilia
Golgi
Ribosome
Ribosome
Chloroplast
Mitochondria
Nucleoid
Cytoplasm
Glycocalyx
Nuclear pore
Cell wall
Plasmid
ER
Nucleolus
Cell membrane Flagella
Nucleus
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Nuclear
membrane
Prokaryote
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•
•
•
•
•
•
•
•
vs
Nucleoid region
One chromosome
No histones
No membrane bound organelles
70S ribosomes
Complex cell walls
Binary fission
Small size
Bacteria, Archaea
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Eukaryote
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•
•
•
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•
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•
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Nuclear membrane
Paired chromosomes
Histones
Membrane bound organelles
80S ribosomes
Simple or no cell walls
Mitosis
Larger size
Fungi, Parasites
Prokaryotic Cell
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•
•
•
Average size: 0.2 -1.0 µm diam  2 - 8 µm length
Common shapes: Cocci, Rods, Spirals
Most bacteria are monomorphic (one shape)
A few are pleomorphic due to the environment
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Prokaryote Cell Arrangements
• Determined by the planes in
which it divides
• Pairs: diplo – Neisseria
• Chains: divide in 1 plane –
Streptococcus, Streptobacillus
• Tetrads (4)- divide in 2 planesAerococcus
• Clusters: divide in multiple planes Staphylococcus
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External Structures of Prokaryotes
Fimbriae
Flagella
Glycocalyx
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• Glycocalyx
• Flagella
• Fimbriae
• Pili
Glycocalyx
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•
•
•
Viscous, sticky
Gelatinous carbohydrate
Made in cell & secreted
Types:
– Capsule is neatly organized and firmly
attached to cell wall
– Slime layer is unorganized and loosely
attached to cell wall
• Purpose:
– Protection against drying
– Attachment to surfaces
– Virulence – inhibits phagocytosis
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Glycocalyces - Capsule & Slime Layer
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Flagella
• Found in bacilli (rods)
• Long, semi-rigid appendages
• Purpose:
– Motility (movement)
• Parts:
– Flagellin in helix around
hollow core
– Hook for attachment
– Basal body - anchors to
the wall and membrane
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Figure 4.8
Flagella
• Purpose: motility
• Moves : by rotating flagella (like a propeller)
– In liquid – run – tumble - run
http://www.youtube.com/watch?v=891M1TH99_8
– On agar - swarms
– Move toward or away from stimuli (taxis)
• Flagella proteins are H antigens
– Used to identify organisms
(e.g., E. coli O157:H7)
– Differs by species/strain
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Flagella Arrangement
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Axial Filaments
• Found in spirochetes
• Endoflagella –
– Anchored at one end of a
cell
– Form bundles spiraling
around cell under a sheath
• Rotation causes cell to move
http://www.youtube.com/watch?v=O0y7X5acK8M
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Fimbriae
• Found in gram negative
bacilli
• Many, short, straight, thin
filaments
• Made of protein - pilin
• Allow attachment
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Pili
•
•
•
•
Made of protein - pilin
Longer than fimbriae
Only 1 or 2 per cell
Used to transfer DNA from
one cell to another by
conjugation
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Cell Wall
• Complex, semi-rigid structure
• Prevents osmotic lysis, provides shape
• Made of peptidoglycan (in bacteria)
Cell wall
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Peptidoglycan- in bacterial cell walls
• Consists of repeating disaccharides
– N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)
• Linked by polypeptides
– Includes amino acid isomer side chains attached to NAM
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Gram-Positive cell walls
• Thick layer of Peptidoglycan
• Teichoic acids:
– Lipoteichoic acid links to plasma membrane
– Wall teichoic acid links to peptidoglycan
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Gram-Negative Cell Walls
•Thin layer of peptidoglycan in periplasmic space
•Outer membrane of phospholipids, lipoproteins, and
lipopolysaccharides
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Gram-Negative Outer Membrane
 Protection from phagocytes, complement, antibiotics
 O lipopolysaccharide antigen
( E. coli O157:H7)
 Lipid A is an endotoxin
 Porins (proteins) form channels through membrane
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Comparison of Cell Walls
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Gram-positive
cell walls
1. Thick layer of
peptidoglycan
2. No periplasmic
space
3. Teichoic acids
4. No outer
membrane
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Gram-negative
cell walls
1. Thin layer of
peptidoglycan
2. Periplasmic space
3. No teichoic acids
4. Outer phospholipid
membrane
Atypical Cell Walls
• Acid-fast bacteria
– Mycolic acid
• Mycoplasma
– Lack cell walls
– Sterols in plasma membrane
• Archaea
– Wall-less, or
– Walls of varying polysaccharides and proteins
– Do not have peptidoglycan in cell walls
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Cell Membrane
Plasma membrane, Cytoplasmic membrane
• Composed of:
– Phospholipid bilayer
– Proteins
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Fluid mosaic model
Plasma Membrane
Purpose
• Selective
permeability:
Regulates
movement of
substances in
and out of cell
• ATP production
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Bacterial Cytoplasmic Membranes
• Movement of molecules
• Active Transport
– requires energy from the system
• Passive Transport
– Passive processes
– Diffusion
– Facilitated diffusion
– Osmosis
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Passive processes of movement
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Figure 3.18
Osmosis
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Figure 3.19
Effects of solutions on cells
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Figure 3.20
Prokaryotic Cytoplasmic Membranes
• Function
– Active processes
– Active transport
– Group translocation
– Substance chemically modified during transport
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Mechanisms of active transport
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Figure 3.21
Bacterial Cytoplasmic Membranes
Animation: Active Transport: Overview
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Bacterial Cytoplasmic Membranes
Animation: Active Transport: Types
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Group translocation
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Figure 3.22
Cytoplasm
• The substance inside the plasma membrane
• Thick, semi transparent
• Made of 80% water, enzymes, carbohydrates
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Internal contents
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•
•
•
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Nucleoid region – chromosomal DNA
70S Ribosomes – protein synthesis
Plasmids – extrachromosomal DNA
Inclusions – storage of polysaccharides, lipids for energy
Cytosol – liquid portion of cytoplasm
Ribosome
Nucleoid region
Plasmid
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Figure 4.6a, b
Ribosomes
• There are two subunits: a small one (30S), and a bigger one
(50S). When a ribosome needs to be formed for translation, the
subunits attach to each other and form a 70S unit.
The "S" is a measure of the rate of sedimentation in
centrifugation, rather than a measure of weight. That's why those
two subunits put together are 70S, and not 80S.
The subunits themselves are made of RNA and proteins.
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Ribosomes
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Endospores
Produced by Bacillus, Clostridium
• Resting cells
• Resistant to desiccation,
heat, and chemicals
• 1 cell – 1 spore
NOT reproductive
• Sporulation or
Sporogenesis:
– Endospore formation (8-10hr)
• Germination:
– Return to vegetative state
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The formation of an endospore
http://www.youtube.com/watch?v=NAcowliknPs
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Figure 3.24
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Table 10.2