2. anatomy and physiology of prokaryotic cells
TRANSCRIPT
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Lecture 2Anatomy and Physiology of
Prokaryotic and Eukaryotic Cells
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Prokaryotic Cells
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Bacterial Shape and Arrangement
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Streptococcus chain
© Dr. David M. Phillips/Visuals Unlimited
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Sarcinae cube
© David B. Fankhauser, University of Cincinnati, http://biology.clc.uc.edu/Fankhauser/
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Staphylococcus aureus cluster
© Dr. Fred Hossler/Visuals Unlimited
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Spiral-shaped bacterial cell
© Michael Abbey/Visuals Unlimited
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Prokaryotic Cell Structure
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Cytoplasmic Membrane
• Surrounds cytoplasm and defines boundaries of cell
• Acts as barrier, but also functions as an effective and highly discriminating conduit between cell and surroundings
• Made up of phospholipid bilayer
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Figure 4.14c
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Phospholipid
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Figure 4.14b
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Movement of Molecules through Cytoplasmic Membrane
• Several ways for molecules to move through membrane
1. Simple Diffusion
2. Osmosis
3. Facilitated Diffusion
4. Active Transport
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Simple Diffusion
• Does not require expenditure of energy
• Process by which some molecules move freely into and out of the cell
• Small molecules such as carbon dioxide and oxygen
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Microbiology: An Introduction, 9eby Tortora, Funke, Case
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 4.18: The principle of osmosis - Overview.
(a) At beginning of osmotic pressure experiment
(b) At equilibrium
(c) Isotonic solution — no net movement of water
(d) Hypotonic solution — water moves into the cell and may cause the cell to burst if the wall is weak or damaged (osmotic lysis)
(e) Hypertonic solution — water moves out of the cell, causing its cytoplasm to shrink (plasmolysis)
Glass tube
Rubberstopper
Rubberband
Sucrosemolecule
Watermolecule
Cellophanesack
Cytoplasm Solute Plasma membrane
Cell wall
Water
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Transport Proteins
• Transport proteins (or transporters) responsible for:
• Facilitated Diffusion
• Active Transport
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Microbiology: An Introduction, 9eby Tortora, Funke, Case
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 4.17: Facilitated diffusion.
Transportedsubstance
Transporterprotein
Outside
Inside
Glucose
Plasmamembrane
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Cell Wall
• Composed of peptidoglycan
• Comprised of alternating NAG and NAM molecules
• Attached to each NAM is four amino acid peptide: tetrapeptide
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Categories of Bacteria
• Two Major Categories:
• Difference due to difference in chemical structures of their cell walls– Gram positive: stains purple– Gram negative: stains red
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Gram + Cell Wall
• Thick Layer of Peptidoglycan
• Contains techoic acid: chains of ribitol-phosphate or glycerol-phosphate to which sugars or alanine attached
• Techoic Acid sticks out above the peptidoglycan layer
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Gram – Cell Wall
• More complex than Gram + cell wall
• Thin layer of peptidoglycan– Sandwiched between the cytoplasmic
membrane and outer membrane
• Outside of peptidoglycan is outer membrane
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Figure 4.13c
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Outer Membrane
• Unlike any other membrane in nature
• A lipid bilayer with the outside layer made of lipopolysaccharides instead of phospholipids
• Also called LPS
• Contains Porins
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Periplasm
- Region between cytoplasmic membrane and the outer membrane
- Gel-like fluid
• Filled with secreted proteins and enzymes
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External Structures
• Glycocallyx
• Flagella
• Axial Filaments
• Fimbrae and Pili
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Glycocallyx
• Gel-like structure– Functions in protection and attachment– Two types- capsule and slime layer– Involved in attachment, enabling bacteria to
stick to teeth, rocks– Enables bacteria to brow as biofilm
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Capsule in Acinetobacter species by gram negative staining
Courtesy of Elliot Juni, Department of Microbiology and Immunology, The University of Michigan
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Filamentous Protein Appendages
• Anchored in membrane and protrude from surface
• Flagella: long structure responsible for motility
• Fimbrae and Pili: shorter, responsible for attachment
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Four types of bacteria with flagella
• Montrichious- one flagella
• Amphitrichous- flagella at both ends
• Lophitrichous- many flagella at the end of the cell
• Peritrichous- flagella all over entire cell
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Figure 4.7 - Overview
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Movement of Bacteria
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Axial Filament
• Present in Spirochetes
• Attach at end of cell, spiral around, underneath an outer sheath
• Move like a corkscrew
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Figure 4.10 - Overview
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Fimbrae and Pili
• Shorter and surround the cell• Similar structural theme to filament of
flagella• Fimbrae- enable cell to adhere to surfaces,
including other cells• Pili- join bacterial cells in preparation for
the transfer of DNA from one cell to another
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Internal Structures of Prokaryotic Cells
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Cytoplasm
• Substance of cell inside the cytoplasmic membrane
• About 80% water
• Thick, aqueous, semitransparent, elastic
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Chromosome
• Found within a central location known as nucleoid
• Single, circular, double stranded
• Consists of all DNA required by cell
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Plasmids
• Some bacteria contain plasmids- small circular double-stranded DNA
• Typically cell does not require genetic information carried on plasmid
• However, it may be advantageous
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Ribosomes
• Site of protein synthesis
• Relative size and density of ribosomes and their subunits expressed as distinct unit (S)
• Two units of prokaryotic ribosomes: 50S + 30S= 70S
• Eukaryotic ribosomes: 80S
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Microbiology: An Introduction, 9eby Tortora, Funke, Case
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 4.19: The prokaryotic ribosome.
(a) Small subunit (b) Large subunit (c)
50S
50S
30S 30S
(c) Complete 70S ribosome
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Inclusions
• Store excess nutrients
• Examples: Polysaccharide granules- glycogen and starch
• Lipid inclusions
• Metachromatic granules- inorganic phosphate that can be used to synthesize ATP
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Endospores
• Occurs in members of genera Bacillus and Clostridium
• Dormant cell produced by a process called Sporulation
• Germination- when they exit the dormant state and then become a vegetative cell
• Several species of endospore formers can cause disease
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Eukaryotic Cells
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Plasma Membrane
• Very similar in structure and function to cytoplasmic membrane of prokaryotes
• Differences in types of proteins found in membranes
• Also contain carbohydrates, sterols
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External Structures
• Cell wall: much simpler then prokaryotic cell walls, no peptidoglycan
• Glycocallyx: sticky carbohydrate
• Flagella: long in relation to size of cell
• Cilia: numerous and short
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Internal Structures
• Cytoplasm
• Ribosomes
• Organelles
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Ribosomes
• Attached to surface of endoplasmic reticulum or free floating
• 40S + 60S 80S
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Organelles
• Structures with a specific shape and specialized function
• Nucleus: DNA found here
• Endoplasmic reticulum
• Golgi complex
• Lysosomes
• Mitochondria: ATP production