Lecture 2Anatomy and Physiology of
Prokaryotic and Eukaryotic Cells
Prokaryotic Cells
Bacterial Shape and Arrangement
Streptococcus chain
© Dr. David M. Phillips/Visuals Unlimited
Sarcinae cube
© David B. Fankhauser, University of Cincinnati, http://biology.clc.uc.edu/Fankhauser/
Staphylococcus aureus cluster
© Dr. Fred Hossler/Visuals Unlimited
Spiral-shaped bacterial cell
© Michael Abbey/Visuals Unlimited
Prokaryotic Cell Structure
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
Figure 4.14c
Phospholipid
Figure 4.14b
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
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
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
Transport Proteins
• Transport proteins (or transporters) responsible for:
• Facilitated Diffusion
• Active Transport
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
Cell Wall
• Composed of peptidoglycan
• Comprised of alternating NAG and NAM molecules
• Attached to each NAM is four amino acid peptide: tetrapeptide
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
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
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
Figure 4.13c
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
Periplasm
- Region between cytoplasmic membrane and the outer membrane
- Gel-like fluid
• Filled with secreted proteins and enzymes
External Structures
• Glycocallyx
• Flagella
• Axial Filaments
• Fimbrae and Pili
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
Capsule in Acinetobacter species by gram negative staining
Courtesy of Elliot Juni, Department of Microbiology and Immunology, The University of Michigan
Filamentous Protein Appendages
• Anchored in membrane and protrude from surface
• Flagella: long structure responsible for motility
• Fimbrae and Pili: shorter, responsible for attachment
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
Figure 4.7 - Overview
Movement of Bacteria
Axial Filament
• Present in Spirochetes
• Attach at end of cell, spiral around, underneath an outer sheath
• Move like a corkscrew
Figure 4.10 - Overview
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
Internal Structures of Prokaryotic Cells
Cytoplasm
• Substance of cell inside the cytoplasmic membrane
• About 80% water
• Thick, aqueous, semitransparent, elastic
Chromosome
• Found within a central location known as nucleoid
• Single, circular, double stranded
• Consists of all DNA required by cell
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
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
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
Inclusions
• Store excess nutrients
• Examples: Polysaccharide granules- glycogen and starch
• Lipid inclusions
• Metachromatic granules- inorganic phosphate that can be used to synthesize ATP
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
Eukaryotic Cells
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
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
Internal Structures
• Cytoplasm
• Ribosomes
• Organelles
Ribosomes
• Attached to surface of endoplasmic reticulum or free floating
• 40S + 60S 80S
Organelles
• Structures with a specific shape and specialized function
• Nucleus: DNA found here
• Endoplasmic reticulum
• Golgi complex
• Lysosomes
• Mitochondria: ATP production
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