A Typical Bacterial Cell
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How does prokaryotes differ from eukaryotes? Most prokaryotes lack internal membrane system
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What are bacterial cell shapes? Cocci(spheres), Bacilli(rods), Vibrios(comma), Coccobacilli(very short rods), Spirilla(rigid helices), Spirochetes(flexible helices),Mycelium, Pleomorphic(variable in shape)
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What are the examples of smallest and largest bacteria? Smallest - Mycoplasma
Largest - Epulopiscium fishelsoni
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What causes bacteria to have a particular size and shape? To increase the S/V ratio for more efficient nutrient uptake and protection from predator
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Bacterial Cytoplasmic Structures
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Types of Cytoskeletons - Microtubules
- Microfilaments
- Intermediate filaments
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Examples of Cytoskeletons - FtsZ
- MreB/MbI
-CreS
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FtsZ - Forms a ring at the center of a dividing cell
- Required for the formation of septum that wull separate the daughter cells
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MreB/MbI - Only found in rod shaped cell
- Determine cell shape in rod-shaped cell
- Determine cell shape by properly positioning the machinery needed for peptidoglycan synthesis
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CreS - Rare
- Give bacteria the curved shape
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What are inclusions? Granules of organic/inorganic material that are stockpiled by the cell for future use
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Types of inclusions 1. Storage inclusions - Storage for nutrients, metabolic end products, energy, building blocks
2. Microcompartments- Have specific functions (Carboxymes as example)
3. Gas vacuoles - Provide buoyancy in gas vesicles
4. Magnetosomes- Identify earth's magnetic field
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What is the Nucleoid? - Location of chromosomes and associated proteins
- Not membrane bounded therefore mix with cytoplasma
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How microbes managed to fit their chromosomes into the small space of nucleoid? 1. Using physical factors - Macromolecular crowding and Supersoiling
2. Using architectural proteins - NAPs (HU Protein)
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What is Plasmids? 1. Double -stranded DNA molecules that can exist independently of the chromosome
2. Episomes - Can integrate into chromosome and replicate with the chromosome
3. Contain gene that confer selective advantage to host
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The Bacterial Endospore
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What is endospores? Complex, dormant structure formed by rods and cocci bacteria only
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How are endospores structurally different from vegetative cells? Consist of a core surrounded by several layers varying in composition.
1. Core - Has ribosomes and nucleoid and low water content
2. Inner Membrane
3. Germ cell wall- Contain peptidoglycan that will form a cell wall in vegetative state
4. Cortex - occupy half of the endospore's volume
5. Outer membrane
6. Coat- Composed of a high cross-linked different proteins
7. Exosporium - Made up of glycoproteins
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What makes endospores so resistant to harsh environmental conditions? There are various layers to protect its enzymes and DNA
1. The coat - protects the endospores from chemicals and lytic enzymes (lysozymes)
2. The inner core - Extremely impermeable to various chemicals, including those that damage the DNA
3. The core - High water content, high amount of Ca-DPA, low pH Ph
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Bacterial Plasma Membranes
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How bacterial lipid changes in different temperatures? Saturation levels of membrane lipid depends on the environment conditions.
1. Hot - Have more saturated and long-chained fatty acid
2. Cold - Have more unsaturated and short-chained fatty acids
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What is growth factors? Molecules that bacteria need for survival but can't synthesize and need to obtain from the environment
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Classes of growth factors 1. Amino acids - Protein synthesis
2. Purines and Prymidines - Nucleic acid synthesis
3. Vitamins - Enzyme Cofactors
4. Heme - Hemoproteins
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How bacteria uptake nutrients? Microbes can only take in dissolves particles across a selectively permeable membrane by passive and active transports
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What are the transport systems used? 1. Facilitated Diffusion
2. Active Transport
3. Group Translocation
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Passive Diffusion 1. Molecules move down the concentration gradient
2. Water, oxygens and carbon dioxide move across the membrane this way
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Facilitated Diffusion Diffusion of molecules across the plasma membrane down the concentration gradient with the assistance of protein carrier/ channel
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Primary Active Transport (ABC Transporter, Uniport) Uses energy provided by ATP hydrolysis to move substance against a concentration gradients
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Secondary Active Transport (Using proton and sodium gradient, Cotransport-Symport/Antiport) uses ion concentration gradients to cotransport substances
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Group Translocation (Phosphorelay System) A molecule is chemically modified as it is brought into the cell
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What is the advantage of active transport compared to facilitated transport? Allow bacteria to uptake nutrients when they liv in a low nutrient concentration environment
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Why microorganisms require iron? Important for building molecules needed in energy-conserving processes
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What is siderophores? Low molecular weight molecules secreted by bacteria that helps to bind ferric ion and supply it to the cell when the iron uptake is difficult
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Bacterial Cell Wall
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What are the types of bacteria based on Gram Stain? Gram-positive bacteria and Gram-negative bacteria
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What is Peptidoglycan? Rigid structure outside the cell membrane
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Gram-positive bacteria - Stain purple
- Thick peptidoglycan
- Contain large amount of teichoic acids(negatively charged)
- Small periplasmic space
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Gram-negative bacteria - Stain red/pink
- Thin peptidoglycan
- No teichoic acids but have lipopolysaccharides
- Bigger periplasmic space
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Functions of cell wall - Maintain bacteria shape
- Protect cell from osmotic lysis and toxic materials
- Contribute to pathogenicity
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Peptidoglycan structure are composed of what identical subunits? 1. Two alternating sugars - NAG and Nam
2. Amino acids - Alternating L- and D- amino acids
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Three amino acids not found in proteins of other organism - D-glutamic acid
- D-alanine
- Meso-diaminoplemic acid
- Help to protect the cell wall against degradation by most peptidase
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Peptidoglycan chains are crosslinked by peptides for strength - Composed of alternating D- and L-amino acids
- Gram-positive bacteria have more cross-linking
- Gram-negative bacteria have lesser crowss-linking
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Lipopolysaccharide consist of and its functions? 1. Lipid A - Endotoxins which is harmful
2. Core polysaccharide - Contributes to negative charge on cell surface
3. Side O chain- Helps bacteria to escape human immune system by changing the O side chain
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What are the function of Teichoic acids? - Help maintain cell envelope
- Protect from environmental substances
- May bind to host cells
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External Structures
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What are the external structures of bacteria and archaea? - Pili/Fimbriae
- Flagella
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Function of Fimbriae Attachment to surface
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Functions of Type IV Pili - Motility
- Twitching
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Function of Sex Pili Transfer of DNA from one bacterium to another
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What is Flagella? Threadlike, locomotor appendages extending outward from plasma membrane and cell wall
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Functions of Flagella? - Motility
- Swarming
-Attachment to surfaces
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Each bacterial flagellum is composed of? - Filament
- Hook
- Basal body
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What is self-assembly? Why this make sense in flagellum? - A system's components organize into a functional structures as the result of interactions between the components without external directions
- Because many components of the flagellum lie outside the cell envelope and must be transported out of the cell for assembly
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Components Outside of the Cell Wall
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What are the outermost layers of bacterial cell and its function? - Glycocalyx (Capsules/Slime Layers)
- S Layers
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Glycocalyx - Consist of a network of polysaccharides extending from the surface of the cells
- Capsules and Slime Layer
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Capsule - Well organized
- Not easily removed
- Resistance to phagocytosis
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Slime Layer - Unorganized
- Easily removed
- AId in motility
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S Layer - Structured layers of proteins/ glycoproteins that self-assemble
- Adhesion to surface
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How does an S-Layer differ from a proteinaceous capsule? Monomer of S-Layer have the ability to self-assemble
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Bacterial Motility and Chemotaxis
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What are the types of motility? 1. Swimming - Flagella
2. Swarming - Flagella
3. Spirochete motility
4. Twitching motility
5. Gliding motility
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Bacterial Flagellar Movement - A rigid helix that rotates like a propeller to push the bacterium through the water
- CCW- Froward motion
- CW- Cell stop and tumble
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Mechanism of Flagellar Movement 2 parts of motor producing torque - Rotor and Stator
1. Rotor - C ring and MS ring turn and interact with stator
2. Stator- Mot A and Mot B proteins produce energy through PMF
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What are the power used by most flagellar motors? - Difference in charge
- Difference in pH
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Swarming - Occur in group
- Mediated by flagella
- Occurs on moist surfaces
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Spirochete - Flagella located around the cell and remain within periplasmic space
- Rotate when the outer membrane rotate
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Myxococcus spp. exhibit both twitching and gliding motility 1. Twitching - Jerky movement brought by the type IV pili
2. Gliding - Smooth
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What is chemotaxis? Movement towards a chemical attractant or away from a chemical repellent
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