Week 4 Flashcards
4 stages of microbial growth cycle, how is it analyzed and grown?
Lag, Exponential/Logarithmic, Stationary, and Death phase
Explain the lag phase of the microbial growth cycle
-Cells require time to sense/adjust to environment, bacteria adapts to growth condition
-Bacteria maturing, cannot divide yet
-Synthesis of RNA, enzymes + other molecules
-No growth yet, prep phase
Explain the exponential/logarithmic phase of the microbial growth cycle
-Cells grow actively at max rate, characterized by cell doubling (will continue at constant exponential rate)
-Slope of (log scale) line=growth rate: number of cell divisions/unit time normally hours
-Rate of growth depends on nutrients and conditions, cannot continue indefinitely since medium is depleted of nutrients and enriched with the wastes from the batch cultures
-Split into 2 phases, early and late
□ Early: cells grow at max rate
□ Late: slowing of growth ate due to cell density, competition for nutrients, accumulating waste products, etc.
-Chemostat ensure continuous log growth by constantly adding/removing equal amounts of culture medium
Explain the stationary phase of the microbial growth cycle
-Result is horizontal linear part of curve
-Cells still metabolically active just because they’re not physically growing anymore, cannot produce anymore biomass, run out of nutrients or the environment is not optimal
-Due to growth-limiting factor, overall population growth plateaus
Explain the death phase of the microbial growth cycle
With no new nutrients and/or production of toxic byproducts, all cells die off
what are the components of the prokaryotic cell?
cytoplasm
cytoplasmic membrane
cell wall
flagellum
pili
nucleoids
describe flagellum in the prokaryotic cell
- Flagellum (singular, flagella plural) in bacteria and archaea
○ Long, helical appendages extends from cell membrane, used for motility
○ Different arrangements, memorize, given image, asked which one it is
describe pili
- Most bacteria and archaea have pili on surface
○ Small hair-like protein filaments used for attachment and/ror exchange of genetic material
○ Can transfer DNA
○ Sex pili long, hollow, filamentous extensions from cell surface
○ Aka conjugation pili
○ Fimbriae are shorter versions of pili, used for adhesion, can be used by pathogens to attach to host cells and initiate disease
○ Stalks as attachment organelles formed by bacteria: extensions of cell envelope secretes adhesion factors to anchor bacterium in environment
describe nucleoids and what it contains
a packaged bacterial chromosome maybe plasmids
plasmids
-extrachromosomal DNA, small, circular, double-stranded DNA molecules, extra-chromosomal elements (circular)
-replicates autonomously
-contains additional/advantageous genetic info not required for every-day survival
what are the modes of gene transfer?
○ Horizontal gene transfer (HGT): transfer of genes between organisms outside of traditional reproduction
○ Vertical gene transfer: transmission of genes from parents generation to offspring (binary fission)
what are the 3 ways of genetic diversity and recombination?
Transformation:
cells uptake DNA from environment, donor cell releases DNA into environment, recipient takes from surrounding area
Transduction:
DNA transfer through bacteriophages that infect bacteria, move genetic material between cells, the range fo specificity of bacteriophage is very narrow, usually within a species or relative
Conjugation:
bacteria directly transfers DNA between cells via pili, binds to recipient cell, moves through hollow tube from donor cell
within the cytoplasmic membrane, describe the fluid mosaic model
Membrane composed of phospholipid bilayer embedded with proteins
-Proteins are the gatekeepers, multiple functions
-phospholipid layer prevents free movement, proteins facilitate transport
describe phospholipids, structure, function
§ Amphipathic molecules (polar/hydrophilic head towards aq environment, hydrophobic tails away from water
§ Can vary head groups and fatty acid side chains (can be saturated, unsaturated, polyunsaturated, or contain cyclic structures
□ Saturated lipids: melt at higher temperatures, increase order/rigidity
□ Unsaturated lipids melt at lower temperature increase fluidity
□ Organism in cooler environments have unsaturated fatty acids in lipids
what are planar molecules in prokaryotes
-fills gaps between hydrocarbon chains
-controls structure (rigid)
-eukaryotes: agents are sterols
-bacteria: hopanoids or hopanes
describe archaeal membranes, structure, bonds
-lipid tails differ, have isoprene chains with methyl side chain every 4 carbons, meaning little diversity
-resistant to high temps, very dense
-glycerol-ether-lipid bonds joins lipid tails to glyverol
-stereochemistry of archaeal glycerol is mirror image of bacteria
-some monolayer (2 phospholipid tails fused together)
describe the prokaryotic cytoplasm membrane
-has diffusion barrier
-membranes serve as site to anchor proteins
-energy conservation, site of proton gradient
describe the bacterial cell envelope of gram-positive bacteria
-thick cell wall
-layers of peptidoglycan
-threaded by teichoic acids
-lacks outer membrane
pros: thick, strong, protection against osmotic lysis
cons: susceptible to lysomes and other attacks
describe the bacterial cell envelope of gram-negative bacteria
-thin cell wall
-periplasm separates two membranes containing peptidoglycan
-outer membrane has lipolysaccharides and transmembrane proteins
what are LPS
-lipopolysacchraides are outer memrane parts of gram negative bacteria
-permeability barrier
-a complex glycolipid with 3 regions: O-antigen, core polysaccharide, Lipid A anchors core polysaccharide in outer membrane
-acts as endotoxin (harmless when pathogen’s intact, becomes toxic and starts immune response when released from lysed cell)
