Ddd - Bacterial Structure, Function And Growth

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nucleoid"

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is the region of the cytosol in which the chromosome is tightly packed- just a description of a cellular region, not a membrane-bound organelle

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bacterial genomes

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are composed of a single, circular, double strand of DNA.

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• Plasmids:

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non-chromosomal, self-replicating DNA molecules (much smaller than entire bacterial chromosome). Generally contain specialized genes that are not necessary for survival of the bacteria-- these genes often contain virulence factors and resistance factors to antibiotics.
 This is important. Plasmids are modular elements, interchangeable between bacteria, that confer drug resistance and virulent effects on the host. Sort of "plug and play" action here.

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• Bacteriophages:

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viruses that infect bacteria.
 Temperate phages: integrate viral DNA into bacterial DNA (like retroviruses in eukaryotes).
 Phage conversion: phage-mediated change in the phenotype (virulence, resistance, etc) of a bacterium

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bacteria have ribosomes but lack

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lack membrane bound organelles: ER, mitochondria, etc

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intracellular cytoskeletal elements of bacteria

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 FtsZ: prokaryotic analogue to eukaryotic tubulin. Aids in cell division.
 MreB: analogue to actin. Influences elongation of Bacillus vs. Coccus.
 CreS: analogue to intermediate filaments. Influences specific 'curving' of shape (ie spirillum vs. bacillus

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 FtsZ:

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prokaryotic analogue to eukaryotic tubulin. Aids in cell division.

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 MreB:

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analogue to actin. Influences elongation of Bacillus vs. Coccus.

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 CreS:

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analogue to intermediate filaments. Influences specific 'curving' of shape (ie spirillum vs. bacillus

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capsule

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slime layer made of polysaccharidse that hinders phagocytosis by macrophages

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o Flagellae:

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organs of motility ("tails"). Allow swimming through liquid media. Used in chemotaxis, positive (movement towards a desired chemical) or negative (movement away from an undesirable chemical).
• Notice that chemotaxis is predicated on a signal transduction system to detect the presence of chemicals.

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two set "modes" of flagella, directed by rotation of the flagellae:

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rotated counterclockwise, promotes directed motion or swimming;

rotated clockwise, promotes being more or less stationary ('tumbling').

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o Cytosol:

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notice that there are no compartmental barriers between bacterial DNA and ribosomes- thus the mRNA is transcribed and translated all in the same place without a transport mechanism between them.

prokaryotes, you find polycistronic mRNAs that contain multiple encoded genes (one mRNA makes a variety of different proteins), instead of the cap-dependent translation seen in eukaryotes.

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• Gram-negative

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have two layers of cell wall surrounding the cytoplasmic membrane, with a periplasmic space between them: one is called the outer membrane, the other is a peptidoglycan-rich layer.
 Notice that the (thin, compared to Gram-positive) peptidoglycan layer is the inner of the two cell wall layers.
 Gram-negative bacteria have lipopolysaccharide (LPS) chains coming off their outer cell wall layer- these cause toxic effects in the host.
 They also have, in their outer layer, porin complexes that act as transmembrane channels.

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• Gram-positive

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has only one (peptidoglycan-rich) cell wall layer surrounding the cytoplasmic membrane.
 Gram-positive bacteria have, as mentioned, extensive cross-linking of their peptidoglycan layers-- this is mediated by teichoic acids and lipoteichoic acids which serve as scaffolds on which the cross-linking can occur. (teichoic acids are immersed in the peptidoglycan layer; lipoteichoic acids, as you might expect, are anchored in the lipid cytoplasmic membrane.)

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bacterial growth

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lag
exponential
stationary

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exponential phase
bacteria increases at a rate of ___ each generation

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2n each generation
doubling time varies by species

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stationary phase

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number of new bacteria equals the number of dying bacteria. net viable bacterial population stays constant