Bacterial Structure, Function, and Growth Flashcards
What is the bacterial cell wall composed of?
Peptidoglycan chains of repeating units of N-acetylglucosamine and N-acetylmuramic acid. The muramic acid is linked to tetra peptide chains of diaminopimelic acid, D-glutamic acid, and D-alanine. D-ala cross links with DAP (gram negative) or L-lysine (gram positive) to link two peptidoglycan chains together.
What is a major difference between gram negative and gram positive cell walls?
Gram negative have thin, sparsely crosslinked peptidoglycan layers. Gram positive have thick, extensively cross linked peptidoglycan layers that also contain teichoic acids.
What do gram negative bacteria also contain in their outer membrane?
The outer membrane is a lipid bilayer that contains lipopolysaccharides and porin proteins (forming pores). Lipopolysaccharides consist of “Lipid A” molecules of fatty acids attached to a disaccharide, diphosphate backbone and are highly endotoxic (endo = not excreted). The LPS portion extends out from the membrane and contains a highly conserved “core” polysaccharide and an O side chain of repeated oligosacchrides that are somatic antigens. The somatic antigen can be used to attack and identify the bacteria.
Where is the peptidoglycan cell wall located in gram negative bacteria?
In the periplasmic space between the cytoplasmic membrane and the outer membrane.
What are the bacterial representative proteins for tubulin, actin, and intermediate filaments, respectively?
Tubulin = FtsZ (funcitons in cell division) Actin = MreB (functions in cell shape, polarity, and chromosome segregation) Intermediate Filaments = CreS (functions in cell shape)
How do Peptidoglycan chains cross link in gram positive bacteria?
Muranic acid linked with tetra peptide chains containing L-lysine. L-lysine links with glycine residues which then link to D-alanine residues on neighboring peptidoglycan chains.
What are the two types of teichoic acids and how do they function?
Teichoic acids (found in gram positive bacteria) consist of repeating polyglycerol-P or polyribitol-P backbones which covalently bond to the peptidoglycan layer. They also contain lipoteichoic acids that insert into the cytoplasmic membrane, thus binding the cytoplasmic membrane with the cell wall.
What are three other structures found on the surface of many bacteria?
Capsules: loose outer surfaces usually made of polysaccharides (sometimes AAs), help the bad resist phagocytosis but are still antigenic, can be used in vaccines. Flagella: Appendages originating in the cytoplasmic membrane, provide motility, clockwise=tumble, counter-clock=swimming, antigenic (H-antigens). Pili: fimbriae long antigenic proteins that often allow cell adherence or function as sex pili and transmit DNA.
What two energy systems are present in bacteria?
ATP: biochemical pathways. PMF: proton motive force functions in flagellar movement. ATPase interconverts the PMF (electrochemical gradient) and ATP energy sources.
How does respiration occur in bacteria?
Respiration typically occurs only in aerobes, but some can do anaerobic respiration. Aerobic respiration is similar to mitochondrial respiration, with a H+ gradient built across the cytoplasmic membrane and electron transport proceeding through cytochomes in the mmbr. Organic compounds are oxidized in this pathway with oxygen acting as the final e acceptor. Other molecules may also act as final e- acceptors (nitrate/trite), hence anaerobic respiration. This also creates the gradient for the proton motive force.
What is the overall redox reaction in fermentation?
The fermentation pathway results in the the reduction and oxidation of many individual organic compounds, but has a net redox of zero.
What is an R-factor?
R-factors are plasmids that carry genes encoding resistance to pathogenic bacteria.
What do temperate bacteriophages do?
Temperate bacteriphages infect bacteria like any other phage, but their DNA becomes incorporated into the bacterial genome. They often carry genes that encode bacterial toxins, other bacterial virulence factors, or resistance to antibiotics. This is termed phage conversion and is partially responsible for the production of diphtheria toxin by the diphtheria bacteria.
What are the four phases of bacterial growth and what characterizes each?
Lag phase: bacteria undergo physiological adjustment to grow. Exponential phase: bacteria grow as quickly as environment allows. Stationary phase: Nutrients diminish and toxins accumulate, bacteria may become resistant to penicillin or other antibiotics that act on replicating cells. Death phase: Some colonies are less hardy and begin to die off, some will lyse, some will simply not be viable.
What are the differences between indifferent aerobes, facultative aerobes, and mircroaerophilic bacteria?
Indifferent aerobes ferment with or without O2 (streptococcus), facultative aerobes respire with O2 or ferment without (E. coli, Staphylococcus), Microaerophilic bacteria grow best at low O2 or without it (Campylobacter jejuni)
