Bacterial Struc, Func, & Growth Flashcards
What does the cell wall do?
Resists osmotic lysis (the internal osmotic pressure is typically ~5 atmospheres for gram-negative species and ~20 atmospheres for gram-positive species)
Maintains cell shape
What are the cytoskeletal elements?
FtsZ = tubulin (around waist, division)
CreS (crescentin) = IF (overall shape)
MreB and ParM = actin (shape, polarity, chromosomal segregation)
Compare & contrast Gram + & - bacteria
Gram +: Cytoplasmic membrane covered by a THICK peptidoglycan layer (lots of x-linking) with teichoic acid
Gram -: Cytoplasmic membrane, periplasmic space that has a thin layer of peptidoglycan, OM with LPS, lipoproteins, and porins
How does gram staining work?
When a decolorizer such as alcohol or acetone is added, it interacts with the lipids of the cell membrane. A gram-negative cell loses its outer lipopolysaccharide membrane, and the inner peptidoglycan layer is left exposed. The CV–I complexes are washed from the gram-negative cell along with the outer membrane. In contrast, a gram-positive cell becomes dehydrated from an ethanol treatment. The large CV–I complexes become trapped within the gram-positive cell due to the multilayered nature of its peptidoglycan. The decolorization step is critical and must be timed correctly; the crystal violet stain is removed from both gram-positive and negative cells if the decolorizing agent is left on too long (a matter of seconds).
Describe capsules
Capsules are loose, gelatinous outer surface layers that usually consist of complex polysaccharides
Basically, they make the surface slimy and resist phagocytosis
Most are antigenic, and some are used as components of vaccines (e.g., Streptococcus pneumoniae or Hib)
Describe flagella
Peritrichous: distributed over their surface, or
Polar: several at one end of the cell
Chemotaxis involves the control of flagellar rotation (counterclockwise results in swimming; clockwise results in tumbling).
Motile bacteria that exhibit chemotaxis spend more time swimming and less time tumbling when attractants or repellents are present, resulting in directed motion. Most flagella are antigenic
Describe Pili
Long, slender, proteinaceous, antigenic, hair-like structures on the surface of many bacteria.
Role in bacterial adherence to surfaces and tissues
Sex pili that play a role in bacterial conjugation are found in small numbers on some bacterial cells.
What are the two big features of the ctyoplasmic membrane? aka IM
anatomical and physiological barrier between the inside and outside of the bacterial cell.
- Selective permeability: impermeable to all charged substances, even H+ (only hydrophobic molecules or uncharged molecules no larger than glycerol can diffuse through it)
- Electron transport system: located in cyto membrane; principal source for generating the proton motive force during respiration
Other functions:
- transport of metabolites into the cytoplasm
- biosynthesis of lipids and other cell envelope components,
- certain aspects of DNA replication
- flagellar rotation.
What are the 4 phases of growth?
- Lag phase: physiologic adjustment for the starting cells; induction of new enzymes and the establishment of a proper intracellular environment for growth
- Exponential (logarithmic) phase: rate of increase in cell number/mass is proportional to the cell number/cell mass already present. Cells continually double (20min - 1day)
- Stationary phase: growth is balanced by death; essential nutrients are consumed and toxic products of metabolism accumulate. May exhibit markedly increased resistance to antibiotics such as penicillin or other β-lactam antibiotics that act on growing cells.
- Death phase: the # of viable bacteria will decrease over time. If spontaneous cell lysis (autolysis) occurs, the mass of intact bacteria in the culture will also decrease.
Curve looks like: __/¯¯¯¯¯\
Describe bacterial nutrition requirements
Heterotrophic: require an organic carbon source
Autotrophic: obtain their carbon exclusively from CO2
Fastidious: deficient in one or more biosynthetic pathways; require essential growth factors (AAs, vitamins, purines, pyrimidines and inorganic ions).
Obligate intracellular: can only grow within eukaryotic cells
Describe bacterial responses to O2
Strict Aerobe: requires O2, cannot ferment
Strict Anaerobe: Killed by O2, fermentive metabolism
Indifferent (aka aerotolerant anaerobe): ferments in presence or absence of O2
Facultative: Respires with O2; ferments in absence of O2
Microaerophilic: Grows best at low O2 concentrations; can grow without O2
What are the 2 forms of energy currency in bacteria?
ATP: used for biosynthetic reactions
EC gradients (the proton motive force): used for flagellar rotation and certain substrate transport systems.
Bacteria also require reducing power in the form of NADH and NADPH to drive various metabolic interconversions.
Describe fermentation and respiration
Fermentation: organic compounds serve as both electron donors and acceptors; NO NET OXIDATION of substrates occurs.
Respiration: generate ATP through electron transport and use molecular oxygen as the final electron acceptor. In ANAEROBIC respiration, certain bacteria may use inorganic substrates such as nitrate or nitrite as terminal electron acceptors instead of O2.
Heterotrophic bacteria obtain both energy and reducing power by subjecting nutrients to fermentation or respiration.
Explain why unique bacterial components are important as potential targets for antimicrobial therapy.
Antimicrobials work on the principle of SELECTIVE TOXICITY (selective inhibition of microbial growth at drug concentrations tolerated by the host).
Some components of bacteria are not present in eukaryotes (or are sufficiently different) are effective as targets for antimicrobial agents.
What are the principal targets of antimicrobial agents? (hint: there are 5)
- Cell wall
- Outer and cytoplasmic membrane
- Bacterial ribosome (30S or 50S subunit)
- Nucleic acid synthesis (go after DNA gyrase, topoisomerase, RNA pol)
- Metabolic inhibition (target folic acid synth, reduction of folate, lipid synth, anaerobic metabolism)
