Bacteria Structure and Function (complete) Flashcards
Describe the rigid cell wall of bacteria. What are the functions?
- External to cytoplasmic membrane that contain peptidoglycan
- G(+) and G(-) have different cell wall structures
Functions:
1) Resists osmotic lysis
2) Maintains cell shape
Describe the peptidoglycan layer of bacteria
- Forms rigid mesh surrounding cytoplasm
- Consists of polymer of repeating units (GlcNAc and MurNAc)
- these are crosslinked!
How does lysozyme interact with bacteria when inside the body?
- Hydrolyzes peptidoglycan by cleaving glycosidic bond between MurNAc and GlcNAc
- contributes to innate immune system
Describe the peptidoglycan layer in gram negative bacteria
- THIN!
- Sparsely cross-linked
Describe the peptidoglycan layer of gram positive bacteria
- THICK!
- Extensively cross-linked
- Also contains teichoic acids
Describe the outer membrane of gram negative bacteria. What are the functions?
- A lipid bilayer
- Contains lipopolysaccharide, lipoproteins, and porins
Functions:
1) Barrier to antibiotics
2) Protects against detergents and toxic compounds
Lipoproteins in the outer membrane of gram negative bacteria are covalently linked to what?
Peptidoglycans
What is the function of porins in the outer membrane of gram negative bacteria?
- Form transmembrane channels
- Allow diffusion of hydrophilic molecules across membrane
Describe the outer membrane of gram positive bacteria
- Have two layers or leaflets
- Outer leaflet: LPS, Lipid A, core polysaccharide, O side chain
- Inner leaflet: phospholipids
Describe teichoic acids.
- A repeating polyglycerol-P or polyribitol-P backbone
- Covalently attached to peptidoglycan layer
- Help anchor the cell wall to membrane
Describe capsules
- Loose, gelatinous outer surface layers
- Consist of complex polysaccharides
- Enhance virulence b/c it can resist phagocytosis of humans
Describe flagella
- Appendages used for motility
- Some bacteria have flagella all over surface (peritrichous)
- some have just one (polar)
Describe pili (fimbraie)
- Long, slender, proteinaceous, antigenic hair-like structures
- Play role in adherance to surfaces and tissues
- Abs against pili may block adherance
Also used for bacterial sexy time (aka transfer of chromosomes btwn bacteria)
Describe the cytoplasmic membrane
- Barrier between the inside and outside of bacterial cell
- Lipid bilayer made of phoslipids, proteins
Functions:
1) selective permeability
2) e(-) transport system
Describe the cytoplasm
- Consists of aqueous solution of proteins and metabolites
- Where metabolic processes occur
Include:
1) Ribosomes
2) Nucleoid
Describe ribosomes in bacteria
- Where protein synthesis occurs
- Polyribosomes form when several ribosomes come together to interact with a single mRNA
Describe the nucleoid in bacteria
- A specific area of the cytoplasm
- Where DNA is located — tightly packed, coiled
- No nuclear membrane surrounding the nucleoid
Describe the bacterial chromosome
- a single, double stranded CIRCULAR DNA molecule
Describe plasmids
- Extra-chromosomal, self-replicating DNA molecules
- Not essential for bacterial viability
One type of plasmid called R factors:
- carry genes that determine resistance to antibiotics (Rrrrrr is for Rrrrrresitance!!!)
Describe bacteriophages
Viruses that infect bacteria
- inject DNA in bacterial cell
- Viral DNA fuses w/ bacterial DNA
- More viral proteins produced —> more viruses
Explain the importance of different cell wall structures in bacteria
Bacterial shape determined by intracellular cytoskeletal elements and rigid cell wall
- Structure determines function
Describe a typical bacterial growth curve.
- Bacteria are placed in a new environment and growth is measured
- Divided into 3-4 phases (lag, exponential, stationary, death)
y-axis: log bacterial #
x-axis: time
Explain the characteristics of lag phase
THINK: Adjustment phase
- Produces new enzymes to new environment!
- Establishes proper intracellular environment for optimal growth in this here new place
Explain the characteristics of exponential phase
THINK: growth phase
- rate of increase in cell #/mass is proportional to cell #/mass already present
- constant interval required to double #/mass (GENERATION TIME)
Explain the characteristics of stationary phase
THINK: plateau phase
- Essential nutrients consumed; toxic metabs accumulate
- Growth slows/ceases
- Where most bacteria spend their time
Explain the characteristics of death phase
THINK: death phase of course
- Doesn’t always happen, but some bacteria can’t withstand stationary phase
- there’s a decrease in total #/mass
- Only seen when bacteria lyse!!! (makes sense, eh?)
What are the different classifications for bacteria according to nutrition requirements?
1) Aerobe
2) Anaerobe
3) Indifferent
4) Facultative
5) Microaerophilic
Describe aerobe bacteria’s nutritional requirements for growth response
GR: aerobic conditions
- Requires O2
- Cannot ferment
Describe anaerobe bacteria’s nutritional requirements for growth response
GR: anaerobic conditions
- Killed by O2
- Fermentative metabolism
Describe indifferent bacteria’s nutritional requirements for growth response
GR: aerobic and anaerobic
- Ferments in presence or absence of O2
Describe facultative bacteria’s nutritional requirements for growth response
GR: aerobic and anaerobic
- Respires w/ O2
- Ferments in absence of O2
Describe microaerophilic bacteria’s nutritional requirements for growth response
GR: anaerobic (primary) and aerobic (small amount of growth)
- Grows best at low [O2]
- can grow w/o O2
Define respiration
- When O2 is used as the final e(-) acceptor in the electron transport/ATP generation process
- Anaerobic resp: some bacteria may use inorganic substrates (nitrate, nitrite) as e(-) acceptors (not O2)
Define fermentation
- Organic compounds serve as both e(-) donors and acceptors
- No net oxidation/reduction between substrates and products
Explain how metabolic “energy currency” is generated
Two types of currency:
1) ATP
2) Electrochemical gradients (proton motive force)
- Generated by fermentation/respiration
- Bacteria also need “reducing power” (NADPH, NADH)
Explain why unique bacterial components are important as potential targets for antimicrobial therapy
- Ensures you kill less of the host
- Selective inhibition of microbial growth at [drug] tolerated by host (aka SELECTIVE TOXICITY)
What are the major groups of antibiotics used for human medicine?
1) Cell wall-active antimicrobials
2) Outer/cytoplasmic membrane-active antimicrobials
3) Protein synthesis inhibitors at ribosomal level
4) Nucleic acid synthesis inhibitors
5) Metabolic inhibitory antimicrobials
What are the principal targets for cell wall-active antimicrobials?
Peptidoglycan
Examples
1) Beta-lactams
2) Vancomycin
3) Cycloserine
What are the principal targets for outer/cytoplasmic membrane-active antimicrobials?
- Outer and cytoplasmic membranes (duh)
- Use polymyxins to disrupt the membranes — they are cationic surfactants
What are the principal targets for protein synthesis inhibitors at ribosomal level?
Bacterial ribosomes (b/c they are different from mammalian ribos!!!)
Examples:
1) Aminoglycosides
2) Tetracyclines
3) Chloramphenicol
4) Macrolides
What are the principal targets for nucleic acid synthesis inhibitors?
Nucleic acid synthesis … :P
Examples:
1) Quinolones
2) Rifampicin
What are the principal targets for metabolic inhibitory antimicrobials?
Specific metabolic reactions
Examples:
1) Sulfonamides (folic acid formation)
2) Trimethoprim (folic acid metabolism)
3) Isoniazid (lipid synthesis)
4) Metronidazole (anaerobic metabolism)
