Microbial Metabolism Flashcards
The ____ differences between bacteria (prokaryotes) and eukaryotes can be utilized for the development of antibacterial therapies
metabolic
True or False. Bacteria exist in a diploid state.
FALSE. they exist in a haploid state
What is the reproduction process of bacteria called?
binary fission
The discrete area where the double-stranded DNA circle is located is called ____
nucleoid
In binary fission, a single cell divides into ___ daughter cells
two (binary)
What are the 4 phases to a typical bacterial growth curve?
1) lag phase
2) exponential phase
3) stationary phase
4) decline phase
Name this phase:
nutrients are deplete and toxic waste products/ metabolites are accumulating in media. viable cell count remains constant
stationary phase
Name this phase:
bacteria multiply rapidly by binary fission and populations doubles at a constant rate
exponential phase
Name this phase:
cells accumulate metabolites necessary for maximal cell growth, but little to no actual cell division
lag phase
Name this phase:
decrease in number of live bacteria
decline phase
Name this phase:
bacteria are less susceptible to killing by antimicrobials
stationary phase
Name this phase:
spore-forming bacteria (Gram (+)) initiate sporulation process
stationary phase
Which phase has little to no cell division?
lag, stationary and decline phases
In which phase are bacteria most susceptible to antimicrobials?
lag and exponential phase
In which phase are more bacteria killed than are generated?
decline phase
In which phase are bacteria doubling at a constant rate?
exponential phase
What are the requirements for growth (3)?
1) energy source
2) source of carbon and nitrogen
3) water and various ions
Growth in culture is determined by what factors?
1) pH optimum
2) aerobic vs. anaerobic
3) nutrients/ composition of media
4) temperature
How is cell density determined?
colony counts on agar plates or by turbidity (spectrophotometry)
These bacteria exclusively utilize respiration to meet its energy need
aerobic
These bacteria utilizes fermentation to meet its energy needs
anaerobe
These bacteria can respire or ferment
facultative anaerobes
These bacteria grow best at low oxygen levels but can grow without oxygen as well
microaerophilic
What are two ROS that are highly toxic to cells?
1) hydrogen peroxide (H2O2)
2) superoxide anion (O2-)
What are the two major mechanisms bacteria use to counteract ROS?
1) catalase
2) SOD (superoxide dismutase)
What’s the mechanism of catalase?
catalyzes the breakdown of H2O2 to H20 and O2
What’s the mechanism of SOD?
help detoxify O2-
True or False. Both prokaryotes and eukaryotes have SOD
True
Bacteria that lack catalase and SOD are ____ to oxygen and are likely _____
1) sensitive
2) anaerobic
Do microaerophilic bacteria contain catalase and SOD?
yes, in small amounts
Do facultative anaerobes contain catalase and SOD?
yes
What type of energy production is this?
molecular oxygen is the terminal electron acceptor
aerobic respiration
What type of energy production is this?
compounds other than oxygen such as nitrate or sulfate are used as terminal electron acceptors
anaerobic respiration
What type of energy production is this?
anaerobic process where organic metabolic intermediate derived from a fermentable substrate is used as final electron acceptor
fermentation
Which type of energy production is the most efficient?
aerobic respiration
Which type of energy production is the least efficient?
fermentation
True or False. End products of fermentation can be measured and sometimes diagnostic for certain bacteria
True
What are some targets that are unique to bacteria that we can use for selective toxicity?
1) nucleic acid synthesis
2) DNA replication
3) transcription/ translation
How can we selectively inhibit microbial nucleic acid biosynthesis?
folate. bacteria have to synthesize it while humans must ingest it as part of our diet. Recall that folate is essential to the synthesis of purines and thymidine. antibiotics can thus target folate synthesis
How can we selectively inhibit microbial DNA replication?
target bacterial DNA gyrase
What is bacterial DNA gyrase do?
responsible for unwinding and winding of DNA during replication
What drug targets bacterial DNA gyrase?
quinolones
In bacteria, transcription and translation occur simultaneously (co-transcriptional translation), how is this possible?
no nuclear membrane to separate the processes
What bacterial ribosome is an important target of antimicrobial action?
70S
What is the general structure of peptidoglycan?
polysaccharide polymer cross-linked by peptide
Peptidoglycan is a linear chain of alternating sugars, what are these sugars?
1) N-acetyglucosamine (NAG)
2) N-acetlymuramic acid (NAM)
What are the steps to peptidoglycan biosynthesis?
1) activation of sugars by adding UDP
2) a pentapeptide is added to UDP-NAM
3) UDP-NAM-pentapeptide is attached to bactoprenol through pyrophosphate link with release of UMP
4) NAG is added to NAM-pentapeptide-bactoprenol complex
5) bactoprenol carries the complex across the membrane
6) disaccharide (NAM and NAG) is added to end of the growing peptidoglycan chain by transglycosylases
7) bacteroprenol is recycle and converted back to pyrophosphate bactoprenol
Where in the cell does peptidoglycan biosynthesis start and where does it end?
starts on the inner surface of membrane (cytoplasm)
ends on the outer surface of membrane
What is the role of bactoprenol?
lipid carrier that transports NAM-NAG precursor across the membrane
How does vacomycin work as antibiotic?
prevents elongation of peptidoglycan chain
How does bacitracin work as antibiotic?
prevents recycling of bactoprenol
True or False. Antibiotics are used to block peptidoglycan synthesis at the same steps
False. different steps are used as targets for antibiotics
Once the growing chain of peptidoglycan is on the outer leaflet of cell membrane, what’s the next process in its biosynthesis?
transpeptidation - cross-linking of the pentapeptide side chains, making the mesh-like structure
The pentapeptide added to UDP-NAM must be in a specific order, what is it?
aa #1: variable aa#2: variable aa#3: diamino amino acid aa#4: D-ala aa#5: D-ala
Where does transpeptidation occur on the growing peptidoglycan chain?
between the free amine of the diamino amino acid in the third position and D-ala in the fourth position of the other peptide chain
Transpeptidases are also called _____
penicillin binding proteins (PBP)
True or False. During peptidoglycan formation amino acids are added without the help of transfer RNA and ribosomes.
TRUE
