Test 3-2 Flashcards
The metabolic differences between bacteria (prokaryotes) and eukaryotes can be utilized for
for the development of antibacterial therapies
Lag phase:
The initial period of adaptation to a new environment which is essential for the cell to accumulate metabolites necessary for maximal cell growth. There is an increase in metabolic activity so bacteria are sensitive to antimicrobials. There is little to no cell division.
Exponential (logarithmic) phase:
Bacteria multiply rapidly by binary fission, and the populations doubles at a constant rate. During this phase bacteria are most susceptible to killing by certain antibiotics.
Stationary phase:
During this time nutrients are depleted and toxic waste products/metabolites are accumulating in media resulting in a decreased growth rate. Viable cell count remains constant because bacteria have stopped dividing but are not yet dying. Bacteria are much less susceptible to killing by antimicrobials. During this phase spore forming bacteria initiate the sporulation process.
Decline phase:
More bacteria are killed than are generated resulting in a decrease in the number of live bacteria.
Obligate aerobe:
bacteria that require oxygen and metabolize by respiration (M. tuberculosis, P. aeruginosa, B. anthracis)
Obligate anaerobe:
bacteria that are inhibited or killed by oxygen and utilize fermentation exclusively for energy production (C. botulinum, Bacteroides)
Facultative anaerobe (the majority of pathogens):
bacteria that grow well under aerobic or anaerobic conditions. If oxygen is available they respire, if not they use fermentation.
Microaerophilic:
Require 5-10% oxygen for optimal growth (Campylobacter jejuni)
Superoxide Dismutase rxn
2O2- + 2H+ —> H2O2 + O2
Catalase or Peroxidase rxn
H2O2 + H2A* —> 2H2O + A
Catalase rxn if H2O2
H2O2 + H2O2 —-> 2H2O + O2
Bacteria that lack superoxide dismutase, catalase and peroxidase are very sensitive to
oxygen and likely anaerobic
aerobic bacteria express wtih enzymes?
superoxide dismutase, catalase and peroxidase
Reproduction: Binary Fission
Bacteria exist in a haploid state
Only one chromosome
A double-stranded DNA circle contained in a discrete area called a nucleoid
Binary Fission is:
An exact copy of the genome is made and,
a single cell divides into 2 (binary) daughter cells
Replication: DNA polymerization
- Replication always begins at the origin (ori)
- Bacterial DNA gyrase required for unwinding/winding DNA and are the target of quinolones
- Semiconservative replication
- each strand serves as a template therefore each resultant strand has a copy of the original genomic DNA
Requirements for growth
- Energy source
- Raw materials to build proteins, structures, and membranes
The minimum requirement for growth is
a source of carbon and nitrogen, an energy source, water and various ions
Growth in culture is determined by
pH optimum,
aerobic versus anaerobic
nutrients/composition of media
temperature
Cell density is determined by
colony counts on agar plates or by turbidity (spectrophotometry)
groups of bacteria based on metabolic properties
Autotroph: generate their own energy (eg from sunlight)
Heteroptroph: Uses organic carbon for growth
Phototroph: …
Chemoheterotrophs: Use organic compounds as both their energy source and their carbon source
most pathogenic bacteria are
chemoheterotrophs
Aerobic
- Exclusively utilizes respiration to meet its energy need
- examples: M. tuberculosis, P. aeroginosa, B. anthrasis
Anaerobe
- Exclusively utilizes fermentation to meet its energy needs
- Examples: C. botulinum, Bacteriodes
oxygen does what to anaerobes?
kills dem
Facultative anaerobes can
- respire or ferment
- (E. coli, Shigella dysenteriae, S. aureus)
Microaerophilic - grow best
best at low O2 but can grow without O2 as well (ex. C. jejuni)
Two highly reactive forms of oxygen are very toxic to cells
Hydrogen peroxide (H2O2) Superoxide anion (O2-)
Bacteria counteract reactive oxygen species by two major mechanisms
- Catalase, catalyzes the breakdown of H2O2 to H2O and O2
- SOD (superoxide dismutase) is expressed by both prokaryotes and eukaryotes to help detoxify O2-
Bacteria that lack SOD and Catalase are
very sensitive to oxygen and likely anaerobic
Microaerophilic bacteria (obligate anaerobes) and oxygen:
-small amount of catalase and superoxide dismutase
faculative anaerobes (obligate anaerobes) and oxygen:
-have catalase and superoxide dismutase
Obligate anaerobes: and O2
cannot grow in the presence of oxygen
Obligate aerobes:and O2
- require the presence of molecular oxygen for metabolism and growth
- produce superoxide dismutase and catalase which can detoxify hydrogen peroxide and superoxide radicals that are toxic byproducts of aerobic metabolism
facultative anaerobes. and O2
grow in either the presence or absence of oxygen
msot bacteria
Aerobic respiration:
- Energy-generating mode used by all aerobic bacteria. Molecular oxygen is the terminal electron acceptor.
- most efficient for ATP gen
Anaerobic respiration:
Energy generating mode used in some facultative organisms and some obligate anaerobes. Inorganic compounds other than molecular oxygen serve as terminal electron acceptors (e.g. nitrate or sulfate).
Fermentation:
- Anaerobic process utilized by some bacterial species. An organic metabolic intermediate derived from a fermentable substrate serves as the final electron acceptor
- LEAST EFFICIENT for ATP gen
final electron acceptor of fermentation?
organic molecule
final electron acceptor of aerobic respiration?
mol O2
Many bacteria can be identified based on what end products
end products of pyruvate
Nucleic acid biosynthesis
- Nucleotides are the building blocks for DNA and RNA, as well as the energy storage molecules ATP and GTP
- Nucleotides are also components of cofactors (NAD, FAD, coenzyme A), biosynthetic intermediates (UDP-glucose), and second messengers (cAMP, cGMP)
- Agents that selectively inhibit microbial nucleic acid biosynthesis are important
what is essential to the synthesis of purines and thymidine?
folate
folic acid is derived from what in bacteria
-derived from what in humans?
paraaminobenzoic acid (PABA) -NOT derived must have in diet
sulfonamides mechanism of action
(dont really need to know this) block dihydropteroate synthase (converts dihydropteroate diphosphate + PABA (para-aminobenzoic acid) to dihydrofolic acid
DHFR INHIBITORS mech of action
(dont really need to know this) blocks dihydrofolate reductase (DHFR) whcih converts dihydrofolic acid to tetrahydrofolic acid which ultimately is converted into purines and thymidine
Are DHFR INHIBITORS and sulfonamides present in mammals?
only DHFR is
ability to shuffle along the mRNA to srart a new protein is a characteristic of
only the 70S bacterial
NOT the 80S eukaryotic
Bacterial protein synthesis.
Binding of the 30S subunit to the messenger RNA with the formyl methionine transfer RNA (fMet-tRNA) at the AUG start condon allows assembly of the 70S ribosome. The fMet-tRNA binds to the peptidyl site. The next tRNA binds to its condon at the A site and accepts the growing peptide chain. Before translocation to the peptidyl site. The process is repeated until a stop codon and the protein are released.
Peptidoglycan fun facts
- Internal to the capsule (if one exists) but external to cytoplasmic membrane (not found on Mycoplasma and Chlamydia)
- Provides protection (physical/mechanical, osmotic, chemical and biological agents)
- Determines shape
- Gram stain distinguish major types of envelopes: Gram (+) and Gram (-) cell wall
- Both Gram (+) and Gram (-) have a PG layer
- Peptidoglycan is found uniquely on prokaryotes
general structure of peptidglycan
- meshlike layer around cell
- polysaccharide polymer crosslinked by peptide
- pentaglycine bridge found in S. aureus (gram positive): expands the cross link
- Peptides are cross-linked through a peptide bond between the terminal D-Ala from one chain and a Lys (or other diamino amino acid) from the other chain.
monosaccharides of peptidoglycan that make up the polysaccharides?
1) N-acetylglucosamine
GlcNAc
G
—–>NAG
2) N-acetylmuramic acid
MurNAc
M
—->NAM
polysaccharide formation steps
1) in cytoplasm - attaching to UDP - ACTIVATION
2) A pentapeptide is added to UDP-NAM (independent of mRNA and ribosomes. It is produced enzymatically.)
3) UDP-NAM-pentapeptide is attached to the bactoprenol through a pyrophospate link with the release of UMP (first two AA are variable; the thrid must be a di-amino Lys
4) NAG is added to NAM-pentapeptide-bactoprenol complex (conveyer belt type molcule) (ON INSIDE)
5) The bactoprenol carrier transports the completed NAG-NAM pentapeptide repeat unit across the membrane (ON OUTSIDE)
6) The disaccharide unit is attached to the end of the growing peptidoglycan chain by enzymes called transglycosylases
7) Pyrophosphobactoprenol is converted back to phospho-bactoprenol and recycled
Bactoprenol is
is a lipid transport molecule that acts as a conveyor belt to transport peptidoglycan precursors across the cell membrane.
Transpeptidation:
Occurs between the free amine of the diamino amino acid in the third position of the pentapeptide (or the N-terminus of the attached pentaglycine chain), and the D-alanine at the fourth position of the other peptide chain, releasing the D-alanine precursor = tetrapeptide linkage via transpeptidases (penicillin binding proteins)
Do acid fast bacteria contain proteoglycan in their cell wall/
YES - gram +/- and acid fast
acid fast bac are more similar to…
gram + bc no outer membrane
endotoxin is a component of:
gram negative bacteria
What is a virulence factor that inhibits phagocytosis by macrophages?
capsule
no division in which phase of growth?
LAG phase …. theyre metabloically active only
bacteria are no longer metabolically active at which stage of growth?
Statinary phase!
during which phases are bacteria most senitive and elast sensitive to antimicrobials
MOST during lag and exponential phase BC theyre incorporating the antimicrobials into their systems
LEAST during stationary phase.. theyre not metabolically active anymore
endospores begin to form in which phase of growth?
stationary phase…
what unwinds the DNA in bacterial rep?
DNA gyrase
co-transcriptional translation
No nuclear membrane in bacteria so you can have both transcription and translation at the same time
what blocks transglycosylation
vancomycin
Is peptidoglycan a structure that is only found in bacteria?
YES
During peptidoglycan formation amino acids are added without the help of transfer RNA and ribosomes?
YES- addition to NAM
what test differentiates between staphylococcus and streptococcus/Enterococcus species?
catalsae test
catalase + cocci =
staphylococcus spp
catalase - cocci =
streptococcus and enterococcus spp
what culture media is used to test for hemolysis
Blood agar
what test differentiates amongst enterobacteriacea groups?
lactose fermentation
