Microbial Metabolism, Structure, and Function Flashcards
What kind of DNA do bacteria have?
One circular chromosome, composed of double-stranded DNA, located in the Nucleoid
When are bacteria most susceptible to antimicrobials?
During the Lag Phase and the Exponential Phase
When are bacteria less susceptible to antimicrobials?
Stationary phase
What phase does sporulation occur in?
Stationary phase
What phase is the bacteria actively metabolizing?
Exponential phase
What are the minimum requirements for growth?
A source of carbon and nitrogen, an energy source, water, and various ions
What four factors determine growth in culture?
pH optimum
Aerobic vs anaerobic
Nutrients/composition of media
Temperature
How is cell density determined?
Colony counts on agar plates or by turbidity using spectophotometry
Aerobic Bacteria
- Exclusively use respiration to meet energy needs
- E.g. M. tuberculosis, P. aeroginosa, B. anthrasis
Anaerobic Bacteria
- Exclusively use fermentation to meet energy needs
- E.g. C. botulinum, Bacteriodes
- **Much LESS efficient than respiration
- Will be KILLED BY OXYGEN
Facultative anaerobes
Can respire or ferment
E.g. E. Coli, Shigella dysenteriae, S. aureus
Microaerophilic
Grow best at low oxygen but can grow without it as well
E.g. C. jejuni
How do bacteria counteract the highly reactive forms of oxygen (e.g. Hydrogen Peroxide H2O2 and Superoxide Anion O2-)?
- Catalase (catalyzes the breakdown of H2O2 to H2O and O2)
- SOD (Superoxide Dismutase; expressed by both prokaryotes and eukarotes to detoxify O2-)
Bacteria that lack SOD and Catalase are…
Sensitive to oxygen and likely Anaerobic
Fermentation
Pyruvate is converted to various end products, which then can be used to identify bacteria in the lab
5 targets of antibiotics
- Cell wall synthesis
- DNA replication
- RNA synthesis
- Protein synthesis
- Antimetabolites
Nucleic Acid Biosynthesis: Nucleotide Uses
Building blocks of DNA and RNA, ATP and GTP, cofactors (NAD, FAD, coenzyme A), biosynthetic intermediates (UDP-glucose), and second messengers (cAMP, cGMP)
Folate is essential in the synthesis of…
Purines and Thymidine
Why is folic acid a good target for bacterial toxicity?
Bacteria derive their folic acid from para-aminobenzoic acid (PABA), while mamalian cells use pre-formed folate from the diet
What enzyme do Sulfonamides act on?
Dihydropteroate synthase (DHPS); NOT present in mammals
What enzyme does Trimethoprim act on?
Dihydrofolate reductase (DHFR); present in mammals, but DIFFERENT
Binary Fission: what unwinds bacterial DNA?
Bacterial DNA gyrase
What targets bacterial DNA gyrase?
Quinolones
What is different about transcription/translation in bacteria?
They are coupled (Co-Transcriptional Translation) as they do not have a nucleus
- 70s ribosomes (vs. 80s in eukoaryotes) binds free 5’ end of mRNA as DNA is transcribed
- Multiple ribosomes are bound to mRNA forming a polyribosome
Structure of Peptidoglycan in E. coli
Bond DAP of the peptide in one chain to the Ala at position FOUR of an adjacent chain
General structure of a Peptidoglycan
Peptides are cross-linked through a peptide bond between the terminal D-Alanine from one chain and a Lysine (or other diamino acid) from the other chain
Other names for N-acetylglucosamine
NAG, GlcNAc, G
Other names for N-acetylmuramic acid
NAM, MurNAc, M
Step 1 of Cell Wall Biosynthesis
Activation of carbohydrate subunits with UDP
Step 2 of Cell Wall Biosynthesis
A pentapeptide is added to UDP-NAM
***Important: this step is INDEPENDENT of mRNA and ribosomes; it is produced ENZYMATICALLY
What is the order of the amino acids coming off NAM-UDP?
L-ala (variable)— D-glu (variable) — L-lys (diamino acid; Lysine, diaminopilemic acid) — D-ala — D-ala
***The D-ala’s do not change; they are important in cross-linking
Step 3 of Cell Wall Biosynthesis
UDP-NAM-pentapeptide is attached to the BACTOPRENOL through a pyrophosphate link with the release of UMP
What is Bactoprenol?
Lipid carrier found in the cytoplasmic membrane
Step 4 of Cell Wall Biosynthesis
NAG is added to NAM-pentapeptide-bactoprenol complex
Step 5 of Cell Wall Biosynthesis
The bactoprenol carrier transports the completed NAG-NAM pentapeptide repeat unit across the membrane
Step 6 of Cell Wall Biosynthesis
The disaccharide unit is attached to the end of the growing peptidoglycan chain by enzymes called TRANSGLYCOSYLASES
Step 7 of Cell Wall Biosynthesis
Pyrophosphobactoprenol is converted to phosphobactoprenol and recycled
What is the mechanism of Vancomycin?
Prevents Penapeptide-NAM-NAG from attaching to Peptidoglycan
What is the mechanism of Bacitracin?
Prevents Bactoprenol from crossing the membrane
Peptidoglycan synthesis - Outer leaflet of cell membrane: Transpeptidation
Occurs between the free amine of the diamino acid in the 3rd position of the pentapeptide (or the N-terminus of the attached pentaglycine chain) and the D-alanine at the 4th position of the other peptide chain, RELEASING THE D-ALANINE PRECURSOS
Transpeptidases
Mediate transpeptidation reaction
-Also called Penicillin Binding Proteins (PBP) because they are targets for penicillins and other B-lactam antibiotics
