Microbiology Quiz 1 Flashcards
What’s unique about bacteria nucleoid?
NO splicing occurs!
Differences b/t euk and prok ribosomes?
Euk = 80S
Prok = 70S
*GOOD drug target
Do all bacteria have cell wall?
YES except Mycoplasma
Structure of cell wall?
- Contain unique N-acetyle glucosamine (NAG) linked to N-acetyl muramic acid (NAM) by a glycosidic bond (*lysozyme splits this - antibacterial). Polymer = peptidoglycan!
- Crosslinking by bonding b/t a.a. side chains (*penicillin blocks this)
What are Gram positive bacteria?
- PURPLE
- Thick peptidoglycan layer with other carbohydrate polymers.
- Teichoic acids
- Ab response is primarily against POLYMERs not to peptidoglycan.
- No phospholipid outer membrane
What are Gram negative bacteria?
- RED
- TWO membrane flanking cell wall: Thin peptidoglycan layer, cell wall contains lipoproteins, attached to which is the outer membrane (contains LPS which comprises the O-antigen!)
- Porins: allow passive diffusion of molecules of certain sizes (limits access to the cell wall - makes antibiotics less effective).
What is periplasmic space?
- only present in Gram NEGATIVE organisms.
- space b/t outer and inner membranes
- enzymes that degrade antibiotics are located here: Penicillinases
What is LPS?
- LPS located on outer layer of OM is known as ENDOTOXIN;
- polysaccharide attached to Lipid A: unique to Gram NEGATIVE organism _ the part that drives endotoxic shock
Steps in Gram stain?
- Crystal Violet
- Iodine (forms water insoluble complex with crystal violet)
- Decolorize with 70% ethanol (*ONLY Gram NEGATIVE decolorize)
- Counterstain with Red stain
(***purple sticks to the wall, red sticks to the membrane)
Is capsule essential for viability?
- NO, but essential to pathogenesis.
- Does NOT stain with Gram stain.
- Ab and vaccines often directed against capsule.
What are the ways bacteria use to adhere?
- Pili or Fimbrae (assembled by polymerization of Pilin molecules)
- Adhesins
- Polysaccharide glycocalyx (slime layer or capsule structure that helps adhere and avoid phagocytosis)
What is “Generation Time”?
The time it takes for the organism to double.
What limits bacterial growth?
- Exhausted nutrient supplies
- Toxic metabolic products
- Immune system
- Antibiotics
Major nutrients required for bacterial growth?
- C
- N
- P
- S
- Metals (Fe - respiratory enzymes: ability to scavenge Fe is KEY to virulence; microbes use SIDEROPHORES _ secreted by bacteria with HIGH affinities for iron.)
What are the factors that are often secreted by bacteria?
- Exotoxins
- Proteases
- Enzymes to degrade polysaccharides
- Lipases
- Nucleases (DNases): provide microbes with nucleotides, carbon, nitrogen, phosphorus
- Phsopholipases: degration of phospholipids from host cell membrane
What are fastidious bacteria?
Bacteria that require a LOT of growth factors to grow, such as H. influenza.
What are prototrophic bacteria?
Bacteria that can synthesize everything they need to grow, such as E. coli.
What are some physical requirements for microbial growth?
- Temperature (usually 37C is optimal)
- pH (7-7.2)
- Osmolarity (high [NaCl] or[sugar] can inhibit bacterial growth)
Phases of bacteria growth?
- Lag phase: adapting to new environment
- Log phase: cell # increase in log manner
- Stationary phase: growth = death
- Death: death more than growth
What is glyoxalate shunt?
- Used during growth in lipids.
- Isocitrate + Acetyl-CoA = Malate. When glucose is NOT abundant, they use lipids instead, less use of NADH and FADH2 (*Isocytrate lyase/Malate synthase)
What are some products from Pyruvate during Anaerobic oxidation?
- Lactic acid (Lactate dehydrogenase)
- Butyric acid (ODOR!) as well as other alcohols and acetone
- Acetate, propionic acid (swiss cheese??!), lactic acid
“Leo the lion goes GR”
Loss electron = Oxidation
Gain electron = Reduction
What is Stickland Reaction?
Some clostridia carry out specialized fermentation that exchanges the NAD/NADH b/t two pathways, one based on Ala - Acetate, Glycine - Acetate.
Obligate Aerobes?
O2 required for growth, NO fermentation
Faculative Aerobes?
Functional respiratory system and fermentative capacity. - MANY pathogens (contains catalase, superoxide dismutase)
Obligate Anaerobes?
Can NOT handle ROS, produces H2O2 in presense of O2 - toxic.
Aerotolerant Anaerobes?
INDIFFERENT to oxygen
Microaerophiles?
Normal atmosphere is 20% O2, but they perfer 5% O2.
Advantages of using bacteria as genetic tools?
- Small size
- Haploid genome (NO recessive/masking of mutations)
- Small genome (4000 genes)
- Rapid growth
- Isolated on agar plates
- Mutates easily
- **Transcription and translation occur at the same time.
Types of mutations?
- Missense (change of single a.a.)
- Nonsense (premature termination)
- Deletions (remove of large region)
- Insertions (add large region)
- Frameshift (changes reading frame)
- Silent (NO change in phenotype)
- Revertant (suppressor mutation: mutations occur at a different nucleotide than the original mutation that restore the WT phenotype)
What are Auxotroph?
can NOT synthesize an essential metabolite (NO growth on minimal medium supplemented)
What are Prototroph?
WT that can grow on minimal medium
Types of genetic recombination?
- General (homologous): extensive sequence homology
- Site specific: limited homology and site specific recombinase
- Illegitimate: NO homology, random insertions.
Life cycle of virulent phage?
- Adsorption
- Penetration
- Synthesis of early proteins
- Replication of viral DNA
- Synthesis of late proteins
- Assembly of phage
- Takes less than 1 hr
What’s special about lysogenic cycle when compared to lytic cycle?
- Phage attach/inject/recombine into host genome = Prophage
- C1 repressor is produced, REPRESSOR of lytic growth, prophage is replicated as a passenger on the chromosome.
- When DNA damage, starvation, or stress destroys the repressor, lytic genes are expressed, lytic cycle begins.
What is bacteria host defense against phages?
Restriction Enzymes!
- Recognize particular palindromic sequences
- DNA methylation protects host DNA from self-restriction digestion.
What makes up transposons?
- Flanked by insertion elements.
- Insertional elements contain a transposes flanked by inverted repeats.
- *Insertion is RANDOM!
- **Often encode antibiotic resistance genes.
Methods of gene transfer?
- Transformation: nonspecific uptake of DNA (extracellular)
- Transduction: uptake of DNA by phage or transposon
_generalized transduction/specialized transduction (*difference being specialized transfers not only host DNA but phage genes as well) - Conjugation: active exchange of DNA b/t bacteria
Methods of conjugation?
- F-plasmid: in F+ cell, codes for pilus, once formed, associates with F- cell, injects strands of DNA. * Hfr - High Frequency Recombination strain, F plasmid incorporated into chromosome = can transfer donor chromosomal genes to the F- cells.
- R-factors: resistance transfer factors. Encode enzymes that inactive or destroy antibiotic: contain transposons so resistance can move b/t R-factors.
