Microbiology Quiz 1

Question 1

What’s unique about bacteria nucleoid?

Answer 1

NO splicing occurs!

Question 2

Differences b/t euk and prok ribosomes?

Answer 2

Euk = 80S
Prok = 70S
*GOOD drug target

Question 3

Do all bacteria have cell wall?

Answer 3

YES except Mycoplasma

Question 4

Structure of cell wall?

Answer 4

• 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)

Question 5

What are Gram positive bacteria?

Answer 5

• PURPLE
• Thick peptidoglycan layer with other carbohydrate polymers.
• Teichoic acids
• Ab response is primarily against POLYMERs not to peptidoglycan.
• No phospholipid outer membrane

Question 6

What are Gram negative bacteria?

Answer 6

• 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).

Question 7

What is periplasmic space?

Answer 7

• only present in Gram NEGATIVE organisms.
• space b/t outer and inner membranes
• enzymes that degrade antibiotics are located here: Penicillinases

Question 8

What is LPS?

Answer 8

• 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

Question 9

Steps in Gram stain?

Answer 9

• 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)

Question 10

Is capsule essential for viability?

Answer 10

• NO, but essential to pathogenesis.
• Does NOT stain with Gram stain.
• Ab and vaccines often directed against capsule.

Question 11

What are the ways bacteria use to adhere?

Answer 11

• Pili or Fimbrae (assembled by polymerization of Pilin molecules)
• Adhesins
• Polysaccharide glycocalyx (slime layer or capsule structure that helps adhere and avoid phagocytosis)

Question 12

What is “Generation Time”?

Answer 12

The time it takes for the organism to double.

Question 13

What limits bacterial growth?

Answer 13

• Exhausted nutrient supplies
• Toxic metabolic products
• Immune system
• Antibiotics

Question 14

Major nutrients required for bacterial growth?

Answer 14

• 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.)

Question 15

What are the factors that are often secreted by bacteria?

Answer 15

• Exotoxins
• Proteases
• Enzymes to degrade polysaccharides
• Lipases
• • Nucleases (DNases): provide microbes with nucleotides, carbon, nitrogen, phosphorus
• • Phsopholipases: degration of phospholipids from host cell membrane

Question 16

What are fastidious bacteria?

Answer 16

Bacteria that require a LOT of growth factors to grow, such as H. influenza.

Question 17

What are prototrophic bacteria?

Answer 17

Bacteria that can synthesize everything they need to grow, such as E. coli.

Question 18

What are some physical requirements for microbial growth?

Answer 18

• Temperature (usually 37C is optimal)
• pH (7-7.2)
• Osmolarity (high [NaCl] or[sugar] can inhibit bacterial growth)

Question 19

Phases of bacteria growth?

Answer 19

• Lag phase: adapting to new environment
• Log phase: cell # increase in log manner
• Stationary phase: growth = death
• Death: death more than growth

Question 20

What is glyoxalate shunt?

Answer 20

• 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)

Question 21

What are some products from Pyruvate during Anaerobic oxidation?

Answer 21

• Lactic acid (Lactate dehydrogenase)
• Butyric acid (ODOR!) as well as other alcohols and acetone
• Acetate, propionic acid (swiss cheese??!), lactic acid

Question 22

“Leo the lion goes GR”

Answer 22

Loss electron = Oxidation

Gain electron = Reduction

Question 23

What is Stickland Reaction?

Answer 23

Some clostridia carry out specialized fermentation that exchanges the NAD/NADH b/t two pathways, one based on Ala - Acetate, Glycine - Acetate.

Question 24

Obligate Aerobes?

Answer 24

O2 required for growth, NO fermentation

Question 25

Faculative Aerobes?

Answer 25

Functional respiratory system and fermentative capacity. - MANY pathogens (contains catalase, superoxide dismutase)

Question 26

Obligate Anaerobes?

Answer 26

Can NOT handle ROS, produces H2O2 in presense of O2 - toxic.

Question 27

Aerotolerant Anaerobes?

Answer 27

INDIFFERENT to oxygen

Question 28

Microaerophiles?

Answer 28

Normal atmosphere is 20% O2, but they perfer 5% O2.

Question 29

Advantages of using bacteria as genetic tools?

Answer 29

• 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.

Question 30

Types of mutations?

Answer 30

• 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)

Question 31

What are Auxotroph?

Answer 31

can NOT synthesize an essential metabolite (NO growth on minimal medium supplemented)

Question 32

What are Prototroph?

Answer 32

WT that can grow on minimal medium

Question 33

Types of genetic recombination?

Answer 33

• General (homologous): extensive sequence homology
• Site specific: limited homology and site specific recombinase
• Illegitimate: NO homology, random insertions.

Question 34

Life cycle of virulent phage?

Answer 34

• Adsorption
• Penetration
• Synthesis of early proteins
• Replication of viral DNA
• Synthesis of late proteins
• Assembly of phage
• Takes less than 1 hr

Question 35

What’s special about lysogenic cycle when compared to lytic cycle?

Answer 35

• 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.

Question 36

What is bacteria host defense against phages?

Answer 36

Restriction Enzymes!

• Recognize particular palindromic sequences
• DNA methylation protects host DNA from self-restriction digestion.

Question 37

What makes up transposons?

Answer 37

• Flanked by insertion elements.
• Insertional elements contain a transposes flanked by inverted repeats.
• *Insertion is RANDOM!
• **Often encode antibiotic resistance genes.

Question 38

Methods of gene transfer?

Answer 38

• 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

Question 39

Methods of conjugation?

Answer 39

1. 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.
2. R-factors: resistance transfer factors. Encode enzymes that inactive or destroy antibiotic: contain transposons so resistance can move b/t R-factors.