Periplasm is
Answer: A
Correct answer: the area between the inner and outer membranes of gram-negative bacteria
The periplasm is the compartment between the plasma membrane and the outer membrane, and it contains the thin peptidoglycan layer along with binding proteins, hydrolytic enzymes and the β-lactamases that destroy penicillin. Gram-positive cells have no outer membrane, so no true periplasm.
Please log in or register to report this question.
Prosthecae helps in __________
Answer: B
Correct answer: nutrient absorption and attachment to surfaces
A prostheca is a stalk-like extension of the cell wall and membrane. It increases the surface area available for absorbing nutrients - a real advantage in dilute water - and, with a holdfast at its tip, anchors the cell to a surface. Caulobacter is the classic example.
Please log in or register to report this question.
Which of the following has peptidoglycan as a major constituent of cell wall?
Answer: B
Correct answer: Gram-positive bacteria
Peptidoglycan is the major constituent of the gram-positive wall - half or more of its dry weight, in many layers. Gram-negative bacteria have only a thin single layer, most of their wall being outer membrane, and fungal walls are made of chitin and glucans, with no peptidoglycan at all.
Please log in or register to report this question.
Which type of force drives the flagellar motion?
Answer: A
Correct answer: Protonmotive force
The flagellar motor is driven by the proton-motive force - protons flowing back into the cell through the Mot channels - and not by ATP. This is why a cell whose respiration is poisoned stops swimming even while it still has ATP, and it distinguishes the bacterial flagellum sharply from the ATP-driven eukaryotic one.
Please log in or register to report this question.
When rod shaped bacteria appear in pairs, what is the arrangement called?
Answer: A
Correct answer: Diplobacilli
Rods that remain attached in pairs after dividing are diplobacilli; in chains, streptobacilli. The diplo- and strepto- prefixes describe the grouping and the -bacilli or -cocci ending the shape.
Please log in or register to report this question.
Which one of these has a Chinese letter arrangement?
Answer: D
Correct answer: Corynebacterium diphtheriae
Corynebacterium diphtheriae divides by snapping fission: the cells bend sharply apart but stay joined at one end, giving the V and L shapes described as a Chinese-letter or palisade arrangement. It is a useful diagnostic clue in a stained smear.
Please log in or register to report this question.
Cord factor is a ___________
Answer: C
Correct answer: mycolic acid derivative
Cord factor is trehalose dimycolate - a sugar esterified with two mycolic acids, the long-chain fatty acids peculiar to the mycobacterial wall. It makes M. tuberculosis grow in the serpentine cords that give it its name, and it contributes to virulence by damaging mitochondria and inhibiting the migration of leucocytes.
Please log in or register to report this question.
Which is most likely to be exposed on the surface of a gram-negative bacterium?
Answer: A
Correct answer: Pore protein (porin)
Porins span the outer membrane and form water-filled channels through which small hydrophilic molecules diffuse in, so they are exposed at the surface. Lipoteichoic acid belongs to gram-positive cells; the energy-generating proteins are in the inner membrane; and the phospholipids of the outer membrane face inwards, with LPS on the outer leaflet.
Please log in or register to report this question.
Which of the following bacterial genera (that produces endospore) have medical importance?
Answer: C
Correct answer: Both (a) and (b)
The two medically important endospore-forming genera are Clostridium - tetanus, botulism, gas gangrene - and Bacillus, which includes anthrax and a food-poisoning species. The endospore matters clinically because it survives boiling, drying and disinfectants, so autoclaving is needed to destroy it.
Please log in or register to report this question.
The cell walls of many gram positive bacteria can be easily destroyed by the enzyme known as
Answer: B
Correct answer: lysozyme
Lysozyme hydrolyses the β-1,4 bond between NAM and NAG in peptidoglycan. A gram-positive cell, whose wall is mostly peptidoglycan and exposed to the outside, is destroyed by it readily; a gram-negative one is protected by its outer membrane. Lysozyme is present in tears, saliva and egg white as a first line of defence.
Please log in or register to report this question.
