This set of Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Morphology and Fine Bacteria Structure – Cell Wall”.
1. Peptidoglycan layer is present in large quantity in?
a) Gram-positive bacteria
b) Gram-negative bacteria
Explanation: Gram-positive bacteria usually have a much greater amount of peptidoglycan in their cell walls than do Gram-negative bacteria. It may account for 50 percent or more of the dry weight of the wall of some Gram-positive species, but only about 10 percent of the wall of Gram-negative bacteria.
2. Peptidoglycan is made up of __________
b) N-acetylmuramic acid
c) N-acetylglucosamine, N-acetylmuramic acid
d) N-acetylglucosamine, N-acetylmuramic acid, amino acids
Explanation: Peptidoglycan differs somewhat in composition and structure from one species to another, but it is basically a polymer of N-acetylglucosamine, N-acetylmuramic acid, Amino acids like-L-alanine, D-alanine, D-glutamate, and a diamino acid.
3. Teichoic acid present in Gram-positive bacteria can bind to which ion?
a) Fe ions
b) Phosphorus ions
c) Mg ions
d) Sulphur ions
Explanation: Teichoic acid bind magnesium ions and there is some evidence that they help to protect bacteria from thermal injury by providing an accessible pool of these cations for stabilization of the cytoplasmic membrane.
4. Cord factor is a ___________
b) teichoic acid derivative
c) mycolic acid derivative
Explanation: Cord factor (trehalose dimycolate) is a mycolic acid derivative which is toxic and plays an important role in the diseases caused by C.diphtheriae and M.tuberculosis.
5. The outer membrane of the Gram-negative cell wall is anchored to the underlying peptidoglycan by means of which of the following?
a) Braun’s Lipoprotein
Explanation: The outer membrane of the Gram-negative cell wall is anchored to the underlying peptidoglycan by means of Braun’s lipoproteins. The membrane is a bilayered structure consisting mainly of phospholipids, proteins and lipopolysaccharides(LPS).
6. Which among the following acts as receptors for bacteriophage attachment in Gram-negative bacteria?
b) O antigens
c) Lipid A
d) Teichoic acid
Explanation: The polysaccharide O antigens which extend like whiskers from the membrane surface into the surrounding medium. Many of the serological properties of Gram-negative bacteria are attributable to O antigens like they can serve as receptors for bacteriophage attachment.
7. Porins are special proteins act as channels in the outer membrane of Gram-negative bacteria.
Explanation: The outer membrane can allow smaller molecules such as nucleosides, oligosaccharides, monosaccharides, peptides and amino acids to pass across by means of channels in special proteins called porins.
8. NAG and NAM of peptidoglycan layer is linked by _________
a) beta-(1,4) glycosidic linkage
b) alpha-(1,4) glycosidic linkage
c) alpha-(1,6) glycosidic linkage
d) beta-(1,6) glycosidic linkage
Explanation: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) of peptidoglycan layer are linked by beta-(1, 4) glycosidic linkage. Each strand contains from 10 to 65 disaccharide units.
9. Gram-negative bacteria are more resistant to antibiotics due to the presence of?
a) Thin peptidoglycan wall
b) Outer lipopolysaccharide layer
c) Porin proteins
d) Teichoic acid
Explanation: Gram-negative bacteria consists of an outer membrane made up of lipopolysaccharides beneath the thin peptidoglycan layer. The outer membrane serves as a barrier to various external chemicals and enzymes that could damage the cell. It also protects the bacteria from antibiotics.
10. Which of the following are present in teichoic acids?
a) ribitol residues
b) glycerol residues
c) glucose residues
d) ribitol or glycerol residues
Explanation: The teichoic acids are water soluble polymers, containing ribitol or glycerol residues joined through phosphodiester linkages. The glycerol or ribitol is joined to a sugar residue such as glucose, galactose or N-acetyl glucosamine.
11. Bayer’s junctions are sites which help in joining which of the following?
a) cytoplasmic membrane and outer membrane
b) outer membrane and capsule
c) cytoplasmic membrane and periplasmic space
d) peptidoglycan layer and cytoplasmic membrane
Explanation: The cytoplasmic membrane and outer membrane are joined at sites termed Bayer’s junctions. In these regions, the outer surface of the cytoplasmic membrane is continuous with the inner surface of the outer membrane creating pores that vary in diameter from 25 to 50 nm.
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