1. Cord factor is a ___________
a) protein
b) teichoic acid derivative
c) mycolic acid derivative
d) carbohydrate
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.
2. 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
b) Phospholipids
c) Proteins
d) Lipopolysaccharide
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).
3. Which among the following acts as receptors for bacteriophage attachment in Gram-negative bacteria?
a) Cilia
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.
4. Porins are special proteins act as channels in the outer membrane of Gram-negative bacteria.
a) True
b) False
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.
5. 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: -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.
6.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.
7. Which of the following are present in teichoic acids?
a) Which of the following are present in teichoic acids?
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.
8. 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.
9. Polyisoprenoid branched-chain lipids, are present in which of the following?
a) Archaebacteria
b) Eubacteria
c) Archaebacteria and Eubacteria
d) Cannot be determined
Explanation: In Archaebacteria, the lipids are polyisoprenoid branched-chain lipids, in which long-chain branched alcohols(phytanols) are ether linked to glycerol. In Eubacteria, the phospholipids are phosphoglycerides, in which straight-chain fatty acids are ester-linked to glycerol.
10. Cytoplasmic membrane and the cell material bounded by it plus the outer membrane of cell is known as _________
a) Protoplast
b) Cytoplast
c) Spheroplast
d) Cell membrane
Explanation: A protoplast is that portion of a bacterial cell consisting of the cytoplasmic membrane and the cell material bounded by it. When the cell has two membranes, the cytoplasmic membrane of the protoplast plus the outer membrane of the cell wall, the cell is called a spheroplast rather than protoplast.