1. What are the pitch length of alpha-helix and the number of residues per turn?
a) 5.3 Armstrong, 6.4 residues
b) 3.4 Armstrong, 5.6 residues
c) 3.6 Armstrong, 5.4 residues
d) 5.4 Armstrong, 3.6 residues
Explanation: The pitch of alpha-helix is 5.4 Armstrong, and residues per turn are 3.6 residues. Generally, the alpha-helix of a protein contains on an average around 12 residues, and have a length of around 18 Armstrong. The alpha-helix is stable majorly due to its strong hydrogen bonding.
2. The peptide C=O bond of the nth residue of the backbone of alpha-helix points along and forms a hydrogen bond with the peptide N—H group of which among the following residue?
a) (n+1)th
b) (n+2)th
c) (n+3)th
d) (n+4)th
Explanation: The peptide C=O bond of the nth residue of the backbone of alpha-helix points along and forms a hydrogen bond with the peptide N—H group of the (n+4)th residue.This arrangement results in the formation of a strong hydrogen bond, which has nearly optimum N—O distance (2.8 Armstrong). Moreover, in the core of the helix, the atoms are in van der Waals contact, because the core of the helix is tightly packed.
3. Beta-sheets are sometimes also called as “pleated sheets”.
a) True
b) False
Explanation: Beta-sheets occur in two varieties i.e. antiparallel beta-sheets and parallel beta-sheets. The conformation of these structures is that the hydrogen bonding is optimal and form fully extended conformation having dihedral angles equal to +/- 180 degrees. Hence, they have a rippled or pleated edge-on appearance therefore, they are sometimes called as “pleated sheets”.
4. Regular secondary structures such as alpha-helices or the strands of beta-sheets are often connected by a stretch of a polypeptide that changes direction abruptly. What are these structures?
a) Incomplete sheets
b) Inverse helix
c) Small helix
d) Turns or beta-bends
Explanation: Turns or beta-bends often connect alpha-helices or the strands of beta-sheets. These structures mostly occur on the surface of proteins. These structures usually contain a few amino acid residues (about 4).
5. Parallel beta-sheets are more stable than antiparallel beta-sheets.
a) true
b) false
Explanation: The above statement is not true. Parallel beta-sheets are less stable than antiparallel beta-sheets. This is because the hydrogen bonds of parallel sheets are distorted compared to those of the antiparallel sheets.
6. Which among the following are the principal component of the outer layer of the skin (epidermis) and its related appendages, such as hair, horn, nails, and feathers?
a) Calrectin
b) Connexin
c) Collagen
d) Keratin
Explanation: Keratin is the principal component of the outer layer of the skin (epidermis) and its related appendages, such as hair, horn, nails, and feathers. It is mechanically durable and does not easily react. It occurs in all higher vertebrates. There are more than 50 keratin genes that are present in humans.
7. Which is the most abundant protein in all vertebrates?
a) Keratin
b) Tapasin
c) Connexin
d) Collagen
Explanation: Collagen is the most abundant protein in all vertebrates. It occurs in all multicellular animals. It is a strong, insoluble fiber and is the major stress-bearing component of connective tissue.
8. Which disease results from the dietary deficiency of vitamin C?
a) Jaundice
b) Malaria
c) Cancer
d) Scurvy
Explanation: The deficiency of vitamin C in diet results in Scurvy. Collagen is a triple helix and contains some hydroxylated residues. The enzyme (prolyl hydroxylase) that catalyzes this reaction requires vitamin C to maintain its activity.
9. Which disease is caused by the regular ingestion of the seeds from the sweet pea?
a) Scurvy
b) Diabetes
c) AIDS
d) Lathyrism
Explanation: Regular ingestion of the seeds from the sweet pea causes lathyrism. It contains an enzyme that inactivates the enzyme lysyl oxidase. Lysyl oxidase is the only enzyme involved in the cross-linking process.
10. Helix capping is the phenomenon in which, the side chains of which two flanking residues fold back to form hydrogen bonds with one of the four-terminal residues of the helix?
a) Pro, Val
b) Gly, Val
c) Val, Ile
d) Asn, Gln
Explanation: There are some flanking residues outside the alpha-helix or beta-sheets. Helix capping is the phenomenon in which, the side chains of the flanking Asn and Gln residues fold back to form hydrogen bonds with one of the four-terminal residues of the helix.