This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Secondary Structure of Protein”.
1. Which among the following structure represents the local spatial arrangement of a polypeptide without regard to the conformation of its side chains?
a) Primary structure
b) Tertiary structure
c) Quaternary structure
d) Secondary structure
View Answer
Explanation: Secondary structure is the special arrangement of the polypeptide chain in three-dimension. It may form some special structures such as helices, sheets, and turns, etc. These structures are very common in a protein.
2. The peptide group in a protein has a rigid, planar structure. Which interactions give the peptide bond its partial double bond character?
a) Covalent
b) Non-covalent
c) Hydrophobic
d) Resonance
View Answer
Explanation: Due to the resonance occurring between the double bond and the lone pair of the oxygen atom, the peptide bond has a partial double bond character. This partial double bond character makes the peptide planar.
3. What are the most common regular secondary structures found in proteins?
a) Alpha-helix and turns
b) Beta-sheets and loops
c) Loops and turns
d) Alpha-helix and beta-sheets
View Answer
Explanation: The most commonly found secondary structures in a protein are the alpha-helix and beta-sheets. Both of these secondary structures are very common and very important for a protein molecule. They play a significant role in the functioning of the respective proteins.
4. Who discovered the alpha-helix structure in a protein molecule?
a) Lynn Margulis
b) Francis Collins
c) Louis Pasteur
d) Linus Pauling
View Answer
Explanation: Linus Pauling discovered the alpha-helix structure in a protein molecule. Lynn Margulis gave the theory of endosymbiosis. Francis Collins discovered the gene for Cystic Fibrosis. Louis Pasteur is also known as the father of immunology.
5. The alpha-helix is a right-handed helix.
a) False
b) True
View Answer
Explanation: The above statement is true. The alpha-helix is a right-handed helix i.e. when the right hand is curled, the curled fingers show the direction of the polypeptide chain if the thumb points towards the direction of the helix rise.
6. 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
View Answer
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.
7. 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
View Answer
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.
8. Beta-sheets are sometimes also called as “pleated sheets”.
a) False
b) True
View Answer
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”.
9. 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
View Answer
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).
10. Parallel beta-sheets are more stable than antiparallel beta-sheets.
a) True
b) False
View Answer
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.
11. 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
View Answer
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.
12. Which is the most abundant protein in all vertebrates?
a) Keratin
b) Tapasin
c) Connexin
d) Collagen
View Answer
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.
13. Which disease results from the dietary deficiency of vitamin C?
a) Jaundice
b) Malaria
c) Cancer
d) Scurvy
View Answer
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.
14. Which disease is caused by the regular ingestion of the seeds from the sweet pea?
a) Scurvy
b) Diabetes
c) AIDS
d) Lathyrism
View Answer
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.
15. 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
View Answer
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.
Sanfoundry Global Education & Learning Series – Protein Engineering.
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