This set of Structural Biology Multiple Choice Questions & Answers (MCQs) focuses on “Protein Motifs”.
1. What are motifs?
a) Combination of super secondary structures
b) Combination of secondary structures
c) Combination of primary structures
d) Combination of tertiary structures
View Answer
Explanation: The motifs are also as super secondary structures. These are the combination of the different 2° structures like alpha helices, beta sheets. Different types of 2° structures get linked by several forces like ionic interactions, disulfide bridges and forms functional or non-functional protein units.
2. Choose the correct statement.
a) Motifs are built of only alpha helices
b) Motifs are built of alpha helices and beta sheets
c) Motifs are built of only one type of secondary structure
d) Motifs can be built of any type of secondary structure
View Answer
Explanation: There are no such restrictions on which type of secondary structures can form the super secondary structures. Any type of 2° structures or their combinations can form the super secondary structures with different characteristics.
3. Which is a functional motif with a basic structure?
a) Helix-loop-helix
b) Helix-turn-helix
c) Beta hairpin
d) Both helix-loop-helix and helix-turn-helix
View Answer
Explanation: Both helix-loop-helix and helix-turn-helix motifs are very simple in structure but have important functions like Ca binding site. Others are involved in the building of a protein.
4. Which kind of motif does parvalbumin have in its structure?
a) Beta hairpin
b) Helix-turn-helix
c) Helix-loop-helix
d) Beta-alpha-beta
View Answer
Explanation: Parvalbumin is a protein which is involved in muscle relaxation. It has a polypeptide chain with nearly 110 amino acids. It has 3 helix-loop-helix structures in it. The function of this protein depends on calcium binding.
5. The calcium binds to _________ region of the helix-loop-helix motif.
a) Depends on the amino acids building polypeptide
b) Loop
c) Helix
d) Depends on its site of occurrence
View Answer
Explanation: In Parvalbumin, the calcium binds to the loop region of the helix-loop-helix. The loop acts as a ligand for the binding of the calcium ion. And the motif acts as a scaffold.
6. Which among the following is the simplest motif in terms of structure?
a) Beta-alpha-beta motif
b) Helix-loop-helix motif
c) Greek key motif
d) Hairpin beta motif
View Answer
Explanation: The beta-hairpin motif is simplest one among the motifs taking their structures into consideration. The beta-hairpin motif has a loop joining two anti-parallel beta strands.
7. What is the length of the loop region found in beta hairpin?
a) 2-5 amino acid residues
b) 3-7 amino acid residues
c) 4-8 amino acid residues
d) 1-2 amino acid residues
View Answer
Explanation: The length of the amino acid sequence present in the loop region varies from one motif to another. In the beta-hairpin motif, the length of the loop is around two to five and it is found that those loops have no specific functions.
8. The bovine trypsin is an example of ____________ motif.
a) Beta-alpha-beta
b) Beta-hairpin
c) Greek key
d) Helix-turn-helix
View Answer
Explanation: It is the best example of a beta-hairpin motif. It is a small motif with a ribbon lie structure. The function of this motif is inhibiting the activity of another protein called digestive protease trypsin.
9. The snake venom, erabutoxin has two __________ motifs.
a) Beta-alpha-beta
b) Beta-hairpin
c) Helix-turn-helix
d) Helix-loop-helix
View Answer
Explanation: Erabutoxin is a protein found in the snake venom. It has five beta strands in total at the core, out of which 4 beta strands are connected by loops making 2 beta-hairpin motifs. The remaining one beta strand is free. It mainly acts by blocking the activity of the receptors like acetylcholine in the nerve cells.
10. A typical Greek key motif consists of ___________
a) 2 parallel and 2 anti-parallel beta strands placed side by side
b) 4 parallel beta strands placed side by side
c) 4 anti-parallel strands placed side by side
d) 1 parallel strand and 3 anti-parallel strands placed side by side
View Answer
Explanation: Greek key motif has repeating units of anti-parallel beta strands resembling an ornamental pattern which were used by ancient Greece. Here, all the four anti-parallel beta strands are linked by loops.
11. Staphylococcus nuclease has _________ motif in its structure.
a) Beta-hairpin
b) Greek key
c) Beta-alpha-beta
d) Helix-loop-helix
View Answer
Explanation: The Staphylococcus nuclease is an enzyme with several Greek key motifs. These motifs have no specific function alone. But the structure as a whole, Staphylococcus nuclease degrades the Deoxyribose Nucleic Acids.
12. One protein can have only one Greek key motif.
a) True
b) False
View Answer
Explanation: There are no such restrictions that one protein can have only one Greek key motif. In fact, the Greek keys motif occur as a set of repeating units. So, there will be several Greek key motifs in a protein.
13. In a motif, two parallel beta strands are connected by __________
a) Loops
b) Curns
c) Alpha helices
d) Anti-parallel beta sheets
View Answer
Explanation: In parallel beta strands, the free amino group of one beta strand and the free carboxyl group of another beta strand will be at opposite ends. So, it requires an alpha helix to connect both the ends. This results in a beta-alpha-beta motif.
14. If a beta-alpha motif is suspended in a solution, then which part of it gets exposed to the solvent?
a) Alpha helix
b) Beta strand
c) Depends on the solution in which it is suspended
d) Depends on the amino acid sequence
View Answer
Explanation: In most cases, the alpha helices of the beta-alpha-beta packs the beta strands of the beta-alpha-beta motif from the solvent. The beta strands which will be having hydrophobic residues will be covered with hydrophilic amino acid residues of the alpha helix.
15. Triosephosphate isomerase has repeating units of beta-alpha-beta-alpha motifs.
a) True
b) False
View Answer
Explanation: Triosephosphate isomerase is an enzyme which has repeating units of beta-alpha-beta motifs. Here, there will be three beta strands instead of two beta strands connected by two alpha helices. Hence, one of the beta strands will be shared by two motifs. This is also called a beta-alpha-beta-alpha motif.
Sanfoundry Global Education & Learning Series – Structural Biology.
To practice all areas of Structural Biology, here is complete set of Multiple Choice Questions and Answers.
If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]
