This set of Structural Biology Multiple Choice Questions & Answers (MCQs) focuses on “Conformational Analysis of Proteins”.
1. In theory, if a given side is longer than alanine then ________
a) They will form strong sulphur bonds
b) They will have several different conformations
c) They will have a single stable conformation
d) They will behydrophobic
View Answer
Explanation: The bonds which will be formed between the carbon atoms of the side chains rotates in several different ways and results in different conformations.
2. For 2 tetrahedral carbon atoms, the most energetically favoured conformation is _________
a) Polar conformation
b) Non-Polar conformation
c) Staggered conformation
d) Chair conformation
View Answer
Explanation: Staggering is nothing but when it is viewed along with the rotation axis, the substituent group of one carbon atom will be between other carbon atoms. This makes them energetically favourable.
3. If there are two amino acids in a side chain, what will be the relative degrees of rotation between their carbon atoms?
a) 360°
b) 0°
c) 60°
d) 120°
View Answer
Explanation: The amino acids in the side chain will rotate 120° to attain the most stable conformation possible. These 120° of rotation won’t allow the carbon atoms to be in the same line. If carbon atoms are aligned in the same line then there will be repulsion between those resulting in highly unstable structure.
4. What is the maximum number of staggered conformation possible for alanine – alanine projection?
a) 3
b) 4
c) 7
d) 8
View Answer
Explanation: Alanine – Alanine is linked to one another by carbon-carbon bonds. This C – C bond can rotate clockwise or anti-clockwise in three ways without overlapping its functional groups on one another.
5. In valine, the substitution on beta carbon is _________
a) One methyl group and two hydrogen
b) Two methyl group and one hydrogen
c) Two ethyl group and two hydrogen
d) Two ethyl group and one hydrogen
View Answer
Explanation: The chemical formula of valine is C5H11NO2. From this formula it is easy to make out that out of 5 carbons, 1 carbon is of the carboxyl group, 1 carbon is alpha carbon, 1 carbon is beta carbon and the remaining 2 carbons belong to the methyl groups.
6. The phenomenon in which one conformation of many possible conformations is likely to frequently occur is known as __________
a) Isomers
b) Enantiomers
c) Rotamers
d) Primers
View Answer
Explanation: Assume that there are say 5 possible energetically favourable conformations for a particular pair of amino acids in the side chain. Then the probability of occurrence of those conformations is not equal. Anyone conformation will have more possibility of occurrence. Such a conformation is called as rotamers.
7. Rotamer libraries used for ___________
a) Amino acid modelling
b) Protein modelling
c) Carbohydrate modelling
d) Lipid modelling
View Answer
Explanation: The rotamer libraries are a collection of conformations that are favoured during interaction of 2 or more amino acids. These libraries help while designing the drug or a protein by predicting the favoured conformation.
8. Which amino acid can attain a wide range of conformations during protein formation?
a) Proline
b) Histidine
c) Leucine
d) Glycine
View Answer
Explanation: Glycine is the lightest among all of the amino acids having only one hydrogen atom in its side chain. Hence it can easily attain different conformations without any restrictions. Usually, the amino acid with bulk side chains has less possibility of adopting a diverse range of conformations.
9. Aminoacetic acid is conserved in homologous sequences of proteins.
a) True
b) False
View Answer
Explanation: When two proteins have some similarities in their structure, they are said to be homologous to each other. High proportions Aminoacetic acid which is also called as Glycocoll is conserved because of their ability to allow unusual conformations in the main chain of proteins. Glucocoll being small in structure with light side chains can form different conformations. Hence they are conserved in homologous sequences of proteins.
10. Choose the correct statement.
a) Conformation of proteins depends only on environmental factors
b) Conformation of proteins is affected by environmental factors
c) Conformation of proteins doesn’t depend on environmental factors
d) Conformation of proteins depends only on the amino acid sequence
View Answer
Explanation: Conformation mainly depends on the amino acid sequence. But it also depends on environmental factors. Some of the environmental factors influencing the protein conformations are temperature, pH, humidity.
11. Which amino acid is responsible for slight pucker in the backbone of protein?
a) 2-Aminopropanoic acid
b) 2-Aminoethanoic acid
c) Pyrrolidine-2-carboxylic acid
d) 2-Aminobutanedioic acid
View Answer
Explanation: In most of the times, Pyrrolidine-2-carboxylic acid which is also called as proline, is responsible for puckering in the protein backbone. This is because of the pyrrole ring of proline. The pyrrole ring is attached to the backbone of the proline. Hence proline won’t be able to participate in the bond formation and induces a pucker.
12. The function of a protein does not depend on its conformation.
a) True
b) False
View Answer
Explanation: The protein conformation is the one which decides the fate of a protein. For example, some of the proteins won’t be functional until and unless a staggering is induced in the protein. One protein can attain several conformations by varying its dihedral angles like phi, psi. But it will become functional only when the dihedral angles enter the sterically allowed region of the Ramachandran plot.
Sanfoundry Global Education & Learning Series – Structural Biology.
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