This set of Structural Biology Multiple Choice Questions & Answers (MCQs) focuses on “Protein Beta Structures”.
1. Which of the following is a secondary structure which is a combination of various regions of polypeptide?
a) Alpha helix
b) Pi helix
c) Alpha loop alpha
d) Beta sheet
View Answer
Explanation: Alpha helix is a single linear chain existing in the form of a helix. It has several restrictions as well. In contrast, beta structures are made of several polypeptides linking each other in the form of sheets.
2. Which type of bond is responsible for the formation of beta pleats?
a) Sulphur bridges
b) Hydrophobic interactions
c) Protium bonds
d) Ionic interactions
View Answer
Explanation: Protium bonds or hydrogen bonds link the adjacent polypeptide chains by liberating a water molecule and linking NH group of one amino acid to a CO group of adjacent amino acid.
3. The “sheet” structure of beta pleats arises from ____________
a) Tetrahedral bonding at carboxyl carbon
b) Tetrahedral bonding at the alpha carbon
c) Dihedral bonding at the nitrogen of amino group
d) Tetrahedral bonding at the nitrogen of amino group
View Answer
Explanation: The alpha carbon of amino acid building a beta structure has 4 bonds surrounding it with a certain angle and aligning the alpha carbons adjacent to each other and in the same line.
4. What position do side chains of amino acids occupy in the beta sheet?
a) Project above the alpha carbon
b) Project below the alpha carbon
c) Project up and down alternatively
d) Depends on the type of amino acids
View Answer
Explanation: Side chains of the amino acid building a beta sheet project up and down alternatively. For example, the side chain of the amino acid 1 project upwards and the side chain of the adjacent amino acid 2 projects down.
5. What are the two standard types of beta sheets?
a) Parallel and non-parallel
b) Parallel and antiparallel
c) Anti and syn
d) Strands and pleats
View Answer
Explanation: Beta strands interacts with each other to form beta sheets. Many of the times, these interactions are called types of beta sheets. They are parallel beta pleats and anti-parallel beta pleats. This classification has remained unchanged from the day of its discovery.
6. The parallel beta sheets have ___________
a) Narrow and wide spaces between the H-bond pairs
b) Equal spaces between H-bond pairs
c) Random spaces between H-bonds
d) No spaces
View Answer
Explanation: In parallel beta sheets, we can observe spaces between each and every H-bond pairs. These characteristics can be used to distinguish between parallel and anti-parallel beta pleats. Parallel beta pleats have equal spaces between the H-bond pairs. In anti-parallel beta pleats, there will alternate wide and narrow spaces.
7. What are the mixed beta structures?
a) Combination of alpha helix and beta sheets
b) Combination of parallel and anti-parallel beta sheets
c) Combination of parallel beta structures and gamma helix
d) Combination of anti-parallel beta structures and alpha helix
View Answer
Explanation: In most of the proteins, both parallel, as well as anti-parallel beta sheets, will be present. This combination of parallel and anti-parallel beta sheets are known as mixed beta sheets.
8. The beta structures are rigid.
a) True
b) False
View Answer
Explanation: Even though the beta pleats are arranged like a sheet, they are not rigid. They have significant flexibility. This helps them to change the conformations of proteins.
9. Usually, the twists of beta pleats are ________ in nature.
a) Right-handed
b) Left-handed
c) Unpredictable
d) Depends on its function
View Answer
Explanation: All the beta sheets like parallel, anti-parallel and mixed beta sheets twists in right-handed fashion. And it is found that beta structures undergo twisting while forming proteins.
10. All the amino acids can take part in the construction of beta sheets. The reason behind this is _________
a) The right-handed twists
b) Absence of sulphur bridges
c) The space between adjacent beta strands
d) Alternative up and down arrangements of side chains around alpha carbons
View Answer
Explanation: We know that some of the amino acids favours the formation of alpha helix and called as good helix formers whereas other amino acids are bad helix formers. But in beta sheets, we can not see such kind of phenomena. The main reason for this is here the side chains of amino acids are alternatively arranged above and below the alpha carbon. So there will be no steric hindrance.
11. What position do beta sheets occupy in Ramachandran plot?
a) 1st quadrant
b) 2nd quadrant
c) 3rd quadrant
d) 4th quadrant
View Answer
Explanation: Beta sheets have negative phi value and positive psi value. Hence they occupy the third quadrant in the Ramachandran plot.
12. What is the angle between the side chains of the amino acids constructing the amino acid and the plane of the beta sheets?
a) 0°
b) 45°
c) 90°
d) 180°
View Answer
Explanation: The side chains will be perpendicular to the plane of beta sheets making an angle of 90° with it. This helps to easily fit bulky side chains of amino acids into the beta sheets. Those side chains will be projected outside the beta pleats.
Sanfoundry Global Education & Learning Series – Structural Biology.
To practice all areas of Structural Biology, here is complete set of Multiple Choice Questions and Answers.
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