Biochemistry Questions and Answers Part-8

1. Which of the following does not affect the stability of an α-helix?
a) Electrostatic repulsion
b) Bulkiness
c) Interaction between R groups spaced three residues apart
d) Occurrence of alanine and glycine residues

Answer: d
Explanation: The occurrence of Proline and Glycine residues affect the stability of an α-helix.

2. Which of the following is not true about secondary protein structure?
a) The hydrophilic/hydrophobic character of amino acid residues is important to secondary structure
b) The ability of peptide bonds to form intramolecular hydrogen bonds is important to secondary structure
c) The alpha helix, beta pleated sheet and beta turns are examples of protein secondary structure
d) The steric influence of amino acid residues is important to secondary structure

Answer: a
Explanation: The hydrophilic/hydrophobic character of amino acid residues is important to protein tertiary structure rather than to secondary structure. In secondary structure, it is the steric size of the residues that is important and residues are positioned to minimize interactions between each other and the peptide chain.

3. β-pleated sheets are the examples of _________
a) Primary structure
b) Secondary structure
c) Tertiary structure
d) Quaternary structure

Answer: b
Explanation: Secondary structure of proteins is of two forms α-helix and β-pleated structures.

4. A coiled peptide chain held in place by hydrogen bonding between peptide bonds in the same chain is?
a) Primary structure
b) α-helix
c) β-pleated sheets
d) Tertiary structure

Answer: b
Explanation: A coiled peptide chain held in place by hydrogen bonding between peptide bonds in the same chain is α helix.

5. A structure that has hydrogen bonds between polypeptide chains arranged side by side is?
a) Primary structure
b) α-helix
c) β-pleated sheets
d) Tertiary structure

Answer: c
Explanation: A structure that has hydrogen bonds between polypeptide chains arranged side by side is β-pleated sheets.

6. Which of the following are known as helix breakers?
a) Proline and glycine
b) Isoleucine and leucine
c) Valine
d) Threonine

Answer: a
Explanation: Proline and glycine are known as helix breakers as they disrupt the regularity of the alpha helical backbone conformation.

7. Which of the following is false about NMR spectroscopy?
a) NMR is an abbreviated form of Nuclear Magnetic Resonance
b) The intramolecular magnetic field around an atom in a molecule changes the resonance frequency giving structural information about the atom
c) The intermolecular magnetic field around an atom in a molecule changes the resonance frequency giving structural information about the atom
d) It is a technique that exploits magnetic properties of atomic nuclei

Answer: c
Explanation: The intramolecular magnetic field around an atom in a molecule changes the resonance frequency giving structural information about the atom.

8. Which of the statements is false about multiple sequence alignment?
a) Both protein and nucleic acid secondary structures can be used
b) More useful in RNA
c) These alignments can be made more accurate by the inclusion of secondary structure information
d) A significant increase in accuracy

Answer: b
Explanation: Less useful in RNA. This is because base pairing is highly conserved than sequence.

9. Secondary structure is defined by _________
a) Hydrogen bonding
b) Vander Waals forces
c) Covalent bonding
d) Ionic bonding

Answer: a
Explanation: Hydrogen bonding is present between the amine hydrogen and carbonyl oxygen atoms in the peptide backbone.

10. Which of the following is a false statement?
a) α-Keratin is α helical
b) Collagen is α helical
c) Hemoglobin has a quaternary structure
d) α-Keratin is β pleated structure

Answer: d
Explanation: Fibrous structural protein, α-Keratin is α helical.