1. ______________ is used for sequencing of peptides.
a) X-ray crystallography
b) Spectrophotometry
c) NMR spectroscopy
d) Mass spectrometry
Explanation: Mass spectrometry is a technique that measures the mass to charge (m/z) ratio for the ions in the gas phase. Therefore, mass spectrometry is used for the sequencing of peptides. Mass spectrometry can also be used to identify a protein; hence, it is also called protein mass fingerprinting.
2. Which of the following is related to the primary structure of proteins?
a) Alpha helix
b) Beta-sheets
c) Loops
d) Amino acid sequence
Explanation: The primary structure of a protein is formed by the joining of amino acids through a peptide bond. Hence, the primary structure dictates the amino acid sequence of the polypeptide. Alpha helix, beta-sheets, and loops are all related to higher levels of organization.
3. The primary structure of a protein is held together by non-covalent interactions such as peptide bonds, made during transcription.
a) True
b) False
Explanation: Both covalent and non-covalent interactions exist in a protein molecule. In the primary structure of protein only covalent bonds are present, such as peptide bonds. Hence, the above statement is false. The correct statement is – “The primary structure of a protein is held together by covalent interactions such as peptide bonds, made during translation.”
4. A protein molecule contains amino acid residues and not amino acids because when a peptide bond is formed _________ is lost.
a) nitrogen molecule
b) hydrogen molecule
c) oxygen molecule
d) water molecule
Explanation: In the process of formation of a peptide bond (also known as the amine bond) a water molecule is lost. Hydrogen atom from the amino group of one amino acid and a hydroxyl group from the carboxyl group of another amino acid combine to form a water molecule.
5. A polypeptide chain contains two terminals – one carboxyl-terminal (C terminal) and the other amino-terminal (N terminal). Which of the following is true?
a) N terminal is synthesized last during translation
b) C terminal is synthesized first during translation
c) N terminal is represented on the right side and C terminal on the left side
d) N terminal is represented on the left side and C terminal on the right side
Explanation: During translation, the first amino acid attached has an amino free end and the last amino acid has a carboxyl free end. Hence, the N terminal is represented on the left side and C terminal on the right side.
6. 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
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.
7. 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) Covalentt
c) Hydrophobic
d) Resonance
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.
8. 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
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.
9. Who discovered the alpha-helix structure in a protein molecule?
a) Lynn Margulis
b) Francis Collins
c) Louis Pasteur
d) Linus Pauling
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.
10. The alpha-helix is a right-handed helix.
a) false
b) true
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.