This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Primary Structure of Protein”.
1. The structure formed by joining the amino acids by a peptide bond is called ________ structure of a protein.
a) quaternary
b) tertiary
c) secondary
d) primary
View Answer
Explanation: When amino acids are just linked together by a peptide bond to form a long linear chain of a polypeptide, it is called the primary structure of proteins. Secondary, tertiary, and Quaternary structure are all higher levels of organization and require non-covalent interactions.
2. Which of the following interactions is crucial for the primary structure of proteins?
a) Hydrogen bond
b) Di-sulfide bond
c) Vander Waals interactions
d) Peptide bond
View Answer
Explanation: Protein’s primary structure is made of amino acids linked together by a peptide bond. Thus, the peptide bond is crucial for the primary structure of proteins. Hydrogen bond, disulfide bond, Vander Waals interactions are all required in a higher level of organization.
3. Which of the following represents the two-dimensional structure of proteins?
a) Quaternary
b) Tertiary
c) Secondary
d) Primary
View Answer
Explanation: The primary structure of Protein represents the two-dimensional structure of proteins. The primary structure of proteins just contains amino acids linked together to form a long chain of a polypeptide. Quaternary, tertiary, and secondary structure refers to the three-dimensional structure of proteins.
4. For a protein with 100 amino acids, how many possible sequences are there?
a) (100)20
b) (2)100
c) (100)2
d) (20)100
View Answer
Explanation: The general rule is, for a protein having ‘n’ residues, there are (20)n possible combinations. There are 20 different types of amino acids occurring naturally in proteins. Therefore, (20)100 is the correct answer.
5. The minimum number of residues that appear to be necessary for a polypeptide to fold into a discrete and stable shape that allows it to carry out a function is near 40.
a) False
b) True
View Answer
Explanation: The above statement is true. Generally, proteins containing 40 or fewer residues are called peptides, whereas proteins containing more than 40 residues are called polypeptides. Multi-subunit protein is formed by joining identical and/or non-identical subunits.
6. In metal chelate affinity chromatography, divalent cations such as Zn+2 or Ni+2 is attached on the electrophoretic matrix and it binds to ___________
a) Trp tag
b) Ala tag
c) Gly tag
d) His tag
View Answer
Explanation: When 6 histidine residues are inserted consecutively through recombinant DNA technology, it is called as His tag. It has a high affinity for nickel. This strategy is used for the purification of recombinant proteins.
7. The polyacrylamide gel electrophoresis (PAGE) of proteins is based on the following properties of proteins.
a) Size and charge only
b) Size and shape only
c) Electric charge only
d) Size, shape and electric charge
View Answer
Explanation: The separation in PAGE is based on gel filtration i.e. the size and shape, as well as electrophoretic mobility i.e. electric charge. There are two types of PAGE viz. i) SDS PAGE and ii) Native PAGE.
8. __________ is used as a reducing agent in SDS PAGE.
a) Sodium dodecyl sulfate (SDS)
b) Ammonium persulphate (APS)
c) Bisacrylamide
d) 2-mercaptoethanol
View Answer
Explanation: 2-mercaptoethanol (beta-mercaptoethanol) is used as a reducing agent in SDS PAGE. It breaks the disulfide bonds and denatures the protein molecule. SDS is not a reducing agent, it disrupts non-covalent interactions between peptides. Ammonium persulphate (APS) and Bisacrylamide do not show any reducing properties.
9. Trypsin cleaves peptide bonds on the ‘c’ terminal side of the positively charged residues Arg and Lys, if the next residues is not _____
a) His
b) Gly
c) Ala
d) Pro
View Answer
Explanation: Trypsin is a proteolytic enzyme with high specificity. It cleaves the peptide bond on the ‘c’ terminal side of the positively charged residues Arg and Lys, if the next residues is not Pro. It is used in the cleavage of protein molecules for protein sequencing.
10. Cyanogen bromide (CNBr) cleaves the peptide bond on the ‘C’ terminal side of the _______ residues.
a) Trp
b) Ser
c) Ala
d) Met
View Answer
Explanation: Cyanogen Bromide is an endopeptidase (a type of proteolytic enzyme). It cleaves the peptide bond on the ‘C’ terminal side of the Met residues. It is used to cleave recombinant proteins, therefore it finds wide application in gene cloning.
11. ______________ is used for sequencing of peptides.
a) X-ray crystallography
b) Spectrophotometry
c) NMR spectroscopy
d) Mass spectrometry
View Answer
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.
12. Which of the following is related to the primary structure of proteins?
a) Alpha helix
b) Beta-sheets
c) Loops
d) Amino acid sequence
View Answer
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.
13. The primary structure of a protein is held together by non-covalent interactions such as peptide bonds, made during transcription.
a) True
b) False
View Answer
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.”
14. 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
View Answer
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.
15. 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
View Answer
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.
Sanfoundry Global Education & Learning Series – Protein Engineering.
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