Biochemistry Multiple Choice Questions on “The Covalent Structure of Proteins”.
1. Which of the following statements is false?
A. Primary structure of a protein determines how it folds up into a unique three dimensional structure
B. Secondary structure of a protein determines how it folds up into a unique three dimensional structure
C. Three dimensional structure of a protein determines the function of a protein
D. Amino acid sequence is absolutely invariant for a particular protein
Answer: B
Clarification: Primary structure of a protein determines how it folds up into a unique three dimensional structure, which in turn determines the function of a protein.
2. Who deduced the double-helical structure of DNA?
A. Frederick Sanger
B. Mendel
C. Watson and Francis Crick
D. Anton van Leeuwenhoek
Answer: C
Clarification: In 1953 James D. Watson and Francis Crick deduced the double-helical structure of DNA and proposed a structural basis for its precise replication.
3. Two chains of amino acids in an insulin molecule are held together by __________
A. Sulfide bridges
B. Disulfide bridges
C. Peptide bond
D. Covalent linkage
Answer: B
Clarification: When we consider amino acid sequence of bovine insulin, the two peptide chains are joined together by disulfide cross linkages.
4. Tertiary conformation of proteins is maintained by 3 types of bonds namely ionic, hydrogen and __________
A. Sulfide
B. Disulfide
C. Covalent
D. Peptide
Answer: B
Clarification: Ionic interactions, hydrogen and disulfide linkages stabilizes tertiary structure of a protein.
5. Hemoglobin is a __________
A. Monomer
B. Dimer
C. Trimer
D. Tetramer
Answer: D
Clarification: It is a tetramer with 2 α chains and 2β chains.
6. Which of the following is false?
A. The two main types of secondary structure are the α helix and β pleet structures
B. α helix is a right handed coiled strand
C. The hydrogen bonding in a β-sheet is between strands rather than within strands
D. The hydrogen bonding in a β-sheet is within strands rather than between strands
Answer: D
Clarification: The sheet conformation consists of a pair of strands lying side-by-side. The carbonyl oxygen in one strand hydrogen bond with the amino hydrogen of the adjacent strand.
7. Native state of a protein can be disrupted by __________
A. Temperature
B. pH
C. Removal of water
D. Presence of hydrophilic surfaces
Answer: D
Clarification: Native state of a protein can be disrupted by temperature, pH, Removal of water and presence of hydrophobic surfaces.
8. Which of the following is true?
A. The disulfide bridges formed by reduction of the sulfhydryl groups on cysteine stabilizes protein tertiary structure
B. The disulfide bridges formed by oxidation of the sulfhydryl groups on cysteine destabilizes protein tertiary structure
C. The disulfide bridges formed by oxidation of the sulfhydryl groups on cysteine stabilizes protein tertiary structure
D. The disulfide bridges formed by reduction of the sulfhydryl groups on cysteine destabilizes protein tertiary structure
Answer: C
Clarification: The disulfide bridge formed by oxidation of the sulfhydryl groups on cysteine stabilizes protein tertiary structure, allowing different parts of the protein chain to be held together covalently.
9. Identify the wrong statement.
A. Hemoglobin is a globular protein
B. Hemoglobin is a fibrous protein
C. Fibrous proteins are insoluble in water
D. Collagen is a fibrous protein
Answer: B
Clarification: Hemoglobin is a globular protein and collagen is a fibrous protein.
10. In 3° structure of proteins, folding and shaping is done by __________
A. Hydrophobic interactions
B. Polar interactions
C. Hydrogen bonding
D. None of the mentioned
Answer: A
Clarification: Globular proteins have a tertiary structure with hydrophobic amino acid residues and a surface region of hydrophilic residues; these hydrophobic interactions are responsible for the folding and shaping of 3° structure of proteins.
.