Proteins Flashcards
- During the formation of the peptide bond which of the following takes place?
a) Hydroxyl group is lost from its carboxyl group of one amino acid and a hydrogen atom is lost from its amino group of another amino acid
b) Hydrogen atom is lost from its carboxyl group of one amino acid and a hydroxyl group is lost from its amino group of another amino acid
c) Hydroxyl group is lost from its carboxyl group of one amino acid and a hydroxyl group is lost from its amino group of another amino acid
d) Hydrogen atom is lost from its carboxyl group of one amino acid and a hydrogen atom is lost from its amino group of another amino acid
Answer: a
Explanation: The α-amino group of one amino acid acts as a nucleophile to displace the hydroxyl group of another amino acid forming a peptide bond.
- Peptide bond is a _________
a) Covalent bond
b) Ionic bond
c) Metallic bond
d) Hydrogen bond
Answer: a
Explanation: Two amino acids are covalently joined through a substituted amide linkage called a peptide bond.
- A tripeptide has _________
a) 3 amino acids and 1 peptide bond
b) 3 amino acids and 2 peptide bonds
c) 3 amino acids and 3 peptide bonds
d) 3 amino acids and 4 peptide bonds
Answer: b
Explanation: Monopeptide is a peptide containing single amino acid, dipeptide contains two amino acids joined by one peptide bond and tripeptide contains three amino acids joined by two peptide bonds.
- The factor which does not affect pKa value of an amino acid is _________
a) The loss of charge in the α-carboxyl and α-amino groups
b) The interactions with other peptide R groups
c) Other environmental factors
d) Molecular weight
Answer: d
Explanation: The loss of charge in the α-carboxyl and α-amino groups, the interactions with other peptide R groups and other environmental factors can affect the pKa.
- Which of the following is a 39-residue hormone of the anterior pituitary gland?
a) Corticotropin
b) Glucagon
c) Insulin
d) Bradykinin
Answer: a
Explanation: Corticotropin is a 39-residue hormone of the anterior pituitary gland that stimulates the adrenal cortex
- The average molecular weight of an amino acid residue in a protein is about _________
a) 128
b) 118
c) 110
d) 120
Answer: c
Explanation: The average molecular weight of an amino acid residue is nearer to 128. Because a molecule of water is removed to create each peptide bond, average molecular weight is 128 – 18 = 110.
- Which of the following is not the classified form of conjugated proteins?
a) Lipoproteins
b) Glycoproteins
c) Metalloproteins
d) Complete proteins
Answer: d
Explanation: On the basis of the chemical nature of their prosthetic groups conjugated proteins are classified into lipoproteins, glycoproteins and metalloproteins.
- Which part of the amino acid gives it uniqueness?
a) Amino group
b) Carboxyl group
c) Side chain
d) None of the mentioned
Answer: c
Explanation: Different amino acids contain different side chains which make them unique.
- Which of the following information is responsible to specify the three-dimensional shape of a protein?
a) The protein’s peptide bond
b) The protein’s amino acid sequence
c) The protein’s interaction with other polypeptides
d) The protein’s interaction with molecular chaperons
Answer: b
Explanation: The amino acid sequence of a protein determines its three-dimensional shape.
- Unfolding of a protein can be termed as _________
a) Renaturation
b) Denaturation
c) Oxidation
d) Reduction
Answer: b
Explanation: The proteins lose their quaternary, tertiary, secondary structure and return to its native state by denaturation process.
- What are the following is not a factor responsible for the denaturation of proteins?
a) pH change
b) Organic solvents
c) Heat
d) Charge
Answer: d
Explanation: pH change, organic solvents, and heat are the factors responsible for the denaturation of proteins.
