This set of Chemistry MCQs for IIT JEE Exam focuses on “Biomolecules – Proteins – 2”.
1. Proteins are formed primarily from ______ bonds.
Explanation: When many alpha amino acid units arranged themselves in a chain (or any other suitable structure), a protein is formed. These units are linked together by peptide bonds between NH2 groups and COOH groups.
2. Identify the correct statement.
a) Peptide bond is formed by the loss of water molecule
b) A protein is made of only one type of amino acid
c) Dipeptides consists of different amino acids
d) Glycylalanine is a tripeptide
Explanation: The reaction between two molecules of same of different amino acids proceeds through the linking of COOH group of one and the NH2 group of the other along with the loss of H2O and formation of a peptide bond. The product is called a dipeptide.
3. How many peptide linkages does a hexapeptide have?
Explanation: A hexapeptide is a compound formed by the combination of six same or different amino acids with the help of the amino and carboxyl groups. The six amino acids are connected by five peptide bonds.
4. Proteins are _______
Explanation: When the number of amino acids in a peptide is more than ten, it is a polypeptide. But when a polypeptide has more than a 100 amino acid residues, with molecular mass higher than 10000u, it is called a protein. However, this is not true in all cases (like insulin).
5. Alanylglycyl phenylalanine is an example of a ______
Explanation: It is a tripeptide made from alanine, glycine and phenylalanine. It is abbreviated as Ala-Gly-Phe. The carboxyl group of alanine and the amino group of glycine combine to form one peptide bond. The second peptide linkage is formed between COOH of glycine and NH2 of phenylalanine.
6. Which of the following bonds in not found in fibrous proteins?
c) Hydrogen bonds
Explanation: Fibrous proteins are linear polypeptide chains that lie parallel to each other. Peptide binds are prevalent in the individual chains, whereas the threads are held together by hydrogen and disulphide bonds, to form a fibre-like structure.
7. Which of the following is not a fibrous protein?
Explanation: Keratin is a fibrous protein found in skin, nails, hair and wool. Myosin is present in muscles and collagen in tendons. Albumin is a globular protein.
8. The sequence in which amino acids are arranged in a protein is called ______ structure.
Explanation: Proteins have one or more polypeptide chains, in which each chain consists of a specific sequence of amino acids linked with each other. This is called the primary structure and is the most basic level. Any change in primary structure creates a different protein.
9. Which type of bonds govern the secondary structure of proteins?
Explanation: The secondary structure refers to the shape in which the polypeptide chain exists. There are two possible structures which arise due to the regular folding of the backbone of the polypeptide chain due to hydrogen bonding between CO and NH groups of peptide bond.
10. Which of the following is soluble in water?
Explanation: Fibroin (silk), collagen (tendons) and elastin (skin) are fibrous proteins which are insoluble in water. Insulin is an example of a globular protein which is water soluble.
11. The structure in which all peptide chains are stretched out to full extension and laid side by side through intermolecular hydrogen bonds is called ______
b) β-pleated sheet
c) tertiary structure
d) quaternary structure
Explanation: β-pleated sheet is one of the secondary structures of proteins formed due to intermolecular hydrogen bonding. The structure resembles the pleated folds of drapery and hence the name.
12. Fibrous and globular proteins are classified on the basis of ______ structure.
Explanation: Tertiary structure represents the overall folding of the polypeptide chains or the further folding of secondary structures. It gives rise to two major molecular shapes, i.e., fibrous and globular.
13. A protein ‘X’ was found in a biological system with a unique 3-D structure and biological activity. ‘X’ is known as _______
a) tertiary structure
b) quaternary structure
c) native protein
d) globular protein
Explanation: Native state of a protein is its most energetically stable state. When a native protein is subjected to physical change, the hydrogen bonds are disturbed, and the globules unfold.
14. The primary structure of protein is unaffected by denaturation.
Explanation: Denaturation is the process of altering the physical and biological properties of proteins without affecting chemical composition. It is caused by subjecting the protein to physical changes like temperature, pH, etc. During this, the secondary and tertiary structures are destroyed but the primary structure remains intact.
15. Boiling an egg is an example of reversible denaturation.
Explanation: The egg white gets coagulated on boiling. The globular proteins in egg white (albumin) change to a rubber like insoluble mass. This is irreversible denaturation as the protein cannot return to its original state.
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