Previous Year Questions:
1. Chitin is absent in which group ? (Dec 2008)
1) Bacteria 2) Arthropods
3) Fungus 4) Mollusca
Ans. 1 - Bacteria
Explanation: Chitin is a polysaccharide found in the exoskeleton of arthropods like insects and crustaceans, as well as in the cell wall of fungi, it can also be found in the shells of some molluscs, it is not found in bacteria. Hence option 1 is correct.
2. Which of the following is a most hydrated polymer? (June 2010)
1) Cellulose 2) Pectin
3) Lignin 4) Callose
Ans. 2 - Pectin
Explanation: The degree of hydration of a polymer depends on its ability to form hydrogen bonds with water molecules. Among the options provided, pectin is generally considered the most hydrated polymer. Pectin is a polysaccharide found in the cell walls of plants, particularly in fruits, and it has a high affinity for water due to its many hydroxyl groups, which can form hydrogen bonds with water molecules.
3. The -COOH group of cellular amino acids can form which of the following bonds inside the cell? (June 2016)
1) Ether and ester bond
2) Ester and amide bond
3) Amide and ether bond
4) Amide and carboxylic anhydride bonds.
Ans. 2 - Ester and amide bonds
Explanation: When amino acids combine to form proteins through a process called protein synthesis or translation, the carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH2) of another amino acid, resulting in the formation of an amide bond (-CO-NH-). This bond is known as a peptide bond when it occurs in proteins.
Ester bonds involve the reaction between a carboxyl group and an alcohol group, resulting in the formation of a molecule known as an ester. This type of bond is not typically formed between amino acids inside cells.
Ether bonds involve the linkage between an oxygen atom and two carbon atoms. While ethers can form in certain biological processes, they are not directly formed by the carboxyl group of amino acids.
Carboxylic anhydride bonds involve the formation of an anhydride group (-C(O)-O-C(O)-) by the elimination of water from two carboxylic acid molecules. This type of bond is less common in biological systems compared to amide bonds in proteins.
Therefore, the correct answer is option 2) Ester and amide bond.
4. Proline is (June 2009)
1) imino acid 2) present in α - helix
3) a rare amino acid 4) Optically inactive
Ans. 1 - imino acid
Explanation: "Imino" refers to a functional group containing a nitrogen atom double-bonded to a carbon atom, often represented as -NH-. In the case of proline, the "imino" refers to its distinctive structure, where the side chain forms a cyclic structure with the nitrogen atom, resulting in the imino group (-NH-) being part of the amino acid's backbone. This unique structure contributes to the rigidity and special characteristics of proline within proteins.
5. Among the following which is essential amino acid (Dec 2001)
1) Serine 2) Phenyl alanine
3) Aspartic acid 4) Tyrosine
Ans. 2 - Phenyl alanine
Explanation: There are nine essential amino acids. Histidine, Isoleucine, Lysine, Leucine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine. You can remember it from the mnemonic HILL MP TTV.
6. Among the following which amino acid can act as buffer against addition of acid at physiological pH (pH=7)? (Dec 2005)
1) Glycine 2) Histidine
3) Arginine 4) Phenylalanine
Ans. 2 - Histidine
Explanation: Histidine has a pKa near physiological pH, meaning it can exist in both its protonated and deprotonated forms at pH 7, making it an effective buffer.
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