NEET Practice Questions (MCQs) with Answers & Solutions

In the dry solid form, amino acids exist as zwitterions, where the carboxyl group is present as a carboxylate ion (-COO-) and the amino group is present as an ammonium ion (-NH3+). The term 'zwitterion' (from German 'Zwitter', meaning hybrid) refers to this dipolar ion form. Therefore, option o2 is correct.

The pH value at which an amino acid does not migrate towards any electrode is called the isoelectric point. At this pH, the amino acid exists as a zwitterion with no net charge, hence it does not move in an electric field.

A mixture of amino acids can be separated by both electrophoresis and chromatography. Electrophoresis separates molecules based on their charge and size, while chromatography separates them based on their affinity to the stationary and mobile phases.

Three different amino acids can form different types of tri-peptides. The number of possible sequences is given by the permutations of 3 different amino acids taken 3 at a time, which is 3! (3 factorial), equal to 6.

Explanation: (i) False - The group attached to Cl (carbon 1) in the cyclic structure of glucose acts as a reducing agent, but this glucose is not a part of sucrose. In sucrose, glucose is non-reducing. (ii) True - The group attached to Cl (carbon 1) in the cyclic structure of glucose acts as a reducing agent, and this glucose is one monosaccharide unit of maltose. (iii) True - In maltose, two monosaccharide units are joined to each other via a glycosidic bond. (iv) False - The group attached to C4 in the cyclic structure of galactose does not act as a reducing agent. The reducing group is at carbon 1.

Explanation: Cellulose is a polysaccharide consisting of a linear chain of several hundred to many thousands of β-D-glucose units. The β(1→4) linkages in cellulose result in a straight, unbranched chain that forms strong fibrous structures.

Explanation: (i) Lysine is basic due to the presence of an extra amino group in its side chain. (ii) Glycine is neutral as it has no additional functional groups in its side chain. (iii) Arginine is basic due to the presence of a guanidino group in its side chain. (iv) Alanine is neutral as it has a simple alkyl side chain.

Let's break down the reactions and match them with the corresponding groups:

1. Glucose forms oxime with hydroxylamine: This reaction indicates the presence of a carbonyl group (aldehyde or ketone). Hence, this matches with 'b'.

2. Glucose is oxidized by nitric acid to give saccharic acid: This reaction indicates the presence of an aldehyde group at the end of the carbon chain, which gets oxidized to a carboxylic acid. Hence, this matches with 'd': OHC-C-C-C-C-CH2OH.

3. Glucose is oxidized by bromine water to give gluconic acid: This oxidation specifically targets the aldehyde group, forming a carboxylic acid while the rest of the carbon chain remains the same. Hence, this matches with 'a': OHC-C-C-C-C-C.

4. Glucose forms penta-acetate with acetic anhydride in the presence of pyridine: This indicates the presence of hydroxyl groups which are acetylated. Hence, this matches with 'c': OHC-C(OH)-C(OH)-C(OH)-C(OH)-CH2OH.

So, the correct matching is i-b, ii-d, iii-a, iv-c.

Let's match each structure with its shape, example, and bond types:

1. Primary structure: This refers to the linear sequence of amino acids in a protein. Insulin is a classic example of a protein with a defined primary structure, and disulfide bonds can be present. Hence, i-c-Q.

2. Secondary structure: This refers to local folded structures that form within a polypeptide due to interactions between atoms of the backbone. The β-pleated sheet is one such structure, and hydrogen bonds are crucial for its stability. Hence, ii-a-P.

3. Tertiary structure: This refers to the overall three-dimensional structure of a single protein molecule. Myoglobin is an example of a protein with a well-defined tertiary structure, and it can have multiple bond types including hydrogen bonds, disulfide bonds, ionic bonds, and van der Waals forces. Hence, iii-b-P,QR,S.

4. Quaternary structure: This refers to the structure formed by several protein molecules (polypeptide chains), usually called protein subunits. Hemoglobin is an example, and it involves multiple types of bonds including hydrogen bonds, ionic bonds, and van der Waals forces. Hence, iv-d-P,QR.

So, the correct matching is i-c-Q, ii-a-P, iii-b-P,QR,S, iv-d-P,QR.