NEET 2016 Phase 1 question paper with solutions

1. Background: human insulin is made up of two separate polypeptide chains, called the A-chain (21 amino acids) and the B-chain (30 amino acids), each held together internally by peptide bonds between amino acids.

2. For the hormone to become fully functional, these two separate chains must be joined together through a special type of bond formed after the protein is made (a post-translational modification).

3. This connection is achieved specifically through disulphide bridges, formed between cysteine residues — specifically linking positions A7 to B7, and A20 to B19.

4. Hydrogen bonds and simple covalent bonds are too weak or too generic respectively to describe this specific, well-defined linkage, and a phosphodiester bond is the type of bond found in nucleic acid backbones (DNA/RNA), not in linking protein chains.

5. Hence, the correct answer is C: Disulphide bridges.

1. Checking option B (jointed appendages): Arthropods are defined by having limbs with movable joints, so this is a genuine arthropod feature.

2. Checking option C (chitinous exoskeleton): A hard outer covering made of chitin is a defining feature of arthropods, providing protection and support.

3. Checking option D (metameric segmentation): Arthropods show a body divided into repeating segments, so this is also a genuine feature.

4. Checking option A (parapodia): Parapodia are paired, fleshy, paddle-like outgrowths used for locomotion and respiration, but these structures are actually found in annelids (like the marine worm Nereis), not in arthropods.

5. Conclusion: Since parapodia belong to annelids and not arthropods, this is the feature not present in Arthropoda. Hence, the answer is option A.

1. Recall that the fungal cell wall is composed of a tough polysaccharide called chitin, along with other substances like proteins and lipids.

2. Rule out the other options: cellulose is found in plant cell walls, peptidoglycan is found in bacterial cell walls, and hemicellulose is not the major fungal wall component.

Hence, the correct answer is Option C, chitin.