Question

Dehydration reaction is observed in the formation of all except
(a) Cystine
(b) Lecithin
(c) Adenosine
(d) Collagen

Answer 1

Hint: Dehydration reactions involve the loss of water from the reacting molecule or ion. In this type of reaction, one of the products is always water (H₂O). These reactions commonly occur during the attachment of two units (compound). The H (hydrogen) molecule comes from one unit and OH (hydroxyl) comes from the other unit.

Complete answer:
A dehydration reaction is observed in the formation of all except collagen. The formation of collagen occurs through the ‘aldol reaction.’ The aldol reaction involves the formation of carbon-carbon bonds (C-C) and no elimination of H₂O happens in such a process.

Other reactions which involve dehydration reaction are:
1. Formation of cystine by the addition of two cysteine molecules via a disulfide(S- S) bond. Since water is removed in disulfide bond formation, hence, it is a dehydration reaction.
2. The formation of lecithin occurs by ester bond formation in which water is removed. Hence, It is a dehydration reaction.
3. The formation of adenosine occurs by the addition of adenine residue to the ribose sugar by the glycosidic bond. Water is removed in this reaction as well, so, is also a dehydration reaction.
So, the correct answer is, ’Collagen’.

Additional Information:
- Collagen is formed from procollagen which is made up of vitamin C and proteins.
- Lecithin is a type of fat molecule.

Note: The collagen is the main structural protein in the various connective tissues of the human body. It is also the most abundant protein in mammals, making up to 25- 35% of whole- body protein. It is present in abundance in the corneas, blood vessels, the gut, intervertebral discs, and dentin of the teeth, in the human body.