Question

Which one of the following is proteinaceous in nature?
(a) Thyroxine
(b) Insulin
(c) Progesterone
(d) Oxytocin

Answer 1

Hint: Hormones are signal molecules that are synthesized by a group of cells and released into the bloodstream to act on a distantly located target tissue. The hormone which is proteinaceous in nature is particularly involved in keeping the blood sugar levels in check.

Complete answer:
Hormones help in communication between the two organs. It helps in keeping the internal environment in check. They can be divided into two gross categories based on their chemical nature: Lipid-soluble hormones and water- soluble hormones. Water-soluble hormones include amine hormones, peptide hormones, and protein hormones. Protein hormones are a chain of amino acids whose number exceeds 49 and ranges between 50 to 200. E.g. Insulin which is secreted by the pancreas.
- The lipid- soluble hormones include steroid hormones and thyroid hormones. Progesterone, released from female gonads i.e ovary, is a steroid hormone because it is derived from cholesterol.
- Thyroid hormones like thyroxine are synthesized by attaching iodine to the amino acid tyrosine. As benzene rings are present in the amino acid tyrosine, thyroxine or tetraiodothyronine(T4) is also lipid- soluble.
- Amine hormones are synthesized by decarboxylation and modification of certain amino acids. E.g epinephrine released by the adrenal glands.
- Peptide hormones are the polymers of amino acids. It consists of chains of 3 to 49 amino acids. E.g. Oxytocin discharged from the posterior pituitary gland.
- Insulin is a polypeptide with two chains of amino acids linked through disulfide bridges. It is responsible for removing glucose from the blood and storing it in the form of glycogen. It also decreases the possibility of a cell to undergo gluconeogenesis where glucose is produced from substrates such as proteins and fats.
So, the correct answer is ‘Insulin.’

Note:
- Insulin is secreted from the Beta or B-cells of Islets of Langerhans. These are hormone- secreting cells of the pancreas.
- Alpha or A-cells of Islets of Langerhans secretes glucagon, whose function is opposite to insulin. It raises the level of glucose in the blood.