Which one of the following pairs of chemical substances is correctly categorised?
A
Secretin and rhodopsin – Polypeptide hormones
B
Calcitonin and thymosin – Thyroid hormones
C
Pepsin and prolactin – Two digestive enzymes secreted in stomach
D
Troponin and myosin – Complex proteins in striated muscles
The answer is D.
Solution
Troponin is a complex protein present at regular intervals on the thin (actin) filament, and myosin is the polymerised protein forming the thick filament; both are proteins of striated muscle. This pair is correctly categorised. Secretin is a peptide hormone of the gut, but rhodopsin is the visual pigment of the rods of the retina, not a hormone. Calcitonin is secreted by the thyroid, but thymosin is secreted by the thymus. Pepsin is a digestive enzyme of the stomach, but prolactin is a hormone of the anterior pituitary. Hence the correctly categorised pair is troponin and myosin – complex proteins in striated muscles.
ConceptContractile proteins
Locomotion and Movement in past papers
65 questions from this chapter have appeared across 25 exam years.
