Which one of the following pairs of chemical substances, is correctly categorised ?
- Secretin and rhodopsin - Polypeptide hormones
- Pepsin and prolactin - Two digestive enzymes secreted in stomach
- Troponin and myosin - Complex proteins in striated muscles
- Calcitonin and thymosin - Thyroid hormones
Answer
(3) Troponin and myosin - Complex proteins in striated muscles
Solution
As per NCERT, each actin (thin) filament of a striated muscle carries tropomyosin and troponin, and each myosin (thick) filament is a polymerised protein made of meromyosins.
⇒ Troponin and myosin are proteins of striated (skeletal) muscle.
∵ Rhodopsin is a visual pigment (not a hormone), prolactin is a pituitary hormone (not an enzyme), and thymosin is secreted by the thymus (not the thyroid), the other pairs are wrong.
Answer: (3)