How do protein kinases affect enzymes?

Correct Answer: A

Rationale: Correct Answer: A Rationale: 1. Protein kinases add a phosphate group to enzymes through phosphorylation. 2. Phosphorylation alters enzyme activity and can activate or deactivate enzymes. 3. This process regulates enzyme function and signaling pathways. Summary of other choices: B. Incorrect - Protein kinases do not increase enzyme release; they modify enzyme activity. C. Incorrect - Protein kinases do not break down enzymes; they regulate their activity. D. Incorrect - Protein kinases do not increase enzyme secretion; they modify enzyme function through phosphorylation.

Correct Answer: A

Rationale: The correct answer is A: External laryngeal nerve. This nerve runs along the medial surface of the thyroid gland, providing motor innervation to the cricothyroid muscle. The other choices are incorrect because: B: Hypoglossal nerve innervates the tongue, C: Internal laryngeal nerve supplies sensory innervation to the larynx, and D: Vagus nerve innervates various organs in the thorax and abdomen.

Correct Answer: a

Rationale: The correct answer is A: This muscle is optimized for endurance training. Dark (red) muscle contains more myoglobin, which stores oxygen and enhances endurance performance. This muscle type is rich in mitochondria, allowing for sustained energy production. Choice B is incorrect because dark muscle actually has more mitochondria. Choice C is incorrect because dark muscle contains more slow-twitch fibers, which are fatigue-resistant and contribute to endurance. Choice D is incorrect because dark muscle predominantly consists of slow-twitch fibers, making it optimized for endurance rather than speed.

Correct Answer: C

Rationale: The correct answer is C: High plasma levels of glucose. When blood glucose levels rise after a meal, pancreatic beta cells sense this increase and release insulin to facilitate glucose uptake into cells for energy production or storage. This is known as the glucose-stimulated insulin release mechanism. Low plasma levels of calcium (choice A), high plasma levels of potassium (choice B), and low blood volume (choice D) do not directly stimulate insulin release and are unrelated to the regulation of insulin secretion.

Correct Answer: C

Rationale: Estrogen, progesterone, and testosterone are indeed secreted by the gonads. Estrogen and progesterone are primarily produced by the ovaries in females, while testosterone is mainly produced by the testes in males. These hormones play crucial roles in reproductive functions and secondary sexual characteristics. Choices A and B are incorrect because testosterone induces virilization (masculinizing effects) while estrogen and progesterone are more associated with feminizing effects. Choice D is incorrect because estrogen, progesterone, and testosterone are not secreted by the adenohypophysis, which mainly produces and releases other hormones such as growth hormone and prolactin.