MCAT (Biological and Biochemical) 3

Question 1

Which cell type in the nervous system forms the myelin sheath in the peripheral nervous system?

Accepted Answer

Schwann cells

Answer

Schwann cells myelinate axons in the peripheral nervous system, while oligodendrocytes perform the same function in the central nervous system.

Question 2

A substrate analog that binds irreversibly to an enzyme's active site is best described as what kind of inhibitor?

Accepted Answer

Suicide (mechanism-based) inhibitor

Answer

Suicide inhibitors (mechanism-based inhibitors) bind covalently and irreversibly to the active site, permanently inactivating the enzyme.

Question 3

Which phase of meiosis is responsible for genetic recombination through crossing over?

Accepted Answer

Prophase I

Answer

Crossing over between homologous chromosomes occurs during Prophase I of meiosis, at the tetrad stage (synapsis), increasing genetic diversity.

Question 4

Which hormone stimulates the reabsorption of sodium in the collecting duct of the kidney?

Accepted Answer

Aldosterone

Answer

Aldosterone, a mineralocorticoid secreted by the adrenal cortex, acts on the collecting duct to increase Na+ reabsorption and K+ secretion.

Question 5

What is the Michaelis constant (Km) a measure of?

Accepted Answer

Substrate affinity for the enzyme

Answer

Km is the substrate concentration at which reaction velocity is half of Vmax; a lower Km indicates higher affinity of the enzyme for its substrate.

MCAT - Medical College Admission Test Practice Test