MCAT Question of the Day

If chromosome puffs represent uncoiled or decondensed regions of DNA, this suggests that the DNA sequence has to be “read”, either for DNA replication or protein synthesis. Since the insect larva is undergoing different developmental changes in response to hormones, the synthesis of various proteins needed during each subsequent stage seems more probable. The hormone appears to be “activating” genes along the DNA so that transcription of these DNA sequences can occur.

The symptoms described, i.e. redness and heat, would result from more red, warm blood in the area (dilation of blood vessels). Similarly, swelling and pain would result from additional fluids in the area stimulating pain receptors (more fluid leakage from capillaries).

Phagocytosis by macrophages, inflammation, and interferon are all general, nonspecific responses by the immune system. Each type of antibody, on the other hand, is normally produced in response to a specific antigen (usually associated with a specific invading organism).

The movement of skeletal muscles is initiated in the cerebrum. Posture and balance are influenced, in part, from sensory signals originating in the joints, tendons, and muscles themselves (proprioception), as well as from the utricle, saccule, and semicircular canals in the inner ear.

The A and B antigens on the red blood cells donated from the Type AB donor will be agglutinated by anti-B in the plasma of the Type A recipient, anti-A (in the Type B recipient), and both anti-A and anti-B (in the Type O recipient). Type AB donors are universal acceptors, but Type O are universal donors.

When the product of an enzymeatic pathway inhibits any of the previous steps in the pathway, this is referred to as feedback inhibition. Enzyme specificity refers to the conditions appropriate for an enzyme to work. Competitive inhibition occurs when a substance occupies the active site that normally binds to the substrate involved in the reaction. The question states that isoleucine fits into the allosteric site.

The characteristics described are shared by structures including gills, lungs, and even the skin of frogs (which can serve as an extra respiratory organ underwater).

The major osmotic blood proteins are too large to leave the capillaries. Thus, colloid osmotic pressure (COP) normally remains the same at both ends of the capillary. However, blood pressure decreases in vessels as distance from the heart increases, resulting in hydrostatic pressure being lower than COP at the venule end.

No previous knowledge about insects, hormones, or metamorphosis is required. The ability to logically apply the given information is required. If juvenile hormone inhibits metamorphosis, removal of the hormone should cause metamorphosis to occur earlier.

The origin of a muscle is the end which attaches to a site (bone) that does not move when the muscle contracts. In contrast, the insertion is the end that does move when the muscle contracts. The same bone can serve as the origin (site) for one muscle while serving as the insertion (site) for a different muscle.