Free MCAT-TEST sample questions

Correct answer: A multimeric structure with multiple active sites that influence each other's substrate affinity.

Cooperative binding, characterized by a sigmoidal kinetic curve, is a hallmark of allosteric enzymes that are typically composed of multiple subunits (a multimeric structure). The binding of a substrate molecule to one active site induces a conformational change in the enzyme that is transmitted to the other subunits, altering their affinity for the substrate. This communication between subunits is the basis of cooperativity. A single active site cannot exhibit cooperativity. Non-competitive inhibitors affect Vmax but do not induce the characteristic sigmoidal curve of positive cooperativity. Covalent modification is a form of regulation but is not the direct structural cause of cooperativity itself.

Correct answers: Randomly assigning female students to two groups: one group is reminded of the stereotype that men are better at physics before a test, and the other group is not.; Randomly assigning female students to two groups: one group takes a test described as a 'problem-solving task' and the other takes the same test described as a 'diagnostic physics test'.

This design directly manipulates the independent variable (stereotype threat activation) and measures its effect on the dependent variable (test performance) while using random assignment to control for confounding variables. This is a classic experimental design to test for stereotype threat.

This design tests stereotype threat by manipulating the context. Describing the test as 'diagnostic' is known to invoke stereotype threat for stereotyped groups, while framing it as a neutral 'problem-solving task' mitigates this threat. Comparing performance between these two randomly assigned groups effectively isolates the effect.

Correct answer: Aspartic Acid, then Valine, then Lysine

At pH 6.0, aspartic acid (pI=2.8) is well above its pI and will have a net negative charge. Valine (pI=6.0) will have a net charge of zero. Lysine (pI=9.7) is well below its pI and will have a net positive charge. A cation-exchange column contains a negatively charged stationary phase. Therefore, the negatively charged aspartic acid will be repelled and elute first. The neutral valine will have minimal interaction and elute next. The positively charged lysine will bind tightly to the column and elute last, likely requiring a change in buffer pH or salt concentration to be released.

Correct answer: An increased end-systolic pressure and a decreased stroke volume.

Chronic hypertension increases the afterload, which is the pressure the left ventricle must overcome to eject blood into the aorta. This requires the ventricle to generate a higher pressure during systole, leading to an increased end-systolic pressure. The increased afterload makes it harder for the ventricle to eject blood, resulting in a larger end-systolic volume and consequently a smaller stroke volume (the width of the PV loop). The loop shifts to the right and becomes taller and narrower.

Correct answer: True

This statement is true. Negative reinforcement strengthens a behavior by removing an unpleasant stimulus (e.g., taking an aspirin removes a headache, making you more likely to take aspirin for future headaches). Punishment (specifically, positive punishment) weakens a behavior by adding an unpleasant stimulus (e.g., getting a speeding ticket makes you less likely to speed). The key distinction is that reinforcement (both positive and negative) always increases a behavior, while punishment always decreases a behavior.

Correct answer: Velocity increases and pressure decreases.

The continuity equation states that for an incompressible fluid, the product of the cross-sectional area (A) and velocity (v) is constant. As the artery constricts, A decreases, so the velocity (v) must increase. Bernoulli's principle states that for a horizontal pipe, an increase in fluid speed is associated with a decrease in pressure. Therefore, as the blood velocity increases through the stenosis, the lateral pressure it exerts on the artery walls decreases.

Correct answer: Hypokalemia, hypernatremia, and metabolic alkalosis.

Aldosterone's primary functions in the distal convoluted tubule and collecting duct are to increase the reabsorption of sodium (Na+) and water, and to increase the secretion of potassium (K+) and hydrogen ions (H+). Excessive aldosterone would lead to increased Na+ reabsorption (hypernatremia), increased K+ secretion (hypokalemia), and increased H+ secretion (metabolic alkalosis).

Correct answer: Social exclusion

Social exclusion refers to the process by which individuals or groups are pushed to the fringe of society and prevented from participating fully due to factors like poverty, lack of skills, or discrimination. In this context of gentrification, the original residents are being socially and culturally excluded from their own changing neighborhood, even if they haven't been physically displaced yet. Anomie is normlessness, cultural lag is the gap between material and non-material culture, and residential segregation is the physical separation of groups, which is related but less specific than the feeling of exclusion described.

Correct answer: It shifts the curve to the right, decreasing oxygen affinity.

2,3-BPG is a negative allosteric regulator of hemoglobin. It binds preferentially to the deoxygenated (T-state) form of hemoglobin, stabilizing this low-affinity conformation. By stabilizing the T-state, it makes it more difficult for oxygen to bind, thereby decreasing hemoglobin's overall affinity for oxygen. This results in a rightward shift of the oxygen-hemoglobin dissociation curve, which facilitates oxygen release to the tissues.

Correct answer: Two peptides: Ala-Gly-Cys-Met and Lys

Cyanogen bromide (CNBr) specifically cleaves the peptide bond on the carboxyl (C-terminal) side of methionine (Met) residues. In the sequence Ala-Gly-Cys-Met-Lys, the cleavage will occur after the Met residue. This will break the bond between Met and Lys, resulting in two fragments: the tetrapeptide Ala-Gly-Cys-Met and the single amino acid Lys.