MCAT Questions well answered

MCAT QuestionsWhich ideal solution exhibits the greatest osmotic pressure? a. 0.1 M MgCl2 b. 0.2 M NaCl c. 0.2 M CaCl2 d. 0.5 M Glucose C because the solution listed has the greatest concentration of solute particles. CaCl2 dissociates into three ions (van Hoff factor of 3), making the solution listed 0.6 M in solute particles. Glucose has an i of 1. Which event is directly mediated by a ligand-gated ion channel? a. Release of Ca2+ from the sarcoplasmic reticulum of a muscle fiber to initiate muscle contraction b. Influx of Na+ across the axon membrane of a somatic neuron during action potential propagation c. Influx of Na+ across the motor end plate resulting in the depolarization of the muscle fiber membrane d. Re-entry of Ca2+ back into the sarcoplasmic reticulum of a muscle fiber to end muscle contraction C because the influx of Na+ across the motor end plate occurs when Na+ ion channels bind the ligand acetylcholine. A single point mutation in a gene results in a nonfunctional protein. Individuals heterozygous for this mutation were identified using a Southern blot. Which pair of wild-type (WT) and mutant alleles most likely contains the mutation? The answer to this question is A because a Southern blot uses a restriction digest to differentiate between mutant and wild-type alleles. In order for a Southern blot to be useful, the mutation should either create or eliminate a restriction site, most of which are palindromes and 4 to 6 base pairs long. The mutation shown in this option is the only one that disrupts a palindromic sequence, AAGCTT. This sequence is the recognition sequence for HindIII.