MCAT Questions - a. 0.1 M MgCl2 b. 0.2 M NaCl c. 0.2 M CaCl2 d. ...

MCAT Questions Which ideal solution exhibits the greatest osmotic pressure?

• 0.1 M MgCl2
• 0.2 M NaCl
• 0.2 M CaCl2
• 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?

• Release of Ca2+ from the sarcoplasmic reticulum of a muscle fiber to initiate muscle contraction
• Influx of Na+ across the axon membrane of a somatic neuron during action potential propagation
• Influx of Na+ across the motor end plate resulting in the depolarization of the muscle fiber membrane
• 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. 1 / 2

A vDNA sequence encoding a protein is inserted into a host genome by IN. The protein is translated from the hypothetical mRNA sequence shown.

5-GGCAACUGACUA-3

Based on the passage, the segment of the original viral genome that encoded this protein had what nucleotide sequence?

• 5-GGCAACUGACUA-3
• 5-TAGTCAGTTGCC-3
• 5-CCGTTGACTGAT-3
• 5-UAGUCAGUUGCC-3

The answer to this question is A because according to the passage, viral DNA integrated into a host cell genome by integrase would originate from a retrovirus. mRNA transcribed from retroviral DNA is either used to synthesize viral proteins, or used as the RNA genome for progeny viruses. Thus, the sequence of the nucleotide in the original viral genome will be the same as that of the transcribed mRNA. It is a Scientific Reasoning and Problem Solving question because you are asked to recall that HIV is a retrovirus with an RNA genome and use your understanding of reverse transcriptase to use a given transcribed mRNA sequence to determine the original viral genome sequence.ODNs are competitive inhibitors of vDNA for binding to IN.Which experiment would best provide data to support the mechanism by which an ODN inhibits IN activity?

• Keep IN concentration constant and measure the initial velocity of the reaction at increasing vDNA

concentrations in the presence and absence of the ODN.

• Keep vDNA concentration constant and measure the initial velocity of the reaction at increasing

concentrations of IN in the presence and absence of the ODN.

• Keep ODN and IN concentration constant and measure initial velocity of the reaction at increasing

concentrations of vDNA.

• Keep IN and vDNA concentrations constant and measure initial velocity of the reaction at increasing

concentrations the ODN.The answer to this question is A because according to the passage, ODNs are competitive inhibitors of viral DNA for integrase. Competitive inhibition can be determined through rate experiments by applying

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