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Tutor profile: Hannah V.

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Hannah V.
Tutor for eight years
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Questions

Subject: MCAT

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Question:

The active site of enzyme Z is known to contain a valine. If there was a missense mutation in the active site of enzyme Z, which of the following substituted amino acids would least impact enzyme Z's function? A. V --> E B. V --> I C. V --> T D. V --> G

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Hannah V.
Answer:

ANSWER: B. V --> I EXPLANATION: A missense mutation results from a base substitution in a codon that causes it to code for a different amino acid. There are two types of missense mutations: conservative and nonconservative. Conservative missense mutations indicate that the new amino acid that the codon codes for is similar in property, size, and structure to the original amino acid; whereas, nonconservative mutations result when the new amino acid varies greatly in size, property, and/or structure from the original amino acid. In the context of this question, we are looking to see which missense mutation would least impact the enzyme thus we are looking for a conservative missense mutation. Valine (V, Val) is a nonpolar amino acid. Other nonpolar amino acids include Leucine (L, Leu), Isoleucine (I, Ile), Methionine (M, Met), and Alanine (A, Ala). Substituting with another nonpolar amino acid will likely result in a conservative mutation and will not impact enzyme function. So, answer B. V --> I would likely not majorly impact the enzyme's function as both are nonpolar and of similar size. The other answer choices are incorrect because each of them results in the addition of an amino acid with very different properties. E (Glutamic acid, glu) is charged, T (Threonine, Tre) is polar, and G (Glycine, Gly) has its sidechain embedded within the backbone. All of these changes would significantly impact the structure and function of the active site.

Subject: Chemistry

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Question:

You have a solution of NaCl but you do not know if the solution is unsaturated, saturated, or supersaturated. How can you determine what type of solution it is?

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Hannah V.
Answer:

ANSWER: First observe the solution to see if a precipitate is already present. If there is no precipitate present than we know it is not a supersaturated solution. To determine if it is saturated or unsaturated, add additional NaCl and see what happens. If a precipitate forms than the solution was saturated, but if no precipitate forms than the original solution was unsaturated. EXPLANATION: To answer this question, you must first understand the differences between unsaturated, saturated, and supersaturated solutions. An unsaturated solution is a solution in which the solute concentration is lower than its equilibrium solubility. A saturated solution is a solution in which the solute concentration is equal to equilibrium solubility. And a supersaturated solution is a solution in which the solute concentration is greater than its equilibrium solubility. If you exceed the equilibrium solubility, a precipitate will form. So in the context of our question, if there was no precipitate initially, this means that the amount of solute in our solution was either at or below the equilibrium solubility so it cannot be a supersaturated solution. If we add more NaCl and a precipitate forms, this indicates that we have exceeded the solutes equilibrium solubility by adding more NaCl so, the solution must have been saturated. And finally, if all the added NaCl dissolves, we know that the solute concentration must have originally been below the equilibrium solubility indicating that it was an unsaturated solution.

Subject: Biology

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Question:

If an mRNA transcript has a mutation in an intron what will happen during translation of this mRNA in a eukaryotic cell?

Inactive
Hannah V.
Answer:

ANSWER: This will not impact the translation of this transcript and the resulting protein will not be impacted by this specific mutation. EXPLAINATION: Translation is the process by which a transcript, a single-stranded piece of mRNA transcribed from the DNA, is translated into a protein. To prepare for translation, eukaryotic cells modify the mRNA by adding a poly-A tail, 5'-cap, and splicing. During splicing the introns (noncoding regions) are cut out and the exons (the expressed regions) are joined together. Once all the mRNA modifications are made, the transcript becomes known as mature mRNA and is ready to be translated into a protein. So, since the mutation was in an intron, a noncoding and excised region, it will not impact the translation of the mRNA.

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