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Tutor profile: Michelle W.

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Michelle W.
Medical Student Specializing in STEM Subjects and MCAT Test Prep
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Questions

Subject: MCAT

TutorMe
Question:

In an experiment, nerve fibers are treated with a drug that inhibits the sodium potassium pump. If an action potential were induced in these neurons, which portion of the action potential would be most affected? What would you expect concentrations of Na and K to be inside and outside of the cell relative to an untreated cell?

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Michelle W.
Answer:

The repolarization would be most affected. The role of the sodium potassium pump is to return a cell to its resting potential by pumping sodium out of the cell and potassium inward. Inhibition of this pump would prevent this process. We would expect to see more potassium outside of the cell and more sodium inside of the cell compared to a normal cell.

Subject: Biochemistry

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Question:

You are working in a research lab studying DNA binding proteins. You are given amino acid sequences for known proteins and asked to identify which ones may participate in DNA binding. Describe how you would identify possible binding proteins.

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Michelle W.
Answer:

In order to analyze which proteins are likely to bind DNA, you have to identify likely patterns you would see in the amino acid sequences of these proteins. Amino acids are differentiated by side groups that all have different properties - size, charge, polarity, etc. DNA binding proteins must contain amino acids that are able to form bonds with DNA. The structure of DNA includes a phosphodiester backbone, which contains many negatively charged phosphate groups. Therefore, DNA binding proteins would likely contain lots of positively charged amino acids. These include arginine, lysine, and histidine.

Subject: Biology

TutorMe
Question:

In the context of population genetics, explain how a balanced polymorphism exists for the sickle cell trait when it confers a deleterious phenotype.

Inactive
Michelle W.
Answer:

The sickle cell trait exists in a balanced polymorphism because of the heterozygote advantage. Normally, deleterious recessive alleles quickly decline in frequency due to the negative effects on phenotype. However, with the sickle cell trait, the existence of a heterozygous phenotype conveys an advantage in areas of the world with malaria. Individuals with no copies of the sickle cell trait are highly susceptible to malaria while individuals with two copies of the sickle cell trait are afflicted with severe sickle cell disease. Heterozygotes, on the other hand, are less affected by malaria but still retain some normal red blood cell function. Thus, these individuals that are carriers are able to reproduce and pass the sickle cell trait onto their offspring, maintaining its frequency in the population.

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