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Tutor profile: Natalie M.

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Natalie M.
College Professor for seven years
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Questions

Subject: Chemistry

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Question:

A runner builds up 0.844 g of lactic acid, C3H5O2, while out on a run. How many moles of lactic acid did he build up?

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Natalie M.
Answer:

0.0107 mol. Carbon = 12.011 g/mol x 3 = 36.033 Hydrogen = 1.0079 g/mol x 5 = 5.0395 Oxygen = 15.999 g/mol x 2 = 31.998 36.033 + 5.0395 + 31.998 = 73.0705 g/mol for the entire molecule. 0.844 g lactic acid x 1 mol 73.0705 g lactic acid = 0.0107 mole lactic acid Since we know g, we need to cancel out grams. We do that by dividing grams by grams. This means 1 mole is on the top of the grams.

Subject: Biochemistry

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Question:

p53 is a protein that regulates the cell cycle. Proper function of this protein results in tumor suppression by regulating cell death. Cancer results from improper function where cells do not die as necessary, causing uncontrolled cell growth. Mutations in the amino acid sequence of the p53 protein lead to loss of function and account for an estimated 50% of all cancers. There are six “hot spots” on p53: six amino acids that are more commonly seen mutated than other spots. One of these spots is an arginine residue that is close to a glutamic acid and a leucine in the folded protein. This arginine has been seen to be mutated to a tryptophan, which disrupts the folded state of the protein. Why does this mutation indicate that electrostatic forces might be more important than hydrophobic interactions in keeping this specific protein folded?

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Natalie M.
Answer:

The arginine is positively charged at physiological pH, while the glutamic acid is negatively charged. Therefore, there is an electrostatic interaction via a salt bridge between these two that helps p53 keep it's shape. The mutation changes this out for a tryptophan, which is hydrophobic. Since there is a hydrophobic amino acid near this hot spot, the leucine, there is the possibility of hydrophobic interactions between these two. However, the protein falls apart with this mutation, hence the hydrophobicity is not enough to hold the protein in a 3D shape.

Subject: Basic Chemistry

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Question:

A water researcher is taking samples from many different lakes and ponds to check the levels of electrolytes in them. He needs to be sure his sample from the lake represents the entire lake. Is the lake heterogenous or homogenous?

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Natalie M.
Answer:

Heterogenous. The lake does not have an even distribution of plant and animal life, plus if there are any streams that feed into the lake, the chemicals that make up the lake will not be even distributed. If anything falls into the lake from the side (such as due to erosion, or animal deposits), this will not be evenly distributed.

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