C. Choose only one correct answer for each of the following quest (4 pts each).

Question

C. Choose only one correct answer for each of the following quest (4 pts each). C1. According to Watson and Crick, what is significant about the base pairing found inthe a) It was a mechanism for copying. e) The DNA could be circular )All of the above b) It allowed the DNA to twist in a helix of the above )None C2. Which of the following three amino acids have hydrophobic side chains? e) Cys, Arg, and Phe a) Ala, Glu, and His d) Leu, Phe, and Pro b) Glu, tyr, and Met e) Gly, Ile, and His C3. Why SDS is added to gel electrophoresis? b) SDS kills bacteria in the protein sample. a) SDS e) SDS is a reducing agent needed in electrophoresis d) SDS makes all the protein molecules highly negative. colors the proteins for visualization. e) All of the above. D. (10 pts) Match the amino acids in the left column with the appropriate properties in the right column. (1) Co is not chiral (a) Met (b) Gly (c) His _(d) Gin (c) Tyr (2) Sulfur-containing amino acid (3) Absorption at-280 nm (4) Amide group-containing amino acid (5) pKR near physiological pH E (6 pts) What happens to the double-helical form of DNA as pH increases well above the neutral point? (See the figure below.) Why does this happen? Maximum 25 words. E 1.0 0.8 0.6 6 0.4 0.2 7 8 9 10 11 pH

Explanation / Answer

C1. Option A is correct.
Complementary base pairing allows for faithful copying of information during replication and transcription.

C2. Option D is correct.
Hydrophobic amino acids = Leu, Phe, and Pro

C3. Option D is correct.
SDS imparts the negative charge to all polypeptides. So, proteins migrate based on their size during electrophoresis.

D.
Met = Sulfur-containing amino acid
Gly = Achiral amino acid
His = pKR is near the physiological pH
Gln = Amide group-containing amino acid
Tyr = Absorption maxima at 280 nm

E. From the graph, it is clear that as the pH increases above the neutral point, the fraction of double helical DNA decreases.

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