Tutor profile: Julia M.

Which of the following would make the best PCR primer?

A. 5' AATCGATTC 3' B. 5' CAAATCAAG 3' C. 5' AATTATACA 3' D. 5' CGCTACGCG 3' The correct answer is D because the ideal PCR primer has multiple cytosines (C's) and guanines (G's) at the 5 and 3 prime ends, because C & G form 3 hydrogen bonds, and are therefore more strongly bonded than adenine (A) & thymidine (T), which only form 2 hydrogen bonds.

Denaturing a protein will break which of the following:

A. the covalent bond between the N and C termini of two leucine residues B. the hydrogen bond between two glycine residues in a B-sheet C. the hydrophobic bonds between two aspartic acid residues D. the C-C bond in the deoxyribose backbone of DNA The correct answer is B. Denaturing a protein will disrupt the quaternary, tertiary, and secondary structure. Answer A describes the primary structure, so it is incorrect. Answer B describes the secondary structure, so it is correct. Answer C is incorrect because aspartic acid residues would not be expected to form hydrophobic bonds because aspartic acid is a polar & acidic amino acid. Answer D is incorrect because denaturing DNA would not disrupt the backbone, however, it would disrupt hydrogen bonds between complementary base-pairs.

A particular genome is composed of 29% guanine. What percentage of the genome is adenine?

A. 29% B. 21% D. 16% E. 19% The correct answer is B. In order to answer this question, it is easiest to think % CG + % AT = 100 % of the genome since C & G complementary base pair, and A & T complementary base pair. So the best first step is to double the % C because C & G hydrogen bond in the DNA double helix, when you do so, you get 58%. Next, you take 100 - % CG = % AT, so you take 100 % of the total genome - 58 (the % c + g) = % of A & T in genome, after doing this math you get 42%. Lastly, you divide the 42% by two, because 42 is the total percent of A & T base pairs. Dividing 42 by 2 gives you a total of 21 %.