Question

1. prior to protein synthesis, the dna

a. attracts trnas with appropriate amino acids.
b. serves as a template for the production of mrna.
c. contains anticodons that become codons.
d. must first undergo replication.

1. which of the following have nitrogenous bases correctly paired in dna?

a. adenine—uracil; guanine—cytosine
b. adenine—thymine; guanine—cytosine
c. adenine—guanine; thymine—cytosine
d. adenine—adenine; guanine—guanine

1. in figure 24.1 above, when replication is finished, strand 1 and 2 will have

the same base composition as
a. strands 1 and 3. b. strands 2 and 3. c. strands 3 and 4. d. strands 1 and 4.

Explanation:

Question 23

• Option A: tRNAs are attracted to mRNA during translation, not DNA prior to protein synthesis.
• Option B: DNA serves as a template for mRNA synthesis (transcription) which is a step prior to protein synthesis (translation).
• Option C: DNA has no anticodons. Anticodons are on tRNA.
• Option D: DNA replication occurs for cell - division (to make new cells), not directly prior to protein synthesis.

• Option A: Uracil is in RNA, not DNA. In DNA, adenine pairs with thymine.
• Option B: In DNA, adenine pairs with thymine (\(A - T\)) and guanine pairs with cytosine (\(G - C\)) according to Chargaff's rules.
• Option C: Adenine and guanine are both purines and do not pair. Thymine and cytosine are pyrimidines and do not pair.
• Option D: Like - to - like base pairing (adenine - adenine, guanine - guanine) does not occur in DNA.

• DNA replication is semi - conservative. Each new DNA molecule consists of one old (parent) strand and one new strand.
• Strand 1 is an old strand. After replication, the new strand complementary to strand 1 will be similar in base composition to strand 3 (because strand 3 is complementary to strand 1's original complement).
• Strand 2 is an old strand. After replication, the new strand complementary to strand 2 will be similar in base composition to strand 4 (because strand 4 is complementary to strand 2's original complement).

Answer:

B. serves as a template for the production of mRNA.

Question 24