Question

1. if there is an exposed purine during transcription, a. any purine will be joined to it. b. a specific purine will be joined to the exposed purine, depending on which purine is exposed. c. a phosphate group will be joined to the exposed purine. d. any pyrimidine will be joined to it. e. a specific/pyrimidine will be joined to the exposed purine, depending on which purine it is. note: the following codon table is to be used for problems 48 to 50. (it may also be helpful on other questions on this exam.) 48. the piece of rna below includes the region that codes for the binding site for the initiator trna needed in translation. 5-guuucccguauacauggccccguggggggc-3 which amino acid will be on the trna that is the first to bind to the a site of the ribosome? a. met b. arg c. cys d. ala e. tyr 49. below is the sequence from the 3 end of an mrna. 5-...ccguaccaggccucauuuauugguaacggaaaaaaaaaaaaaa-3 if you were told that this sequence contains the stop codon for the protein encoded by this mrna, what is the anticodon on the trna in the p site of the ribosome when release factor binds to the a site? a. 5-cca-3 b. 5-ccg-3 c. 5-ugg-3 d. 5-uua-3 e. 5-acc-3 50. which of the following pairs of codons might you expect to be read by the same trna because of wobble? a. cuu and uuu b. gau and gaa c. cac and cau d. aau and agu e. uuc and uua

Explanation:

• Question 47: In transcription, base - pairing rules apply. Purines (adenine (A) and guanine (G)) pair with specific pyrimidines (thymine (T) or uracil (U) in RNA and cytosine (C)). So a specific pyrimidine will be joined to the exposed purine.
• Question 48: The start codon AUG codes for methionine (Met). The initiator tRNA with the anticodon complementary to AUG brings methionine.
• Question 49: Stop codons are UAA, UAG, and UGA. When release factor binds to the A - site, the tRNA in the P - site has an anticodon complementary to the stop codon in the mRNA. If the stop codon is in the mRNA, the anticodon on the tRNA in the P - site and the codon in the A - site are related by base - pairing.
• Question 50: Wobble occurs at the third position of the codon. In the genetic code, codons that differ only at the third position may be recognized by the same tRNA. CAC and CAU both code for histidine and can be read by the same tRNA due to wobble.

Answer:

1. e. a specific pyrimidine will be joined to the exposed purine, depending on which purine it is.
2. a. Met
3. d. 5'-UUA-3'
4. c. CAC and CAU