DNA Replication
In what direction is RNA synthesized?
5' --> 3'
Which of the following enzymes is required to actively enhance the separation of DNA strands during replication?
Helicase
tRNA charged with cysteine can be chemically treated so that the amino acid changes its identity to alanine. If some of this charged tRNA is added to a protein-synthesizing extract that contains all the normal components required for translation, which of the following statements represents the most likely outcome after adding an mRNA that has both Cys and Ala codons in the normal reading frame?
A. Cysteine would be added each time the alanine codon was translated.
B. Alanine would be added each time the cysteine codon was translated.
C. The protein would have a deficiency of cysteine residues.
D. The protein would have a deficiency of alanine residues.
E. The protein would be entirely normal.
C. The protein would have a deficiency of cysteine residues.
Because the extract contains all normal components, the Cys-tRNA charged with alanine will compete with Cys-tRNA charged with cysteine for binding to the cysteine codons. Thus, the protein will have some alanines put in the place of cysteine, leading to a deficiency of cysteine residues. Answer A is incorrect because the tRNA recognizes the cysteine codon, not the alanine codon. Answer B is incorrect because of the competition
mentioned previously.
Which of the following explains why several different proteins can be synthesized from a typical prokaryotic mRNA?
16 1
What term is used to describe the DNA strand synthesized continuously toward the replication fork?
Leading strand
What is the sequence (conventionally written) of the RNA product of the DNA
template sequence, GATCTAC?
5'-GUAGAUC-'3
Template: GATCTAC
The RNA product has a sequence that is complementary to the template strand, with U replacing T.
In the readout of the genetic code in prokaryotes, which one of the following processes acts before any of the others?
A. tRNAi alignment with mRNA
B. Termination of transcription
C. Movement of the ribosome from one codon to the next
D. Recruitment of termination factors to the A site
E. Export of mRNA from the nucleus
The answer is A. tRNAi alignment with mRNA
It is important to note that the question is asking about prokaryotic mechanisms. In prokaryotes, there is no nucleus (thus, E cannot be correct), and translation begins before transcription is terminated (coupled translation–transcription, thus B is incorrect). Therefore, before the ribosome can move from one codon to the next (translocation), or the protein synthesis machinery terminates (via termination factors), the initiating tRNA must bind and align with the mRNA to initiate translation, indicating that answer A is the first step of the choices listed that must occur.