Bio 190 Ch 17

A particular triplet of bases in the template strand of DNA is 5' AGT '3. The corresponding codon for the mRNA transcribed is

3' UCA 5'

DNA template strand 5'----3' DNA complementary strand 3'---5' Given the locally unwound double strand above, in which direction does the RNA polymerase move?

3'--->5' along the template strand.

RNA polymerase moves in which direction along the DNA?

3'->5' along the template strand.

Choose the answer that has these events of protein synthesis in the proper sequence: 1. An aminoacyl-tRNA binds to the A site. 2. A peptide bind forms bwtween the new amino acid and a polypeptide chain. 3. tRNA leaves the P site, and the P site remains vacant. 4. A small ribosomal subunit binds with mRNA. 5. tRNA translocates to the P site.

4, 1, 2, 5, 3

Which point mutation would be most likely to have catastophic effect on the functioning of a protein?

A base deletion near the start of a codon.

Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translocation, is likely to have the mosrt serious effect on polypeptide product?

A deletion of two nucleotides.

Which of the following does not occur in prokaryotic gene expression, but does in eukaryotic gene expression?

A poly-A tail is added to the 3'end of an mRNA and a cap is added to the 5' end.

Which of these is the function of a poly (A) signal sequence?

It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~10-35 nucleotides away.

Why might a point mutation in DNA make a difference in the level of protein's activity?

It might substitute an amino acid in the active site.

A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of a phenylalanine. The consequence of this for the cell will be that

Proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.

Using RNA as a template for protein synthesis instead of translating proteins directly from the DNA is advantageous for the cell because

RNA acts as an expendable copy of the genetic material

Which of the following is true for both prokaryotic and eukaryotic gene expression?

RNA polymerase binds to the promoter region to begin transcription.

Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

Several transcription factors (TFs)

An experimenter has altered the 3' end of the tRNA corresponding to eh amino acid methionine in such a way as to remove the 3' AC. Which of the following hypotheses describes the most likely result?

The amino acid methionine will not bind.

In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after he has removed its 5' cap and poly(A) tail. Which of the following would you expect him to find?

The molecule is digested by exonucleases since it is no longer protected at the 5' end.

The TATA sequence is found only several nucleotides away form the start site of transcription. This most probably relates to which of the following?

The number of hydrogen bonds between A and T in DNA

From the following list, which is the first event in translation in eukaryotes?

The small subunit of the ribosome recognizes and attaches to the 5' of mRNA.

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds me the mRNA codon is

UUU

Alternative RNA splicing

can allow the production of proteins of different sizes from a single mRNA

Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes

excision of introns

A mutation in which of the following parts of a gene is likely to be most damaging to a cell?

exon

What are the coding segments of a stretch of eukaryotic DNA called?

exons

A transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approcimately 400 amino acids. This is best explained by the fact that

many noncoding stretches of nucleotides are present in mRNA

If A, B, C are all required for growth, a strain that is mutant for the gene encoding enzyme A would be able to grow on which of the following media?

minimal medium supplemented with nutrient "B" only

Introns are significant to niological evolution because

their presence allows exons to be be shuffled

Which of the following is a function of a single peptide?

to translocate polypeptides across the ER membrane.