Ch 17

1. What are polyribosomes?

Groups of ribosomes reading a single mRNA simultaneously

Ribosomes containing more than two subunits

Multiple copies of ribosomes associated with giant chromosomes

Aggregations of vesicles containing ribosomal RNA

Ribosomes associated with more than one tRNA

2. 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' cap of mRNA

Base pairing of the activated methionine - tRNA to AUG of the messenger RNA

The larger ribosomal subunit binds to smaller ribosomal subunits

Covalent bonding between the first two amino acids

Elongation of the polypeptide

3. The "universal" genetic code is now know to have exceptions. Evidence for this could be found if which of the following is true?

If prokaryotic organisms are able to translate a eukaryotic mRNA and produce the same polypeptide

If several codons are found to translate to the same amino acid, such as serine

4. What is the effect of a nonsense mutation in a gene?

It changes an amino acid in the encoded protein

It has no effect on the amino acid sequence of the encoded protein

It introduces a premature stop codon into the mRNA

It alters the reading frame of the mRNA

It prevents introns from being excised

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

Intron

Exon

5ʹ UTR

3ʹ UTR

All would be equally damaging.

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

RNA is much more stable than DNA

RNA acts as an expendable copy of the genetic material

Only one mRNA molecule can be transcribed from a single gene, lowering the potential rate of gene expression

TRNA, rRNA and others are not transcribed

MRNA molecules are subject to mutation but DNA is not

7. When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following would you be able to isolate?

An assembled ribosome with a polypeptide attached to the tRNA in the P site

Separated ribosomal subunits, a polypeptide, and free tRNA

An assembled ribosome with a separated polypeptide

Separated ribosomal subunits with a polypeptide attached to the tRNA

A cell with fewer ribosomes

8. In the structural organization of many eukaryotic genes, individual exons may be related to which of the following?

The sequence of the intron that immediately precedes each exon

The various domains of the polypeptide product

The number of polypeptides making up the functional protein

The number of restriction enzyme cutting sites

The number of start sites for transcription

9. The tRNA shown in Figure 17.4 has its 3ʹ end projecting beyond its 5ʹ end. What will occur at this 3ʹ end?

The codon and anticodon complement one another.

The amino acid binds covalently

The excess nucleotides (ACCA) will be cleaved off at the ribosome

The small and large subunits of the ribosome will attach to it

The 5ʹ cap of the mRNA will become covalently bound

10. A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which might this illustrate?

Any mutation in the sequence is selected against

The sequence evolves very rapidly

The sequence does not mutate

The sequence is found in many but not all promoters

The sequence is transcribed at the start of every gene

11. 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

None of the proteins in the cell will contain phenylalanine

The cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons

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

The ribosome will skip a codon every time a UUU is encountered

None of the above will occur; the cell will recognize the error and destroy the tRNA

12. Which of the following help(s) to stabilize mRNA by inhibiting its degradation?

TATA box

Spliceosomes

Introns

5ʹ cap and poly (A) tail

RNA polymerase

13. Garrod hypothesized that "inborn errors of metabolism" such as alkaptonuria occur because

Enzymes are made of DNA, and affected individuals lack DNA polymerase

Certain metabolic reactions are carried out by ribozymes, and affected individuals lack key splicing factors

Genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes

Metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional deficiencies

14. A transcription unit that is 8000 nucleotides long may use 1200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that

There is redundancy and ambiguity in the genetic code

Many nucleotides are needed to code for each amino acid

Nucleotides break off and are lost during the transcription process

Many noncoding stretches of nucleotides are present in mRNA

There are termination exons near the beginning of mRNA

15. RNA polymerase moves in which direction along the DNA?

5' --> 3' along the template strand

5' --> 3' along the double-stranded DNA

3' --> 5' along the template strand

3' --> 5' along the coding strand

3' --> 5' along the coding (sense) strand

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

It might result in a chromosomal translocation

It might exchange one stop codon for another stop codon

It might exchange one serine codon for a different serine codon

It might substitute the N terminus of the polypeptide for the C terminus

It might substitute an amino acid in the active site

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

After transcription, a 3ʹ poly-A tail and a 5ʹ cap are added to mRNA

Translation of mRNA can begin before transcription is complete

RNA polymerase binds to the promoter region to begin transcription

MRNA is synthesized in the 3ʹ → 5ʹ direction

The mRNA transcript is the exact complement of the gene from which it was copied