Bio Chapter 17

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?

A) an assembled ribosome with a polypeptide attached to the tRNA in the P site

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

A) many noncoding stretches of nucleotides are present in mRNA.

Sickle-cell disease is probably the result of which kind of mutation?

A) point

If proteins were composed of only 12 different kinds of amino acids, what would be the smallest possible codon size in a genetic system with four different nucleotides?

B) 2

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 bond forms between 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.

B) 4, 1, 2, 5, 3

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

B) The amino acid binds covalently

When does translation begin in prokaryotic cells?

B) as soon as transcription has begun C) after the 5ʹ caps are converted to mRNA

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that

B) the rules for base pairing between the third base of a codon and tRNA are flexible.

(Figure 17.1) According to Beadle and Tatumʹs hypothesis, how many genes are necessary for this pathway?

C) 2

A peptide has the sequence NH2-phe-pro-lys-gly-phe-pro-COOH. Which of the following sequences in the coding strand of the DNA could code for this peptide?

C) 5ʹ TTT-CCC-AAA-GGG-TTT-CCC

The nitrogenous base adenine is found in all members of which group?

C) ATP, RNA, and DNA

The genetic code is essentially the same for all organisms. From this, one can logically assume all of the following except

C) DNA was the first genetic material.

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

C) It introduces a premature stop codon into the mRNA.

During splicing, which molecular component of the spliceosome catalyzes the excision reaction?

C) RNA

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

C) The amino acid methionine will not bind.

What type of bonding is responsible for maintaining the shape of the tRNA molecule?

C) hydrogen bonding between base pairs

Where does tRNA #2 move to after this bonding of lysine to the polypeptide?

D) Exit tunnel

Why might a point mutation in DNA make a difference in the level of proteinʹs activity?

D) It might substitute an amino acid in the active site.

Each of the following options is a modification of the sentence THECATATETHERAT. Which of the following is analogous to a frameshift mutation?

D) THECATATTHERAT

Which of the following nucleotide triplets best represents a codon?

D) a triplet in the same reading frame as an upstream AUG

Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes

D) excision of introns.

What amino acid sequence will be generated, based on the following mRNA codon sequence?

D) met-ser-ser-leu-ser-leu

Gene expression in Archaea differs from that in other prokaryotes. It shares features with which of the following?

E) bacteria and eukaryotes

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the

E) both C and D

What is the sequence of a peptide based on the following mRNA sequence? 5ʹ . . . UUUUCUUAUUGUCUU 3ʹ

E) phe-ser-tyr-cys-leu

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

A) 3ʹ UCA 5ʹ.

RNA polymerase moves in which direction along the DNA?

A) 3ʹ → 5ʹ along the template strand

As a ribosome translocates along an mRNA molecule by one codon, which of the following occurs?

A) The tRNA that was in the A site moves into the P site.

Which of the following DNA mutations is the most likely to be damaging to the protein it specifies?

A) a base-pair deletion

(Figure 17.1) A mutation results in a defective enzyme A. Which of the following would be a consequence of that mutation?

A) an accumulation of A and no production of B and C

Garrod hypothesized that ʺinborn errors of metabolismʺ such as alkaptonuria occur because

A) genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes.

What are polyribosomes?

A) groups of ribosomes reading a single mRNA simultaneously

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

A) the number of hydrogen bonds between A and T in DNA

Introns are significant to biological evolution because

A) their presence allows exons to be shuffled.

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

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

RNA polymerase in a prokaryote is composed of several subunits. Most of these subunits are the same for the transcription of any gene, but one, known as sigma, varies considerably. Which of the following is the most probable advantage for the organism of such sigma switching?

B) It might allow the polymerase to recognize different promoters under certain environmental conditions.

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

B) RNA acts as an expendable copy of the genetic material.

Which of the following statements best describes the termination of transcription in prokaryotes?

B) RNA polymerase transcribes through the terminator sequence, causing the polymerase to fall off the DNA and release the transcript.

Which of the following statements are true about protein synthesis in prokaryotes?

B) Translation can begin while transcription is still in progress.

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

B) a base deletion near the start of a gene

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

B) a deletion of 2 nucleotides

When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by

B) a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.

What is a ribozyme?

B) an RNA with enzymatic activity

Alternative RNA splicing

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

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

B) exon

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

B) exons

The process of translation, whether in prokaryotes or eukaryotes, requires tRNAs, amino acids, ribosomal subunits, and which of the following?

B) polypeptide factors plus GTP

(Figure 17.3) The dipeptide that will form will be

B) proline-threonine.

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

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

Each eukaryotic mRNA, even after post-transcriptional modification, includes 5ʹ and 3ʹ UTRs. Which are these?

B) the untranslated regions at either end of the coding sequence

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

C) 5ʹ cap and poly (A) tail

The enzyme polynucleotide phosphorylase randomly assembles nucleotides into a polynucleotide polymer. You add polynucleotide phosphorylase to a solution of adenosine triphosphate and guanosine triphosphate. How many artificial mRNA 3 nucleotide codons would be possible?

C) 8

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

C) Any mutation in the sequence is selected against.

Which enzyme causes a covalent bond to attach lysine to the polypeptide?

C) RNA polymerase

In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?

C) RNA polymerase II

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

C) RNA polymerase binds to the promoter region to begin transcription.

Each of the following options is a modification of the sentence THECATATETHERAT. Which of the following is analogous to a single substitution mutation?

C) THECATARETHERAT

Which of the following is (are) true of snRNPs?

C) They join together to form a large structure called the spliceosome.

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

C) UUU.

Of the following, which is the most current description of a gene?

C) a DNA sequence that is expressed to form a functional product: either RNA or polypeptide

When a tRNA molecule is shown twisted into an L shape, the form represented is

C) its 3-dimensional shape.

(Figure 17.1) If A, B, and 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?

C) minimal medium supplemented with nutrient ʺBʺ only

What is the most abundant type of RNA?

C) rRNA

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

C) the various domains of the polypeptide product

In which of the following actions does RNA polymerase differ from DNA polymerase?

D) RNA polymerase can initiate RNA synthesis, but DNA polymerase requires a primer to initiate DNA synthesis.

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

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

Figure 17.4 represents tRNA that recognizes and binds a particular amino acid (in this instance, phenylalanine). Which codon on the mRNA strand codes for this amino acid?

D) UUC

In the 1920s Muller discovered that X-rays caused mutation in Drosophila. In a related series of experiments, in the 1940s, Charlotte Auerbach discovered that chemicals she used nitrogen mustardshave a similar effect. A new chemical food additive is developed by a cereal manufacturer. Why do we test for its ability to induce mutation?

D) We want to prevent any increase in mutation frequency.

(Figure 17.1) If A, B, and C are all required for growth, a strain mutant for the gene encoding enzyme B would be capable of growing on which of the following media?

D) minimal medium supplemented with ʺCʺ only

Which component of the complex described enters the exit tunnel through the large subunit of the ribosome?

D) newly formed polypeptide

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

D) several transcription factors (TFs)

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

D) to translocate polypeptides across the ER membrane

A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence phe-leu-ile-val would be

E) 3ʹ AAA-GAA-TAA-CAA 5ʹ.

A frameshift mutation could result from

E) either an insertion or a deletion of a base.

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

E) the small subunit of the ribosome recognizes and attaches to the 5ʹ cap of mRNA

The ʺuniversalʺ genetic code is now known to have exceptions. Evidence for this could be found if which of the following is true?

If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only).