bio exam 3 test bank pt 1 questions(chp 17)

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?

2

enzyme A---->enzyme B---->C According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?

2

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'

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 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.

4,1,2,5,3

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

5' 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?

8

The universal genetic code is now known to have exceptions. Evidence for this could be found if which of the following is true? A) If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only). B) If one stop codon, such as UGA, is found to have a different effect on translation than another stop codon, such as UAA. C) If prokaryotic organisms are able to translate a eukaryotic mRNA and produce the same polypeptide. D) If several codons are found to translate to the same amino acid, such as serine. E) If a single mRNA molecule is found to translate to more than one polypeptide when there are two or more AUG sites.

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

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

ATP, RNA, and DNA

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

Which of these is the function of a poly (A) signal sequence? A) It adds the poly (A) tail to the 3 end of the mRNA. B) It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~10 —35 nucleotides away. C) It allows the 3 end of the mRNA to attach to the ribosome. D) It is a sequence that codes for the hydrolysis of the RNA polymerase. E) It adds a 7-methylguanosine cap to the 3 end of the mRNA.

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

Which of the following statements best describes the termination of transcription in prokaryotes? A) RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate with the transcript and cut it free from the polymerase. B) RNA polymerase transcribes through the terminator sequence, causing the polymerase to fall off the DNA and release the transcript. C) RNA polymerase transcribes through an intron, and the snRNPs cause the polymerase to let go of the transcript. D) Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the chromosome. E) RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing through the gene and release the mRNA.

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? A) Extensive RNA processing is required before prokaryotic transcripts can be translated. B) Translation can begin while transcription is still in progress. C) Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles. D) Translation requires antibiotic activity. E) Unlike eukaryotes, prokaryotes require no initiation or elongation factors.

B) Translation can begin while transcription is still in progress

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? A) a deletion of a codon B) a deletion of 2 nucleotides C) a substitution of the third nucleotide in an ACC codon D) a substitution of the first nucleotide of a GGG codon E) an insertion of a codon

B) a deletion of 2 nucleotides

The genetic code is essentially the same for all organisms. From this, one can logically assume all of the following except A) a gene from an organism could theoretically be expressed by any other organism. B) all organisms have a common ancestor. C) DNA was the first genetic material. D) the same codons in different organisms usually translate into the same amino acids. E) different organisms have the same number of different types of amino acids.

C) DNA was the first genetic material

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

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

An experimenter has altered the 3 end of the tRNA corresponding to the amino acid methionine in such a way as to remove the 3 AC. Which of the following hypotheses describes the most likely result? A) tRNA will not form a cloverleaf. B) The nearby stem end will pair improperly. C) The amino acid methionine will not bind. D) The anticodon will not bind with the mRNA codon. E) The aminoacylsynthetase will not be formed.

C) The amino acid methionine will not bind

Of the following, which is the most current description of a gene? A) a unit of heredity that causes formation of a phenotypic characteristic B) a DNA subunit that codes for a single complete protein C) a DNA sequence that is expressed to form a functional product: either RNA or polypeptide D) a DNA—RNA sequence combination that results in an enzymatic product E) a discrete unit of hereditary information that consists of a sequence of amino acids

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

In which of the following actions does RNA polymerase differ from DNA polymerase? A) RNA polymerase uses RNA as a template, and DNA polymerase uses a DNA template. B) RNA polymerase binds to single-stranded DNA, and DNA polymerase binds to double-stranded DNA. C) RNA polymerase is much more accurate than DNA polymerase. D) RNA polymerase can initiate RNA synthesis, but DNA polymerase requires a primer to initiate DNA synthesis. E) RNA polymerase does not need to separate the two strands of DNA in order to synthesize an RNA copy, whereas DNA polymerase must unwind the double helix before it can replicate the DNA.

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

Which of the following nucleotide triplets best represents a codon? A) a triplet separated spatially from other triplets B) a triplet that has no corresponding amino acid C) a triplet at the opposite end of tRNA from the attachment site of the amino acid D) a triplet in the same reading frame as an upstream AUG E) a sequence in tRNA at the 3 end

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

Gene expression in Archaea differs from that in other prokaryotes. It shares features with which of the following? A) eubacteria only B) eukaryotes only C) protists only D) fungi only E) bacteria and eukaryotes

E) bacteria and eukaryotes

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?

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

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

RNA

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

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

RNA polymerase II

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

THECATARETHERAT

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

THECATATTHERAT

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

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

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

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

UUU

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

a base deletion near the start of a gene

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

a base-pair deletion

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

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

What is a ribozyme?

an RNA with enzymatic activity

enzyme A---->enzyme B---->C A mutation results in a defective enzyme A. Which of the following would be a consequence of that mutation?

an accumulation of A and no production of B and C

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

When does translation begin in prokaryotic cells?

as soon as transcription has begun

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

bonding of the anticodon of the codon and the attachment of amino acids to tRNAs

Alternative RNA splicing

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

A frameshift mutation could result from

either an insertion or a deletion of a base

Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes

excision of introns

A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) in the ribosome already. Where does tRNA #2 move to after this bonding of lysine to the polypeptide?

exit tunnel

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

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

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

What are polyribosomes?

groups of ribosomes reading a single mRNA simultaneously

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

hydrogen bonding between base pairs

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

it introduces a premature stop codon into the mRNA

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

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

its 3-dimensional shape

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

many noncoding stretches of nucleotides are present in mRNA

enzyme A---->enzyme B---->C 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?

minimal medium supplemented with "C" only

enzyme A---->enzyme B---->C 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?

minimal medium supplemented with nutrient "B" only

A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) in the ribosome already. Which component of the complex described enters the exit tunnel through the large subunit of the ribosome?

newly formed polypeptide

A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) in the ribosome already. Which enzyme causes a covalent bond to attach lysine to the polypeptide?

peptidyl transferase

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

point

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

polypeptide factors plus GTP

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.

What

rRNA

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

several transcription factors

The TATA sequence is found only several nucleotides away from 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

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

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

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

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

the untranslated regions at either end of the coding sequence

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

the various domains of the polypeptide product

Introns are significant to biological evolution because

their presence allows exons to be shuffled

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

they join together to form a large structure called the spliceosome

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

to translocate polypeptides across the ER membrane

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 mustards have a similar effect. A new chemical food additive is developed by a cereal manufacturer. Why do we test for its ability to induce mutation?

we want to prevent any increase in mutation frequency