Question 1

Which of the following is true of transcription in domain Archaea?
A) It is regulated in the same way as in domain Bacteria.
B) There is only one kind of RNA polymerase.
C) It is roughly simultaneous with translation.
D) Promoters are identical to those in domain Eukarya.
E) It terminates in a manner similar to bacteria.

Accepted Answer

The answer of Which of the following is true of...

Question 2

Which of the following statements is 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.

Accepted Answer

In prokaryotes, the processes of transcription and translation occur simultaneously. This means that translation can begin while transcription is still in progress due to the lack of a nuclear membrane separating the two processes.

Question 3

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

Accepted Answer

The most current description of a gene is that it is a DNA sequence that is expressed to form a functional product, which can be either RNA or polypeptide. This definition takes into account the fact that some genes code for non-protein products, such as functional RNAs, and that a single gene can give rise to multiple protein variants through alternative splicing or other mechanisms. Options A, B, and E are outdated or incomplete descriptions of genes, while option D is incorrect because enzymatic products can be produced by proteins encoded by genes, but genes themselves do not typically result in enzymatic products.

Question 4

When the genome of a particular species is said to include 20,000 protein-coding regions, what does this imply?
A) There are 20,000 genes.
B) Each gene codes for one protein.
C) Any other regions are "junk" DNA.
D) There are also genes for RNAs other than mRNA.
E) The species is highly evolved.

Accepted Answer

The answer of When the genome of a particular species...

Question 5

Why might a point mutation in DNA make a difference in the level of protein's activity?
A) It might result in a chromosomal translocation.
B) It might exchange one stop codon for another stop codon.
C) It might exchange one serine codon for a different serine codon.
D) It might substitute an amino acid in the active site.
E) It might substitute the N-terminus of the polypeptide for the C-terminus.

Accepted Answer

A point mutation that substitutes an amino acid in the active site of a protein can alter the protein's activity because the active site is where the protein interacts with its substrates or other molecules to carry out its function. Even a small change in one amino acid can affect the shape and properties of the active site, making it less efficient or even nonfunctional. Choice A (chromosomal translocation) involves a large-scale rearrangement of genetic material and is unlikely to be caused by a single point mutation. Choice B (exchange of stop codons) and Choice C (exchange of synonymous codons) would not alter the protein sequence or activity. Choice E (substitution of N-terminus for C-terminus) would radically alter the protein structure and function.

Question 6

Which of the following DNA mutations is the most likely to be damaging to the protein it specifies?
A) a base-pair deletion
B) a codon substitution
C) a substitution in the last base of a codon
D) a codon deletion
E) a point mutation

Accepted Answer

A base-pair deletion causes a frameshift mutation, in which the reading frame is shifted by one or more nucleotides, resulting in a completely different amino acid sequence downstream of the mutation. This can have significant impact on the structure and function of the protein. The other mutations listed may still cause changes in the amino acid sequence, but they are less likely to be as damaging as a frameshift mutation.

Question 7

What is the effect of a nonsense mutation in a gene?
A) It changes an amino acid in the encoded protein.
B) It has no effect on the amino acid sequence of the encoded protein.
C) It introduces a premature stop codon into the mRNA.
D) It alters the reading frame of the mRNA.
E) It prevents introns from being excised.

Accepted Answer

A nonsense mutation introduces a premature stop codon into the mRNA, causing translation to stop prematurely and resulting in a truncated, nonfunctional protein.

Answer: B 
 A silent mutation would have no effect on the amino acid sequence of the encoded protein, whereas a nonsense mutation would introduce a premature stop codon, resulting in a truncated protein.

Answer: D 
 An insertion or deletion mutation could alter the reading frame of the mRNA, causing a frameshift mutation. A nonsense mutation would introduce a premature stop codon, but it would not necessarily alter the reading frame.

Answer: A, C 
 A missense mutation changes an amino acid in the encoded protein, whereas a nonsense mutation introduces a premature stop codon into the mRNA.

Question 8

The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in
A) a base-pair substitution.
B) a nucleotide mismatch.
C) a frameshift mutation.
D) a polypeptide missing an amino acid.
E) a nonsense mutation.

Accepted Answer

The deletion of a single codon in the genetic code of people with cystic fibrosis results in the absence of a specific amino acid in the polypeptide chain, rather than a frameshift or a substitution. This is because a codon, which is a sequence of three nucleotides, codes for a single amino acid. Removing one codon thus removes one amino acid from the polypeptide, not altering the reading frame or substituting nucleotides.

Question 9

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 two 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

Accepted Answer

A deletion of two nucleotides causes a frameshift mutation, altering the reading frame of the mRNA and potentially affecting every subsequent amino acid in the polypeptide, likely resulting in a nonfunctional protein.

Question 10

The following question refers to this figure of a simple metabolic pathway:
 
-According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?
A) 0
B) 1
C) 2
D) 3
E) It cannot be determined from the pathway.

Accepted Answer

Beadle and Tatum's hypothesis states that one gene is responsible for one enzyme. In this pathway, there are two enzymes, so two genes are necessary.

Question 11

A frameshift mutation could result from
A) a base insertion only.
B) a base deletion only.
C) a base substitution only.
D) deletion of three consecutive bases.
E) either an insertion or a deletion of a base.

Accepted Answer

A frameshift mutation occurs when a nucleotide is either inserted or deleted from the DNA sequence, causing a shift in the reading frame. Both choices A and B would result in a frameshift mutation, while choice C would only result in a missense or silent mutation depending on the substitution. Choice D would result in the loss of a single amino acid but not a frameshift mutation.

Question 12

In comparing DNA replication with RNA transcription in the same cell, which of the following is true only of replication?
A) It uses RNA polymerase.
B) It makes a new molecule from its 5' end to its 3' end.
C) The process is extremely fast once it is initiated.
D) The process occurs in the nucleus of a eukaryotic cell.
E) The entire template molecule is represented in the product.

Accepted Answer

DNA replication involves copying the entire template molecule, resulting in a complete representation of the original DNA sequence in the newly synthesized DNA. In contrast, RNA transcription only transcribes specific regions of DNA into RNA, not the entire DNA molecule.

Question 13

Which of the following mutations is most likely to cause a phenotypic change?
A) a duplication of all or most introns
B) a large inversion whose ends are each in intergenic regions
C) a nucleotide substitution in an exon coding for a transmembrane domain
D) a single nucleotide deletion in an exon coding for an active site
E) a frameshift mutation one codon away from the 3' end of the nontemplate strand

Accepted Answer

A single nucleotide deletion in an exon coding for an active site is most likely to cause a phenotypic change because it can directly affect the protein's function by altering its active site, potentially leading to a loss or change in function.

Question 14

Gene expression in the domain Archaea in part resembles that of bacteria and in part that of the domain Eukarya. In which way is it most like the domain Eukarya?
A) Domain Archaea have numerous transcription factors.
B) Initiation of translation is like that of domain Eukarya.
C) There is only one RNA polymerase.
D) Transcription termination often involves attenuation.
E) Post-transcriptional splicing is like that of Eukarya.

Accepted Answer

Archaea have numerous transcription factors similar to Eukarya, which is a key feature distinguishing their gene expression from bacteria, which typically have fewer transcription factors.

Question 15

In order for a eukaryotic gene to be engineered into a bacterial colony to be expressed, what must be included in addition to the coding exons of the gene?
A) the introns
B) eukaryotic polymerases
C) a bacterial promoter sequence
D) eukaryotic ribosomal subunits
E) eukaryotic tRNAs

Accepted Answer

Bacteria use different promoters than eukaryotes to initiate transcription, so a bacterial promoter sequence must be included in order for the bacterial colony to express the eukaryotic gene. The introns, polymerases, ribosomal subunits, and tRNAs are not necessary for this process.

Question 16

Suppose that a mutation alters the formation of a tRNA such that it still attaches to the same amino acid (phe)but its anticodon loop has the sequence AAU that binds to the mRNA codon UUA (that usually specifies leucine leu).
A) The modified tRNA will cause this mRNA to make only nonfunctioning product.
B) The tRNA-leu will not be able to enter the site of the ribosome to bind to the UUA.
C) One mutated tRNA molecule will be relatively inconsequential because it will compete with many "normal" ones.
D) The tRNA will be so unstable that it will not participate in translation.
E) The mutated tRNA will result in an amino acid variant in all copies of the protein.

Accepted Answer

The presence of one mutated tRNA molecule among many normal ones means it will have a relatively minor effect due to competition with the normal tRNAs that correctly interpret the mRNA codon.

Question 17

Which small-scale mutation would be most likely to have a catastrophic effect on the functioning of a protein?
A) a base substitution
B) a base deletion near the start of a gene
C) a base deletion near the end of the coding sequence, but not in the terminator codon
D) deletion of three bases near the start of the coding sequence, but not in the initiator codon
E) a base insertion near the end of the coding sequence, but not in the terminator codon

Accepted Answer

A base deletion near the start of a gene has the potential to cause a frameshift mutation, shifting the reading frame of the codons downstream of the deletion. This can result in a completely different amino acid sequence being produced, and therefore a dysfunctional protein.

Question 18

If a protein is coded for by a single gene and this protein has six clearly defined domains, which number of exons below is the gene likely to have?
A) 11
B) 5
C) 8
D) 12
E) 14

Accepted Answer

Each domain in the protein is likely to be encoded by a separate exon. Therefore, the gene would require at least six exons to encode the six domains. However, additional exons may be present for regulatory regions or alternative splicing. Option C provides the closest number of exons to meet the minimum requirement.

Question 19

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?
A) We worry that it might cause mutation in cereal grain plants.
B) We want to make sure that it does not emit radiation.
C) We want to be sure that it increases the rate of mutation sufficiently.
D) We want to prevent any increase in mutation frequency.
E) We worry about its ability to cause infection.

Accepted Answer

Testing for the ability to induce mutation is important to prevent any increase in mutation frequency that may have negative effects. If a chemical is found to increase mutation rates, it may lead to the development of genetic disorders or diseases. Testing for mutation-inducing properties is a crucial step in ensuring the safety of new chemical food additives.

Question 20

When the function of the newly made polypeptide is to be secreted from the cell where it has been made, what must occur?
A) It must be translated by a ribosome that remains free of attachment to the ER.
B) Its signal sequence must target it to the ER, from which it goes to the Golgi.
C) It has a signal sequence that must be cleaved off before it can enter the ER.
D) It has a signal sequence that targets it to the cell's plasma membrane where it causes exocytosis.
E) Its signal sequence causes it to be encased in a vesicle as soon as it is translated.

Accepted Answer

When a polypeptide is meant to be secreted, it must be translated by a ribosome that is attached to the endoplasmic reticulum (ER). The presence of a signal sequence on the polypeptide allows it to be targeted to the ER. Once in the ER, the polypeptide undergoes further modifications and is transported to the Golgi apparatus before being secreted out of the cell.

Quiz 17: From Gene to Protein

Which of the following is true of transcription in domain Archaea?

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

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

When the genome of a particular species is said to include 20,000 protein-coding regions, what does this imply?

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

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

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

The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in

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?

The following question refers to this figure of a simple metabolic pathway: -According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?

A frameshift mutation could result from

In comparing DNA replication with RNA transcription in the same cell, which of the following is true only of replication?

Which of the following mutations is most likely to cause a phenotypic change?

Gene expression in the domain Archaea in part resembles that of bacteria and in part that of the domain Eukarya. In which way is it most like the domain Eukarya?

In order for a eukaryotic gene to be engineered into a bacterial colony to be expressed, what must be included in addition to the coding exons of the gene?

Suppose that a mutation alters the formation of a tRNA such that it still attaches to the same amino acid (phe) but its anticodon loop has the sequence AAU that binds to the mRNA codon UUA (that usually specifies leucine leu) .

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

If a protein is coded for by a single gene and this protein has six clearly defined domains, which number of exons below is the gene likely to have?

When the function of the newly made polypeptide is to be secreted from the cell where it has been made, what must occur?