Question 1

What molecular structure are codons part of?

Accepted Answer

Codons are part of mRNA, which is the molecule that carries genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm for protein synthesis. The sequence of codons in the mRNA determines the order of amino acids in the protein being synthesized.

Question 2

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

Accepted Answer

A point mutation in DNA that results in a substitution of an amino acid in the active site of the protein can change the way the protein interacts with its substrate, leading to a change in the protein's activity level. This is because the active site is the area of the protein where substrate binding and chemical reactions take place, and changing even one amino acid in this region can alter the shape and function of the protein.

Question 3

Which of the following contradicts the one-gene,one-enzyme hypothesis?

Accepted Answer

The one-gene, one-enzyme hypothesis suggests that each gene encodes a single enzyme. However, option D contradicts this by indicating that a single gene can produce different proteins through alternative splicing, which means one gene can lead to multiple protein products.

Question 4

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

Accepted Answer

A nonsense mutation introduces a premature stop codon into the mRNA, resulting in a truncated protein that is likely non-functional. This is because the stop codon signals the end of translation, preventing the ribosome from synthesizing the entire protein.

Question 5

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

Accepted Answer

In prokaryotes, transcription and translation happen almost concurrently. As soon as the mRNA is transcribed from the DNA, ribosomes can start translating it into protein without any need for extensive RNA processing or specific initiation and elongation factors. This process is known as coupled transcription-translation. Hence, option B is the correct answer.

Question 6

A frameshift mutation could result from

Accepted Answer

A frameshift mutation occurs when one or more bases are inserted or deleted from the DNA sequence, causing a shift in the reading frame of the codons. This can result in a completely different amino acid sequence being produced by the ribosome during translation. Therefore, either an insertion or a deletion of a base can cause a frameshift mutation. Substitution of a single base may alter the amino acid sequence, but it does not typically cause a frameshift mutation. Deletion of three consecutive bases would also cause a frameshift mutation, but this type of mutation is less common than single base insertions or deletions.

Question 7

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

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 8

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?

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 9

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

Accepted Answer

Testing for ability to induce mutation is important because we want to prevent any increase in mutation frequency. Mutations can lead to harmful effects, such as cancer, and so it is important to ensure that any new food additives do not increase the risk of mutations in humans consuming the food.

Question 10

What happens during the process of transcription?

Accepted Answer

During transcription, RNA polymerase synthesizes a complementary strand of RNA using the DNA template. This process results in the formation of mRNA, which carries the genetic information from DNA to the ribosomes for translation into proteins.

Question 11

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

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 12

Changes in a single nucleotide pair within a gene is called

Accepted Answer

A point mutation is a change in a single nucleotide pair within a gene, which can include substitutions, insertions, or deletions. Translocation involves the movement of a segment of DNA from one chromosome to another, while a silent mutation does not affect the function of the gene. Evolution refers to changes in the genetic makeup of a population over time. Therefore, the best choice is C, as it accurately reflects the change in a single nucleotide pair within a gene.

Question 13

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

Accepted Answer

This choice provides the most current and widely accepted definition of a gene. It accurately reflects the fact that genes can code for either RNA or protein products, and that the expression of genes can be regulated in various ways. Choices A and B are both outdated and oversimplified, while choices D and E are incorrect.

Question 14

The molecule that links the genotype and phenotype of an organism,is (are)

Accepted Answer

The answer of The molecule that links the genotype and...

Question 15

Which of the following is directly related to a single amino acid?

Accepted Answer

The three-base sequence of mRNA, known as a codon, directly corresponds to a single amino acid during protein synthesis.

Question 16

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

Accepted Answer

A gene with six domains is likely to have five introns, as introns typically separate the exons that code for each domain.

Question 17

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).

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 18

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

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 19

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

Accepted Answer

During DNA replication, the entire template molecule is represented in the product, which is not the case during RNA transcription. In transcription, only a portion of the DNA molecule (the gene being transcribed) is used to synthesize a complementary RNA molecule. Choices A, B, C, and D are not true for DNA replication, as it uses DNA polymerase, makes a new molecule from its 5' end to its 3' end, is a relatively slow process, and can occur in both the nucleus and cytoplasm of a eukaryotic cell.

Question 20

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

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.

Quiz 17: From Gene to Protein