Question 1

Why are people who have poor DNA repair mechanisms at greater risk for cancer development?

Accepted Answer

Everyone experiences some mutational events as a result of spontaneous DNA replication error or exposure to mutagens or carcinogens in the environment. Many of these mutational events are correctly repaired and have no lasting consequences. However, when they remain unrepaired and occur in a gene-coding region for cell growth regulation, they can have permanent consequences for the individual, including a greater risk for cancer development.

Question 2

A person who is worried that he may have inherited the gene mutation for Huntington disease is told that he has the "wild-type" form of this gene. What is thebestinterpretation of this finding?

Accepted Answer

The most common form of a normal functional gene is known as the wild type. Thus, a person with the wild-type form of the HD gene has a functional gene with no increased risk for developing the disease.

Question 3

Which statement about single-nucleotide polymorphisms (SNPs) is true?

Accepted Answer

Point mutations are substitutions of one base for another and can occur in DNA or RNA. This type of change does not result in an extra base or a lost base, just a substitution. This type of base change is known as a single-nucleotide polymorphism (SNP). Frameshift mutations are deletions or insertions of DNA bases, not one-for-one substitutions. SNPs do not interconvert introns and exons.

Question 4

Which DNA segment deletion would cause a frameshift mutation?

Accepted Answer

Because an amino acid is encoded in the DNA by a "triplet" of bases, deletion of any number of bases that is not a multiple of three will alter the reading frame and result in a frameshift mutation. Although deletion of "triplet" bases can result in a change in some areas of the amino acid sequence and have an influence on protein function, the essential reading frame is not disrupted.

Question 5

Which factor has the greatest influence on protein tertiary structure?

Accepted Answer

Tertiary structure is the folding of the linear structure and occurs as a result of remote amino acids interacting with each other. These interactions, including bod formation, allow parts of the linear structure to draw closer together in some areas and have greater distances in other areas. These shape-changing factors influence a protein's activity. The poly-A tail only finishes the transcription and is not translated. Additional proteins in specific association are a protein's quaternary structure. The specific amino acids in close proximity to each other in a peptide help for the protein's secondary structure.

Question 6

A new experimental drug has been developed that reduces the activity of microRNA in the beta cells of the pancreas of people with type 2 diabetes mellitus. Ifthisdrug was specific only for pancreatic beta cells, what would be its effect?

Accepted Answer

MicroRNA is a small, noncoding piece of RNA that regulates gene expression at the RNA level by binding to parts of targeted mRNA molecules, making them partially double stranded, which cannot be translated. This action "silences" the translation ability of selected mRNA molecules and increases the rate at which they are degraded. This experimental drug has the potential to increase insulin production by allowing insulin-coding mRNA to be present longer and not have its translation inhibited by being double stranded. MicroRNA has no effect on a protein once it has been produced. Thus, the degradation of formed insulin is not changed.

Question 7

Jack and Jill go up a hill that has high levels of gamma radiation emission. Jack suffers 10 point mutational events in a noncoding region, and Jill suffers only one frameshift mutation in the insulin gene-coding region of all her pancreatic beta cells. What are the possible and probable outcomes of these events for both people?

Accepted Answer

It is most likely that the mutational events in a noncoding region will not interfere with correct reading of any genes. These changes in the noncoding regions can make Jack's DNA more identifiable. With Jill having a frameshift mutation in the gene-coding region, it is likely that she will not be able to produce functional insulin and will have type 1 diabetes mellitus, requiring insulin replacement. Because this large mutational event (all the pancreatic beta cells) is occurring only in somatic cells, Jill cannot pass this problem on to her children.

Question 8

What is the expected outcome when a person (twin A) experiences a large deletion of DNA in one of his noncoding regions and his monozygotic twin (twin B) doesnot?

Accepted Answer

Mutations of any type that occur in noncoding regions are responsible for making one person's DNA different from and identifiable from another person's DNA. Even identical twins (monozygotic twins) do not have absolutely identical DNA by the time they are born, although they probably did when the embryo first split into two embryos. By the time identical twins are born, they usually have at least 100 base pairs different from each other in the noncoding regions. As they live their lives, each twin continues to accumulate more and different mutations so that as they age, these identical twins become less identical in their DNA.

Question 9

What makes a frameshift mutational event more serious than a point mutational event?

Accepted Answer

Frameshift mutations are disruptions of the DNA reading frame (not the chromosome) as a result of having a whole base or group of bases added or deleted. They can occur in somatic cells or germline cells. When this type of mutation occurs in gene-coding regions, it always disrupts the reading frame from the start of the mutation to the end of the gene. The result is complete alteration of amino acid position and prevention of synthesis of a functional protein. A normal protein cannot be made from a gene with a frameshift mutation. Although mutations may accumulate over a lifetime, frameshift mutations do not occur more often than point mutations as a person ages.

Question 10

What is the expected result of a "nonsense" point mutation?

Accepted Answer

A nonsense point mutation results in an inappropriate placement of a stop signal, which has a negative effect on protein function. This type of mutation prevents the completion of a protein. The protein may not be synthesized at all if the stop signal is present early in the reading sequence. If it is present later in the sequence, protein synthesis stops prematurely and results in a short or truncated protein that usually has little if any function.

Question 11

How does an acquired mutation in a somatic cell gene leading to cancer development affect a person's ability to pass on a predisposition for that cancer typeto hisorher children?

Accepted Answer

Somatic cell mutations occur only in ordinary body cells, not in germline cells (eggs or sperm). Thus, somatic mutations cannot be passed on to one's children. The presence of somatic mutations is a major cause of sporadic cancer in a person, but this predisposition cannot be inherited by his or her children.

Quiz 2: Protein Synthesis