Chapter 15 Mutations and Repair

Approximately what percentage of human cancers are associated with mutations of the p53 gene?

50%

silent mutation

A mutation that changes a single nucleotide, but does not change the amino acid created.

How does a missense mutation cause red blood cells to sickle?

Glutamic acid is changed to valine, altering the structure of the hemoglobin protein and causing the hemoglobin subunits to stick to one another.

What statement about carcinogens is true?

Most of them are also mutagenic.

A heritable change in genetic material is known as a(n)

Mutation

A mutant gene that results in uncontrolled cell growth is known as a(n)

Ocogene

How does a frameshift mutation affect protein function?

Protein function is most likely inhibited because an entirely new amino acid sequence occurs downstream of the mutation.

How do somatic mutations affect an individual's offspring?

The mutation does not occur in germ line cells and therefore does not affect offspring.

What is an oncogene?

a mutant gene that promotes uncontrolled cell growth

What is a point mutation?

a mutation that affects only a single base pair

What is a base substitution?

a mutation that occurs when one base is replaced by another

promoter

a possible increase or decrease in the rate of transcription

nonsense mutation

changes a normal codon into a stop codon

Tumor-suppressor genes lead to cancer by mutations that:

eliminate their function

Induced mutations are caused by:

environmental agents

Which of the following are causes of spontaneous mutations?

errors made by DNA polymerase during replication insertion of a transposon into a gene free radicals produced during metabolic processes that change nucleotide structure

____________________mutation typically inhibits protein function because it changes the amino acid sequence downstream of the mutation site.

frameshift

The activity of an oncogene is:

higher than that of the normal gene

The gene that encodes the Ras protein becomes an oncogene when a mutation reduces the ability of the protein to:

hydrolyze GTP

Most carcinogens are also:

mutagens

A(n) ______ mutation affects only a single base pair.

point

splice junctions

possible change in the ability of pre-mRNA to be properly produced

translational regulatory element

possible change in the ability of protein to be produced from mRNA

Mutations outside a gene's coding sequence can affect gene expression. Which of the following sites, when mutated, would affect transcription?

promoter operator site

Sperm and egg cells are termed germ line cells. In contrast, cells of the skin, muscle, heart, and liver are examples of

somatic cells

What type of mutation results from abnormalities that naturally occur during biological processes?

spontaneous

Ultraviolet light can cause the formation of a(n)__________________,___________ in DNA

thymine dimer

A nonsense mutation causes the___________________ of the protein to be terminated prematurely. This reduces the length of the polypeptide and thus alters its function.

translation

Xeroderma pigmentosum and Cockayne syndrome are genetic diseases that affect:

DNA repair

True or false: The function of a normal tumor-suppressor gene is to promote cell division.

False

How are timing and size of the patch of tissue affected by a somatic mutation related?

The earlier in development the mutation occurs, the larger the patch.

How do growth factors promote cell division?

They activate pathways that trigger gene transcription.

How do nonsense mutations affect protein function?

Translation is terminated where the mutation occurs, producing a truncated polypeptide which is unlikely to function correctly.

True or false: All living things possess mechanisms allowing them to minimize mutation.

True

True or false: Carcinogens include UV light and certain chemicals in cigarette smoke.

True

True or false: New mutations are much more likely to be harmful than beneficial to the individual.

True

A missense mutation may not affect protein structure and function if the altered amino acid has:

a similar side chain

What is a thymine dimer?

a site where two adjacent thymine bases become covalently cross-linked to each other

In most cases, how many genetic changes in a cell lineage typically occur before cancer develops?

at least 10

A point mutation in which one base pair is replaced by another is known as a(n)

base substitution

Which of the following are ways that ionizing radiation can alter DNA structure?

breaks in one or both DNA strands base deletion

How do point mutations affect DNA sequences?

by adding or subtracting a single base pair by substituting one base for another

How can a missense mutation in a proto-oncogene cause cancer?

by altering the function of the encoded protein

A silent mutation results in a polypeptide with an unchanged amino acid sequence because the genetic code is:

degenerate

Mutations can be divided into two main types. Spontaneous mutations result from abnormalities in biological processes, while__________________mutations are caused by environmental agents that enter the cell and alter the structure of DNA.

induced

Which of the following are examples of somatic cells?

liver, skin, muscle

Mutations in noncoding sequences:

may affect gene expression

intergenic region

not as likely to have an effect on gene expression

The gene that encodes the Ras protein is an example of a(n):

oncogene

missence mutation

one amino acid is changed

Mutations that occur in noncoding sequences may affect gene

regulation

Xeroderma pigmentosum causes a predisposition to skin cancer because it impairs the ability to:

repair UV-induced lesions

framshift mutation

the amino acid sequence is changed downstream of the mutation

Silent mutations have no effect on the amino acid sequence of a polypeptide because:

the base substitution results in a codon that specifies the same amino acid as the original sequence

In nucleotide excision repair, what serves as the template for synthesis of new DNA to replace the damaged strand?

the complementary strand of DNA

What does a gene mutation affect?

the sequence of bases in a particular gene

Sickle cell disease is caused by a missense mutation that affects:

the shape of red blood cells the structure of the hemoglobin protein the tendency of hemoglobin proteins to aggregate when the oxygen concentration is low

Somatic mutations are not transmitted to an individual's offspring because:

they do not occur in the gametes

Elimination of the function of a(n) ______ gene promotes cancer.

tumor-suppressor

Maintenance of genome integrity and negative regulation of cell division are the two main functions of:

tumor-suppressor genes

Which of the following genetic diseases affect DNA repair systems in humans?

xeroderma pigmentosum Cockayne syndrome