Chapter 13: Gene Mutations and Cancer

Vocabulary review covering somatic vs. germ-line mutations, sources of mutations, point mutation categories, and the genetic basis of cancer development.

Germ-Line Mutations

Mutations that occur in sex cells (gametes: sperm or egg cells) and can be passed directly from parent to offspring, causing every cell of the offspring to carry the mutation and potentially affecting future generations.

Somatic Mutations

Mutations that occur in body cells (non-sex cells) and affect only the individual organism itself (such as localized tissue damage or cancer), without being passed down to offspring or future generations.

Spontaneous Mutations

Mutations that arise naturally as a result of abnormalities in normal biological processes, such as rare errors made by DNA polymerase during DNA replication.

Induced Mutations

Mutations caused by environmental influences or external agents known as mutagens that interact with DNA.

Mutagens

Environmental factors (chemicals or radiation) that alter DNA structure and cause mutations.

Carcinogens

Cancer-causing agents; many mutagens also act as carcinogens (for example, tobacco smoke mutates DNA and causes lung cancer).

Ionizing Radiation

Radiation such as X-rays and gamma rays that acts as a mutagen by creating highly reactive free radicals.

UV Radiation

Ultraviolet light from sunlight that acts as a mutagen by inducing the formation of thymine dimers, which are abnormal covalent bonds between adjacent thymine bases in DNA.

Tobacco Smoke

A mixture of over 7,000 chemicals, tobacco smoke acts as a potent carcinogen and mutagen, significantly increasing the risk of various cancers, especially lung cancer.

Point Mutation

A type of gene mutation involving a change in a single nucleotide. An example is sickle cell disease.

Neutral Mutation

A point mutation that changes a codon, but due to the redundancy (degeneracy) of the genetic code, encodes the same amino acid, having no effect on the amino acid sequence or protein structure.

Missense Mutation

A point mutation that changes a codon so that it encodes a different amino acid, usually causing protein function to be reduced or abnormal (e.g., Sickle cell disease, $Glu \rightarrow Val$).

Nonsense Mutation

A point mutation that changes a normal codon into a premature stop codon (UAA, UAG, or UGA), resulting in an incomplete, truncated, and typically completely nonfunctional protein.

Proto-oncogenes

Regulatory genes that normally function to stimulate the cell cycle and promote cell growth; when mutated, they become hyperactive oncogenes that drive excessive cell division.

Oncogenes

Hyperactive mutated forms of proto-oncogenes that drive excessive cell division.

Frameshift Mutations

A mutation caused by one or morenucleotides being inserted or deleted. It alters the reading frame and results in a new sequence of amino acids, which are nonfunctional protiens.

Tumor Suppressor Genes

Regulatory genes that normally function to inhibit the cell cycle and prevent uncontrolled division or trigger apoptosis; when mutated and inactivated, cells lose their regulatory brakes.