Gene Mutations

Target #17- I can describe a gene mutation

• Gene mutation: a permanent heritable change in the sequence of bases in DNA– Effect can cause a

range of consequences from no effect to complete protein synthesis inactivity

– Can occur on somatic cells and on sex cells

Target #18- I can explain the three causes of gene mutation

• Three causes of gene mutation– Errors in replication

• Rare source of mutation• DNA polymerase is responsible for

proof-reading the new strand against the old strand

• Usually mismatched pairs are replaced with the correct nucleotide

• Occurs 1 in every 1 billion nucleotides

–Mutagens• Environmental influences

– Radiation, certain organic chemicals

• Rate of mutation is usually low because DNA repair enzymes constantly monitor and repair damages

–Transposons• Specific DNA sequences

that have the ability to move to different genes–Can either increase or

decrease the expression of the affected gene

• Nicknamed “jumping genes”• Example– Indian corn has both

white and red/black kernels»Caused by a

transposon interrupting the expression of the gene for black kernel pigment

Target #19- I can describe point mutations

• Point Mutation– Occurs in one or more

nucleotides– Includes the

substitution, insertion or deletion of nucleotides• Can alter the type of

amino acid being produced, which may result in the wrong protein being synthesized

– Generally occurs during DNA replication

Target #20- I can state what occurs during a substitution mutation

• Substitutions–One base is changed to a different base–Usually affect no more than a single amino

acid• May have no effect at all• Example

– If a mutation changed one codon of mRNA from CCC to CCA, the codon would still code for the same amino acid (Proline)

– If a change occurs in the first base of the codon CCC, like to ACC, then the amino acid would be different.

Target #21- I can state how frameshift mutations affect protein activity

• Insertions & Deletions–Point mutations in

which one base is added or subtracted from the DNA sequence–Also known as

frameshift mutations• Result in a shift of the

reading frame of the genetic message• Can result in the

changing of the whole protein–Results in a change in,

or loss of, the protein’s function

Target #22- I can summarize why genetic mutations may be harmful

• A harmful change caused by genetic mutations may result in the growth of cancer cells– Development of cancer involves a series of

accumulating mutations that can be different for each type of cancer• Several genes are involved with the suppression of tumor

formation, but when mutated cause cancer– Proto-oncogenes and tumor-suppressor genes

• When those genes are mutated, they do not transcribe/translate cell cycle regulating proteins correctly– Results in the cell cycle not being controlled, and/or apoptosis is

not occurring

– Characteristics of Cancer Cells• Genetically unstable• Do not correctly regulate the cell cycle• Escape the signals for cell death

Target #23- I can summarize why genetic mutations may be beneficial

• Some genetic mutations have beneficial effects– Results in the production of proteins with new or

altered functions that can be useful to organisms in different or changing environments• Example: mutations have helped many insects resist

chemical pesticides

– Also results in organisms who are more successful at surviving and producing offspring• The source of all changes in organisms over time via

evolution start with genetic mutations