12.4 Mutations

Think About It!

Complete the 2 tables on the first page of your handout. Try this without using your notes first and only refer to your notes on transcription and translation if you are struggling.

From your tables and both translated sequences, what do you think a mutation is?

What is a mutation? And what can a mutation do?

 A mutation is a

permanent change in the DNA sequence of

a gene.  Mutations in a gene's DNA sequence can alter the amino acid sequence of the protein encoded by the gene.

Mutations happen REGULARLY

• May occur in somatic cells offspring) (aren’t passed to • Skin cancer and leukemia • May occur in gametes (eggs & sperm) and be passed to offspring • Certain types of cancer: the eye tumor retinoblastoma and Wilms tumor, a childhood malignancy of the kidney.

• Most mutations have no effect on gene expression • Many mutations are repaired by enzymes • Some mutations may improve an organism’s survival (beneficial) and/or produce genetic variety

Mutations to control genes can transform one body part into another. Scientists have studied flies carrying Hox mutations that sprout legs on their foreheads instead of antennae! Polydactyly – Common disorder with extra fingers and/or toes

How do mutations happen?

 The DNA sequence of each gene determines the amino acid sequence for the protein it encodes. We can think about the DNA sequence of a gene as a sentence made up entirely of three letter words:

Thesunwashotbuttheoldmandidnotgethishat.

 The DNA sequence is interpreted in groups of three nucleotide bases, called codons.

The sun was hot but the old man did not get his hat.

 Each codon or 3-letter word in this case, specifies a single amino acid in a protein.

The sun was hot but the old man did not get his hat.

This sentence represents a gene. Each letter corresponds to a each word represents a . and What would happen if you shifted the three-letter "reading frame“? You would end up with:

T hes unw ash otb utt heo ldm and idn otg eth ish at.

Or

Th esu nwa sho tbu tth eol dma ndi dno tge thi sha t.

What other types of mutations can occur in DNA sentences?

Point mutations

are single nucleotide base changes in a gene's DNA sequence. This type of mutation can change the gene's protein product in the following ways:

3 Types of Point Mutations

1.

2.

3.

Missense mutations

single amino acid change within the protein. result in a

Nonsense mutations

shortened. create a premature "translation stop signal" (or "stop" codon), causing the protein to be

Silent mutations

amino acid changes within the protein. do not cause  Ex’s:  Cystic Fibrosis  Neurofibromatosis  Sickle Cell Anemia  Tay-Sachs  Color Blindness

Missense Mutation

Nonsense Mutation

Insertion mutations & deletion mutations

  Add or remove one or more DNA bases. Insertion and deletion mutations cause

frameshift mutations

, which change the grouping of nucleotide bases into codons. This results in a shift of "reading frame" during protein translation.

Insertion Mutation

Deletion Mutation

But… mutations can also be beneficial • • • • Lactose Tolerance Antibiotic Resistance HIV Immunity Malarial Resistance from Sickle Cell Anemia

Or they could be induced

• • • Mutagens • Carcinogens • Radiation • UV light Environmental • Heavy metals • Chemical exposure (VOC’s) Bacteria and Viruses

Skin Cancer

Skin cancer occurs when errors (mutations) form the in the DNA of healthy skin cells. The mutations cause the cells to grow out of control and form a mass of cancer cells The World Health Organization’s International Agency for Research on Cancer (IARC) announced that it has moved UV tanning beds to its highest cancer risk category - "carcinogenic to humans." The use of tanning beds before age 30 is associated with a 75% increase in melanoma risk.

Lung Cancer

Smoking causes 87% of all lung cancer cases. Smokers have approximately one chance in 10 of developing lung cancer over his/her lifetime.

Videos

Sickle Cell: http://www.dnalc.org/resources/3d/17-sickle-cell.html

Mutating virus: http://video.nationalgeographic.com/video/national geographic-channel/shows/naked-science/ngc-deadly-mutation/ Radiation leading to mutations and cancer: http://www.dnai.org/lesson/go/1738/1419 Addition and deletion mutations: http://highered.mcgraw hill.com/sites/0072556781/student_view0/chapter11/animation_quiz_4.html