12.4 Mutations

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?Think About It!

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.

May occur in somatic cells (arent passed to offspring)Skin cancer and leukemia

May occur in gametes (eggs & sperm) and be passed to offspringCertain types of cancer: the eye tumor retinoblastoma and Wilms tumor, a childhood malignancy of the kidney.

Mutations happen REGULARLY

Most mutations have no effect on gene expression

Many mutations are repaired by enzymes

Some mutations may improve an organisms 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.

This sentence represents a gene. Each letter corresponds to a and each word represents a .

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.

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

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 MutationsMissense mutations result in a single amino acid change within the protein.

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

Silent mutations do not cause amino acid changes within the protein. Exs:Cystic FibrosisNeurofibromatosisSickle Cell AnemiaTay-SachsColor Blindness

Missense Mutation

Nonsense Mutation

Insertion mutations & deletion mutationsAdd 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

Lactose ToleranceAntibiotic ResistanceHIV ImmunityMalarial Resistance fromSickle Cell Anemia

But mutations can also be beneficial

MutagensCarcinogensRadiationUV lightEnvironmentalHeavy metalsChemical exposure (VOCs)Bacteria and VirusesOr they could be induced

The World Health Organizations 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.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 cellsSkin Cancer

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

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

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