Mutations.ppt

7/27/2019 Mutations.ppt

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Mutations

Changes in the DNA code


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Mutation

A mutation is any change to the DNA.The can be as simple as a single basechange (A to C) or as severe asdeleting a whole section of the DNA.

The next pages give information on

different types of mutations in genesand how they effect the proteins thatthey code for.


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Learning Objectives

What are the different types of mutations

Understand how each type effects theprotein

Be able to identify different mutations

from examples and predict their effecton the protein CA biology standards 1,2, 4, 7, 8


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Table of Contents

Types of Mutations Single Base Mutations

Point Silent mutations

Missense Nonsense

Frameshift

Addition Deletion

ChromosomalMutations

Inversion Deletion Translocation


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Point Mutation

A point mutation is a single change inthe DNA nucleotide sequence. Thechange occurs when 1 base issubstituted for a different base.

Another name for point mutation issingle-base substitution


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The picture above shows the last 5 codonsof a wildtype or normal mRNA. In thenormal protein the last four amino acids are

met hionine, lys ine, phe nolalanine, glycine.

A point mutation is a single base change.

Find the base that changed & use themRNA codon chart to see how it effects theprotein. ( Click on the picture below to check your answer)

?mRNA

codon

chart
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SilentMutations

In this example, the amino acid did notchange. If you look at the mRNA codonchart you will see that the 3rd base oftenhas no effect on the amino acid. This isdue to the wobble theory.

Mutations that have no effect on the aminoacid sequence are called silent mutations


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Missense

In the example below, the mutation isstill a point mutation since only 1 base isexchanged for another.

Find the base that changed & use themRNA codon chart to see how it effects

the protein. ( Click to check your answer)

?mRNA

codon

chart


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Missense When a mutation occurs in the 1st or 2nd letter in a

codon it always changes the amino acid.

This type of mutation is called missense. Eventhough only 1 amino acid changed, many times thisdrastically effects the way the protein folds andworks.

The inherited disease, sickle cell anemia, is anexample of this type of mutation.

Return


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Nonsense

The last type of point mutation is callednonsense.

Find the base that changed & use themRNA codon chart to see how it effectsthe protein. ( Click to check your answer)

mRNA

codon

chart

? ? ? ?


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This last type of point mutation is callednonsense because it puts a termination (stop

codon) in early, thereby cutting the aminoacid sequence (protein) short.

This changes the protein structure and willmost likely prevent the protein from doing its

job at all.

Nonsense

Return


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Point Mutation Self Quiz

1. Determine the mRNA and amino acidsequence for the strand of normal DNA.

2. Determine the mRNA and amino acidsequence for the mutated strands of DNA.

3. Compare the mutated strands to the normalstrands.

4. Identify the type of mutation which hasoccurred.


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Normal DNA sequence ATGTTGGCTTTACGGATTTTGA TACAACCGAAATGCCTAAAACT


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Normal DNA sequence

Answers ATGTTGGCTTTACGGATTTTGA TACAACCGAAATGCCTAAAACT


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Mutant DNA ATGTTGGCCTTACGGATTTTGA TACAACCGGAATGCCTAAAACT


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Mutant DNA #1 Answers ATGTTGGCCTTACGGATTTTGA TACAACCG G AATGCCTAAAACT


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Frameshift Mutations

Frameshift mutations cause the readingframe of the codons to shift. This is causedby the addition or deletion of one or morenucleotides.

When this occurs in a gene, usually theresult is such a drastic change to the proteinstructure that the protein cannot work at all.


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Frameshift Mutations

An example of the shifted reading frame thatoccurs from a deletion can be seen in the sentencebelow: Original sentence: The fat cat ate the wee rat.

Frame shift mutation: The fat caa tet hew eer at

.

In the example sentence, a single letter wasdeleted and this shifted all the letters after that

point. This results in a missense protein that will probablynot be able to fold correctly.


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Frameshift Self Check

For the two example on the followingpages determine the following: Addition or deletion Use the mRNA chart to see how the amino

acid sequence is effected

Predict whether the changes will have noeffect, minor effect, or major effect on theproteins structure and ability to do its job.


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Frameshift

Self Check

(Click to check your answer)

mRNA codon chart? ? ? #1

#2? ? ? ?


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Frameshift

Self Check

#1: Deletion causing missense . Major effect#2: Addition causing nonsense . Major effect

Important to note that these are just examples. Both types of frameshift mutations can cause either missense or nonsense.Both of these will most likely have a major effect on both the

protein structure and its ability to do its job.

mRNA codon chart#1

#2


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Chromosomal Mutations

Chromosomal Mutations are due to major changes in the DNA. Click on the picture

below to see an animation of the 3 types of chromosomal mutations

QuickTime and aTIFF (Uncompressed ) decompressor

are needed t o s ee this picture.

Quic kTime and aTIFF (Uncompressed ) decompressor

are needed t o s ee this picture.QuickTime and a

TIFF (Uncompressed ) decompressor are needed t o s ee this picture.
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The sentence below is an example of achromosomal mutation. Identify which

of the 3 types it is.

Original : The fat cat ate the wee rat. Mutation: The fat tar eew eht eta tac .

(Click for answer)

Inversion


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Effect of Mutations

In all cases that we looked at, the mutationseffected the protein itself. However, there aremany types of mutations that do not changethe protein itself but change

where and how much of a protein is made. Type of cell that makes the protein Too much or too little of the protein is made

When a protein is made made at the wrong time

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