mutations power point

8/3/2019 Mutations Power Point

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MutationsMutations


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What Are Mutations?What Are Mutations?

Changes in thenucleotide sequence ofDNA

May occur in somaticcells (arent passed tooffspring)

May occur in gametes(eggs & sperm) and bepassed to offspring


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Are Mutations Helpful orHarmful?

Mutations happenregularly

Almost all mutations areneutral Chemicals & UV radiation

cause mutations

Many mutations arerepaired by enzymes


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Are Mutations Helpful orHarmful?

Some type of skincancers and leukemia

result from somaticmutations

Some mutations mayimprove an organismssurvival (beneficial)


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Mutations Causes:

Radiation e.g. UV

Chemical e.g. Cigarette Smoke

Spontaneous

Types:

In body cells, can lead to cancer.

In sex cells, can lead to new traits in offspring.


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Types of Mutations


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Types of Mutation

Mutations can be classified according to their effects on theprotein (or mRNA) produced by the gene that is mutated.

1. Silent mutations (synonymous mutations). Since thegenetic code is degenerate, several codons produce the sameamino acid. Especially, third base changes often have no effect

on the amino acid sequence of the protein. These mutationsaffect the DNA but not the protein. Therefore they have noeffect on the organisms phenotype.

2. Missense mutations. Missense mutations substitute oneamino acid for another. Some missense mutations have very

large effects, while others have minimal or no effect. Itdepends on where the mutation occurs in the proteinsstructure, and how big a change in the type of amino acid it is. Example: HbS, sickle cell hemoglobin, is a change in the beta-globin gene,

where a GAG codon is converted to GUG. GAG codes for glutamic acid,which is a hydrophilic amino acid that carries a -1 charge, and GUG codesfor valine, a hydrophobic amino acid.


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3. Nonsense mutations convert an amino acid into a stopcodon. The effect is to shorten the resulting protein.Sometimes this has only a little effect, as the ends of proteinsare often relatively unimportant to function. However, oftennonsense mutations result in completely non-functionalproteins. an example: Hb- McKees Rock. Normal beta-globin is 146 amino acids

long. In this mutation, codon 145 UAU (codes for tyrosine) is mutatedto UAA (stop). The final protein is thus 143 amino acids long. Theclinical effect is to cause overproduction of red blood cells, resultingin thick blood subject to abnormal clotting and bleeding.

4. Sense mutations are the opposite of nonsense mutations.

Here, a stop codon is converted into an amino acid codon.Since DNA outside of protein-coding regions contains anaverage of 3 stop codons per 64, the translation processusually stops after producing a slightly longer protein. Example: Hb- Constant Spring. alpha-globin is normally 141 amino

acids long. In this mutation, the stop codon UAA is converted to CAA(glutamine). The resulting protein gains 31 additional amino acids

before it reaches the next stop codon. This results in thalassemia, asevere form of anemia.


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Chromosome Mutations

May Involve:

Changing the

structure of achromosome

The loss orgain of part ofa chromosome


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Chromosome Mutations

Five types exist:

Deletion

Inversion

Translocation

Nondisjunction Duplication


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Deletion

Due to breakage A piece of a

chromosome is lost


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Inversion

Chromosome segmentbreaks off

Segment flips around

backwards Segment reattaches


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Duplication

Occurs when agene sequence isrepeated


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Translocation

Involves twochromosomes thatarent homologous

Part of onechromosome is

transferred toanother chromosomes


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Translocation


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Nondisjunction

Failure of chromosomes toseparate during meiosis

Causes gamete to have too many

or too few chromosomes Disorders:

DownSyndrome three 21st

chromosomes Turner Syndrome single X chromosome

Klinefelters Syndrome XXY

chromosomes


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Chromosome Mutation

Animation


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Gene Mutations

Change in thenucleotide sequence

of a gene May only involve a

single nucleotide

May be due tocopying errors,chemicals, viruses,

etc.


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Types of Gene Mutations Include:

Point Mutations

Substitutions

Insertions

Deletions Frameshift


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Point Mutation

Change of a singlenucleotide

Includes thedeletion, insertion, orsubstitution of ONEnucleotide in a gene


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Point Mutation

Sickle Celldisease is the

result of onenucleotidesubstitution

Occurs in thehemoglobin gene


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Frameshift Mutation

Inserting or deletingone or more

nucleotides Changes the readingframe like changing asentence

Proteins built

incorrectly


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Frameshift MutationOriginal:

The fat cat ate the wee

rat.Frame Shift (a added):

The fat caa tet heweer at.


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Amino Acid Sequence

Changed


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Gene Mutation

Animation


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Extra Fingers


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Female Downs SyndromeFemale Downs Syndrome

292n = 47


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Turners SyndromeTurners Syndrome

302n = 45

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