USC FNP bridge course 4.5 genetic mutations

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Genetic Mutations

All genetic mutations that result in disease are inherited.

a change in the nitrogenous base sequence of DNA that causes a change in the product encoded by that gene.

can be a small change (one nucleotide) or a large change (large sequences of the chromosome are altered).

Can be neutral or silent (cause no change in the DNA base sequence), advantageous (can enhance the benefits for that cell) or disadvantageous ( cell can loose phenotypic traits it needs or even harmful and likely to be removed from the gene pool when the individual cell dies).

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Environmental/ Chemical mutatagens

agents in the environment such as chemicals and radiation that directly or indirectly bring about mutations.

-radiation- x rays and gamma rays are forms of radiation that are potent mutagens because of their ability to ionize atoms and molecules.

-chemicals

-byproducts of cellular metabolism

-free radicals

-another form of mutagenic radiation is UV light. a noniionizing component of sunlight. Most UV light is screened by the ozone layer. The effect of direct UV light on DNA is the formation of harmful covalent bonds between pyramiding bases. Adjacent thymines in DNA strand can cross link to form thymine dimers that may cause serious damage or death to the cell because it cannot properly transcribe or replicate DNA.

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DNA repair

Frequency of mutation or the mutation rate is the probability that a gene will mutate when a cell divides. Mistakes in DNA replication occur at a very low rate. DNA repair mechanisms are proteins that fix the mutation. Mutations in genes that encode repair protein can increase cancer risk, BRCA1 and BRCA2 genes.

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SNP

Single nucleotide point mutation

Single change in nucleotide sequence.

Copying errors that lead to variations in the DNA sequence at a particular location. Generates biological variation in peoples genes and influence a variety of traits, can be in health or physical appearance or have no observable difference at all.

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Missense mutation

Most common type of mutation involves singe base pairs- base or point mutation.

missense mutation-The base substitution results in an amino acid substitution in the synthesized protein.

Sickle cell disease is caused by a single change in the gene for HgB- a change form glutamic acid to valine in the protein at a specific site cause the shape of the HgB molecule to change.

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Nonsense mutations

A nonsense mutation causes a change to a stop codon.

By creating a nonsense (stop ) codon in the middle oa a mRNA molecule some base substitutions effectively prevent the synthesis of a complete function protein and only a fragment is synthesized this is a base substitution resulting in a nonsense condon.

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Extra nucleotide is inserted and shifts all the other codons down

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Removal of a part of a coding sequence which changes the protein or amino acid.

An example would be CF.

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Frameshift Mutations: Insertion mutation and Deletion

Changes in DNA in which one or more nucleotide pairs are deleted or inserted in the DNA. This mutation can shift the translational reading frame (codons).

Frameshift mutations almost always result in a long stretch of altered amino acids and the production of an inactive protein from the mutated gene until a nonsense codon is encountered and terminates translation.

Huntingtons disease is a progressive neurological disorder caused by extra bees inserted into a particular gene.

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Repeat expansion mutation

the original DNA code for an amino acid sequence is repeated.

DNA polymerase slips and repeats.

Extra amino acids are added to a protein

this happens in huntintingtons disease.