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1

What is a mutation?

A randomly produced, permant heritable change in the genes of an organism

Mostly arise in DNA synthesis

2

Name the different types of mutatuions

Point mutations (affect a single nucleotide) - Base-pair substitutions and frameshift mutations

Macrolesions (alterations in chromosome # or structure)

 

Deletion, Insertion, inversion, rearrangement/translocation (chromosomal), , substitution

3

Base-Pair Substitutions

One base pair is substituted out for another base pair

 

Could cause no change if the same amino acid is coded for

Could cause little change if an amino acid of similar prperties is coded for (i.e. hydrophobic nature)

Could cause a lot of change depending where the mutation occurs (at the active site of an enzyme)

Could also cause a lot of change if a sense codon is changed into a nonsense (stop) codon = production of protein is ended prematurely)

 

2 types:

Transition (substitution of a purine for a purine and a pyrimidine for a pyrimidine = less effect)

Transversion (substituion of a purine for a pyrimidine and vice versa) = more severe effect

4

Frameshift Mutation

Addition or deletion of 1, 2, or 4 nucleotide pairs

Changes the reading frame of the RNA = dramatic change

Could cause a protein coding to end prematurely (b/c it is likely a stop codon would be reached before it should = truncated protein)

NOT framshift if there is an addition or deletion of 3 nucleotide pairs = does not change the reading frame; cna cause mild or severe effects depending on where the mutation occurs in the protein

5

Macrolesions

Severe altrations such as translocations, inversions, deletions, insertions causing a change in the chromosome structure (deletion or insertion of >4 bases)

 

Aneuploid and euploid variations causing change in the chromosome #

 

Deletion of a whole chromosome = typically negative

Addition of a whole chromosome = usually causes genetic toxicity syndrome (ex - Trisomy 21)

6

Insertion Mutation

Addition of one or more nucleotide pairs into a DNA sequence (often due to slipping of DNA Polymerase)

Can also occur as the addition of a larger sequence into a chromosome (caused by unequal crossover in meiosis)

Addition of a whole chromosome can cause genetic toxicity syndrome 

 

Effect is location-dependent:

Insertion at an intron = very little effect

Insertion at an exon = bigger effect

If insert b4 promotor = no effect b/c not within the reading frame of the gene

If insert after the promotor = bigger effect b/c within the gene

 

Effect is also dependent on the number of base-pairs:

framsehift vs non-frameshift mutations

7

Deletion Mutation

Loss of genetic material

Deletion of one or more nucleotide pairs into a DNA sequence

Can also occur as the deletion of a larger sequence into a chromosome (caused by unequal crossover in meiosis)

Deletion of a whole chromosome can also occur

 

Effect is location-dependent:

Deletion at an intron = very little effect

Deletion at an exon = bigger effect

If delete b4 promotor = no effect b/c not within the reading frame of the gene

If delete after the promotor = bigger effect b/c within the gene

If delete enhancer = decrease in RNA and protein

If delete promotor = No RNA or protein

 

Effect is also dependent on the number of base-pairs:

framsehift vs non-frameshift mutations

8

Inversion Mutation

A DNA sequence in reverse order

 

Location dependent:

If inverted at exon = little effect b/c the reading frame is unaffected

If inverted at the enhancer = no effect

If inverted at the promotor = no RNA or protein

 

Creation of a premature stop codon from inversion can also occur

9

Chromosomal Rearrangement

Translocation = a chromosomal segment is attached to a new location in the chromosome

Caused by rearrangmwents of parts between nonhomologous chromosomes 

Causes disease

10

Substitution Mutation

Replacement of one nucleotide in a DNA sequence by another nucleotide OR replacement of one amino acid in a protein by another

 

3 Types: 

Synonomous Substitution - Silent

Nonsynonomous Substitutions - Missense and Nonsense

 

1 base-substituion in either the enhancer or promotor = little effect 

 

11

Silent Substituions

No change in phenotypic expression

 

Caused by:

Change within a noncoding region (intron)

Change with in an exon that causes no replacement of the amino acid in question (i.e. one amino acid is coded for by numerous codons) = Synonomous Substitution

12

Missense Substitutions

A nonsynonomous substitution

A substituion codes for a different amino acid 

 

Conservative - Change to an amino acid of similar properties

Nonconservative -  Change to an amino acid of different porperties = can render to protein nonfunctional or different = causes disease

 

13

Nonsense Substitution

A nonsynonomous substituion

A substitution that causes the appearance of a premature stop codon (UAA, UAG, UGA) = truncated protein

14

If a promotor is relocated = ?

Could cause cancer b/c it could allow for the coding of cancerous genes

15

The DNA code is degenerate = ?

One amino acid can be coded for by more than one codon

16

Example of Deamination of Cytosine

?

17

RNA Processing

Splicing and the addition of caps and tails to mRNA

18

Splicing

The removal of introns during mRNA processing

Almost never seen in porkaryotes but is common in eukaryotes

Allows for continuous coding mRNA sequence

19

Addition of mRNA caps and tails

Caps added at 5' end of first RNA nucleotide; added after trancription begins; required to be read effeciently by translational machinery

 

Tails added to 3' end of last of mRNA sequence; added as a seperate enzymatic reaction after the mRNA id released from the DNA; Poly (A) Tail = sequence of adenine nucleotides; added to protect mRNA molecule from enzyme degredation

20

Allele

Alternative forms of a gene

21

Locus

A specific location on a gene, DNA sequence, or chromosome