Flashcards in Chapter 7:DNA Mutation, DNA repair and Transposable Elements Deck (44):
changes involving whole chromosomes
a change of one or a few base pairs. It may change the phenotype of the organism if it occurs within the coding region of a gene or in the sequences regulating the gene.
mutations which affect the function of genes. It can alter the phenotype by changing the function of a protein.
the process by which the sequence of base pairs in a DNA molecule is altered. It may result in a change to either a DNA base pair or a chromosome
A cell with a mutation is called what?
a mutant cell
There are two classifications of mutations based on the type of cell they occur in, what are they?
Somatic mutation and germ-line mutation
-mutation happening in a somatic cell
-the mutant characteristic affects only the individual in which the mutation occurs is not passed on to the succeeding generation.
- a mutation in the germ line of sexually reproducing organisms
- may be transmitted by the gametes to the next generation producing an individual with the mutation in both its somatic and germ line cells.
the probability go a particular kind of mutation as a function of time
ex: # of mutations per nucleotide pair per generation
ex: number per gene per generation
the number of occurrences of a particular kind of mutation
What are the two types of point mutations?
1. Base pair substitutions
2. Base pair insertions or deletions
Base pair substitutions??
change from one base pair to another in DNA
What are the two general types of Base Pair substitutions?
1. Transition mutation
2. Transversion mutation
a mutation from one purine-pyrimidine base pair to the other purine-pyrimidine base pair.
(A-T to G-C)
a mutation form purine-pyrimidine base pair to a pyrimidine-purine base pair.
( G-C to C-G)
Where do point mutations USUALLY occur. Is that a good thing?
- noncoding region
- yes ...bad if in coding region obv
Base pair substitutions in protein coding genes are also defined in terms of their effects on aa sequences in proteins. What are the four types of mutation effects?
1. Missense Mutation
2. Nonsense Mutation
3. Neutral Mutation
4. Silent Mutation
- a gene mutation in which a base pair change causes a change in the mRNA codon so that a different aa is inserted into the polypeptide. A phenotypic change is noted.
What is an example of a Missense mutation in regards to a genetic disease?
- Sickle cell anemia.......usually it codes for glutamic acid but the mutation codes for valine and results in a phenotypic change in the resulting protein functionality.
a gene mutation in which a base pair change alters an mRNA codon for an aa to a stop (nonsense) codon ( UAG, UAA or UGA)
- causes premature terminating of polypeptide chain synthesis.
- it will be transcribed but translation is where the issue is.
L> Non-functional polypeptide is result.
Example of a nonsense mutation from lecture?
LGR-4 (RARE NONSENSE MUTATION)
L> low bone mineral density and osteoporosis fractures. Electrolyte imbalance, low testosterone, increased risk of squamous cancer carcinoma
- a base pair change in a gene that changes a codon in the mRNA such that the resulting aa produces no detectable change in the FUNCTION of the protein translated from that message.
L>the mutated aa has similar properties to the original aa or the aa that was mutated has no significant importance tot he polypeptide.
L> no phenotypic change
- there is a chance they may benefit from this mutation such that there is an advantage in the changed aa
Example of a Neutral Mutation from lecture??
- APO-AIM more effective at removing cholesterol, helps prevent oxidation. There was an original arginine substituted by cysteine, improving HDL.
L> discovered in a tiny city in Italy.
- aka synonymous mutation
- a mutation that changes a base pair in agent but the altered codon in the mRNA specifies the SAME aa in the protein
- often occurs by changes such as at the third wobble position of a codon.
What type of mutation effect do base pair deletions or insertions have?
- frameshift mutation
- an addition or deletion of one base pair shifts the mRNA's downstream reading frame by one base pair so that incorrect aa's are added to the polypeptide after the mutation site.
Effects of a frameshift?
- may generate new stop codons
- result in longer than normal proteins
- result in significant alterations in aa sequence (primary structure) of a polypeptide.
A frameshift mutation is produced by the insertion or deletion of any number of base pairs in the DNA that is not divisible by ?
Example of a frameshift mutation from lecture?
-Gaucher's disease- insertion base pair of DNA prevents production of enzymes that normally real down glycolipids. Enlarged liver, spine, fractured bones and neurological impairment.
What is a forward mutation?
- changes a wilde type(common one in pop) gene to a mutant gene.
What is a reverse mutation? (back mutation)
- changes a mutant gene at the same site so that it functions in a completely wild type or nearly wild type way.
What are the two types of reverse mutations?
1. True reversion
2. Partial reversion
True reversion mutation?
- reversion is back to the wild type aa
Partial reversion mutation?
- reversion is to some other aa...and complete or partial function may be restored depending on the change.
Partial reversion is generally due to a what?
second point mutation in the same gene; in coding region....3 positions you can have a mutation
- if one is mutated, you can have other mutations in another lace in the codon..not impossible to get the same mutation at the same site.
- intragenic (within gene) suppression: second mutation in the same gene can mask the first mutation.
- a mutation at a different site from that of the original mutation. A suppressor mutation masks or compensates for the effects of the initial mutation, but it does NOT REVERSE the original mutation
Two types of suppressor mutations?
1. Intragenic supression
2. Intergenic supression
- mutation occurs within the same gene where the original mutations occurred but at a different site.
- mutation occurs in a different gene
How do intragenic suppressors work?
- altering a different nucleotide in the same codon where the original mutation occurred or by altering a nucleotide in a different codon/
How do intergenic suppressors work?
- a second mutation in another gene
- genes that cause the suppression of mutations in other genes= suppressor genes
Since intergenic suppressors are the result of a second mutation in another gene ...how do they effect the gene that has the mutation with which it effects?
- change the way in which the mRNA is red by tRNA
L> only suppresses the effects of one type of mutation
Intergenic suppression (non sense suppresors) are divided into three classes what are they?
- one class of tRNA adds a substitute for UAA
- one class adds a fake substitute aa for UAG
- one suppresses AUG