BIO 190- Ch#13 Mutation and DNA repair

what did Lederbergs experiments show us

that mutations are random events that happen before exposure to the virus

what comes before a mutation

damage comes first, if the damage is not repaired then there is a mutation

(but damages are OFTEN repaired)

what does it mean by mutations are spontaneous

hey occur naturally and randomly, without any outside influence like radiation or chemicals

describe this spontaneous mutation :errors in DNA replication

an un repaired mistake by DNA polymerase may cause a point mutation

describe this spontaneous mutation: toxic metabolic products

the products of normal metabolic processes may be reactive chemicals that alter the structure of DNA

describe this spontaneous mutation: changes in nucleotide structure

on rare occasions the linkage between purines and deoxyribose can spontaneously break changes in base structure may cause mis pairing DNA replication

what are induced mutations

mutation caused by an external factor, often called a mutagen. These mutations do not happen randomly—they result from exposure to something in the environment that damages DNA.

name and describe 2 induced mutations

chemical agents: chemical substances such as those found in cigarette smoke that may cause changes in DNA structure

physical agents: such as UV light and X rays that damage DNA

what are 2 ways mutations may occur

- if the DNA polymerase tasked with repair inserts the wrong nucleotide

- if damage is not repaired but DNA replication continues anyways

when DNA is damaged there is no mutation if repaired but there is a mutation if....

DNA polymerase inserts the wrong nuclotides

why does UV light cause mutations

it disturbs hydrogen bonds

how do do x rays cause mutations

they can break chromosomes, these broken chromosomes can be repaired correctly or incorrectly

list the 3 types of point mutations

base substitution, insertion, deletion

what is a point mutation

affects only a single base pair within the DNA

What is base substitution?

a type of point mutation that involves a change where one base is replaced by another

ex: T in top strand is replaced with G and the bottom A strand was replaced with C

what is insertion or deletion

a type of point mutation where a single base pair can be added or deleted

ex: a single base pair (A-T) has been added to the sequence

what are 3 effects on polypeptides that come from base substitutions

silent, missence, and nonsense

what is a silent mutation

causes no change

the third position of the codon on the genetic code had redundancy so it encodes the same protein

What is a missense mutation?

changes one amino acid in the polypeptide

changes a amino acid but does not mean it changes the ultimate protein function

what is a nonsense mutation

changed a normal codon to a stop codon and shortens the polypeptide

the addition or deletion of a single nucleotide causes what type of effect on the polypeptide

frameshift

what is a frameshift mutation

produces a different amino acid sequence

there is a totally different downstream of proteins that will most likely affect the protein function (unless it happens on the intron which is cleared out)

how might is a mutation that occurs on the promotor influence gene expression

may increase or decrease the rate of transcription

how might is a mutation that occurs on the transcriptional regulatory element/operator site influence gene expression

may later the regulation of transcription

how might a mutation that occurs on the splice sites influence gene expression

may alter the ability of pre-mRNA to be properly spliced

how might a mutation that occurs on the translational regulatory element influence gene expression

may alter the ability of mRNA to be translationally regulated

how might a mutation that occurs on intergenic region influence gene expression

intergenic region= in between genes

not likely to affect gene expression

describe a germ line mutation

If a mutation occurs in the DNA of a sperm cell and that sperm fertilizes an egg

the embryo will carry the mutation in all of its cells—including its own sperm or eggs—making it 50/50 possible to pass the mutation on again

describe somatic cell mutation

Not inherited: Somatic mutations cannot be passed to offspring because they don't occur in reproductive cells.

🧫 Affect only part of the organism: Since the mutation happens in one cell, only the cells that descend from it will carry the mutation (this is called a mosaic effect).

what is nucleotide excision repair (NER)

the most common DNA repair system it is found in all eukaryotes and prokaryotes

describe what each does in nucleotide excision repair (NER)

thymine dimer: DNA distortion from UV light

UvrA:

UvrB:

UvrC:

UvrD

DNA polymerase:

UvrA: A+B track along DNA and search for damaged DNA

UvrB: A+B track along DNA and search for damaged DNA

UvrA is released and UvrC bind to UvrB

UvrC: makes a cut on both sides of the thymine dimer

*UvrC is released and UvrD a helicase binds to UvrB then UvrB is released

UvrD: removes the damage region

DNA polymerase: fills the gap and DNA ligase seals the new strand to the original

where do mutations happen

in the DNA

ex: during replication an A-T base pair in a gene is changed to a G-C base pair

Label the following as spontaneous or induced DNA damage

errors in DNA replication:

product of cellular reaction alters DNA structure:

UV light promotes thymine dimer:

X rays cause chromosome break:

covalent bond between a purine and ribose break in a nucleotide:

errors in DNA replication: spontaneous

product of cellular reaction alters DNA structure:spontaneous

UV light promotes thymine dimer: induced DNA damage

X rays cause chromosome break: induced DNA damage

covalent bond between a purine and ribose break in a nucleotide:spontaneous

you are examining a protein produced by two unique strains of virulent bacteria and notice much less of this protein produced in strain A versus strain B the amino acid sequences of the proteins are also different by one amino acid. what does this suggest about possible mutations ?

there is a mutational difference in both the promotor and in the coding sequence of the gene when comparing the two strains

a mutation changes a alanine codon into a valine codon what type of mutation is this

missense mutation

a key difference between germ line and somatic mutations is that

only germ line mutations can be passed to the offspring

a spontaneous mutation is

caused by a abnormality in the biological sequence

mutagens can cause mutations by

chemically altering the DNA molecule

what do UrvA,UrvB, UrvC, and UrvD do

detect irregularity in DNA structure and remove a segment of the DNA strand completely

one gene encodes a protein 1000 amino acids long and the other encodes one that is 1350 amino acids long . what is the mutation

missense mutation at the stop codon

when you burn your tongue what happens to your taste receptor

they are denatured before the the cell makes more

how many amino acids in a protein can be changed by a single nucleotide insertion mutation that causes a frameshift

all of the amino acids starting at the site of insertion