D1.3 Mutation and gene editing Flashcards
what is a gene mutation
a change in the sequence of bases of a particular gene
when can gene mutations occur
they are more likely to occur at certain times in the cell cycle than other times
such as when DNA polymerase fails to proofread errors during replication
what are factors that can change the sequence of bases in DNA
ionising radiation
UV
Chemicals
what is a point mutation
a change in one base in the gene sequence
can change the amino acid being coded by the gene
what is substitution mutation
change of one base to a different base copied by incorrect copying of DNAw
what is insertion mutation
additional base/s are added to the DNA
What is deletion mutation
removal of a base/s from DNA
what are frameshift mutations
mutations in DNA where the number of nucleotides removed or inserted arent in a multiple of 3, leading to every codon afterwards to be read incorrectly during translation
happens due to deletions/insertions
what are nonsense mutations
codes for a stop codon meaning the rest of the code isn’t read
what is missense mutation
results in a different amino acid being coded for
what is a sense mutation
when the mutation has no effect due to degeneracy of the genetic code
what happens if the substitution occurs in a non coding region
the mutation may have a neutral effect on the proteome of the cell
what are single nucleotide polymorphisms
they are the result of base substitution mutations
what is the result of mutations
they increase the likelihoods of polypeptides not functioning properly
what is an example of an insertion mutation
Huntingtons disease
Explain Huntington’s disease
Insertions can result in repeating base sequences of three nucleotides, which lead to abnormal number of triplet repeat sequences
In huntington’s there is an abnormality in the HTT gene
A DNA segment (CAG trinucleotide repeat) is repeated multiple times in a row (10-35)
mutation leads to a higher number of these causing degenerative effects
what is the result of Huntington’s disease
neurodegenerative disease
progressive mental deterioration
involuntary muscle movements
Explain the delta 32 mutation in relation to HIV
the delta 32 mutation is a deletion mutation which prevents the production of CCR5 protein which is a receptor. Without this receptor, HIV finds it harder to bind to the cell and enter
people who have two copies of the mutation are less susceptible to infection
what is a mutagen
a factor capable of causing a mutation
explain ionising radiation as a mutagen
X rays and radiation can damage ions inside the nucleus leading to breakup of DNA
explain non ionising radiation as a mutagen
UV light
less penetrating but if absorbed, can cause adjacent bases on DNA strand to bind to each other instead of opposite base
explain bacterial infection as a mutagen
specific bacterial infections can trigger cancers
explain chemicals as a mutagen
can be carcinogenic. prolonged exposure to chemicals can trigger cancer
explain virus infection as a mutagen
specific infections that may trigger DNA mutations
some can insert part of the virus genome into the host and produce proteins that alter the cell cycle
leads to uncontrolled replication of cells
how is natural selection related to random mutation
is a process that selects features of favourable alleles that have been generated by random mutation
What is a transition substitution mutations
swaps between bases of similar shapes ( between purines or between pyrimidines)
they are less likely to affect the protein and usually dont have any phenotypic effects
what is a transversion substitution mutation
swaps between a purine and a pyrimidine base
what are possible reasons for ‘hot spots’ in mutations
variations in the superstructure of DNA
Regions where accessory proteins are less common, leading to an increased localised error that exceeds the correct rate
what are germ line mutations
mutations occurring in ovaries or testes
they give rise to mutated gametes resulting in inherited diseases
what happens to mutations in somatic cells
they are only passed to the immediate descendant of that cell, and disappear when organisms die
are mutations in somatic cells inheritable
they are not
but they may lead to cancer
how do changes in environment affect mutation and evolution
some individuals in a population may have a selective advantage with increased chance of survival, ultimately lead to changes in the gene pool of a species
what is gene knockout
it produces an organism with one non-functional gene, allowing researchers to investigate the function of that gene
what are examples of model organisms
mice, bacteria, plants
what makes the use of model organisms possible
universality of the genetic code and commonality of basic biological process performed by almost all living organisms
allows prediction of similar effects
how do prokaryotes defend themselves against infection
their response is based on a region of DNA sequences called CRISPR
what is CRISPR
Clustered regularly interspaced short palindromic repeats
sequences in the genome of some prokaryotes that act as a genomic record of a previous viral attack
what works alongside CRISPR
the Cas9 enzyme are bacterial endonuclease that form a double strand break in DNA at a specific target site within a larger recognition sequence
With both, bacteria uses the sequences to recognize and deactivate future invading viruses
what are the steps of CRISPR and Cas9
after bacteria is infected, CRISPR system used to cut up the invading viral DNA and insert pieces of it into their own genome as a memory
Bacteria transcribe the spacers into RNA, forming a complex with the Cas9 enzyme. They monitor the cell for any DNA sequence complementary to the RNA. When complementary DNA sequence is located, the Cas9 enzyme is activated
If matching DNA is encountered, the complex binds and cuts the viral DNA at specific locations to prevent it from replicating
what have scientists been able to do with CRISPR and Cas9
develop precise genome editing technology
Why is CRISPR so useful
due to its precision, there are many opportunities to modify any gene on interest with a reduced risk of accidentally affecting other genes
can be used to edit out gene defects
how can CRISPR be used to treat gene defects
by removing diseased cells, fix them using CRISPR and then return them to patients to treat the gene condition
How can CIRSPR be used to treat sickle cell anaemia
by editing a gene from bone marrow so cells would produce a certain type of haemoglobin
what are conserved genetic sequences
they are identical or similar sequences in nucleic acids across species or a group of species
they are a way of providing evidence about the structure and function of first life on earth
what are the hypotheses behind the mechanism for conserved sequences
functional requirement for the gene products
slower rates of mutation than the background mutation rate
what shows lower mutation rates than less expressed genes
highly transcribed genes
what can the impact of gene expression on mutation rate may be due to
enhanced proofreading and repair mechanisms for the section of DNA
where are highly conserved sequences contained
in non coding regions
