3.8.1 genes Flashcards
alteration of the sequences of bases in dna
what are the different types of mutations?
addition, deletion, substitution, inversion, duplication and translocation.
how do gene mutations occur
spontaneously
what is a gene mutation
a change in the sequence or structure of base pairs in DNA that can alter the structure of proteins
what is a mutagenic agent?
a physical or chemical factor that increases the mutation rate, eg radiation exposure, alcohol etc
why is it important that dna is proofread and when does it occur
to stop mistakes being made during the cell cycle and occurs during the s phase of dna replication
explain what degenerate means
more than one codon can code for each amino acid
explain a positive effect of mutations
they can increase survival and reproduction rate compared to others in their species
what is a substitution mutation
one or more bases are swapped for another (eg. CGG to GGG)
what is a deletion mutation
one or more bases are removed causing a frameshift
what is an addition mutation
one or more bases are added causing a frameshift
what is a duplication mutation
one or more bases are repeated
what is an inversion mutation
a sequence of bases is reversed (eg. 2315 to 5132)
what is a translocation mutation
a piece of one chromosome breaks of and reattaches to another chromosome
what types of mutation are most likely to have no amino acid change and why
inversion and substitution because they only change one base and due to degenerate nature it could code for the same amino acid
explain what a frameshift mutation does
they change the number of bases in dna code so all codons that follow shift and sre changed so dna is transcribed different
what name is used for the non coding sections of a gene
introns
explain how deletion/ addition mutations can lead to a non-functional protein/enzyme
mutation changes base sequence in dna which causes a frameshift in amino acid sequence so tertiary structure of protein can change and enzyme substrate complexes may not be able to form.
what is a silent mutation
a change in the nucleotide sequence that results in the same amino acid sequence.
explain the effect of a frameshift mutation
can cause a non-functioning polypeptide. change in the base sequence can change the tertiary structure of a protein. if its an enzyme, active site can change so ES complexes can no longer form.
what is a stem cell
an undifferentiated cell that continually divides
what is a totipotent cell
can differentiate into any type of body cell. available for a limited time in embryo cells
what is a pluripotent cell
can differentiate into any type of cell. found in embryos fromday 4-16
how does a cell become specialised
only translates part of their DNA
what is a multipotent cell
can differentiate into a limited number of cells
whats a unipotent cell
can only differentiate into one type of cell
where are adult stem cells found
bone marrow
suggest why its better to use IPS cells than pluripotent cells
they are adult somatic cells manipulated to express TF that are usually expressed by pluripotent cells without destroying the embryo. no cloning, no risk of rejection.
what is a genome
total number of genes in DNA in an organism
explain why antibody binds to transcription factor
antibody is complimentary to specific tertiary strcuture
what is a transcription factor
a protein that binds to DNA at promoter region, preventing or allowing transcription
why is oestrogen a transcription factor
diffuses through membrane to nucleus. attaches to oestrogen receptor to form a complex which changes tertiary structure. it then binds to promoter region to increase transcription and allow rna polymerase to bind
oestrogen only affects target cells. explain why
not all cells have specific oestrogen receptors
what is oestrogen
lipid soluble steroid hormone
define epigenetics
heritable changes in gene function that dont change DNA base sequence
what is a epigenome
single layer of chemical tags on the DNA
what is methylation of DNA
addition of a methyl group to cytosine. causes coiling and prevents TF and enzymes from binding so genes are turned off
what is acetylation
addition of an acetyl group on histones. DNA and acetyl are both negatively charged so repel so DNA loosens making DNA more accessible for TF to bind so transcription can occur
what is siRNA
a small, double stranded molecule that binds to mrna. it has complimentary bases to mrna
how does sirna prevent transcription
binds to mrna by complimentary base pairing and cuts mrna which stops translation
how can hypermethylation lead to cancer (epigenetics)
causes DNA to coil so TF and rna polymerase cannot access dna so tumour suppressor cannot be transcribed to produce protein that slows cell division leading to tumour.
what does a tumour suppressor gene do
codes for a protein that slows cell division and regulates mitosis
give an example of a TSG
BRCA-1
what are proto-oncogenes
produce a protein that stimulates cells to divide
what is hyperacetylation
causes DNA to loosen which can lead to overexpression. they can mutate to become oncogenes or can lead to cancer due to uncontrllable cell division
what are oncogenes
mutated genes that cause cancer by causing proteins that stimulate cell division to be constantly activated. cell cycle is sped up
how do oncogenes occur
random mutations or due to carcinogens such as exposure to UV
what is cancer
uncontrollable cell division
how can mutations cause cancer
change base sequence of DNA causing a non functional protein which can lead to uncontrollable cell division
whats the difference between benign and malignant
benign: non cancerous, slow growing, doesnt spread to other parts of the body
malignant: cancerous, fast growing, spread to other parts of the body
what is metastasis
when tumours break off and spread to other parts of the body and can develop their own blood supply and oxygen.
how can tumours cause harm to the body
put pressure on organs. could damage organs. can cause blockages
what is an activator
helps rna polymerase bind at the promoter region to allow transcription
what is a repressor
binds to promoter region and prevents rna polymerase from binding
wat is an inhibitor molecule
can bind to TF, preventing it from binding to promoter region
not all mutations result in a change in the amino acid of the encoded polypeptide. why
degenerate code. mutation in intron
how can a mutation in the tumour suppressor gene result in a tumour
mutation causes gene to be inactivated so doesnt produce protein to slow down cell division which leads to uncontrollable cell division.
