Studied by 15 people
What are 2 causes of tumour growth?
Abnormal methylation of dna Increased exposure to oestrogen
How can mutagenic agents increase the rate of mutation? ( 3 ways)
Acting as a base- chemicals called base analogs can substitute for a base Altering bases - some chemicals can delete or alter bases Changing the structure of dna - some types of radiation can change the structure of dna
What are acquired mutations ?
Mutations that occur in individual cells after fertilisation
What are the 2 types of gene that control cell division?
Tumour suppressor genes Photo-oncogenes
What do tumour suppressor genes do?
Slow cell division by producing proteins that stop cells dividing or cause them to self destruct
What do proto-oncogenes do?
Stimulate cell division by producing proteins that make cells divide
State 6 ways in which tumour cells differ from normal cells?
nucleus larger, darker sometimes more than one
irregular shape
don't produce all proteins needed to function
different antigens on surface
don't respond to growth regulated processes
divide by mitosis more frequently
What is methylation?
Adding methyl group
Why is methylation important?
It regulates gene expression - controls whether gene is transcribed and translated when happening normally
What does hypermethylation of tumour suppressor genes cause?
Genes are not transcribed so proteins are not produced
What does hypermethylation of protooncogenes cause?
Causes them to act as oncogenes
What are the 3 theories as to why increased exposure to oestrogen can increase risk of breast cancer?
can stimulate certain breast cells to divide and replicate
if cells do become cancerous rapid replication could be further assisted by it
is able to introduce mutations directly into the dna of breast cells
What are the risk factors for cancer?
Genetic factors - inherited alleles Environmental- radiation, smoking, alcohol, high fat diet
What would be useful for curing and treating cancer?
Knowing which specific mutations cause which cancers so treatment can be made to target them specifically
What are stem cells?
The unspecialized cells from which differentiated cells develop
Where are stem cells found?
Embryo And in some adult tissue ( where they become specialised cells that need to be replaced)
What are totipotent cells?
Cells that can mature into any type of body cell and occur only for a limited time in mammalian embryos
What are pluripotent cells?
Cells that can mature into any type of body cell except placental cells and occur in mammalian embryos
What are multipotent cells?
Present in adult mammals and are able to differentiate into a few different types of cell eg, red and white blood cells
What are unipotent cells?
Present in adult mammals , only differentiate into one type of cell eg skin cells
Why and how do stem cells become specialised?
They only transcribe and translate part of the dna - some genes expressed and other turned off in different conditions
What happens once a gene is expressed?
MRNA transcribes and translates into proteins, proteins modify the cell, cell becomes specialised for particular function
How are stem cells currently used in medicine?
In bone marrow transplants - contains stem cells which make healthy new blood cells for patient with leukaemia and lymphoma
What are the 3 sources of stem cells and how are they obtained?
Adult stem cells - from body tissue of adult Embryonic stem cells- from embryos at early stages of development Induced pluripotent stem cells (IPS) - created in lab , reprogramming adult cells so they become pluripotent
How can induced pluripotent stem cells be made?
By reprogramming specialised adult body cells so that they become pluripotent - adult cell can be infected with modified virus which infects cell so genes passed on to the dna so will be able to produce the transcription factors that are associated with pluripotent cells
What are transcription factors?
Protein molecules that control transcription of genes
In the nucleus, transcription factors bind to specific DNA sites called.....
Promotors
Where are promoters located?
Near start of target gene
what do activators do?
Stimulate or increase the rate of transcription - help RNA Polymerase bind to the start of target gene and activate transcription
What do repressors do?
Inhibit or decrease the rate of transcription eg they bind to start of target gene preventing RNA polymerase from binding
What is oestrogen and how does it affect expression of genes?
Steroid hormone that can affect transcription by binding to a transcription factor called an oestrogen receptor , forming an oestrogen-oestrigen receptor complex - this complex can act as an activator of transcription
What is RNAi and how does it affect gene expression?
RNA interface- small double stranded rna molecules stop mRNA from target genes being translated into proteins molecules involved are siRNA small interfacing or miRNA micro
How does siRNA work?
Double stranded siRNA Associates with several proteins in the cytoplasm and unwinds, one strand selected and other degraded, strand then binds to target mRNA by complementary base pairing and the proteins cut it into fragments , mRNA can no longer be translated and fragments are degraded in processing body
How is miRNA different to siRNA?
Instead of cutting mRNA into fragments the miRNA protein complex blocks the translation of the target mRNA then it is moved into processing body where it can be degraded or stored
What is epigenetics?
The study of environmental influences on gene expression that occur without a DNA change
What happens if epigenetic marks on DNA are not removed between generations?
Expressions of some genes in the offspring can be affected by environmental changes that affected their parents or grandparents
Where abouts do methyl groups attach to the dna?
At a CpG site which is where a cytosine and guanine base are next to eachother
How does increased methylation affect dna?
Changes structure so that the transcriptional machinery can't interact with the gene so the gene is not expressed
What are histones?
Proteins that dna wars around to form chromatin which makes up chromosomes
How can histones be epigenetically modified?
By the addition or removal of acetyl groups
When histones are acetylated, the chromatin is ............... condensed
Less
What happens when histones are acetylated?
Chromatin is less condensed so the transcriptional machinery can access the dna allowing genes to be transcribed
What happen when acetyl groups are removed from histones?
Chromatin becomes highly condensed, genes can't be transcribed because machinery can't access them
What are the enzymes responsible for removing acetyl groups from histones ?
Histone deacetylylase ( HDAC)
Are epigenetic changes reversible?
Yes
How can drugs be used to treat diseases that are caused by increased methylation and decreased acetylation?
drugs can be used to stop dna methylation - treats disease caused by this
HDAC inhibitor drugs can inhibit the enzyme responsible for decreased acetylation treating the diesease
What is the problem with using drugs to counteract epigenetic changes?
They need to be really specific or they could damage normal cells which could turn cancerous
How are twin studies useful?
Genetically identical so any differences in phenotype must be down to environmental factors
What are genome projects?
Where scientists work to determine the entire genome sequence of an organism.
What are the 3 methods for making dna fragments ?
Using reverse transcriptase
Using restriction endonuclease enzymes
Using gene machine
Explain dna probes
Short strands of dna that have specific base sequence that is complementary to the base sequence of part of the target allele so it will bind to the target allele if it's present in the dna sample . Probe has a label attached so that is can be detected
What are the 2 most common labels used on dna probes?
Fluorescent label- detected using uv light Radioactive label- detected using x Ray Film
Explain the process of using dna probes to locate certain alleles (3 steps)
Sample of dna is digested into fragments using restriction enzymes and separated using electrophoresis
Fragments are then transferred to nylon membrane and incubated with a fluorescently labelled dna probe- of allele is present the probe will bind to it
Membrane is exposed to uv light so if the gene is present there will be a fluorescent band
What are 3 uses of screening with dna probes?
to help identify inherited conditions
to help determine how a patient will respond to specific drugs
to help identify health risks
What is genetic fingerprinting?
Where the number of times a non coding sequence is repeated at different places in the genome is compared between individuals
What are the 3 steps in producing genetic fingerprints?
PCR is used to make dna fragments
Separation of dna fragments by gel electrophoresis
Analysis of genetic fingerprints
Explain the process of separating dna fragments by gel electrophoresis (3 steps)
Dna mixture is placed into a well in a slab of gel and covered with a buffer solution that conducts electricity
An electrical current is passed through the gel - dna fragments are negatively charged so they move towards the positive electrode at the far end
Shorter dna fragments move faster and travel further through the gel so the fragments separate according to length producing a pattern of bands
Explain the analysis and comparison of genetic fingerprints
Equipment is turned off and gel is placed under a uv light - dna fragments can be seen by bands , these bands then make up the genetic fingerprint If both fingerprints have a band at the same location it means they have the same number of VNTRs at the place so it's a match
What are 5 uses of genetic fingerprinting?
determining genetic relationships
determining genetic variability within a population
in forensic science
medical diagnosis
animal and plant breeding
How could you use genetic engineering to determine genetic relationships? (3)
we inherit VNTRs from parents so more bands that match the more closely related
look at much wider relationships to see what descended from where
look at all female side - using dna from mitochondrial only . Male side- look at Y chromosome dna only
Note
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