A level biology aqa topic 8

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 ?

1. Using reverse transcriptase
2. Using restriction endonuclease enzymes
3. 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)

1. Sample of dna is digested into fragments using restriction enzymes and separated using electrophoresis
2. 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
3. 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?

1. PCR is used to make dna fragments
2. Separation of dna fragments by gel electrophoresis
3. Analysis of genetic fingerprints

Explain the process of separating dna fragments by gel electrophoresis (3 steps)

1. Dna mixture is placed into a well in a slab of gel and covered with a buffer solution that conducts electricity
2. An electrical current is passed through the gel - dna fragments are negatively charged so they move towards the positive electrode at the far end
3. 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