the control of gene expression Flashcards
Give six examples of gene mutations
Substitution Deletion Addition Duplication Inversion Translocation
What effects do mutagenic agents have on the rate of mutation
Increase
What can mutations result in
A change in the sequence of amino acids
When mutations only change one codon, why does this sometimes have no effect on the polypeptide coded for
DNA code is degenerate
What is a frame shift
When a mutation causes all the amino acids after the site of mutation to change
What are base analogues
A chemical that can substitute for base in DNA
What are totipotent cells
Cells that can specialise into any type of body cell
What are pluripotent cells
Cells that specialise into any type of body cell, except placental cells.
What are multipotent/unipotent cells
Multipotent Cells can become more than one cell type eg adult stem cells
Unipotent - specialised, can only become one type of cell eg epidermal skin cells
What causes cell specialisation
Only part of the DNA is transcribed and translated
how often can pluripotent cells divide
unlimited number of times
How are unipotent cells involved in the heart
The heart has a supply which are used for repair (Cardiomyocyte)
How are iPS cells created in the lab
Scientist take specialised adult cells and “reprogram” them to express transcription factors normally associated with pluripotent stem cells
What is the name of the site at which activators and repressors bind
promotor sites
How do Activators effect RNA polymerase binding
they make it easier
How do repressors effect RNA polymerase binding
they make it more difficult/stop it happening
What type of transcription factor is oestrogen
Activator
Give two examples of epigenetic control of gene expression and briefly outline each
Increased Methylation - Methyl group attaches to CpG site. This changes DNA structure so the gene is not expressed.
Decreased Acylation - when histone proteins are acylated it is easier for the DNA to be transcribed and the genes to be expressed. Less acylation means the DA is more tightly bound and thus it is harder for the DNA to be transcribed
Can epigenetic changes be passed to offspring
Yes
What causes epigenetic changes to DNA
Environmental factors
Disease
How does an error in epigenetic control of gene expression link to cancer
Abnormal methylation of tumour suppressor genes/protooncogenes prevents them from functioning as they should and allows uncontrolled cell division
Why are epigenetic causes of disease a good target for drugs
They are reversible
What is the role of RNAi
RNAi prevents m RNA strands from being translated into proteins. It does this by physically blocking translation, before moving the mRNA to a processing body to be degraded or stored
Where in cells does RNAi target the mRNA
Cytoplasm
What is a tumour
A mass of abnormal cells
What do tumour suppressor genes and protooncogenes both do
Tumour suppressor genes produce a tumour suppressor protein that prevents cell division or causes apoptosis.
Protooncogenes produces a protein that enables cells to divide at a controlled rate
if a mutation occurs in the protooncogene, what happens
The gene becomes over active and produces lots of proteins that cause uncontrolled cell division
What is a mutated protooncogene called
A mutated protooncogene is called an Oncogene
What are the differences between malignant and benign tumours
Malignant tumours are cancerous, grow rapidly and invade surrounding tissue. Cells can break off and spread through the body
If the tumour suppressor genes become hyper methylated, what happens and how does this link to tumour formation
The genes that code for tumour suppressor protein are not transcribed. This means cells division increases
Give two theories as to how increased oestrogen levels link to breast cancer
It stimulates breast cells to divide. More divisions mean more chance of cancerous cells forming. oestrogen may be able to induce mutations directly in cells
How does sequencing the proteome of pathogens help with the formation of vaccines
It allows identification of the antigens on the pathogens surface
Why is it harder to determine the proteome of humans than of bacteria
Humans have introns and regulatory genes
What feature of the genetic code, as well as transcription and translation mechanisms means that recombinant DNA technology only requires the transfer of DNA fragments
They are universal
Give three methods of manufacturing DNA fragments
Using reverse transcriptase
Using restriction endonuclease enzymes
using a gene machine
What enzymes cut DNA strands and leave sticky ends
restriction endonuclease
Why is it beneficial for DNA strands to have sticky ends
To enable them to be inserted into a complementary section of a vector
What is the difference between in Vivo and in vitro gene cloning
In vivo cloning is where copies of the DNA fragment are made inside a living organism. This is done by transforming the host cell and then identifying the host cells which have taken up the DNA.
In Vitro uses the Polymerase Chain Reaction to make millions of copies in just a few hours
What is a vector
Something used to transfer DNA into a cell
Give two examples of vectors
Plasmids
Bacteriophages
Name the enzyme used to stick the DNA fragment to the vector DNA
DNA ligase
Outline a method for identifying which cells have taken up a vector and its DNA
Insert a marker gene for GFP into the vector DNA. Transformed bacteria will possess the green florescent protein and subsequently will glow florescent green
Why are promotor and terminator regions added to the DNA of vectors
To allow the transformed host cells to produce proteins coded for by the DNA fragment
Outline the polymerase chain reaction
A mixture is set up containing DNA sample, free nucleotides, primers and DNA polymerase.
heated to 95 degrees C to break the hydrogen bonds between the DNA strands cooled to 50-60 degrees C so primers can bind.
The mix is heated to 72 degrees C so DNA polymerase can line up free nucleotides alongside the template and form new complementary strands
2 new copies of the fragment of DNA are formed and one cycle of PCR is complete
Give a benefit of transformed organisms in agriculture
Increased crop yield
Crops produce more vitamins/nutrients
What is the difference between somatic and germ line gene therapy
Germ line is done on sex cells. This means every cell of any offspring produced from these cells will be affected and they will NOT suffer from the disease. This is currently illegal in humans
Somatic is done on adult cells particularly targeting the cells that are most affected by the disorder. Eg cystic fibrosis is damaging to the respiratory system so somatic therapy for CF targets the epithelial cells lining the lungs. This therapy does not affect the sex cells so any offspring could still inherit the disease
If a disease is caused by a dominant allele, how would you use recombinant DNA technology to prevent it being expressed
Insert “junk” DNA into the dominant allele to prevent it form functioning
What are DNA probes
Short strands of DNA. They have a specific base sequence that is complementary to the base sequence of part of the target allele so can be used to locate specific alleles of genes eg on chromosomes
What is attached to a DNA probes
A label
List 3 uses of screening with DNA probes
Identify inherited conditions
determine how a patient will respond to drugs
Identify health risks
What is a VNTR
A non-coding base sequence that repeats over and over
Why do different VNTRs travel different distances in gel electrophoresis
Longer ones are heavier and so travel less distance
List two uses of genetic fingerprints
Determining who the father of a child is
identifying if a person committed a crime
Name the steps involved in In Vivo amplification
Copies are made inside a living organism
1) The DNA fragment is inserted into a vector
2) The vector transfers the DNA fragment into Host Cells
3) identifying transformed host cells (only 5% host cells take up vector /dna so important. Markers are antibiotic resistance or flurescence
How does In Vitro amplification work
Done outside a living organism using the polymerase chain reaction
How much dna is made during each PCR cycle
Each cycle doubles the amount made ie 1st 2x2=4 dna fragments. 2nd 4 x2 = 8 dna fragments etc
If a disease is caused by two mutated recessive alleles how do you alter the genes using gene therapy
You add a working dominant allele to make up for them - you supplement the faulty ones
Give examples of how DNA probes are used in screening
Inherited conditions - Huntington’s disease or cystic fibrosis
Determine how a patient will respond to drugs - breast cancer caused solely by mutation in HER2 protooncogene can be treated with Herceptin
Helps identify health risks - which helps people make informed choices that could reduce the risk of them developing the disease
Ethical problems with screening using DNA probes
It might lead to discrimination by insurance companies or employers if people are know to have a high risk of developing a condition
What is a primer
A short piece of DNA that is complementary to the base at the start of the fragment you want
How might using recombinant DNA technology benefit people
1) Agricultural crops could be produced more efficiently to reduce the risk of famine - drought resistant
2) Transformed crops could be used to produce useful pharmaceutical products eg vaccines available in areas where refrigeration’s (usually needed to store vaccines is not available)
3) medicines could be produced more cheaply and in large quantities and without using animals eg insulin used to come from animals but now human insulin is made using a cloned human insulin gene
4) it has the potential to treat human diseases using gene therapy
What are some of the concerns about using recombinant DNA technology in agriculture
monoculture - where a farmers only plants one type of crop making them vulnerable to the same disease as all the plants are genetically identical.
Reduction in biodiversity
Possibility of super weeds if transformed crops interbreed with wild plants
Contamination of organic crops by wind blown seeds which would mean organic farmers would not be able to sell their crops
What are some of the concerns about using recombinant DNA technology in Industry
A few large biotech firms control some forms of genetic engineering. As the use of this technology increases these companies get bigger making it harder for small companies to compete. Anti globalisation protesters think this is bad
Without proper labelling consumers may not have a choice as to whether or not they eat GM food
What are some of the concerns about using recombinant DNA technology in medicine
Companies who own genetic engineering technologies may limit the use of technologies that could be saving lives
Some people worry that this technology could be used unethically eg making designer babies - currently illegal.
What does VNTR stand for
Variable number tandem repeats
What is a VNTR
Base sequences that don’t code for proteins and repeat over and over
The number of times a persons VNTR sequences repeats is unique, how does this relate to nucleotides
The length of these sequences in nucleotides differs too
What is a genetic fingerprint
A unique way of identifying someone using patterns in their DNA from VNTR
How to make a genetic fingerprint (simple)
Sample of dna taken PCR used to produce DNA fragments Fluorescent tag added DNA fragments undergo electrophoresis DNA fragments are then viewed as bands under UV light
Define Electrophoresis
Separates DNA Fragments to make a genetic fingerprint
Steps of electrophoresis
DNA mixture is placed into a well in a slab of gel and covered in 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 of the gel
Small DNA fragments move faster and travel further through the gel so the DNA fragments separate according to size
Are DNA fragments positively or negatively charged
Negative
