The control of gene expression Flashcards
1
Q
Describe what mutagenic agents are used for
A
To increase the rate of mutation e.g. benzene, X-rays
2
Q
Describe why not all base substitutions cause a change in encoded amino acids
A
Due to the degeneracy of the genetic code, which means the new base triplet will code for the same amino acid
3
Q
Describe why some mutations cause a non-functional protein to be produced
A
Results in frame shift - alteration in base triplets in point of mutation e.g. addition
The sequence of amino acids is altered from the point of mutation and the protein formed is functional
4
Q
Describe what is meant by gene mutations and the different types
A
Gene mutations are changes in the sequence of nucleotide bases in the DNA
Substitution = replacement of one or more bases by one or more different bases
Deletion = removal of one or more bases
Addition = adding of one or more bases
Duplication = where one or more bases is repeated
Translocation = where a sequence of bases is moved from one location in the DNA molecule to another part of the genome.
Inversion = where a sequence of bases is reversed
6
Q
Describe the role of increased oestrogen concentrations in the development of some breast cancers
A
- Areas of high oestrogen concentration (such as body fat tissues in breasts) cause uncontrollable cell division
- Growth of cancer is minimised with drugs that block production/action of oestrogens in the breasts (e.g. Tamoxifen prevents oestrogen binding to receptor)
7
Q
Describe the role of tumour suppressor genes in the development of tumours
A
- Mutation of this gene (this gene codes for the proteins involved in the slowing down of cell division) inactivates the gene so it is not transcribed which results in rapid uncontrollable cell division.
- This results in rapid uncontrollable cell division
- Increased methylation causes these genes to not be transcribed
- The proteins which slow down cell division are not produced leading to uncontrolled cell division and the development of a tumour.
8
Q
Describe the role of proto-oncogenes in the development of tumours
A
- Mutation of this gene (this gene codes for the proteins involved in the control of cell division) can stimulate cells to divide too quickly
- This results in rapid uncontrollable cell division
Decreased methylation causes these genes to be continually transcribed - This increases production of proteins involved in stimulating cell division - which leads to rapid, uncontrolled cell division and the development of a tumour
9
Q
Describe the regulation of translation with RNA interference (RNAi)
A
- RNA interference (RNAi) = RNA molecules that inhibit translation of mRNA produced by transcription by either siRNA (single RNA strand) or miRNA (double RNA strand)
- miRNA/siRNA within a RISC (RNA-induced silencing complex) binds to a molecule of mRNA containing a sequence of bases complementary to its own which causes mRNA to be hydrolysed / translation stopped
10
Q
Describe relevance of epigenetics on disease development and treatment
A
- Epigenetic changes that increase the expression of an oncogene, or that silence a tumour suppressor gene, can lead to tumour development
- Tests can be used to see if a patient has abnormal levels of methyl and acetyl – early indicator of cancer (called a biomarker)
- Could be manipulated to treat cancer i.e. drugs to prevent histone acetylation / DNA methylation that may have caused these genes to be switched on/off
11
Q
Describe the decreased acetylation of histones to inhibit transcription
A
- Decreased acetylation of associated histones
This causes the chromatin to become highly condensed. - Histones bind DNA more tightly which prevents transcription factors binding and genes are not transcribed
- Reversible
12
Q
Describe the increased methylation of DNA to inhibit transcription
A
- Methyl groups added to cytosine bases in DNA
- Nucleosomes pack more tightly together and prevents transcription factors binding and genes not transcribed (RNA polymerase can’t bind)
- Irreversible
13
Q
Describe what is meant by epigenetics
A
Heritable changes in gene function (expression) without changes to the base sequence of DNA, caused by changes in the environment
14
Q
Describe the role of oestrogen in initiating transcription
A
- Oestrogen diffuse across phospholipid bilayer of cell surface membrane
- In cytoplasm, oestrogen binds to a receptor of an inactive transcription factor
- Inactive transcription factor changes shape, resulting in activation of transcription factor
- Diffuses from cytoplasm into nucleus and binds to specific DNA base sequence on a promotor region
- Stimulates transcription of genes by helping RNA polymerase to bind
15
Q
Describe the regulation of transcription using transcription factors
A
- Transcription factors are proteins
- Move from cytoplasm to nucleus to bind to DNA at a specific DNA base sequence on a promotor region
- Stimulate or inhibit transcription of target genes by helping/preventing RNA polymerase (and therefore, promoting or demoting gene expression)
16
Q
Describes the arguments against the use of embryonic stem cells
A
- Embryo is a potential human - ethical consideration
- Induced pluripotent cells can not yet reliably be reprogrammed to produce stem cells - can cause tumours if divide uncontrollably
17
Q
Describes the arguments for the use of embryonic stem cells
A
- They are seen as tiny balls of cells, incapable of feeling pain and therefore, not equivalent to humans
- They would otherwise be destroyed (for methods such as IVF which produce more than needed)
18
Q
Describe the production and features of induced pluripotent stem cells
A
- Produced from adult somatic cells (non-pluripotent cells) and specific protein transcription factors, which cause the cell to express the genes associated with pluripotency
- Used in medical treatment instead of embryonic cells
- there is no immune rejection as they can be made using patient’s own cells
- overcomes some ethical issues with using embryonic stem cells e.g. no destruction of embryo and adults can give permission
19
Q
Describe features of unipotent cells
A
- Found in mature mammals
Can divide and differentiate into just one cell type - Exam board example: cardiomyocytes (cardiac muscle cells) can be made from unipotent stem cells
20
Q
Describe features of multi-potent cells
A
- Found in mature mammals
- Can divide and differentiate into a limited number of cell types
21
Q
Describe features of pluripotent cells
A
- Found in embryos
- Can divide and differentiate into most cell types (every cell type in the body excluding cells from placenta)
22
Q
Describe features of totipotent cells
A
- Occur for a limited time in early embryos
- Can divide and differentiate into every cell type in body (including cells that support embryo e.g. placenta)
23
Q
Describe sequencing projects in complex organisms
A
- Knowledge of the genome cannot easily be translated into the proteome
- Due to the presence of non-coding DNA and regulatory genes (which determine when the genes that code for particular proteins should be switched on and off)
- Human Genome Project – this database determined the sequence of bases of a human genome
24
Q
Describe sequencing projects in simpler organisms
A
- Determining the genome of simpler organisms, allows the assignment of proteins to each gene in the genome (this is called the proteome), creating a database
- This is much easier than larger organisms because there is less non-coding DNA
- Identifying the antigens on the surface of viruses/pathogenic bacteria can help in the development of vaccines
25
Q
Describe sequencing projects
A
Sequencing projects have read the genomes of a range of organisms (e.g. The Human Genome Project)
In the past, they were labour intensive, expensive and could only be done on a small scale
Now, we use automated processes that are more cost effective and can be done on a large scale
26
Describe how you could estimate size of DNA fragments with gel electrophoresis
Carry out the process on DNA fragments of known lengths
Compare the length to position of unknown fragments
27
Describe the uses of genetic fingerprinting in animal and plant breeding
- Shows how closely related two individuals are, so that inbreeding can be avoided
- Select pairs with dissimilar genetic fingerprints
28
Describe the uses of genetic fingerprinting in medical diagnosis
- Useful when specific mutation not known or several could have caused disorder
- Identifies a broader altered genetic pattern, ie a risk factor
29
Describe the uses of genetic fingerprinting in identifying genetic relationships
- More closely related = more similar VNTRs = more similarities in genetic fingerprints
- Paternity testing - father should share around half of VNTRs/bands and ones that don't come from mother must be from father
30
Describe the principles of gel electrophoresis
- Load DNA samples into wells in porous gel and cover them in a buffer solution which conducts electricity
- Pass electrical current through - - DNA is negatively charged so moves towards positive electrode
- Shorter DNA fragments travel faster so travel further
31
Describe variable number tandem repeats (VNTRs)
- Repeating sequences of nucleotides/bases found within non-coding sections of DNA at many sites throughout the genome
- Allow production of a virtually unique genetic fingerprint as the probability of two individuals having the same VNTRs is very low
32
Describe personalised medicine
- Medicine tailored to an individual's genotype/DNA with the use of genetic screening
- Increases effectiveness of treatment eg. identifying particular mutation/allele causing cancer which will allow you to treat with specific drugs you know will be effective for the patient
33
Describe the role of a genetic counsellor
- Explains the results of screening/consequences of a disease
- Discusses treatments available for genetic condition
- Discusses lifestyle choices/precautions that might reduce the risk of a genetic condition developing (eg. regular screening for tumours)
- Explain probability of condition/alleles being passed onto offspring which would enable patients to make an informed decision about having children
34
Describe the examples of the uses of genetic screening
- Screening patients for heritable condition e.g. finding out if they are a carrier to a disease such as cystic fibrosis
- Screening patients for drug responses i.e. how their body will respond to certain drugs
- Screening patients for health risks e.g. for alleles that may indicate a risk to high blood cholesterol levels / chance of breast cancer
35
Describe the process of genetic screening
- Extract DNA and amplify by PCR - restriction enzymes cut DNA at specific base sequences
- Separate fragments by gel electrophoresis according to their length and transfer them to a nylon membrane and treat them to form single strands with exposed bases
- Labelled DNA probe will hybridise (join) with its target allele (then wash to remove unbound probe)
- To show the bound probe you can either expose membrane to UV light (if fluorescently labelled probes are used) or use autoradiography (if radioactive probes are used)
36
Describe the drawbacks of recombinant DNA technology
- GM crops can have an effect on food webs which reduces biodiversity
- Gene therapy long term effect not known - side effects eg. could cause cancer
37
Describe the benefits of recombinant DNA technology
- GM crops increase yield - this increases global food production which combats risk of malnutrition
- Gene therapy has potential to cure many genetic disorders
- Production of pharmaceutical drugs is cheaper
38
Describe the uses of restriction endonuclease in the in-vivo method
- The transfer of DNA fragments from one organism or species, to another
- Transferred DNA can be transcribed/translated into proteins within cells of the recipient (transgenic) organism since the genetic code is universal
39
Describe the role of promoter and terminator regions in the in-vivo method to amplify DNA fragments
Promoter regions tell the RNA polymerase when to start transcription to produce mRNA
Terminator regions tell the RNA polymerase when to stop
40
Describe how fragments of DNA can be produced by using a gene machine
Synthesises fragments of DNA from scratch without the need for a pre-existing DNA template - DNA fragments are therefore produced quickly and accurately without introns
41
Describe how fragments of DNA can be produced by using restriction enzymes to cut a fragment containing the desired gene from DNA
- Different restriction endonucleases cut DNA at specific sequences of bases called a ‘recognition sequence’ - shape of recognition site is complementary to active site
- Some restriction enzymes cut in a staggered fashion and ‘sticky ends’ are formed
42
Describe how fragments of DNA can be produced by conversion of mRNA to complementary DNA (cDNA)
- mRNA isolated from a cell that readily synthesises the protein coded for by the desired gene
- Mix the mRNA with DNA nucleotides and reverse transcriptase - reverse transcriptase will use mRNA as a template to synthesise a single strand of cDNA
- DNA polymerase forms a second strand of DNA (double stranded = gene) using cDNA as a template
43
Describe the basics of recombinant DNA technology
- The transfer of DNA fragments from one organism or species, to another
- Transferred DNA can be transcribed / translated into proteins within cells of the recipient (transgenic) organism since the genetic code is universal
44
