8: The control of Gene expression & Gene Tech Flashcards
(38 cards)
Explain how cells produced from stem cells can have the same genes yet be of different types.
- {not all / different} genes are switched {on / off} /active / activated ;
- correct and appropriate reference to factors /mechanisms for gene switching ;
- e.g. reference to promoters / transcription factors
Explain what is meant by the terms totipotent and pluripotent.
- totipotent cells can give rise to a complete human/**all cell types **;
- pluripotent can only give some cell types;
Define epigenetics
- Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.
State two mutagenic agents.
Physical:
* high energy radiation /ionising particles e.g. named particles/α, β, γ & X-rays;
* x rays/cosmic rays;
* UV (light);
Chemical
* benzene;
* Carcinogen / named carcinogen;
* mustard gas / phenols / tar (qualified)
Biological:
* Named virus (HPV, HBV)
* Named bacterium (H. pylori, S. bovis)
Describe how a deletion mutation alters the structure of a gene. [2]
- removal of one or more bases/nucleotide;
- frameshift/(from point of mutation) base sequence change;
Describe how altered DNA may lead to cancer. [5]
- (DNA altered by) mutation;
- (mutation) changes base sequence;
- of gene controlling cell growth / oncogene / that monitors cell division;
- of tumour suppressor gene;
- change protein structure / non-functional protein / protein not formed;
- (tumour suppressor genes) produce proteins that inhibit cell division;
- mitosis;
- uncontrolled / rapid / abnormal (cell division);
- malignant tumour;
Describe what is meant by a malignant tumour. [4]
- mass of undifferentiated / unspecialised / totipotent cells;
- uncontrolled cell division;
- metastasis / (cells break off and) form new tumours /
- spread to other parts of body;
Explain why fragments of DNA from cancer cells may be present in blood plasma.
*Cancer cells die / break open releasing DNA;
Explain how the methylation of tumour suppressor genes can lead to cancer. [3]
- Methylation (of DNA) prevents transcription of gene;
- Protein not produced that prevents cell division / causes cell death / apoptosis;
- No control of mitosis.
Describe how alterations to tumour suppressor genes can lead to the development of tumours. (4)
- (Increased) methylation (of tumour suppressor genes);
- Mutation (in tumour suppressor genes);
- Tumour suppressor genes are not transcribed / expressed
**OR ** - Amino acid sequence/primary/ tertiary structure altered;
- (Results in) rapid/uncontrollable cell division;
Describe the mechanism by which a signal protein causes the synthesis of mRNA. [6]
- signal protein {binds to / joins to / interacts with / activates}
- receptor on surface membrane;
- messenger molecule moves from cytoplasm and enters nucleus;
- {produces / activates} transcription factor;
- binds to promoter region;
- RNA polymerase transcribes target gene;
Explain how oestrogen enables RNA polymerase to transcribe its target gene. [6]
- Oestrogen diffuses through the cell surface membrane and nuclear envolope (lipid soluble);
- attaches to ERα receptor;
- ERα receptor changes shape;
- ERα receptor leaves protein complex which inhibited it’s action;
- oestrogen receptor binds to promoter region;
- enables RNA polymerase to transcribe target gene.
Compare the structure of dsRNA and DNA. [4]
Similarities; 2 max
* Polynucleotides/polymer of nucleotides;
* Contain Adenine, Guanine, Cytosine;
* Have pentose sugar/5 carbon sugar;
* Double stranded/hydrogen bonds/base pairs.
Differences; 2 max
* dsRNA contains uracil, DNA contains thymine;
* dsRNA contains ribose DNA contains Deoxyribose;
* dsRNA is Shorter than DNA; fewer base pairs in length;
Describe how DNA is replicated in a cell. [6]
- DNA strands separate / hydrogen bonds broken (Helicase);
- Parent strand acts as a template / copied / semi-conservative replication;
- Nucleotides line up by complementary base pairing; (Adenine & Thymine etc)
- Role of DNA polymerase: joins adjacent nucleotides on the developing strand via condensation and formation of phosphodiester bond;
- 5’ to 3’ direction
- Each new DNA molecule has 1 template and 1 new strand
Formed by semi-conservative replication.
Describe a plasmid. [3]
- circular DNA;
- separate from main bacterial DNA;
- contains only a few genes;
Explain what is meant by a vector.
- Carrier of DNA / gene; (context of foreign DNA)
- Into cell/other organism/host;
- E.g.,: Plasmid, Virus, liposome and gene gun.
mRNA may be described as a polymer. Explain why.
- Made up of many (similar) molecules/monomers/nucleotides/units
Suggest why the restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once. [3]
- Enzymes only cut DNA at specific base sequence/recognition site/specific point;
- sequence of bases/recognition site/specific point (on which enzyme acts)
- occurs once in plasmid and many times in human DNA;
- (max 1 if no reference to base sequence or recognition site)
What is a restriction endonuclease enzyme?
- Cuts DNA by hydrolysing the phosphodiester bonds;
- at specific ‘recognition sites’ on both strands of the DNA molecule;
- to form fragments of DNA with either;
- Sticky or Blunt ends
State 3 techniques to ISOLATE a gene.
- mRNA to cDNA using reverse transcriptase.
- Restriction enzymes to cut gene from nuclear DNA
- Use the Gene Machine
State the 5 stages involved in Recombinant DNA technology (in vivo)
- ISOLATION
- INSERTION (into a vector= recombinant plasmid)
- TRANSFORMATION (recombinant plasmid taken up by Bacteria)
- IDENTIFICATION (use of marker genes to easily identify which bacteria have successfully been transformed / GMO / Transgenic)
- CLONING
Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected. [6]
- Isolate TARGET gene / DNA from another organism / mRNA from cell/organism;
- Using restriction endonuclease/restriction enzyme/reverse transcriptase to get DNA;
- Produce sticky ends;
- Use DNA ligase to join TARGET gene and MARKER gene to plasmid; example of marker e.g. antibiotic resistance / GFP;
- Add plasmid to bacteria to grow (colonies);
- Plate onto medium where the marker gene is expressed;
- Bacteria/colonies not killed have antibiotic resistance gene and (probably) the TARGET gene;
- Bacteria/colonies expressing the marker gene have the TARGET gene as well;
Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids.
- Restriction endonucleases/enzymes cuts plasmid; OR Restriction endonucleases/enzymes produces ‘sticky ends’;
** Reject restriction enzymes cuts the gene.*
*Ligase joins gene/DNA and plasmid OR Ligase joins ‘sticky ends’;
Describe the Polymerase Chain Reaction. (5)
Denaturation
* Heat DNA; (95 deg C)
* Breaks hydrogen bonds/separates strands;
* Add primers;
* Add nucleotides;
Annealing
* Cool (to approx 50 deg C)
* (to allow) binding / annealing of primers to DNA;
Synthesis / Extension
* Reheat to approx 70-72 deg C
* Role of heat stable Taq DNA polymerase;
Repeat cycle many times;
