8: The control of Gene expression & Gene Tech Flashcards
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 nucleotides/primers;
Synthesis / Extension
* Reheat to approx 70-72 deg C
* Role of heat stable Taq DNA polymerase;
Repeat cycle many times;
Describe how STRs could be removed from a sample of DNA.
- Restriction endonucleases/enzymes;
- (Cut DNA) at specific base sequences/pairs OR (Cut DNA) at recognition/restriction sites;
What is a DNA probe?
- (Short) single strand of DNA;
- Bases complementary (with DNA/allele/gene);
What is the use of labelled DNA probes?
Used to screen patients for:
- Heritable conditions
- Drug responses
- Health risks
Name three techniques used by scientists to compare DNA sequences.
- Polymerase Chain Reaction
- DNA fingerprinting
- Gel electrophoresis
- DNA sequencing
Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment. [4]
- (Requires DNA fragment) (Taq) DNA polymerase, (DNA) nucleotides and primers;
- Heat to 95 °C to break hydrogen bonds (and separate strands);
- Reduce temperature (40-65°C) so primers bind to DNA/strands;
- Increase temperature (70 to 75 °C), DNA polymerase joins nucleotides (and repeat method);
Why is the DNA heat to 95°C during PCR? [2]
- Produce single stranded DNA
- Breaks WEAK hydrogen bonds between strands
Why do you add primers during PCR?
- Attaches to / complementary to start of the gene / end of fragment;
- Replication of base sequence from here;
- Prevents strands annealing
Explain why ‘base-pairs’ is a suitable unit for measuring the length of a piece of DNA. [3]
- DNA = 2 chains / joined by linking of 2 bases / A with T and G with C/ purine pairs with pyrimidine;
- Bases are a constant distance apart / nucleotides occupy constant distance/
- each base-pair is same length / sugar-phosphate is a constant distance;
Suggest one reason why DNA replication stops in the polymerase chain reaction.
- Limited number of primers/nucleotides; /
Primers / nucleotides ‘used up’. - DNA polymerase (eventually) denatures
What name is used for the non-coding sections of a gene?
Introns
Name 6 types of mutation.
- Addition
- Deleltion
- Substitution
- Duplication
- Inversion
- Translation
- Non-disjunction
Name 5 classes of animal stem cell
TOTIPOTENT
PLURIPOTENT
MULTIPOTENT
UNIPOTENT
Induced Pluripotent
Epigenetic gene silencing involves…..
Methylation of DNA
Deacetylation of Histones
Epigenetic gene activation involves….
Demethylation of DNA
Acetylation of Histones
