Year 13: 8. The control of gene expression Flashcards
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;
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
Describe the mechanism by which a signal protein causes the synthesis of mRNA. [5]
- 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. [5]
- Oestrogen diffuses through the cell membrane;
- 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;
Explain how the methylation of tumour suppressor genes can lead to cancer. [3]
- Methylation 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 what is meant by a malignant tumour.
- mass of undifferentiated / unspecialised / totipotent cells;
- uncontrolled cell division;
OR - metastasis / (cells break off and) form new tumours
- spread to other parts of body;
Describe how altered DNA base sequence 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 how alterations to tumour suppressor genes can lead to the development of tumours. [3]
- (Increased) methylation (of tumour suppressor genes); OR Mutation (in tumour suppressor genes);
- Tumour suppressor genes are not transcribed / expressed OR Amino acid sequence / primary structure altered;
- (Results in) rapid/uncontrollable cell division;
Define epigenetics
- Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.
Name 3 types of single point gene mutation
Substitution
Addition
Deletion
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why.
- Triplets code for same amino acid / DNA is degenerate
- Occurs in introns /non-coding sequence;
Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual.
[5]
(Definition of gene mutation)
1. Change in the base/nucleotide (sequence of chromosomes/DNA);
2. Results in the formation of new allele;
(Has no effect because)
3. Genetic code is degenerate (so amino acid sequence may not change); OR
Mutation is in an intron (so amino acid sequence may not change);
Accept description of ‘degenerate’, eg some amino acids have more than one triplet/codon.
4. Does change amino acid but no effect on tertiary structure;
5. (New allele) is recessive so does not influence phenotype;
(Has positive effect because)
6. Results in change in polypeptide that positively changes the properties (of the protein) OR Results in change in polypeptide that positively changes a named protein; For ‘polypeptide’ accept ‘amino acid sequence’ or ‘protein’.
7. May result in increased reproductive success OR May result in increased survival (chances);
Give an example of an UNIPOTENT stem cell.
Cardiomyocyte
How can a somatic (Specialised body cell) be converted into an iPS cell (induced pluripotent stem cell)
- Provide the appropriate Transcription factors
- Demethylate the DNA
- Acetylate histones
Adding Methyl groups can silence genes by binding to …….
DNA promoter regions
How does RNAi affects protein synthesis?
- Single stranded RNAi binds to complementary bases of ‘target’ mRNA (within the cytoplasm)
- Leads to destruction/hydrolysis of (target) mRNA
- Less translation (by ribosomes) of mRNA
Describe how DNA is replicated in a cell. [5]
- DNA strands separate / hydrogen bonds broken;
- 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 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?
- 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.
- 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
Name one mutagenic agent.
- high energy radiation /ionising particles e.g. named particles/α, β, γ & X-rays;
- benzene;
- x rays/cosmic rays;
- uv (light);
- carcinogen / named carcinogen;
- mustard gas / phenols / tar (qualified);
A deletion mutation occurs in gene 1.
Describe how a deletion mutation alters the structure of a gene.
- removal of one or more bases/nucleotide;
- frameshift/(from point of mutation) base sequence change;
Describe the main stages in the copying, cutting and separation of the DNA. [5]
- heat DNA to 95°C / 90°C;
- strands separate;
- cool so that primers bind to DNA;
- add DNA polymerase/nucleotides;
- use of restriction enzymes to cut DNA at specific base sequence/ breaks phosphodiester bonds
- use of electric current and agar/gel;
- shorter fragments move further;
Describe the polymerase chain reaction. [5]
- Heat DNA to break hydrogen bonds/separates strands;
- Add primers, Add nucleotides & DNA Polymerase
- Cool (to allow) binding of nucleotides/primers;
- Reheat to activate (DNA) polymerase;
- Repeat cycle many times;
Describe a plasmid.
- circular DNA;
- separate from main bacterial DNA;
- contains only a few genes;
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
Suggest why the restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once.
- 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)
Explain what is meant by a vector.
- Carrier of DNA/gene; (context of foreign DNA)
- Into cell/other organism/host;
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
- produce sticky ends;
- use DNA ligase to join TARGET gene to plasmid also include marker gene (example of marker e.g. antibiotic resistance);
- add plasmid to bacteria to grow (colonies);
- (replica) 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 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 within the intergenic regions.
What does VNTR stand for?
Variable Number of Tandem Repeats
mRNA may be described as a polymer. Explain why.
- Made up of many (similar) molecules/monomers/nucleotides/units;
What is a DNA probe?
- (Short) single strand of DNA;
- Bases complementary (with DNA/allele/gene);
Name three techniques used by scientists to compare DNA sequences.
- Polymerase Chain Reaction
- DNA fingerprinting
- Gel electrophoresis
What name is used for the non-coding sections of a gene?
- Introns
Where are VNTR’s located?
- Intergenic regions of chromosomes (Between adjacent genes on the same chromosome)
Explain why fragments of DNA from cancer cells may be present in blood plasma.
- cancer cells die / break open releasing DNA;
Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids.
- Restriction (endonuclease/enzyme) to cut plasmid/vector;
- Ligase joins gene/DNA to plasmid/vector;
Describe how enzymes could be used to insert the GH gene into a plasmid.
- 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’;
