Section 8 - Unit 21: Recombinant DNA technology Flashcards
State the purpose of restriction endonucleases (1 mark)
- Used to cut DNA
State the purpose of electrophoresis (1 mark)
- To separate pieces of DNA
State the name of the enzyme used to cut part of a plasmid (1 mark)
- Restriction endonuclease / enzyme
Describe what features of cut plasmids and lengths of foreign DNA allows their ends to join together (2 marks)
- Sticky ends / unpaired bases
- Which are complementary to each other
Explain how the strands of DNA are separated during the PCR (2 marks)
- Heating
- To break the hydrogen bonds
Explain why are primers required during PCR (1 mark)
- To allow DNA polymerase to attach
OR - Prevents strands from re-joining
Suggest why two different primers are required during PCR (1 mark)
- One primer used at beginning and one used at end
Describe how genetic fingerprinting may be carried out on a sample of panda DNA (6 marks)
- DNA is cut
- Using restriction enzyme
- Use electrophoresis
- To separate according to length
- Transfer to nylon membrane
- Make single-stranded
- Apply probe
- Radioactive / fluorescent
- Reference to VNTRs
- Autoradiography
Explain how genetic fingerprinting could allow scientists to identify the father of a child (2 marks)
- All bands in the child which don’t come from the mother
- Must be in the father’s fingerprint
Explain how electrophoresis separates fragments of DNA (2 marks)
- Move towards anode / because charged
- Different rates of movement related to charge / size
Describe what a DNA probe is (2 mark)
- Piece of DNA
- Single stranded
- Complementary to gene
Explain why radioactive DNA probes are used to locate specific DNA fragments (2 marks)
- DNA invisible on gel
- So radioactive allows detection
Describe how scientists could genetically engineer a type of bacteria to produce the enzyme which activates a drug (6 marks)
- Cut gene out of cell / make gene using mRNA / obtain gene with restriction enzymes
- Cut DNA using restriction enzyme / plasmid cut with restriction enzyme
- Correct reference to sticky ends
- Join DNA using ligase / insert gene into vector
- Plasmid / named vector transferred to cell
- Method of transfer e.g. heat shock
- Reference to marker gene
- Select bacteria containing new gene
Explain one way in which PCR differs from DNA replication in a cell (2 marks)
- Uses heat
- To separate strands
Name the type of enzyme which can be used to produce DNA from mRNA (1 mark)
- Reverse transcriptase
Describe the role of the enzyme ligase (1 mark)
- Joins two pieces of DNA / sticky ends
A plasmid may be used as a vector. Explain what is meant by a vector. (2 marks)
- Carrier of DNA / gene
- Into cell / other organism / host
Molecular biologists often use plasmids which contain antibiotic resistance genes. Explain the reason for this (2 marks)
- Act as marker gene
- Allows detection of cells containing plasmid / DNA
Describe the polymerase chain reaction (6 marks)
- Heat DNA
- Breaks hydrogen bonds / separates strands
- Add primers
- Add nucleotides
- Cool
- (to allow) binding of nucleotides / primers
- DNA polymerase
- Role of (DNA) polymerase
- Repeat cycle many times
Explain what is recombinant DNA (1 mark)
- Contains genes / sections of DNA from two species
What are DNA primers (1 mark)
- Short lengths of single stranded DNA
Describe how genetic fingerprinting is carried out (6 marks)
- DNA extracted from sample
- DNA cut / hydrolysed into segments using restriction endonucleases
- DNA fragments separated using electrophoresis
- Detail of process e.g. mixture put into wells on gel and electric current passed through
- Immerse gel in alkaline solution / two strands of DNA separated
- Cover with nylon / absorbent paper
- DNA fixed to nylon
- Radioactive marker / probe added
- Areas with probe identified using X-ray film / autoradiography
Use your knowledge of enzymes to explain why restriction enzymes only cut DNA at specific restriction sites (3 marks)
- Different lengths of DNA have different base sequences / cut at specific sequence
- Results in different shape of active site
- Therefore (specific sequence) will only fit active site of enzyme
Describe how a gene could be removed from bacterial DNA (2 marks)
- Restriction enzyme
- Cuts DNA at specific point
Explain how the use of a gene probe could enable the presence of a mutant allele of the cystic fibrosis gene to be detected (4 marks)
- Probe will attach (to mutant allele)
- Attaches to one DNA strand
- As a result of complementary base pairing
- Radioactivity detected on film / X-ray / by autoradiography
What is meant by gene therapy (1 mark)
- Introduction of a healthy gene / replacement of a defective gene
Give two advantages of using a virus in gene therapy (2 marks)
- Can enter cells
- Replicates in cells
- Targets specific cells
Explain why the enzyme is called reverse transcriptase (2 marks)
Makes DNA from RNA
Explain how you could use labelled DNA probes to show that the cells of a plant contain a specific gene (4 marks)
- Extract DNA + add endonucleases
- Separate fragments using electrophoresis
- Treat to form single strands
- The probe will bind to the gene
Explain why a plant is able to use an insect gene to synthesise the insect protein within itself (3 marks)
- Genetic code is universal
- So the insect DNA can be transcribed
- Can be translated
Describe how bacteria can be genetically modified to produce human insulin (4 marks)
- Cut out insulin gene / cut open plasmid with restriction enzyme
- Use same restriction enzyme on second DNA
- Reference to sticky ends
- Use ligase to join 2 DNA molecules
- Modified plasmid taken up by bacteria
Explain how DNA can be broken down into smaller fragments (2 marks)
- Restriction endonuclease/enzyme
- Cuts DNA at specific base sequence
OR
(Breaks) phosphodiester bonds
OR
(Cuts DNA) at recognition/restriction site
