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Chapter 21 - Recombi
A level Biology Chapter 21 - Recombinant DNA technology
| Question | Answer |
|---|---|
| A large quantity of the DNA sample is required for this procedure. Name the reaction used to amplify small amounts of DNA into quantities large enough for this procedure. | Polymerase chain reaction |
| Reason for adding DNA polymerase to test tube? | Joins nucleotides together |
| Reason for adding primers to test tube? | enables replication / sequencing to start / keeps strands separate; |
| When a modified nucleotide is used to form a complementary DNA strand, the sequencing reaction is terminated. Suggest how this sequencing reaction is terminated. | (modified nucleotide) does not form bonds / react with other nucleotides; does not “fit” DNA polymerase / enzyme / active site; |
| A sample of DNA analysed by this technique had the following nucleotide base sequence. T G G T C A C G A Give the base sequence of the shortest DNA fragment which would be produced in Tube 2 (modified cytosine) | AC |
| Explain why the DNA fragments move different distances in the gel in gel electrophesis? | Different weights/ sizes etc |
| What makes the DNA fragments visible on the autoradiograph? | radioactive primer |
| Plasmids can be modified by genetic engineering and put in bacteria. EXPLAIN HOW MODIFIED PLASMIDS ARE MADE BY GENETIC ENGINEERING and how the use of markers let bacteria containing these plasmids be detected [6 marks] | isolate wanted gene from mRNA from organism using restriction endonuclease / reverse transcriptase to get DNA and produce sticky ends; use ligase to join wanted gene to plasmid; also include marker gene e.g. antibiotic resistance; |
| Plasmids can be modified by genetic engineering and put in bacteria. Explain how modified plasmids are made by genetic engineering AND HOW THE USE OF MARKERS LET THE BACTERIA CONTAINING THESE PLASMIDS BE DETECTED [6 marks] | add plasmid to bacteria to grow colonies on culture with antibiotic; Use replica plating + bacteria not killed have antibiotic resistance gene + the wanted gene |
| Describe how a gene can be isolated from human DNA. [2 marks] | use restriction enzyme / endonuclease; to cut DNA in specific place / base sequence; |
| Describe how an isolated gene can be replicated by the polymerase chain reaction (PCR) [4 marks] | heat DNA to 90 – 95 °C; strands separate; add primers; and nucleotides; cool so that primers bind to DNA; DNA polymerase forms new strands / joins nucleotides; |
| Describe how a harmless virus, genetically engineered to contain a CFTR gene, can be used to insert the gene into a cystic fibrosis sufferer. [ 2 marks] | virus is inhaled / sprayed into the lungs; gets into cells, inserting the healthy gene; |
| A virus used in gene therapy has RNA as its genetic material and has an enzyme called reverse transcriptase. Inside a human cell, reverse transcriptase uses viral RNA to make viral DNA. Explain why the enzyme is called reverse transcriptase. [1 mark] | Makes DNA from RNA |
| Explain the reason for each of the following in the polymerase chain reaction (PCR). (i) DNA is heated to 95 °C. | to separate polynucleotide strands / form single strands; |
| Explain the reason for each of the following in the polymerase chain reaction (PCR). DNA polymerase used is heat-stable. | not denatured (at 95°C); |
| Explain the reason for each of the following in the polymerase chain reaction (PCR). The reaction mixture is cooled to 40 °C. | for binding of primers / nucleotides (to DNA strands); Allow primers to anneal |
| What is meant by the term gene therapy? | introduction of healthy gene / ‘replacement’ of defective gene; |
| The ADA gene is inserted into a virus. Give two advantages of using a virus in gene therapy. | can enter cells / infect cells / inject DNA into cells; targets specific cells; replicates (in cells); |
| Individuals who have been treated by this method of gene therapy do not pass on the ADA gene to their children. Explain why? | reproductive cells / gamete cells do not contain ADA allele / gene; |
| Give two ways in which the polymerase chain reaction differs from the process of transcription. | transcription uses RNA polymerase; RNA nucleotides / uracil; one template strand / PCR uses both strands; start / stop codons; |
| Use your knowledge of enzymes to explain why restriction enzymes only cut DNA at specific restriction sites. | Different lengths of DNA have different base sequences; Results in different shape of active site; Therefore specific sequence will only fit active site of enzyme; |
| DNA was cut into pieces using a restriction enzyme which produced a staggered cut. A scientist inserted this DNA in plasmids and used the same restriction enzyme to cut the plasmids. Why can the pieces of DNA join to the cut DNA of the plasmids? | Sticky ends so complementary base pairing |
| A plasmid may be used as a vector. Explain what is meant by a vector in this context? | Carrier of DNA / Gene |
| Explain how electrophoresis separates the fragments of DNA? | Move towards anode / move because charged; Different rates of movement related to charge / size; |
| What is a DNA probe? | Piece of DNA; Single stranded; Complementary to / binds to known base sequence / gene; |
| What enzyme is used to stick two sticky ends together? | DNA ligase |
| Explain why radioactive DNA probes are used to locate specific DNA fragments. | DNA invisible on gel / membrane; Allows detection; |
| What are the 3 ways which DNA fragments can be made? | Reverse Transcriptase, Restriction endonuclease, gene machine |
| How can genetic fingerprinting be used? | DNA bases which are non coding are known as Variable number tandem repeats (VNTRS) For every individual number and length of VNTRS has a unique pattern so can be used at crime scenes |
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ksatti12