OxfordAQA International A Level Biology 3.4.10 Recombinant DNA Technology Exam Questions

About OxfordAQA International A Level Biology 3.4.10 Recombinant DNA Technology

Recombinant DNA technology closes Unit 4. You need to explain that DNA fragments can be transferred between organisms because the genetic code is universal and transcription and translation work in the same way. You need to describe three ways of producing fragments (reverse transcriptase, restriction endonucleases and artificial gene synthesis), in vitro amplification by the polymerase chain reaction, and in vivo amplification using promoter and terminator regions, vectors, ligase, host cell transformation and marker genes. You should also evaluate the ethical, financial and social issues of the technology. It draws on protein synthesis, DNA replication and gene regulation, so it is ideal for synoptic questions.

What you need to know

• Why transfer works The genetic code is universal and the mechanisms of transcription and translation are the same in all organisms, so a gene from one organism can be expressed in another.
• Producing fragments Reverse transcriptase makes cDNA from mature mRNA, so it has no introns. Restriction endonucleases cut DNA at specific recognition sequences, often leaving sticky ends. A gene machine synthesises a gene from a known amino acid sequence.
• PCR The DNA is heated to about 95 C to separate the strands, cooled to about 55 C so primers anneal, then heated to about 72 C so DNA polymerase extends the new strands. Each cycle doubles the DNA.
• Vectors and ligase Promoter and terminator regions are added so the gene is transcribed. A plasmid is cut with the same restriction endonuclease, the sticky ends pair, and DNA ligase joins the sugar-phosphate backbones.
• Transformation and markers Host cells take up the recombinant plasmid, for example using calcium ions and heat shock. Marker genes, such as antibiotic resistance or fluorescence, identify cells that have taken up the gene.
• Issues Benefits include producing medicines such as insulin and improving crops. Concerns include safety, effects on wild populations, cost and who controls the technology.

Common mistakes in 3.4.10 Recombinant DNA Technology

• Saying DNA polymerase in PCR is human DNA polymerase. PCR uses a thermostable polymerase that is not denatured at high temperatures.
• Saying ligase forms hydrogen bonds between sticky ends. Complementary bases pair by hydrogen bonds; ligase forms phosphodiester bonds in the backbone.
• Forgetting why cDNA is useful. It has no introns, so it can be expressed in bacteria that cannot remove introns.
• Saying primers are needed to separate the strands. Heat separates the strands; primers give DNA polymerase a starting point.

Try three 3.4.10 Recombinant DNA Technology exam-style questions