How are genes manipulated to make useful products, and what are the applications and ethical issues?
The principles of genetic engineering (recombinant DNA technology), the use of restriction enzymes, ligase, vectors and the polymerase chain reaction, the applications in medicine, agriculture and gene therapy, and the ethical and safety issues.
A CCEA Life and Health Sciences answer on gene technology: the principles of genetic engineering using restriction enzymes, ligase and vectors, the polymerase chain reaction, applications in medicine and agriculture, gene therapy, and the ethical issues.
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What this dot point is asking
CCEA wants you to explain the principles of genetic engineering (recombinant DNA technology), describe the roles of restriction enzymes, DNA ligase, vectors and the polymerase chain reaction, describe the applications of gene technology in medicine and agriculture (including gene therapy), and discuss the ethical and safety issues. It applies the molecular genetics and inheritance dot points to the manipulation of genes for human benefit.
The principles of genetic engineering
The general process has clear steps. First, the gene of interest is isolated, cut out of the source DNA using a restriction enzyme that cuts at a specific base sequence and leaves sticky ends (short single-stranded overhangs). Second, a vector (commonly a plasmid, a small circular piece of bacterial DNA) is cut with the same restriction enzyme, so it has complementary sticky ends. Third, the gene and the cut vector are mixed; their sticky ends pair by complementary base pairing and the enzyme DNA ligase joins them, forming recombinant DNA. Fourth, the recombinant vector is taken up by a host cell (often a bacterium). Because the genetic code is universal, the host transcribes and translates the inserted gene, producing the desired protein.
The polymerase chain reaction
PCR is essential whenever only a small amount of DNA is available, for example a trace at a crime scene, a tiny tissue biopsy, or a sample for genetic testing. By repeatedly doubling the target sequence, PCR produces enough DNA to analyse, profile or use in further engineering. It is a cornerstone of modern molecular biology, forensics and medical diagnosis.
Applications and ethical issues
Gene technology has wide applications. In medicine, genetically engineered bacteria make human proteins such as insulin, growth hormone and clotting factors more cheaply and ethically than extracting them from animals or donors; gene therapy aims to treat genetic disorders by introducing a working allele into a patient's cells; and DNA technology underpins genetic screening and the design of vaccines. In agriculture, crops are genetically modified for pest resistance, herbicide tolerance or improved nutrition. These benefits come with ethical and safety issues: concerns about the unknown long-term effects of genetically modified organisms, the possibility of modified genes spreading to wild populations, questions about who owns and profits from genetic material, worries about designer babies and the use of genetic information, and the need for tight regulation. A balanced answer weighs the clear benefits against these legitimate concerns.
Examples in context
Example 1. Human insulin for diabetes. Before gene technology, insulin was extracted from animal pancreases, which was costly and could cause reactions. Now the human insulin gene is inserted into bacteria that produce identical human insulin in fermenters, providing a reliable, ethical supply. This is the standard example linking gene technology to the treatment of disease.
Example 2. PCR in diagnosis and forensics. PCR amplifies a tiny DNA sample so it can be tested for a disease-causing allele or matched to an individual in a criminal investigation. The ability to make millions of copies from a trace of DNA shows why PCR is central to modern medicine and forensic science.
Try this
Q1. State the function of a restriction enzyme and the function of DNA ligase in genetic engineering. [2 marks]
- Cue. A restriction enzyme cuts DNA at a specific sequence (sticky ends); ligase joins the gene into the vector to form recombinant DNA.
Q2. State what the polymerase chain reaction is used for. [1 mark]
- Cue. To amplify DNA (make many copies of a specific section quickly).
Q3. Give one ethical concern about gene technology. [1 mark]
- Cue. For example the unknown long-term effects of genetically modified organisms, or concerns about the use of genetic information or designer babies.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA A2 56 marksDescribe how the human gene for insulin can be inserted into a bacterium so that the bacterium produces human insulin.Show worked answer →
A full-mark answer gives the steps in order, naming the enzymes and vector.
Isolate the gene: the human insulin gene is cut out of human DNA using a restriction enzyme, which cuts DNA at a specific base sequence and leaves sticky ends.
Prepare the vector: a plasmid (a small circular piece of bacterial DNA) is cut open with the same restriction enzyme, so it has complementary sticky ends.
Join the gene to the vector: the insulin gene and the cut plasmid are mixed; their sticky ends pair by complementary base pairing, and the enzyme DNA ligase joins them to form recombinant DNA (the gene inserted into the plasmid).
Insert into bacteria: the recombinant plasmids are taken up by host bacteria. Because the genetic code is universal, the bacteria transcribe and translate the human gene.
Culture and harvest: the bacteria are grown in fermenters, where they multiply and produce human insulin, which is then extracted and purified.
Markers reward the restriction enzyme cutting the gene and plasmid (sticky ends), ligase joining them into recombinant DNA, uptake by bacteria, and culturing to produce and harvest the insulin.
CCEA A2 55 marksExplain the purpose of the polymerase chain reaction (PCR), and state two applications of gene technology in medicine.Show worked answer →
Explain what PCR does and give medical applications.
Purpose of PCR: the polymerase chain reaction makes many copies of a specific section of DNA quickly (it amplifies DNA). Repeated cycles of heating to separate the strands, cooling so primers attach, and warming so a heat-stable DNA polymerase builds new strands, double the amount of DNA each cycle. This is useful when only a tiny sample of DNA is available.
Two medical applications (any two): producing human proteins such as insulin, growth hormone or clotting factors from genetically engineered bacteria; gene therapy to treat genetic disorders by introducing a working allele; genetic screening and diagnosis of genetic diseases; making vaccines; and DNA profiling for identification.
Markers reward PCR amplifying (making many copies of) a section of DNA, ideally with the cycle of heating and cooling, and two valid medical applications.
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Sources & how we know this
- CCEA GCE Life and Health Sciences specification — CCEA (2016)