Explain the principles and applications of key biotechnology tools and evaluate their implications.

Principles and applications of PCR, gel electrophoresis, recombinant DNA, and CRISPR-Cas9 gene editing, plus ethical implications, for TCE Biology Unit 3.

Generated by Claude Opus 4.88 min answerUpdated 2026-06-02

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What this dot point is asking

Polymerase chain reaction (PCR)

PCR makes millions of copies of a specific DNA sequence from a tiny starting sample. It relies on a heat-stable DNA polymerase (often Taq polymerase) and short single strands called primers that mark the start and end of the target region. The reaction is repeated in cycles of three temperature steps:

Denaturation: heating to around 95 degrees Celsius separates the two DNA strands.
Annealing: cooling to around 55 degrees Celsius lets primers bind to their complementary sequences.
Extension: warming to around 72 degrees Celsius lets polymerase build new strands.

Each cycle doubles the amount of target DNA, so the quantity grows exponentially. PCR is used in disease diagnosis, forensic analysis, and preparing samples for further study.

Gel electrophoresis

Gel electrophoresis separates DNA fragments by size. DNA is loaded into wells in a gel and an electric current is applied. Because DNA is negatively charged (due to its phosphate groups), it moves towards the positive electrode. Smaller fragments move through the gel mesh faster and travel further, so fragments separate into bands by length. Comparing band patterns underlies DNA profiling, used in forensics and paternity testing, and lets scientists check the size of DNA produced in other procedures.

Recombinant DNA technology

Recombinant DNA technology, or genetic engineering, transfers a gene from one organism into another. A typical workflow:

Restriction enzymes cut DNA at specific recognition sequences, often leaving sticky ends.
The same enzyme cuts a vector, usually a bacterial plasmid, leaving matching sticky ends.
The gene and plasmid are joined by the enzyme DNA ligase, forming recombinant DNA.
The plasmid is taken up by a host cell (transformation), which then expresses the gene.

This technology is used to produce human insulin in bacteria, to make genetically modified crops with pest resistance, and to manufacture vaccines and other proteins.

CRISPR-Cas9 gene editing

CRISPR-Cas9 allows precise editing of a specific DNA sequence. A short guide RNA is designed to match the target sequence and directs the Cas9 enzyme to that exact location, where Cas9 cuts both strands of the DNA. The cell then repairs the cut, and during repair scientists can disable a gene or insert a new sequence. CRISPR is faster, cheaper, and more precise than older methods, with potential applications in treating genetic diseases, improving crops, and research.

Applications and implications

Biotechnology brings major benefits: better medicines, faster diagnosis, higher-yielding and more resilient crops, and powerful research tools. It also raises ethical, social, and ecological concerns that you should be able to discuss:

Safety and unintended effects of genetically modified organisms in the environment.
Access and equity, since advanced treatments can be expensive.
Consent and privacy around genetic information.
The ethics of editing human embryos (germline editing), which would affect future generations.

A balanced evaluation weighs the likely benefits against the risks and uncertainties, and recognises that regulation and informed public debate guide how these tools are used.

Exam-style practice questions

Practice questions written in the style of TASC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

TCE 20247 marksA forensic scientist has a tiny DNA sample from a crime scene. Describe how PCR could be used to amplify the sample, naming the three temperature steps of one cycle and what happens at each, and explain how gel electrophoresis could then be used to compare the sample with DNA from a suspect.

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A 7 mark answer covers the three PCR steps and the electrophoresis comparison.

PCR step 1 - denaturation (about $95^{\circ}C$ ): The sample is heated so the hydrogen bonds break and the double-stranded DNA separates into two single strands.
PCR step 2 - annealing (about $55^{\circ}C$ ): The mixture is cooled so primers bind to complementary sequences at the ends of the target region.
PCR step 3 - extension (about $72^{\circ}C$ ): Heat-stable DNA polymerase (Taq) adds free nucleotides to extend new complementary strands. Repeating the cycle doubles the DNA each time, giving millions of copies.
Gel electrophoresis: The amplified DNA is cut with restriction enzymes and loaded into wells in a gel. An electric current moves the negatively charged fragments toward the positive electrode; smaller fragments travel further, separating them into a banding pattern. If the crime-scene banding pattern matches the suspect's pattern, it supports a match.

Markers reward all three correctly named PCR steps with temperatures/events and a correct account of size-based separation in electrophoresis.

TCE 20226 marksDescribe how a gene of interest can be inserted into a bacterial plasmid to produce recombinant DNA, naming the enzymes used, and outline one ethical implication of using genetically modified organisms.

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A 6 mark answer covers the recombinant steps with enzymes plus a reasoned ethical point.

Cutting: The same restriction enzyme cuts both the gene of interest and the plasmid, leaving complementary sticky ends so they can join.
Joining: The gene is mixed with the cut plasmid; DNA ligase forms bonds that seal the gene into the plasmid, creating recombinant DNA.
Insertion and expression: The recombinant plasmid is taken up by a bacterium (transformation), which then transcribes and translates the gene to make the desired protein (for example human insulin) as it reproduces.
Ethical implication: Any one reasoned point, for example: concerns about unknown long-term ecological effects if GM organisms escape and cross with wild populations, or questions about safety, labelling and corporate control of patented organisms.

Markers reward restriction enzyme and ligase named in the correct roles, the transformation step, and one clearly reasoned ethical implication.