19.1.119 · Genetic Technology

Recombinant DNA — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

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📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision

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19.1.1 Recombinant DNA — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain why recombinant DNA can be made and define the terms transgenic organism and GMO.The genetic code is universal — almost every organism uses the same four bases (A, T, C and G), with a few…

Recombinant DNA (rDNA)
Genetically modified organism (GMO)
Universal code
Same chemistry
Expression machinery
Universal genetic code

Part 1 of 8The universal genetic code

1The genetic code is universal

The genetic code is universal almost every organism uses the same four bases (A, T, C and G), with a few exceptions.

The same codons code for the same amino acids in all living organisms.

Genetic information is therefore transferable between species.

A human gene in a bacterium can be transcribed and translated to give the human protein.

Part 2 of 8Recombinant DNA and GMOs

Scientists artificially change an organism's DNA by combining lengths of nucleotides from different sources, usually different species.

2Recombinant DNA (rDNA)

Recombinant DNA (rDNA) altered DNA with introduced nucleotides.

3Transgenic organism

Transgenic organism an organism that contains nucleotide sequences from a different species.

4Genetically modified organism (GMO)

Genetically modified organism (GMO) any organism with introduced genetic material.

Part 3 of 8Why recombinant DNA is possible

Universal code

Universal code mRNA from a foreign gene is read correctly by the host's ribosomes and tRNA.

Same chemistry

DNA in all organisms is made of the same nucleotides, so enzymes can cut and join DNA from any source.

Expression machinery

Expression machinery the gene needs a promoter that the host's RNA polymerase recognises.

All forms of life using the same code is the strongest evidence for evolution.

Part 4 of 8Allowing for differences between hosts

Allowing for differences between hosts

Eukaryote genes contain introns, which bacteria cannot splice out.

A bacterial host uses cDNA copied from mRNA, which has no introns.

Bacteria cannot carry out some post-translational modifications of eukaryote proteins, such as glycosylation.

Yeast or mammalian cells are sometimes used instead.

Part 5 of 8Overview of the process

Isolate the gene of interest.

Cut the gene and the vector with the same restriction enzyme to give complementary sticky ends.

Join them with DNA ligase to make a recombinant plasmid.

Insert the vector into host cells (transformation).

Identify cells that took up the gene using marker genes.

Culture the transformed cells to make the product in large quantities, or grow the transgenic organism.

Part 6 of 8Applications

Area	Example
Medicine	Human insulin from bacteria or yeast; factor VIII for haemophilia; human growth hormone; hepatitis B vaccine antigen from yeast
Agriculture	Bt maize and cotton; herbicide-resistant soya; Golden Rice with beta-carotene
Industry	Enzymes such as amylase and chymosin from microorganisms
Research	GFP reporter genes; knock-out mice

Part 7 of 8Benefits and concerns

Benefits

Benefits a plentiful, pure supply of human proteins with no risk of transmitting animal diseases, higher yield and less pesticide use.

Concerns

Concerns gene transfer to wild relatives, effects on non-target organisms, patents and cost, allergies and ethical questions.

A single transformed cell divides to form a clone, and fermenters supply optimum conditions; downstream processing purifies the product.

Part 8 of 8More from the specification

1Isolating Desired Genes Using Reverse Transcriptase

In genetic engineering, reverse transcriptase enzymes extract mRNA transcripts from donor cells and synthesize complementary single-strand cDNA molecules, eliminating non-coding intron sequences.

2Cleavage of DNA by Restriction Endonucleases

Restriction endonucleases recognize specific palindromic DNA base sequences and cleave phosphodiester bonds to produce sticky or blunt-ended DNA fragments suitable for cloning.

3Constructing Recombinant Plasmids with DNA Ligase

DNA ligase catalyzes the formation of covalent phosphodiester bonds between the sticky ends of the desired gene fragment and plasmid vector molecules, creating recombinant DNA.

4Gel Electrophoresis and Polymerase Chain Reaction

Following the polymerase chain reaction (PCR) amplification of target genes, gel electrophoresis separates DNA fragments by size as negatively charged fragments migrate towards the positive anode in an electric field.

5Electrophoresis

Separation of molecules by size in an electric field

6Microarray

Chip with probes used to detect many genes at once.

7Genome

All the genetic information in an organism.

8Genetic engineering

Deliberate modification of a characteristic of an organism by transferring genes.

9Restriction endonuclease

Enzyme cutting DNA at a specific recognition sequence.

10Reverse transcriptase

Enzyme synthesising DNA from an RNA template

Key terms

Term	Meaning
Recombinant DNA	DNA made by combining nucleotides from different sources.
Transgenic organism	Organism containing DNA from a different species.
GMO	Genetically modified organism: any organism with introduced genetic material.
Universal genetic code	The same codons code for the same amino acids in nearly all organisms.
Genetic engineering	Deliberate modification of a characteristic of an organism by transferring genes.
cDNA	DNA copied from mRNA, without introns.

Avoid these mistakes

Saying the genetic code differs between species — it is universal, which allows gene transfer.

Confusing recombinant DNA with a GMO — rDNA is the DNA, the GMO is the organism containing it.

Using genomic eukaryote DNA directly in bacteria — introns are not spliced out.

Saying transgenic means any modified organism — it contains DNA from a different species.

Last updated: 18 October 2026