Cambridge A Levels A2 Biology Chapter 19 Genetic Engineering
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Cambridge A Levels A2 Biology
Institution
Chapter 19 Genetic Engineering
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Chapter 19 Genetic Engineering
19.1 Principles of Genetic Technology
19.2 Genetic Technology applied to Medicine
19.3 Genetically Modified Organisms in Agriculture
19.1 Principles of Genetic Technology
Genetic Engineering:
Any procedure in which the genetic information in an organism is changed by altering the base
sequence of a gene or by introducing a gene from another organism; the organism is then said
to be a genetically modified organism (GMO).
The aim of genetic engineering is to remove a gene (or genes) from one organism and
transfer it into another so that the gene is expressed.
Recombinant DNA (rDNA):
DNA made by artificially joining together pieces of DNA from two or more different species.
Transgenic Organism:
Any organism that contains DNA from another source, such as from another individual of the
same species or from a different species.
Genetically Modified Organism (GMO):
Any organism that has had its DNA changed in a way that does not occur naturally or by
selective breeding.
Genes are often taken from an organism in a different domain or kingdom, such as a bacterial gene inserted
into a plant or a human gene inserted into a bacterium.
Unlike selective breeding, where whole sets of genes are involved, genetic engineering often results in the
transfer of a single gene.
,Overview of Gene Transfer
1. The gene that is required is identified. It may be cut from a chromosome, made from
mRNA by reverse transcription or synthesised from nucleotides.
2. Multiple copies of the gene are made using the technique called the polymerase chain
reaction (PCR).
3. The gene is inserted into a vector which delivers the gene to the cells of the organism.
Examples of vectors are plasmids, viruses and liposomes.
4. The vector takes the gene into the cells.
5. The cells that have the new gene are identified, often by using marker genes, and
cloned.
Recombinant DNA Technology
Recombinant DNA is a procedure to join DNA from different species followed by
inserting the hybrid (recombinant) DNA into a host cell, which inside the host cell, can
replicate.
Tools involves in Recombinant DNA Technology:
➢ DNA (gene source)
➢ Vectors
▪ Plasmids
▪ Viruses
➢ Enzymes
▪ Restriction endonuclease
▪ DNA ligase
▪ Reverse transcriptase
➢ Gene Markers
➢ Host Cell
vector: a means of delivering genes into a cell used in gene technology;
e.g. plasmids and viruses
,1. Restriction Endonuclease (RE)
❖ Restriction endonucleases are a class of enzymes from bacteria.
❖ These enzymes recognise and cut the DNA of bacteriophages which attack and infect
the bacteria.
❖ The cuts are made at specific places along the sugar–phosphate backbone of the phage
DNA.
The enzymes are known as endonucleases because they cut within DNA molecules rather than removing
nucleotides from the ends.
The role of these enzymes in bacteria is to restrict viral infection, hence the name restriction endonuclease or
restriction enzyme.
❖ Each restriction enzyme recognizes specific, short nucleotide sequences on the DNA and
cuts at these points.
❖ These specific nucleotide sequences are known as recognition sites/restriction sites.
❖ Different restriction enzymes have different restriction sites.
Bacterial DNA is protected from such an attack either by chemical alteration to the bases in DNA or by not
having the target sites.
Examples of Restriction Endonuclease:
i. EcoRI
▪ Isolated from E. coli.
▪ Recognises the DNA sequence of --GAATTC--.
▪ Will cleave(break) the phosphodiester bonds of DNA at the specific nucleotide
sequence of --GAATTC--.
▪ Will make a staggered cut of the double stranded DNA by cutting between G and
A at both strands.
❖ The cut is not straight across but staggered with unpaired bases at each end known as
sticky ends.
❖ Sticky ends are short lengths of unpaired bases.
❖ Sticky ends can be used to rejoin fragments of DNA by forming hydrogen bonds to
complementary sticky ends from the other DNA fragment cut up by the same enzyme.
, Palindromic Sequence: reads the same at both the strands but at opposite directions.
ii. BamHI
▪ Obtained from Bacillus amyloliquefaciens
▪ Recognises the DNA sequence of –GGATCC--.
▪ Will make a staggered cut of the double stranded DNA by cutting between G and
G at both strands.
The restriction enzyme called BamHI always cuts DNA where there is a GGATCC sequence on the 5´ to 3´ strand
and its complementary sequence, CCTAGG, on the 3´ to 5´ strand.
This sequence reads the same in both directions: it is a palindrome. Many, but not all, restriction sites are
palindromic.
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