Directed evolution – key terms

Using directed evolution, scientists can improve the function of enzymes that occur naturally. Below is a list of related keywords and definitions.

Bystander effect

The process whereby cells are killed by a toxic metabolite produced in a neighbouring cancer cell.

Catalyst

A molecule, such as an enzyme, which speeds up the rate of a reversible biochemical reaction. Catalysts are not used up in the reaction.

Cloning

Making multiple copies of a gene. In DNA cloning, a gene is inserted into a vector, such as a plasmid, and transfected into a host cell, which can make multiple copies of the gene.

DNA ligase

An enzyme involved in DNA replication, which joins together Okazaki fragments and repairs DNA. In biotechnology, it is used to join together DNA fragments, by forming phosphodiester bonds between the sugar and phosphate molecules of the DNA backbone. This seals the DNA together, producing recombinant DNA.

Directed evolution

Selecting for a specific trait at a molecular level. For example, variation is introduced into a single gene, which codes for an enzyme, and enzymes with the desired activity are then selected for.

Enzyme

A protein that carries out reversible, specific biochemical reactions in a cell.

Evolution

A gradual change in the traits of a population, which occurs over many generations.

Gene therapy

The treatment of genetic disorders by replacing defective genes with normal or modified genes.

Gene variants

Genes that have been altered or varied, so that they are different from the parent gene. A gene variant may produce a slightly different protein than the parent gene. In the case of a protein like an enzyme, this may affect its ability to catalyse a reaction.

Genetic variation

Variation in the nucleotide base sequence of a gene, which may occur between individuals.

Genotype

The genetic make up of a cell or organism.

Mutation

A change in the genetic material of an organism. Mutations may be point mutations, where a single nucleotide base is deleted or added, or chromosomal mutations, where a larger part of the chromosome is deleted or added.

PCR (Polymerase chain reaction)

A procedure for making multiple copies of a segment of DNA such as a gene, also called gene amplification. A version of PCR can be used to introduce mutations in the gene being amplified.

Phenotype

The observable characteristics and appearance of an organism.

Plasmids

Small, circular extra-chromosomal DNA found in bacteria. Plasmids can replicate independently of the main chromosome. They may contain genes encoding enzymes that confer drug resistance to the bacteria. In biotechnology, they are used as vectors to transfer DNA and produce recombinant DNA.

Prodrug

An inactive form of a drug. Prodrugs are usually activated by enzymes or chemicals. In this case, the activated prodrug produces a toxic metabolite, which can destroy cancer cells.

Reporter gene

A gene used as a marker to detect damage to cells’ DNA, by producing a coloured product that can be measured.

Restriction enzymes (or endonucleases)

Enzymes found mainly in bacteria, which cut DNA at specific sites. In biotechnology, restriction enzymes are used to move genes from one vector or piece of DNA to another, making recombinant DNA.

Selection pressure

Environmental influences or constraints that influence gene transmission from one generation to the next. Individuals whose genes are best suited to the environment will be selected for. These individuals are more likely to survive and pass their genes on to the next generation.

Selective breeding

Breeding or (sexual reproduction) to produce a particular phenotype or trait in the offspring.

Sticky ends

The overhanging fragments of DNA that result from cutting the DNA by restriction enzymes. These fragments can bind to corresponding sticky ends by nucleotide base pairing.

Transfect

Use a virus to transfer DNA into another cell.

Viral vector

A virus that is used to transfer DNA from one organism to another.