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Genetic engineering

Genetic engineering involves changing the DNA of an organism, usually by deleting, inserting or editing a gene to produce desired characteristics.

tertiary structure

The final 3D structure of a protein. This structure is produced when the secondary structure of the polypeptide chain is folded.

Hydrogen bond

An intermolecular attractive force between hydrogen, when it is covalently bonded to a highly electronegative atom (fluorine, oxygen or nitrogen), and an oxygen, nitrogen or fluorine atom on another molecule.


Specific in three dimensions.


The use of biological organisms or enzymes to create, break down or transform a material.


A protein digesting enzyme found in the mammalian small intestine that is activated by trypsin.


Process where microorganisms are cultured so that they reproduce and increase in quantity.

Ionic bonds

Bonds formed by the complete transfer of one or more electron from one atom to another, so both achieve a stable outer shell. The positive and negative ions formed are held together by strong electrostatic forces - these are ionic bonds.


A protein-digesting enzyme found in the mammalian small intestine.


A protein-digesting enzyme found in the mammalian stomach.


The enzyme that catalyses the breakdown of urea and the first pure enzyme to be extracted and crystallised.


A complex carbohydrate made as an energy store plants


The waste material left at the end of the digestive process made up of undigested food, dead cells, bacteria and water


The poisonous waste compound produced when excess amino acids are broken down in your liver


A common term for the digestive system.

What is an enzyme?

1. Enzymes are proteins: Most enzymes are globular proteins. The bonds holding the amino acids together are peptide bonds but hydrogen bonds, disulfide bonds and ionic bonds work together to produce a secondary and tertiary structure.

Energy profile of reaction with and without a catalyst

Most enzymes are globular proteins

2. Enzymes have an active site: Within the globular protein structure of an enzyme is the active site. This is a 3D depression or hollow shape that is vital to the way the enzyme functions. The three dimensional, stereospecific shape of the active site is the result of the folding of the protein molecule. Anything that affects the shape of the active site will affect the ability of the enzyme to bind to the substrate or substrates and catalyse a reaction.

Computer generated model of the enzyme COX-2

This computer generated model of the enzyme COX-2 shows the active site in red (Jeff Dahl, public domain).

3. Enzymes are very specific: An enzyme will only catalyse one type of reaction. Some enzymes are so specific that they will only catalyse one particular reaction. This is due to shape of the active site. The active site is stereospecific – in other words, it is specific in three dimensions. So, for example, it will only bind to one stereoisomer or enantiomer of a substrate molecule, not both (See Chemistry of Life, page 4).

4. Enzymes change the rate of a reaction: They act as catalysts so they do not affect the end products or the equilibrium of the reaction that they catalyse.

A brief history of enzymes

    Dog faeces

    Animal faeces contain enzymes that were used for centuries to soften leather

  • From Roman times to the Victorian era dog faeces and pigeon droppings were used in the tanning process to help produce supple leather. This is the earliest – and perhaps the most unpleasant – example of people using enzymes in industry. At the very end of the 19th century the German chemist Otto Rohm discovered that it was protein-digesting enzymes in the faeces that had the desired effect on the leather. By 1905 he had developed a way of producing proteases to soften leather from cow and pig pancreases – undoubtedly a great relief to leather workers everywhere!
  • In 1835 people noticed that starch was hydrolysed faster by malt than by sulphuric acid. This lead to the idea that there was an catalyst present in living malt that was more effective than the inorganic acid
  • People suspected there was a biological catalyst in yeast which brought about the fermentation of sugar to alcohol long before anyone proved it. In 1877 people started to use the name enzyme (literally `in yeast') for these theoretical chemicals.
  • In 1897 Eduard Buchner extracted the enzyme responsible for fermenting sugar from yeast cells, and showed it could work independently of the living cell structure.
  • Model of urease

    A computer generated model of urease (Ayacop, public domain)

  • The first pure, crystalline enzyme was produced in 1926 by Sumner. It was the enzyme urease, that catalyses the breakdown of urea. He extracted it from jack beans. Sumner showed that the crystals were protein and concluded that enzymes must be proteins. Unfortunately no-one believed him to begin with – although he eventually got a Nobel prize for his work!
  • In 1930-36 the protein nature of enzymes was finally firmly established when the protein digesting enzymes pepsin, trypsin and chymotrypsin from the gut were extracted and crystallised.
  • From then until today scientists have extracted more and more enzymes and have used a variety of techniques to look at their structure to give us our current level of understanding of these vital molecules.
  • The development of biotechnology means enzymes are now used in everything from paper and food manufacture to genetic engineering.