Proteins are one of four main classes of biomolecules1 in living organisms. The others are lipids2, which form our membranes, nucleic acids3 (DNA4 and RNA5), which carry and carry out our instructions, and carbohydrates, which not only give us energy but are also sometimes involved in signalling processes and other cellular processes. Proteins are the most diverse of these four biomolecules.
Enzymes6 are proteins that catalyse7 chemical reactions – they are biocatalysts8. Catalysts make chemical reactions happen much more quickly than is possible spontaneously. Biocatalysts naturally carry out their action in living organisms. Most biochemical9 reactions, if left to their own devices, will take millions of years to occur but can occur within cells in milliseconds due to the action of enzymes.
There are thousands of enzymes within each living organism10 and each has a specific role – controlling essential biological and biochemical reactions by working with specific substrates11 to create specific products.
Some common enzymes found in animals are used in the digestion12 system. Amylase13 is found in saliva14 and helps the breakdown of starches into sugars. Trypsin is found in the small intestine15 and breaks down protein16 into amino acids17. Lipases are a group of enzymes that help digest fat in the gut.
Nature of science
The animation within this article is a model created to help visualise the action of enzymes. Scientists often use models to help build and communicate their understandings about the world.
Related content
Learn more about enzymes:
Enzymes in the lab
Enzymes associated with digestion and food
Enzymes in industry
Enzymes and medicine
Enzymes in extreme environments
Learn more about proteins
Activity ideas
Explore the action of enzymes
- biomolecules: A chemical compound that naturally occurs in living organisms, which consist mainly of carbon and hydrogen, nitrogen, oxygen, phosphorus and sulfur.
- lipid: Any of a group of organic (carbon-containing) compounds, including fats, oils and waxes that are insoluble in water, oily to the touch and, together with carbohydrates and proteins, constitute the principal structural material of living cells. Lipids are characterised by their insolubility in water and solubility in organic solvents.
- acid: A hydrogen-containing substance that is capable of donating a hydrogen ion to another substance.
- DNA: Deoxyribonucleic acid (DNA) is a molecule that contains the instructions needed for an organism to develop and function. These instructions are stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C) and thymine (T).
- RNA: A molecule generated in cells by transcription and required for the synthesis of proteins. RNA (Ribonucleic acid) is made up of a large number of nucleotides to form a long single strand. A chemical code for genetic information.
- enzyme: A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.
- catalyse: To speed up the rate of a chemical reaction.
- biocatalyst: Biocatalysts such as enzymes are proteins that make chemical reactions happen a lot faster than is possible spontaneously in living organisms.
- biochemical: Any organic compound involved in living processes, for example, a protein, carbohydrate or lipid.
- organism: A living thing.
- substrate: 1. In ecology, the surface or sediment where an organism lives and grows. 2. In biochemistry, the substance on which an enzyme works.
- digestion: The mechanical and chemical breaking down of food into smaller components that can be absorbed into a bloodstream.
- amylase: An enzyme present in saliva that can digest starch.
- saliva: A watery fluid produced by the salivary glands in the mouth. It is made up of water, mucus, amylase, lipase and sodium bicarbonate.
- small intestine: That part of the gastrointestinal tract that connects the stomach to the large intestine. It consists of three parts: the duodenum, the jejunum and the ileum.
- protein: Any of a large class of complex compounds that are essential for life. Proteins play a central role in biological processes and form the basis of living tissues. They have distinct and varied three-dimensional structures. Enzymes, antibodies and haemoglobin are examples of proteins.
- amino acid: The basic building block of proteins. A short chain of amino acids is called a peptide, and a long chain of amino acids (normally more than 50) is called a protein.
