Pathway organisers The ushers of chemical reactions Enzymes Pathway organisers The ushers of chemical reactions

What is an enzyme? A biological catalyst, speeding up the rate of a reaction. Catalysts are chemical substances that help to speed up a reaction without being used up. (They are not reactants.) They are only needed in small amounts and are re-useable

Enzymes - Biological Catalysts Enzymes are all proteins They allow biochemical reactions to happen in conditions that the body can tolerate Some biological reactions would never happen without enzymes, they would require very high temperatures that living things could not survive in

Enzymes - Proteins To understand how enzymes work, you will need to know about protein structure. Proteins are very long polymers that become folded up to form 3D shapes This folding occurs in a series of steps: Primary Secondary Tertiary

Primary structure refers to the order of amino acids that make up the chain Secondary structure refers the folding of the structure into coils (helix) or pleated sheets. This is caused by hydrogen bonds between the amino acids Tertiary structure refers to how the helices and pleats interact to make the protein fold in to a 3D globular shape. This is due to many different types of bonding Quaternary structure refers to the interaction of one protein with another

Enzymes – Biological Catalysts Enzymes work by bringing molecules together or positioning them in a way that makes the reaction happen more quickly. The molecules that enzymes act on are called substrates Enzymes are very specific The part of the enzyme that comes into contact with the substrate is called the active site

For enzymes, tertiary is the most important aspect of the protein structure. It creates grooves in specific shapes. Such grooves then form the active site which fits the substrate(s) perfectly If anything disrupts the tertiary structure of the protein, the active site may be changed. If the active site is changed, the enzyme will no longer be functional

Enzyme + Substrate

Enzymes for building

Enzymes for breaking

Jobs that enzymes perform Enzymes work on a variety of reactions; both catabolic and anabolic: The breakdown of glucose The production of ATP (cellular respiration) The destruction (lysis) of worn out cells Breakdown of toxic substances Cell division Digesting food that is eaten

How do enzymes speed up reactions? Enzymes are able to lower the ‘activation energy’ required to get a reaction started

Reaction Rate

Enzymes – ‘ase’ The suffix ‘–ase’ is often used in enzyme names. Amylase Maltase Lactase Catalase Lipase Protease Exceptions: pepsin

Factors affecting enzyme activity Enzyme concentration – more enzyme = faster reaction Substrate concentration – more substrate = faster reaction pH (acid or base) – depends on enzyme, mostly pH 7 Temperature – depends on enzyme, usually best at 25-40˚C Denaturation – irreversible destruction of active site due to exposure to extreme conditions Inhibition – presence of other molecules which slow down or prevent enzyme activity by blocking active site

Substrate & Enzyme Conc.

Temperature & pH: Optimal Conditions Each enzyme will work best at a specific temperature and specific pH This is because pH and temperature can greatly affect the tertiary structure of the enzyme and change the active site

Examples of Optimum pH

Denaturation All proteins (including enzymes) can have their tertiary structure disrupted permanently. This is called denaturation This can happen if the enzyme is: Overheated (beyond ideal temperature) Exposed to extreme changes in pH Exposed to a toxin which irreversibly binds to the active site Denaturation – the irreversible disruption of an enzyme’s tertiary structure, causing it to become totally inactive

Inhibition Enzymes can be affected by the presence of other molecules Molecules which decrease enzyme activity are called inhibitors There are 3 main types of inhibitors: Competitive Non-competitive Toxins/poisons which bind irreversibly to the active site

Competitive Inhibitors Competitive inhibitors bind to the active site of the enzyme, preventing the substrate from binding This is reversible Competitive inhibitors usually have a similar structure to the substrate for that enzyme and  fit into the active site easily

Non-competitive inhibitors Non-competitive inhibitors also bind to the enzyme, but not the active site When the inhibitor binds to the enzyme, it alters the tertiary structure slightly, causing a change in the shape of the active site The change in the active site prevents the substrate from binding to it This is reversible

Toxins Many toxins can bind irreversibly to enzymes, changing the active site permanently Some examples are: Snake venom Nerve gases Heavy metals

Cofactors and coenzymes Some enzymes only function when another chemical component is able to attach to them There are 2 types of these chemical components: Cofactors (inorganic molecules) Coenzymes (organic molecules) These cofactors and coenzymes are usually carrier molecules and transfer electrons or ions from one molecule to another (eg. NADH, FADH2 and NADPH)