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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. Enzyme + Substrate

9. Enzymes for building

10. Enzymes for breaking

11. 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

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

13. Reaction Rate

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

15. 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

16. Substrate & Enzyme Conc.

17. 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

19. Examples of Optimum pH

20. 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

21. 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

22. 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

23. 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

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

26. 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)