Enzymes

Globular proteins - Highly folded & coiled They have a specific tertiary structure They are Biological catalysts They lower the activation energy of a chemical reaction

A small hollow depression made up of a small number of amino acids

Enzymes are specific - A single substrate OR - A specific bond

Determines the shape and electrostatic charge of the active site Contains : hydrogen,ionic and sometimes disulphide bonds

The minimum energy required for a chemical reaction to take place

The enzyme bends the bonds that need to be broken for the reaction to occur

Lock and Key model Induced fit model

1) Substrate collides with active site of enzyme and becomes attached (enzyme-substrate complex forms) 2) Enzyme catalyses breakdown of substrate 3) Products released from active site

Temporary bonds between the amino acids (active site) and the substrate molecule

shape of the enzymes active site and its substrate are not exactly complementary BUT when the substrate enters the active site a conformational change (change of shape occurs which induces catalysis

1) The substrate enters the enzymes active site, forming an enzyme-substrate complex 2) Enzyme undergoes a conformational change 3) This caused the conversion of substrate into product 4) this forms and enzyme product complex 5) the product is realised from the enzymes active site

• Active site is slightly flexible • Substrate interacts active site, changing its shape • This strains bonds in the substrate molecule • Makes them more likely to break

1) Enzyme-Substrate complex forms 2) Active site changes shape so its complementary to the substrate which bends the bonds in the substrate 3) Reduces activation energy

Part of an enzyme where substrate molecules bind and undergo chemical reaction

A tertiary structure protein that lowers the activation energy and acts as a biological catalyst

1) Substrate concentration 2) Enzyme concentration 3) Temperature 4) pH

-Substrate conc increases, ROR increases because there are more substrate molecules to fill the enzymes active site - More frequent collisions so more E-S complexes formed - Saturation point reached - all the enzymes active sites are occupied with substrate molecules - So, adding more substrate molecules won’t have any effect on the ROR - The reaction is going as fast as possible = Vmax - Only way the reaction can go any faster is by increasing enzyme concentration

1) ROR high at the start - lots of active sites available to bind to the substrate 2) Reaction continues - many of the active sites become occupied so rate of product reaction increases at a slower rate 3) Once all the actives sites are occupied the rate levels off = Vmax 4) Enzyme conc is now the limiting factor

• Enzyme conc increases - ROR increases - because more active sites available to bind to substrate molecules • More frequent collisions = more E-S complexes formed • Point reached where all substrates are bound to an enzyme so increasing enzyme conc won’t increase the ROR

• Enzyme coc increases = ROR increases because more enzymes = more active sites available to bind to substrate molecules • Substrate available = rate will continue to increase • All substrates will be bound to an active site so the ROR plateaus • substrate conc is now the limiting factor

• Low temp = slow ROR , because enzyme and substrate have low amounts of kinetic energy • won’t be many collisions = reduced formation of ES complexes • Temp increases = increased number of collisions = more ES complexes formed = ROR Temp too high = hydrogen bonds break within the protein causing it to unravel and denature Enzyme denatured = active site changes shape This means they can’t bind to their substrate = decreases ROR

Increase temp = Increased kinetic energy = more ES complexes formed Then optimum temp the. enzyme denatured

• Hydrogen and Ionic bonds broken • Loss of tertiary structure • Altered shape of active site/Active site not complementary to substrate • Less ES complexes formed

each enzyme has its own optimum pH - deviations in pH from the optimum changes the charges in the amino acids in the active site - This affects the ionic bonding in the tertiary structure - Deviations in pH can also break hydrogen bonds in the tertiary structure - This causes the enzyme to change shape and denature - This decreases the ROR as the pH deviates from the enzymes optimum