- Enzymes are biological catalysts that speed up metabolic reactions and remain unchanged at the end of the reaction.
- Catalysts can speed up reactions as they can speed up reactions without altering the pH or temperature and instead function at temperatures and pressures that sustain life.
- Enzymes are proteins and have protein structure (primary, secondary, tertiary, quaternary) and therefore are coded for by genes
- Some use cofactors.
- Metabolic disorders are the result of deficient enzymes in metabolic pathways
- Enzymes also catalyse the formation of an organism’s structural components e.g. collagen in bone and cartilage in blood vessel walls
- Active site contains about 6 –10 amino acids and the tertiary structure is essential as the shape of the active site must be complementary to the substrate molecule
- Active sites are changed by temperature and pH as this alters the bonds that hold together the bonds of the tertiary structure
- Some cofactors act as co-substrates andsome change the distribution of charge on the enzyme’s surface and make temporary bonds to aid the substrate in binding to the enzyme.
- a cofactor that is permanently bound by covalent bonds to an enzyme molecule.
E.g. Zinc ion bound to the active side ofcarbonic anhydrase
- These bind temporarily to the active site of the enzyme with the substrate and are
organic non-protein molecules whichare chemically changed during the reaction.
The lock and key hypothesis states that the substrate fits perfectly into the enzyme, like a lock and a key would.
- Activation energy is the minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo chemical transformation or physical transport.
- Enzymes lower the activation energy for areaction. ac
Effect of temperature on enzymes
- Extra heat energy causes the molecules to vibrate which increases the rate of successful collisions between molecules and increases the force with which they collide
- Both enzyme and the substrate move faster, therefore the rate of formation of ES complexes increases and the rate of reaction increases.
- Rate of reaction is at its maximum at optimum temperature
- Heat also makes molecules vibrate which may break some of the weaker bonds in the tertiary structure ofthe active site, denaturing it (bonds like the ionic bonds and hydrogen bonds)
- As the active side changes the substrate will no longer fid
- As more heat is applied the enzyme active site changes shape completely and irreversible so the reaction cannot proceed at all.
Psychrophilic– cold loving, enzymes that work at low temperatures
Thermophilic– heat loving, enzymes that work at high temperatures
Effect of pH on enzymes
Acidic – 0-6 pH
Neutral – 7 pH
Alkaline – 8-14 pH
Acids are proton (H+) donors
Buffers – Can donate or accept protons,resist changes to pH
The tertiary structure is alters as the positive charges on the protons break the hydrogen bonds that hold the amino acid in an it’s helix shape.
The ionic charges are also altered and so the active site loses its shape and can no longer fit the substrate molecule.
Effect of substrate concentration
- Initially rate of reaction increases as more enzyme substrate complexes while the substrate concentration is the limiting factor but when the reaction reaches Vmax the limiting factor is the enzyme concentration as all the enzyme active sites are occupied and the maximum turnover rate is reached.
If enzyme concentration is increased the enzyme and substrate swap roles as limiting factors.
1. Competitive inhibtor
- Inhibition of an enzyme where the inhibitor molecule has
- a similar shape to the substrate
- and is therefore complementary to the active site of the enzyme and competes for the active side.
- It blocks the active site and prevents enzyme-substrate complexes.
2. Non-competitive inhibtor
- Inhibition of an enzyme where the inhibitor molecule attaches to the enzyme away from the active site and changes the active site shape to prevent enzyme-substrate complexes forming.
- The active site of the enzyme nolonger has the complementary shape to its substrate.
1. What is enzyme and its function
2. How do enzymes affect the activation energy
3. Effect of temperature / pH / subtrate concentration on enzymes
This is the end of the topic
Drafted by Eva (Biology)