Enzymes
- Created by: katelingoody
- Created on: 23-01-17 14:00
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- Enzymes
- Enzymes are biological catalysts
- They catalyse reactions, so that extreme temperature and pressure conditions are not required.
- Living cells would otherwise die in the extreme conditions required for many reactions to occur
- Many reactions would not be possible without the use of enzymes
- Globular proteins
- Interact with substrate molecules
- Specific tertiary structure
- Can be intracellular (within cells) or extracellular (outside of cells).
- Intracellular: E.g Hydrogen Peroxide (produced as a toxic waste product of many metabolic reactions) is broken down by catalase.
- Extracellular: E.g Digestion of starch in mouth/small intestine by Amylase or proteins by Protease.
- They catalyse reactions, so that extreme temperature and pressure conditions are not required.
- Lock and key hypothesis
- Shape of active sites are complemen-tary to the shape of the substrate
- When a substate molecule collides with an enzyme whose active site is complemtary, it will fit in the active site
- Forms an Enzyme-Substate complex
- When a substate molecule collides with an enzyme whose active site is complemtary, it will fit in the active site
- Enzyme catalyses the reaction, forming an Enzyme-product complex.
- Possible for enzymes to catalyse reverse reactions
- Shape of active sites are complemen-tary to the shape of the substrate
- Rates of reaction
- pH
- Deviation from optimum pH affects ionic bonds due to H+ or OH- of pH
- Shape of active site changes
- Rate of ES Complex formation decreases, i.e enzyme denatures.
- Shape of active site changes
- Large deviations result in permanent denaturing, whereas small deviations can be reversed by restoring optimum pH
- Deviation from optimum pH affects ionic bonds due to H+ or OH- of pH
- Temperature
- Rate of reaction increases up to 40°C (optimum temp)
- Rate rapidly decreases beyond 40°C
- Beyond optimum temp enzymes denature
- Heat breaks Hydrogen bonds
- 3° Structure changes, causing active site to change shape
- Substrate no longer fits into active site
- 3° Structure changes, causing active site to change shape
- Heat breaks Hydrogen bonds
- As temp increases, substrate and enzyme have more KE
- Collisions become more frequent and forceful
- Rate of ES Complex formation increases.
- Collisions become more frequent and forceful
- Rate of reaction increases up to 40°C (optimum temp)
- Enzyme concentration
- Increasing enzyme concentration increase rate as collisions become more likely
- If there is an excess of substrate, rate of reaction will be directly proportional to enzyme concentration
- If substrate is limited, there will come a point where increasing enzyme concentration will have no further effect
- This is because all substrate molecules will occupy enzyme active sites at one time.
- Increasing enzyme concentration increase rate as collisions become more likely
- Substrate concentration
- Rate increases with substrate concentration as more collisions can occur at once.
- If enzyme conc is limited, there will be a point where increasing substrate conc will not affect rate as all active sites will be occupied by substrate molecules.
- Rate increases with substrate concentration as more collisions can occur at once.
- pH
- Induced- fit hypothesis
- Most recent, widely accepted hypothesis
- States that the shape of active sites are not exactly complemen-tary
- Active site changes shape in the presence of a specific substrate to become complemen-tary.
- When a substate molecule collides with an enzyme, if its composition is specifically correct, the shape of the enzyme's active site will change.
- Substatre then fits, so an enzyme-substrate complex can form
- Reaction is catayles and an enzyme-product complex forms.
- Substatre then fits, so an enzyme-substrate complex can form
- Enzyme inhibitors-Reduce the rate of enzyme-catalysed reactions
- Competitive inhibitors
- Similar shape to substrate-able to fit into active site.
- Reduces rate of ES Complex formation.
- Similar shape to substrate-able to fit into active site.
- Non-competitive inhibitors
- Bond to enzymes away from active site
- Called allosteric binding site
- Causes 3° structure of enzyme to change as different bonds form
- Shape of active site changes, so substrate no longer fits.
- So rate of ES Complex formation decreases
- Called allosteric binding site
- Bond to enzymes away from active site
- End-product inhiibitors
- (Not at A Level) Regulates production of end products and use of reactant.
- Competitive inhibitors
- Enzymes are biological catalysts
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