Enzymes Flashcards
What are enzymes?
Proteins with an active site specifically shaped for complementary substrate molecules to bind to
What do enzymes do?
Catalyse metabolic reactions (eg. Respiration) and affect structures in organisms (eg. Production of collagen)
Where can enzyme action be?
Intracellular or extracellular
How do enzymes speed up reactions?
The enzyme-substrate complex lowers the activation energy needed, often making reactions happen at a lower temperature
How does the enzyme-substrate complex lower activation energy?
Hydrolysis - Fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily
Condensation - The enzyme holds the two substrate molecules close together, reducing any repulsion between the molecules so they can bond more easily
Induced fit model
The substrate has to be the right shape to fit the active site AND has to make the active site change shape in the right way as well
How are enzymes specific?
Each different enzyme has a different tertiary structure and so a different shaped active site, specifically shaped to its complementary substrate
How may the tertiary structure of an enzyme be altered?
pH, temperature or a mutation in the gene determining the primary structure
How does temperature affect enzyme activity?
- More heat means more kinetic energy, so molecules move faster / vibrate more and the substrate molecules more likely to collide with the enzymes’ active sites
- Energy of the collisions increases, so each collision is more likely to result in a reaction
- If temperature exceeds optimum, this vibration breaks some of the bonds that hold the enzyme in shape
- So the active site changes shape and no enzyme-substrate complexes can form (enzyme is denatured)
How does pH affect enzyme activity?
- Above and below the optimum pH, the H+ and OH– ions found in acids and alkalis can disrupt the ionic and hydrogen bonds that hold the enzyme’s tertiary structure in place
- The active site changes shape, denaturing the enzyme
How does substrate concentration affect rate?
- The higher the substrate concentration, the faster the reaction as more substrate molecules means a collision between substrate and enzyme is more likely and so more active sites will be occupied
- Until saturation point
- After that, all the enzyme’s active sites are full
How does enzyme concentration affect rate?
- The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme-substrate complex, increasing rate of reaction
- But, if the amount of substrate is limited, there may be enough enzyme molecules for all the available substrate so adding more enzyme has no further effect
Competitive enzyme inhibitors
- Similar shape to the substrate molecules
- Compete with the substrate molecules to bind to the active site
- No reaction takes place but they block the active site so no substrate can fit in it
- If there’s a higher concentration of substrate, then the substrate’s chances of getting to an active site before the inhibitor increase
Non-competitive enzyme inhibitors
- Bind to the enzyme away from its active site
- Causes the active site to change shape so the substrate molecules can no longer bind to it
Investigating rate depending on temperature
1) set up boiling tubes containing the same volume and concentration of hydrogen peroxide
2) add equal volumes of buffer solution
3) put each boiling tube water baths of different temperature
4) use pipette to add the same volume and concentration of catalase to each boiling tube
5) record how much oxygen is produced in the first minute of the reaction
6) repeat experiment at each temperature and calculate mean rate of reaction
