1.5 Enzymes Flashcards
What is the definition of a metabolite?
- Molecule involved in reactions occurring in cells + organisms (aka metabolism).
What does metabolism consist of?
- Chains + cycles of enzyme-catalysed reactions.
What is an anabolic reaction?
- Larger molecules built up from smaller molecules.
What is a catabolic reaction?
- Larger molecules are broken down.
What does metabolism consist of?
- Metabolism = anabolism + catabolism.
What is a catalyst?
- Substance that increases RofR of chem reaction.
- Only small amount of catalyst is required.
- Catalyst is chemically unaffected + can be recovered when reaction is complete.
What is an enzyme?
- Organic catalyst that speeds up metabolic reaction in cells + organisms.
What are the 3 properties of enzymes?
- Do not change nature of the reaction.
- Effective in small amounts.
- Chemically unchanged at end of reaction.
What is a substrate?
- Molecule that binds to active site of enzyme to form enzyme-substrate complex.
- Substrate converted to product + enzyme unchanged.
What is an active site?
- Enzyme molecules usually much bigger than substrate molecules.
- Small part of enzyme molecule that binds to its specific substrate + causes catalysis.
What is the equation for enzyme catalysis?
- E + S ⇌ ES ⇌ P + E
What is the lock and key model?
- Enzyme + substrate have fixed shape.
- Substrate fits into active site like a lock and key.
Why has the lock and key model been disregarded?
- Too simplistic.
- Active site changes shape so that substrate can fit.
What is the induced fit hypothesis?
- When enzyme + substrate combine, active site changes shape to become truly complementary to part of substrate to which it attaches.
- Combination w substrate induces the enzyme’s active site to fit.
- requires ATP.
What is activation energy?
- Energy barrier that must be overcome before reactants reach temporary transition state.
How do enzymes change activation energy?
- Lower activation energy of reactions they catalyse, making reaction occur more readily.
How is specificity related to enzymes?
- Highly specific.
- Only catalyse one type of reaction or only very small group of similar reactions.
Why do enzymes have such a high specificity?
- Active site has precise shape + distinctive chemical properties (presence of certain chem groups + bonds).
- Substrate must be complementary to active site.
What are some different factors that affect enzyme activity?
- Temp.
- pH.
- Substrate conc.
- Enzyme conc.
How does temp affect enzyme activity?
- As it increases, enzyme + substrate move more rapidly, so more likely to collide + react.
- rate of reaction slows as enzymes begin to denature.
What is random thermal movement?
- Movement shown by all particles at temps above absolute zero.
- As temp increases, so does rate of random thermal movement.
What does a graph of temp against rate of reaction look like?
- Gradually increases to a peak then rapidly declines.
How can we work out the optimum temp?
- The point on the curve when enzyme activity is the greatest.
What happens to enzymes when the pH is too low or high?
- They denature.
Why do enzymes denature?
- Structure of protein maintained by bonds within 3D structure of protein.
- Change in pH alters the bonding patterns.
- This changes shape of active site.
When enzymes denature due to too low or high pH, is it permanent or reversible?
-Normally reversible.
- Active site may reappear when enzyme is brought back to optimum pH.
What does a graph of pH against rate of reaction look like?
- Bell curve but starts slightly higher than it ends.
What affect does a lower substrate conc have?
- Rate increases in direct proportion to the increase in substrate conc.
What affect does a higher substrate conc have?
- Rate of reaction becomes constant, showing further increase as substrate conc increases.
What does a graph of substrate conc against rate of reaction look like?
- Gradually increases then levels out to look like an asymptote.
What happens to rate of reaction at lower enzyme concs?
- Rate increases in direct proportion to increase in enzyme conc.
What happens to rate of reaction at higher enzyme concs?
- RofR becomes constant showing no further increase as enzyme conc increases.
What is shown by the first part of an enzyme conc graph?
- Where the enzyme conc is limiting.
What is shown by the second part of an enzyme conc graph?
- Where substrate conc is limiting.
What does an enzyme conc graph look like?
- Linear directly proportional graph, then suddenly levels out to flat.
What is an enzyme inhibitor?
- Substance that slows the rate of an enzyme-controlled reaction by preventing binding of substrate to active site.
What have studies of enzyme inhibitors helped our understanding of?
- Chemistry of active site of enzymes.
- Natural regulation of metabolism.
- Ways in which commercial pesticides + drugs work.
What is a competitive enzyme inhibitor?
- Inhibitor chemically resembles substrate molecule + binds w active site, blocking access to substrate molecules.
What happens w a low conc of a competitive enzyme inhibitor?
- Increasing conc of substrate eventually overcomes inhibition as substrate molecules displace inhibitor.
- Enzyme-substrate collisions more likely then enzyme-inhibitor collisions.
What is a non-competitive enzyme inhibitor?
- Chemically unlike substrate.
- Binds to another (allosteric) site.
- This changes shape of enzyme molecule including active site.
What happens w a low conc of a non-competitive enzyme inhibitor?
- Increasing conc of substrate can neither displace inhibitor nor prevent binding of further inhibitor molecules.
How do competitive inhibitors affect the initial rate of reaction compared to not having an inhibitor?
- Less steep curve than without, but it will eventually reach the same point.
How do non-competitive inhibitors affect the initial rate of reaction compared to not having an inhibitor or having a competitive inhibitor?
- Steeper than competitive but not as steep as without inhibitor.
- Levels off and doesn’t reach the same rate of reaction as the other curves.
What is the end-product inhibition?
- Feature of a chain of enzyme-controlled reactions in which a product of a late reaction in series inhibits the enzyme controlling an earlier reaction.
What is regulation of a metabolic pathway by end-product inhibition an example of?
- Negative feedback.
