2.4 - Enzymes Flashcards
Induced fit hypothesis mechanism
- Enzymes have active sites complementary to the substrate molecule
- When the substrate molecules fit into the enzyme’s active site, the active site changes shape slightly to mould itself around the substrate
- An enzyme-substrate complex is formed, and non-covalent forces such as hydrogen bonds, ionic attractions, London forces and hydrophobic interactions, bind the substrate molecule to the enzyme’s active site.
- The bonds in the tertiary structure of the substrate destabilise
- When the substrate molecules have been converted to the product molecules and these are still in the active site, they form an enzyme-product complex.
- As the product molecules have a slightly different shape from the substrate molecule, they detach from the active site.
- The enzyme molecule is now free to catalyse another reaction with another substrate molecule of the same type.
Induced fit hypothesis short mechanism
- Enzyme active site complementary to substrate
- Substrate binds to enzyme active site
- Enzyme substrate complex forms(ES)
- Bonds in substrate destabilise
- Enzyme-product complex forms
- Products not complementary to enzymes active site
- Product released from active site
- Enzyme active site available to catalyse breakdown of another complementary substrate
Competitive inhibitors mechanism
- The inhibitor has a shape similar to the substrate
- They both compete for the active site, consequently fewer Enzyme-Substrate complexes can be formed
- so the reaction rate is lower than normal
- at higher doses of substrate the inhibition can be overcome as the substrate will greatly outnumber the inhibitor molecule and most collisions will actually form Enzyme-Substrate complexes
Non-competitive inhibitors mechanism
- This binds to the allosteric site away from the active site
- this causes the tertiary structure of the enzyme to change
- this changes the shape of the active site so it is no longer complementary to the substrate
- fewer Enzyme-Substrate complexes can form
- reaction rate is lowered
- higher substrate concentrations cannot overcome the inhibition because the limiting factor is the number of active sites
Factors affecting rate of enzyme-substrate complex formation
- pH
- Temperature
- Surface Area
- Enzyme concentration
- Substrate Concentration
Non-competitive inhibitors on graph
H
Competitive inhibitors on graph
H
Cofactor def
- A substance that has to be present to ensure that an enzyme- catalysed reaction takes place at the appropriate rate.
Coenzyme def
- Small organic, non protein molecules that are able to bind to an active site at the same time as the substrate or just before.
Active site def
-Indented area on the surface of an enzyme molecule, with a shape that is complementary to the shape of the substrate molecule
Catalyst def
- Chemical that speeds up the rate of a reaction by providing an alternative reaction pathway with lower activation energy
- Not used up or chemically changed during reaction
What are enzymes?
Biological catalysts
Features of catalysts
- Not used up in chemical reaction
- Not chemically changed during reaction
Metabolism def
The chemical reactions that take place inside living cells or organisms
Effect of temperature on enzyme activity
-As molecules are heated they gain kinetic energy and move around faster -This results in more frequent successful collisions
• This results in more ESCs forming and therefore a higher (max) rate of reaction and more product formed(more EPCs form)
Effect of pH on enzyme activity
Model answer
• Change in pH or H+ ions alters distribution of charge on the enzyme molecule
• This causes the hydrogen and ionic bonds to be disrupted
• This means the enzyme loses its tertiary structure
• This changes the shape of the active site of the enzyme
• Substrates are no longer attracted to the active site beause the H+ ions
have altered its charge
• Substrates can’t bind to the active site as it is no longer complementary
• No ESCs can form = no product = no reaction
• Enzymes are denatured at extremes of pH (for that enzyme)
Effect of temperature above optimum temperature
-Model answer
- Molecules have more kinetic energy
- Molecules/bonds vibrate too much and weaker bonds are broken (ionic and H) •The tertiary structure of the enzymes are changed
- This means the active site loses its complementary shape
- No ESCs can form as substrate doesn’t fit into active site
- The enzymes have denatured
- This is irreversible so reaction stops
What is pH a measure of?
- pH is a measure of H+ ions
- More H+ ions = more acidic conditions
Effect of optimum temps and pH on enzyme
- Different enzymes have different optimum pHs.
- At their optimum pH, the conc of H+ ions gives the tertiary structure the best shape = most complementary active site.
- At their optimum temperature, the enzymes tertiary structure is at its most stable, as ionic and hydrogen bonds aren’t vibrating too much
- So active site is at its most complementary
What is Q10?
- It is the temperature coefficient
- A measure of the rate of change of reaction when temperature is increased by 10 Degrees
- Most enzymes have a Q10 of about 2
- Means that rate of reaction doubles when temperature increases by 10 Degrees
What is enzyme specificity?
H
Vmax def
- The maximum rate of an enzyme catalysed reaction
- Specific to the type of enzyme
Effect of increasing enzyme concentration on enzyme activity
- No enzyme = no ESC formation = no enzyme catalysed reaction
- More enzyme = more active sites
- More ESCs form so more product = higher rate of reaction
- As long as substrate is in excess, rate of reaction will increase with increase in enzyme concentration
- After a point all substrate molecules are occupying active sites, and a maximum rate will be reached
- Increasing enzyme conc. will have no more effect on the rate, as substrate conc. is in the limiting factor
- When substrate conc. becomes limiting, the rate will decrease as the substrate is used up
Effect of increasing substrate conc. on enzyme activity
- No substrate = no ESC formation = no enzyme catalysed reaction
- More substrate = higher rate of enzyme activity
- More ESCs form so more product forms = higher rate of reaction
- As long as enzyme conc. is in excess, rate of reaction will increase with increase in substrate concentration
- After a point all enzyme molecules are occupied active sites, and a maximum rate will be reached
- Increasing substrate conc. will have no more effect on the rate, as enzyme conc. is in the limiting factor
- When enzyme conc. becomes limiting, the rate will plateau, as all active sites are full, so no more ESCs can form