Enzymes Flashcards
How do enzymes increase the rate of a reaction?
- An enzyme lowers the activation energy of the reaction it catalyses.
What do the properties of an enzyme relate to?
- Properties of enzyme relates to tertiary structure of its active site and ability to combine with other substrates to form an enzyme- substrate complex.
What are enzymes?
- Enzymes are tertiary-structure proteins that catalyse reactions.
Why is the shape of the active site unique and specific? What does this mean, in terms of what can bind to the active site?
- The active site is specific/ unique due to specific folding in tertairy structure of protein.
- Specific shape of active site means that enzymes only attach to substrates that are complementary in shape.
What is activation energy (bio definition?)
- The certain amount of energy required before a reaction can occur.
What are the two models for enzyme action called?
- Lock and key model.
- Induced fit model.
Desribe the lock and key model.
4 key points
- Suggests enzyme active site is a fixed shape.
- Due to random collisions, only one type of substrate (with specific shape) can collide and attach to enzyme: forming enzyme- substrate complex.
- Enzyme active site will put strain on bonds of substrate (lowering activation energy.)
- Products are released/ enzyme can be re-used.
Describe the induced- fit model.
3 key points
- Active site is induced to mould around a subtrate (ie. shape of active site isn’t exactly complementary to substrate.)
- Enzyme - substrate complex occurs –> active site moulding puts strain on the bonds (in substrate), lowering the activation energy.
- Products are released/ active site returns to original shape.
True or False
Lock and key model is accepted model for enzyme function.
- False.
- Induced-fit model is the accepted model for enzyme function.
Give 5 factors that affect the rate of enzyme-controlled reactions.
1.) Temp.
2.) pH
3.) Substrate concentration.
4.) Enzyme concentration.
5.) Inhibitors (competitive/ non-competitive.)
If temperature is too low, how will this affect the rate of an enzyme- controlled reaction?
- Temperature = too low: substrate/ enzyme don’t have enough kinetic energy for successful collisions between enzyme (active site) and the substrate.
- So, fewer enzyme- substrate complexes are formed.
- So, rate of reaction decreases.
If temperature is too high, how will this affect an enzyme- controlled reaction?
- Temp = too high (enzyme has too much kinetic energy so bonds in tertiary structure of the enzyme are going to break.)
- Enzyme/ active site becomes denatured.
- Active site changes shape/ enzyme- substrate complexes cannot form.
- Rate of reaction decreases/ stops.
If pH is too high/ low, how will this affect the enzyme- controlled reaction?
- Too high/ too low pH will interfere with the charges in the amino acids in the active site (too high = too many OH- ions, too low = too many H+ ions.)
- This can break the bonds holding the tertiary structure in place –> change active site shape/ denatures enzyme.
- Enzyme denatures (fewer enzyme- substrate complexes are formed): rate of reaction decreases.
Which bonds will mainly break in tertiary structure of enzyme if pH is too high/ too low?
2 bonds (MAINLY)
- Ionic
- Hydrogen.
True or False
All enzymes in our body work at an optimal pH of 7.
- False.
- Different enzymes in body have a different optimal pH.
If you have an insufficient substrate concentration, how does this affect the rate of reaction?
3 main points
- Decreased rate of reaction.
- Fewer collisions between the enzyme and substrate.
- Fewer enyme- substrate complexes formed.
Why does the graph for rate of reaction against either enzyme- concentration or substrate concentration plateu?
- Reason for graph with enzyme concentration plateau –> empty active sites due to insufficient substrate (substrate = limiting factor.) Rate of reaction remains the same.
- Reason for graph with substrate concentration plateau –> enzyme active sites become saturated/ not enough enzymes (enzymes = limiting factor.) Rate of reaction remains the same.
If you have an insufficient enzyme concentration, how does this affect the rate of reaction?
3 main points
- Enzyme active sites will become saturated with substrate, unable to work faster.
- Fewer enzyme- substrate complexes formed.
- Decreased rate of reaction.
What are competitive inhibitors? What happens to competitive inhibitors at a high substrate concentration?
- Competitive inhibitors have SIMILAR shape to substrate / can bind to active site–> prevents substrate from binding/ reaction from occurring.
- High substrate concentration –> knock compeitive inhibitors out of the active site (ie. substrate out- competes the inhibitor.)
What is the structure that is formed when an inhibitor binds to an enzyme’s active site?
- Enzyme- inhibitor complex.
What are non- competitive inhibitors? Can substrates still bind to active site at high- substrate concentration?
- Non- competitive inhibitors bind to the enzyme (away from the active site.)
- Binding causes the active site to change shape, so substrate can no longer bind (even at a high concentration of substrate.)
You are given graph with rate of reaction against substrate concentration with the curve for no inhibitor plotted. What would the curves for competitive inhibitor/ non- competitive inhibitor look like on the graph and why?
- Competitive inhibitor: curve is below curve of no inhibitor BUT at certain point, the rate of reactions allign/ rate of reaction returns to normal (because high substrate concentrations knocks off competitive inhibitors.)
- Non- competitive inhibitor: curve is below curve of competitive inhibitor (plateus very soon because high substrate concentration won’t knock inhibitor off)/ maximum rate of reaction reached early on.
True or False
Enzymes only catalyse intracellular reactions.
- False enzymes catalyse both intracellular and extracellular reactions.
What do intracellular and extracellular reactions determine?
- Intracellular and extracellular reactions determine structure and functions from cellular to whole-organism level.
How can you work out the pH when you know the H+ concentration?
pH = -log (H+)
How can you work out H+ concentration when you know pH?
(H+) =10⁻pH
What value does (OH-) x (H+) concentrations give you?
10⁻pH
