Enzymes Flashcards
What type of biological molecule are enzymes?
They are proteins.
What are enzymes?
Enzymes are biological catalysts.
They increase the rate of reactions.
Without being chemically used / changed.
Why are enzymes necessary in animals?
They catalyse thousands of biochemical reactions every second, (metabolic reactions) that control human processes.
What does the enzyme do to the activation energy required to trigger the reaction?
Enzymes lower the activation energy required for a reaction to take place.
Suggest the optimum temperature for enzyme-controlled reactions in humans:
37*C. (body temp.)
A significant increase in temp above the optimum temp has an effect on enzyme-controlled reactions.
Explain why this is so:
- Increase causes denaturation due to broken bonds.
- Changed structure due to loss of 3* structure.
- Structural change causes functional change (3* = function).
- No longer catalyse reaction and rate decreases.
State the word that best describes a region on the surface of an enzyme molecule where a substrate can bind.
Active site.
State the word that best describes the energy required for a chemical reaction to take place.
Activation energy.
What does an oxireductase do?
Catalyses redox reactions, through the transfer of hydrogen, oxygen or electrons.
What does a transferase do?
Catalyses the transfer of a group from one compound to another, the process of transamination.
What does a hydrolase do?
Catalyses hydrolysis and condensation reactions.
What does a lysase do?
Catalyses the addition of a group across a double bond.
What does a isomerase do?
Catalyses the rearrangements in a molecule to convert isomers.
What does a ligase do?
Catalyses bond formation between compounds, using energy from the hydrolysis of ATP.
What is produced when the enzyme lactase is added to milk?
Glucose and Galactose.
What contributes to the structure of an enzyme?
The sequence of amino acids linked by peptide bonds.
What does an increase in temp do to the movement of molecules?
Increases movement.
What does an increase in temp do to the chance of collision between enyzme and substrate?
Increases chance of collision.
What term is defined as:
A structural change of a protein that results in the loss of its biological properties.
Denaturation.
How does an enzyme speed up the rate of reaction?
Provides an alternative reaction pathway with lower activation energy.
When high temps denature a protein, what happens to its structure?
The hydrogen bonds and london forces between R groups have been broken leading to a change in the 3* structure.
Casein can be used to test enzyme rates of hydrolysis, what feature allows this to be tested?
Casein changed colour when digested from an opaque white to clear.
Are enzymes globular or fibrous?
Globular.
What is the main role of enzymes?
Catalysing metabolic reactions, he making and breaking of bonds.
What does a catalyst do to the ΔH (Enthalpy Change)?
Has no effect on ΔH
What does a catalyst do the activation energy?
Lowers energy required.
What are the two theories of enzyme action?
- Lock and key mechanism.
- Induced fit hypothesis.
What is the lock and key hypothesis?
- The shape and charge of the substrate are complimentary to the active site.
- They collide and bind to form an enzyme-substrate complex (e.s.c).
- Products released, freeing the active site for the next reaction.
What is the induced fit hypothesis?
- The collision between substrate and active site changes the shape of the enzyme slightly.
- This creates strain on enzyme structure creating stored energy.
- The recoil of the enzyme puts strain on the substrate, forming/breaking bonds.
- Products released no longer fit the A.S.
Name some factors that affect enzyme activity:
- Temperature;
- pH;
- Enzyme / Substrate concentration;
- Inhibitors;
- Co-factors or prosthetic groups.
What is Q10?
The factor which rate of reaction increases for every 10*C rise in temp.
What is the Q10 equation?
Rt x Q10 = Rt + 10
Why does the stomach have a low pH?
To kill bacteria in food.
Do all enzymes have the same optimum pH?
No they are all different.
Explain the effects of increasing conc^ of substrate on frequency of collisions.
- Increasing conc^ increases the frequency of collisions as there are more substrates per area.
- Until all active sites are occupied.
- Then further increases have no effect on the frequency of collisions as they are not thee limiting factor.
What is Vmax?
The maximum rate of reaction.
How is Km found?
Half Vmax.
What is Km?
The conc^ of substrate required to achieve half of Vmax.
Explain the effect of increasing enzyme conc^ on rate of reaction.
Increased enzyme conc^ means more A.S available, more A.S means more collisions, this leads to more ESC formed.
What are the two types of inhibition?
Competitive and Non-competitive.
How does non-competitive inhibition work?
- The inhibitor does not bind to the active site, it binds to another part of the enzyme, the allosteric site.
- This changes the tertiary structure as the shape of the A.S is altered.
- Fewer ESC can be formed.
What is the allosteric site?
Where non-competitive inhibitors bind.
Explain competitive inhibition:
- The inhibitor fits into the active site.
- This forms an enzyme-inhibitor complex (EIC)
- This means the active site is in use and therefore, no ESC’s can be formed.
What is end product inhibition used for?
Controlling metabolic rates.
When an inhibitor is bound to the allosteric site, what happens to the active site:
The shape is changed and therefore cannot form ESC’s.
What is an EIC?
Enzyme-Inhibitor Complex
What is an ESC?
Enzyme-Substrate Complex
What is a prosthetic group an example of?
A coenzyme.
In enzyme experiments, the rate of enzyme activity often gradually decreases. What is most likely to cause this decrease?
The substrate concentration decreases.
What volume of solution is needed to make 15cm^3 of 0.3M lactose solution from a 1.5M stock solution?
3cm^3
Why would we use an initial rate of reaction?
To show maximum rate with no limiting factors.
Describe the induced-fit model of enzyme action.
- Before the reaction, active site is not complimentary to substrate.
- The shape of active site changes as substrate binds to the active site.
- Enzyme-substrate complex forms.
- Distortion of bonds in substrate leads to reaction.
