Enzymes Flashcards
1
Q
What are enzymes and what do they do?
A
- Globular proteins that catalyze biochemical reactions
- They lower the minimum energy or activation energy that reactants need to react
- The reaction is completed much faster
- They are large polypeptides with a tertiary or quaternary structure
- They are specific, they catalyse only one type of reaction
2
Q
What are enzyme substrate reactions and what is the equation?
A
- They take place in a watery environment, where the enzyme and substrate mix and bump into each other
- These collisions allow the substrate to bind to the active site on the enzyme so the reaction can proceed
- Each active site needs a specific substrate
- Enzymes remain unchanged after a reaction and can be used in further reactions
E+S→ES→EP→E+P
(E: Enzyme; S: Substrate; P: Product)
3
Q
What are active sites and what are they used for?
A
- A special area on the molecule where the actual catalytic reaction takes place
- Only one type of substrate fits into the active site
- Enzyme-substrate specificity: one enzyme can only catalyse one type of reaction
- The active site is the result of the folding of the polypeptide chains
- A three-dimensional shape is produced which forms the active site
4
Q
What is the induced fit model and what is the process of enzyme-substrate reaction?
A
- When a substrate enters the active site, it triggers a change in the three-dimensional shape of the enzyme that allows a tighter fit
- It is possible due to the flexibility of the protein molecules that make up the enzyme
- When they merge, the enzyme causes the bonds of the substrate to weaken, therefore reducing the activation energy needed for the reaction
- When the reaction is completed, the products are released from the enzyme
- The active site can slightly change its shape to fit the substrate
5
Q
Explain how enzymes work and what is activation energy?
A
- It reduced the activation energy of a reaction and can therefore speed up the reaction
- Activation energy: the minimum energy that reacting particles require in order for a reaction to occur
6
Q
What is a catalytic reaction?
A
- When an enzyme converts the substance into products
- Enzyme catalysis involves molecular motion and the collisions of substrates with the active site
- Enzymes and substrates react in watery environments
- Catalysis of a reaction is only possible if the substrate and active site happen to be correctly aligned when they collide to allow binding
- The temperatures has to be adequate
7
Q
What does endergonic and exergonic mean?
A
- Endergonic: when a product is formed, energy is adsorbed, usually in the form of heat (endothermic), energy increase
- Exergonic: when a product is formed, energy is released, usually in the form of heat (exothermic), energy decrease
8
Q
How does temperature effect the rate of activity on enzymes?
A
- When temperature is low, molecules tend to move slowly and the chance of collision between substrate and enzyme is low
- When temperature rises, molecules move more rapidly and are more likely to collide
- Each enzyme has an optimum temperature, in which the rate of enzymatic reaction is the highest
- In humans it is 37°C
- When the temperature is higher or lower than optimal, the enzyme becomes denatured and the rate of reaction rapidly decreases
9
Q
What effect does substrate concentration and enzyme concentration have on the rate of activity of an enzyme?
A
- When the substrate concen. is low, there are more enzyme molecules available than substrate and the rate of reaction is low
- When the substrate concen. is high, there is a high chance of collisions between substrate and enzyme molecules (rate rises)
- The increasing stops when all active sites are occupied by substrate molecules, after this point, adding does not affect the rate of reaction
- Once V max is reached (maximal rate of reaction) substrates wait for active sites to become available before binding.
- Same scenario when the enzyme concentration increases. The no. of substrate molecules will be the limiting factor
- Rate of reaction reaches a plateau
10
Q
What effect does the pH have on the rate of activity of an enzyme?
A
- Each enzyme has its own optimum pH at which its activity is the highest
- A change in pH from the optimum affects enzymes and their activity
- Extreme pH values can denature an enzyme by altering the three-dimensional structures of its active site
- The rate of reaction gradually decreases
11
Q
Be able to draw the graphs for the affect of temperature, pH and enzyme/substrate concentration.
A
Check book
12
Q
Explain the denaturation of enzymes.
A
- Because enzymes are proteins, they can be denatured
- Denaturation can be caused by extreme pH values, heat and the presence of heavy metals
- It is an irreversible change to a protein, it can no longer function
- Denaturation destroys the tertiary or quaternary conformation of a protein and sometimes the secondary structure
- If there is only a minor change in temperature of pH, the denaturation may still be reversible (protein can fold back to its original conformation
- The beta sheets and alpha helixes lose their form, is reverts to a primary conformation and there is no longer a functional active site
13
Q
In what way are enzymes used in industry and what is immobilization?
A
- Proteases are used to produce milk powder for babies and carbohydrates help to manufacture corn syrup, also used in brewing
- Sometimes enzymes need to be separated from substrate molecules to prevent enzymatic reactions
- Most enzymes must be active in different temperatures and pH, for this they must be more stable
- This is why they need to be immobilized
- Immobilization: attaching an enzyme to a material so that its movements are restricted
14
Q
Why is immobilization important?
A
- They will not be present in the final product, if they are, it restricts the amount that can be used to process food for human consumption
- Immobilized enzymes permit higher concentrations of enzymes to be used, faster rate of reaction
- Immobilisation allows immediate separation of the enzymes from the reaction mixture, enzymes can then be recycled
15
Q
What is lactose and lactase? What is lactose-intolerance?
A
- Lactose is a disaccharide, consists of glucose and galactose. Lactase is an enzyme than can break down lactose into its monosaccharides
- Lactase is produced in the lining of the small intestine
- People that lack lactase are lactose-intolerant and are unable to break down lactose in dairy products. This intolerance is widespread
- With a lack of lactase, lactose is build up and remains in the digestive system where it is fermented by bacteria
