2.4 - Enzymes Flashcards
What can enzymes do?
- act as a biological catalyst causing reactions to speed up
- they can affect structures and functions of organisms
What are intracellular enzymes?
Enzymes that work within the cell
What are extracellular enzymes?
Enzymes that work outside of the cell
What is an example of an intracellular enzyme?
Catalase:
They work inside the cell to catalyse the breakdown of hydrogen peroxide turning it into oxygen and water
What is an example of an extracellular enzyme?
Amylase:
Secreted from the salivary glands to catalyse the hydrolysis of starch into maltose
What are key features of an enzyme?
- globular protein
- has an active site that a complementary substrate binds to
How is the shape of the active site determined?
It is determined by the enzymes tertiary structure
What is made when and enzyme and substrate bind?
An enzyme substrate complex
How does an enzyme lower the activation energy?
It lowers temperature that the reaction needs to happen at causing it to speed up the rate of reaction by forming an enzyme substrate complex
What are the 2 theories about how enzymes work?
- lock and key method
- induced fit method
How does the lock and key method work?
- the enzyme and the substrate are complementary
- this means that only certain substrates can go with enzymes
- the substrate fits into the active site of the enzyme
- this forms an enzyme substrate complex
- this then breaks the bonds in the enzymes causing the products to form
How does the induced fit theory work?
- the enzyme and the substrate have similar shapes
- the substrate binds with the active site changing the shape slightly to fit more closely
- this forms an enzyme substrate complex
- bonds are either formed or broken to produce the product
What are the 4 factors the effect the rate of enzyme activity/reactions?
- temperature
- pH
- enzyme concentration
- substrate concentration
How does temperature effect enzyme activity?
- the temperature rises and the enzymes gain kinetic energy causeing them to vibrate more
- this means the rate of reaction increases
- when the temperature goes above a certain level it causes the enzymes to denature
- so the substrate is no longer able to bind to the active site
What happens when an enzyme denatures?
It causes some of the bonds to break meaning the active site to change shape
What is the symbol for temperature coefficient?
Q10
How do you work out the temperature coefficient?
Rate at higher temperature / rate at a lower temperature
- temperatures have to be 10 degrees apart
How does pH effect enzyme activity?
It causes the ionic and hydrogen bonds to break so the enzymes active site changes shape, this is because the bonds hold the enzymes tertiary structure together
What happens when the pH is below the optimum?
It causes H+ ions to be produced (found in acids) which can break bonds that are holding the tertiary structure together so the active site changes
What happens when the pH is above the optimum?
It causes OH- ions to be produced (found in alkalis) causing the bonds to break so the active site changes shape
What is Pepsins optimum pH?
pH 2
What is the optimum pH for most enzymes?
pH7
How does the enzyme concentration affect the rate of reaction?
The more enzyme molecules there are in a solution, the more likely it is for a substrate to collide with it to form an enzyme substrate complex, so the rate of reaction increases
What is the limiting factor when the enzyme concentration is increased?
The amount of substrate
How does the substrate concentration affect the rate of reaction?
The higher the substrate concentration the faster the reaction because the enzyme and the substrate are more likely to collide so more active sights will be used
What happens to the rate of reaction when the saturation point is reached (substrate concentration)?
All the active sites are used so adding more substrate will not make a difference. But eventually the concentration decreases with the theme that the reaction is taking place so the rate of reaction decreases overtime
What is a cofactor (enzymes)?
It is a substrate that the enzyme needs to work
What is an enzyme inhibitor?
They stop the enzyme from being able to work
What is end product inhibition (enzymes)?
It is when one or more of the enzymes in a metabolic pathway is inhibited so it is unable to produce the correct product
What is a competitive inhibitor (enzymes)?
The substrate and the inhibitor have the same shape so either can bind to the enzyme, the inhibitor blocks the substrate so it is unable to bind and form a product
Are the effects of a competitive inhibitor reversible?
Yes, the inhibitor is able to detach so the effect is reversible
What is a non-competitive inhibitor?
The inhibitor goes to the enzyme and binds to the allosteric site and changes the shape of the active site so the substrate is unable to bing to the enzyme to form a product
Aren the effects of a non-competitive inhibitor reversible?
No, the inhibitor changes the protein shape of the enzyme so the active site is permanently changed
What is an allosteric sit on an enzyme?
A part of the enzyme that is not near the active site
How do competitive inhibitors affect the rate of reaction?
Competitive inhibitors make the rate of reaction slower because the inhibitors rarely block every active site, but it reaches the same end point
How do non-competitive enzyme inhibitors affect the rate of reaction?
They lower the rate of reaction because the enzymes changes are irreversible so there are less enzymes to break the substrate, so the end point is significantly lower
