2.1 b Control of metabolic pathways Flashcards
What is activation energy?
the energy required to initiate a reaction is called its activation energy. It is the energy barrier substrates must overcome before they become products.
What are catalysts?
catalysts speed up the rate of chemical reactions by lowering the activation energy required for the reactions to proceed.
What are enzymes?
Enzymes are biological catalysts
Why is the presence of enzymes very important?
at normal body temp, chemical reactions would take place at too slow a rate to maintain life if enzymes were not present
What is the function of the enzyme?
Enzymes therefore act by reducing the activation energy for a reaction to occur faster at the lower temp found in living cells
What is the structure of an enzyme?
Enzymes are three dimensional globular protein molecules that are sensitive to both pH and temperature.
The specific part of the enzyme molecule that connects with a substrate molecule is called the active site
The shape of the active site on an enzyme molecule is specific to only one substrate
What determines the sequence of amino acids in the enzyme?
The sequence of bases in the DNA coding for the enzyme
What determines the shape of the active site?
The sequence of amino acids in the enzyme
If the shape of a substrate molecule is complementary to the active site of the enzyme it will have what?
high affinity for the active site
When will it have a low affinity?
Products of enzyme substrate reactions have a low affinity for the active site of the enzyme.
What is induced fit?
the active site begins in an open position which allows the substrate to move in and bind.
binding of the substrate causes a change in the shape of the active site to be a closed position.
This brings the substrate and enzyme closer together, increasing the chance of a reaction
Once the product has formed the shape of the active site returns to the open position and the product moves out.
What is a synthesis reaction?
enzyme joins two molecules together to make the product
What is a degradation reaction?
enzyme breaks down a large substrate molecules into smaller product molecule
Advantage of a multi enzyme complex to the cell?
able to catalyse faster reactions and control order of reactions
how can you control the rate of enzyme reactions?
substrate concentration
enzyme concentration
end product inhibition
competitive and non competitive inhibitors
what happens as the substrate concentration increases?
the rate of reaction increases and then becomes constant
diagram// when the slope is increasing?
as substrate concentration increases more substrate molecules are able to bind with enzyme active site and the rate of reaction increases.
when the diagram platues?
the substrate concentration is high enough that all the active sites are filled. increasing the substrate concentration has no further effect on the rate of reaction which remains constant. enzyme concentration is now the limiting factor
what will further increase the rate of this reaction?
enzyme concentration will need to be increased
What are the three types of inhibitor molecules?
- end product inhibitor (feedback inhibitor)
- competitive inhibitor
- non competitive inhibitor
Explain Feedback Inhibition?
In feedback inhibition the end product binds to an early enzyme in the metabolic pathway altering the shape of the enzyme’s active site and blocking the pathway.
This prevents too much end product from being produced
As the concentration of the end product drops inhibition ceases and the pathway resumes again
Explain Competitive Inhibition?
Competitive inhibitor molecules have a shape similar to that of the substrate.
They bind with the enzyme’s active site preventing the substrate from entering
Because the substrate and inhibitor are in competition for the active site increasing the substrate concentration cause an increase in the rate of reaction
Explain non competitive inhibition?
Non competitive inhibitors bind to the part of the enzyme that is not its active site (allosteric site)
As a result the shape of the active site is altered and the substrate cannot enter
Because the inhibitor and substrate are not in competition for the active site increasing substrate concentration has no effect on the rate of reaction
The rate of reaction remains low
Is competitive or non competitive reversible or irreversible?
Competitive inhibition is reversible
Non Competitive inhibition is irreversible
