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
Examples of non competitive inhibition?
Poisons such as arsenic and heavy metals such as lead and mercury are non competitive inhibitors they act by attaching to the allosteric site of the enzyme and changing the structure of the enzyme
The active site changes shape and its unable to connect with the substrate molecule
TOP TIP example of non competitive inhibitor?
cyanide is a non competitive inhibitor that inhibits the enzymes of aerobic respiration
What occurs at the allosteric site of an enzyme?
non competitive inhibitor to enzyme
In what way does end product inhibition benefit a cell?
control - prevents too much end product being produced
What is each step within a metabolic pathway controlled by?
by one specific enzyme coded for by one specific gene
When is the pathway said to be blocked?
If an enzyme within the pathway is missing or does not work properly due to a mutation the pathway is blocked
When are enzymes always switched on?
Some metabolic pathways are required continuously and the genes that code for their enzymes are always switched on
When are enzymes switched off?
other pathways are only needed on certain occasions
to prevent resources being wasted, the genes that code for the enzymes in the pathways are switched on or off as required in response to signals from within the cell from its environment
Explain the Jacob Monod Theory?
E coli can break down lactose sugar into glucose and galactose by producing the enzyme B-galactosidase
The bacterial cells then use the glucose for cell respiration
The enzyme is only produced when lactose is present
this prevents wastage of valuable cell resources such as ATP and amino acids
What does it mean when genes are switched on?
If genes are switched on (expressed) it is actively coding for the enzyme and the enzyme is produced
What does it mean when genes are switched off?
they are not expressed they do not actively code for the enzyme and is not produced
TOP TIP Jacob monod theory can be used as an example of what?
Genetic control of a metabolic pathway
Explain Enzyme Induction?
The gene coding for the enzyme B-galactosidase is expressed only when lactose is present
This is called enzyme induction
Lactose is the inducer - its presence in the environment signals the gene to be expressed and the enzyme to be produced
Explain Gene action in bacteria jacob monod theory (lactose absent)?
Regulator gene is always on causing the repressor molecule to be produced
Repressor molecule (protein) combines with the operator gene
Repressor molecule switches off the operator gene
Operator gene is unable to function therefore the structural gene remains off
Enzyme is not produced
Explain Gene action in bacteria jacob monod theory (lactose present)?
Regulator gene is always on causing the repressor molecule to be produced
repressor molecule combines with lactose
repressor lactose complex is unable to switch off the operator gene
Operator gene switches on structural gene
enzyme is produced
enzyme breaks down lactose
when all lactose has been broken down the repressor molecule is again free to switch off operator and enzyme production stops
Lactose acts as the inducer molecule
What is Lac operon?
signal molecule is lactose as it combines with the repressor molecule resulting in the structural gene being expressed and B-galactosidase being produced
Describe the role of genes in control of the metabolic pathways?
each step within a metabolic pathway is controlled by one specific enzyme coded for one specific gene
Order of bases in gene determines order of amino acid which determines the shape, structure and function
