2.4.3 Co-factors and enzyme inhibition Flashcards
Define co-factors.
A non-protein substance bound to an enzyme.
What type of molecule is a co-factor and how do they work?
They are inorganic molecules or ions. They work by helping the enzyme and substrate bind together.
Why aren’t co-factors used up or change shape?
Because they aren’t involved in the reaction.
Define co-enzyme.
An organic co-factor.
Do co-enzymes participate in reactions and change shape?
Yes.
What is the role for co-enzymes?
Act as carriers, moving chemical groups between different enzymes. They’re continually recycled during this process.
Define prosthetic group.
When a cofactor is tightly bound to an enzyme.
What is the role of a competitive inhibitor?
To compete with the substrate to bind to the active site, but no reaction takes place - they block the active site so no substrate molecules can fit in it.
During competitive inhibition, what occurs when you increase the concentration of the inhibitor?
Hardly any substrate will bind to the enzyme.
During competitive inhibition, what occurs when you increase the concentration of the substrate?
An increased chance of the substrate binding to the active site - therefore increasing the rate of reaction.
Where do non-competitive inhibitors bind to?
The allosteric site.
When a non-competitive inhibitor binds to the allosteric site, what happens to the active site?
The active site changes shape so the substrate molecules can no longer bind to it.
Why do non-competitive inhibitors not ‘compete’ with substrates?
Because they are a completely different shape so they won’t be able to bind to the active site.
During non-competitive inhibition, what occurs when you increase the concentration of the substrate?
No effect because the enzymes will still be inhibited.
Why are some inhibitors irreversible?
Because they contain strong covalent bonds.
Why are some inhibitors reversible?
Because they contain weak hydrogen bonds.
What is the role of antiviral drugs?
They are reverse transcriptase inhibitors that inhibit the enzyme reverse transcriptase, which catalyses the replication of viral DNA.
What is the role of antibiotics?
Penicillin inhibits the enzyme transpeptidase, which catalyses the formation of proteins in bacterial cell walls - weakens the cell wall and prevents the bacterium from regulating its osmotic pressure.
What is the role of cyanide?
It is an irreversible inhibitor of cytochrome c oxidase, an enzyme that catalyses respiration reactions.
What is the role of malonate?
Inhibits succinate dehydrogenase preventing respiration reactions.
What is the role of arsenic?
Inhibits pyruvate dehydrogenase preventing respiration reactions.
Define metabolic pathway.
A series of connected metabolic reactions.
Define product inhibition.
Many enzymes are inhibited by the product of the reaction they catalyse.
Define end-product inhibition.
The end product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway - regulating the pathway and controlling the amount of end-product that gets made.
What is phosphofructokinases?
An enzyme involved in the metabolic pathway that breaks down glucose to make ATP - ATP inhibits the action of phosphofructokinases - so a high level of ATP prevents more ATP from being made.
What are enzymes sometimes synthesised as?
Inactive precursors in metabolic pathways to prevent them causing damage to cells.
What does part of the precursor molecule inhibit?
Its action as an enzyme. Once this part is removed the enzyme becomes active.
