Enzymes 3 Flashcards
Instead of regulating all enzymes, what is controlled instead?
Many processes organised into pathways
–> regulate 1st step to control the total product from pathway
What are the short + long term controls?
Short = controlling enzyme activity
Long = controlling making of enzyme via transcription
What is feedback activated by in glycolysis?
Low energy signals = ADP + AMP
What is feedback inhibited by in glycolysis?
High energy signals = ATP
Build up of intermediates
= citrate + acetylCoA
What are the 3 types of enzyme inhibition?
Competitive
Non-competitive
Irreversible
In competitive inhibition, how can the inhibitor be outcompeted?
Increasing substrate conc
(for a fixed competitor conc)
= increases rate of reaction
Give an example of a competitive inhibitor
Dihydrofolate reductase used in nucleotide biosynthesis
= Inhibited by Methotrexate
What is irreversible inhibition?
Mimics the substrate
- -> reacts with active site
- -> stops enzyme working indefinitely
What are the 3 types of irreversible inhibitors?
> group-specific covalent modifying agents
transition state analogs
suicide inhibitors
How do group-specific covalent modifying agents work?
React w/ specific type of enzyme functional group on ANY enzyme
What do transition state analogs do?
Structurally similar to transition state
Bind even more tightly to enzyme than substrate binds
–> so v high affinity for active site
What are transition state analogs useful for?
> Understanding catalytic mechanisms
V specific inhibitors of enzymes = pharmaceutical
antigens for immunising lab animals to generate antibodies w/ binding sites complementary to transition state
How do suicide substrates work?
Similar structure to substrate
= binds to active site
–> enzyme reacts covalently (irreversibly) w/ inhibitor
What does mechanism-based inhibition depend on?
Chemical mechanism of catalysis
Give an example of a suicide substrate
Aspirin (acetylsalicylate)
What do non-competitive inhibitors do?
Change enzyme’s affinity for substrate
= more difficult to bind
What effect does increasing substrate conc have on a non-competitive inhibitor reaction?
Doesn’t increase rate of reaction
if regulator conc is constant
Where in a pathway are non-competitive inhibitors normally found?
End product of a pathway
- -> tells regulated step enough product has been made
- -> negative feedback inhibition regulated step
What is allosteric regulation?
Regulation of an enzyme by binding an effector molecule at a site other than active site
–> changes protein conformation
In allosteric the effector must be, what … to the substrate?
Structurally unrelated
How is allosteric inhibition much more sensitive than simple inhibition?
Relatively small amounts of effector needed
Produces relatively large effects
What are the 2 types of covalent modification?
Reversible
= enzyme may exist in enzymatically inter-convertible form
Irreversible
= enzyme may be activated by cleavage
What are the examples of reversible covalent modification?
Phosphorylation using ATP (via kinase) = inactivated
Phosphatase enzyme = reactivates
Adenylation using ATP (via adenyl transferase)
= inactivated
Removing AMP (via adenyl transferase)
= activated
How are enzymes that are potentially harmful synthesised?
As inactive precursors in 1 enviro
–> transferred to another enviro where needs activating
What is a zymogen?
an inactive substance converted into an enzyme + small peptide when activated by a protease
Give an example of a zymogen
How is it formed?
Trypsin
= digestive enzyme that attacks protein
Trypsinogen –> trypsin + hexapeptide
(via action of enterokinase in stomach)
What is premature trypsin normally inhibited by?
A suicide inhibitor
