PH1125 - Enzymes Flashcards
what is an enzyme from a chemical pov?
- well defined sequence of amino acids with well defined 3d structures (proteins)
what is an enzyme from a biologial pov?
- macromolecular bio-catalysts
what does an enzyme do?
- accelerates a biochemical reaction that would otherwise occur over years instead of seconds
are enzymes and proteins changed by the reactions they catalyse?
- no they remain unchanged
what are the properties of enzymatic reactions? (3)
- substrate specific
- efficient
- fast
what is the lock and key model? (2)
- only a substrate (S) that is complimentary to the enzyme (E) can bind to the active site
- once bound a reaction can occur liberating a product(s) (P)
what is the induced fit model? (2)
- in some enzymes the shape of the active site only becomes complimentary after the substrate has bound
- the tertiary structure of the protein change to accommodate the substrate
what happens in an induced fit model? (4)
- as a drug approaches an active site complimentary amino acids residues are drawn towards the substrate
- polar attraction and hydrophobic attractions occur
- this pulls the tertiary structure of the protein out of shape to accommodate the substrate through formation of favourable bonding interactions
- while the substrate remains bound, the active site assumes a different shape
what is the michaelis menten model?
- it was developed to understnad the kinetics of enzymic reactions
what are the assumptions of the michaelis menten model? (3)
- the enzyme binds a single substrate (the model assumes cofactors are already bound)
- there are two distinct steps where the substrate bind reversibly but the product formation is irreversible
- a steady state approximation applies
what is the michaelis-menten equation?
- V = (Vmax [S]) / (Km + [S])
what is Vmax?
- maximum velocity the reaction can achieve
what are the units for Vmax?
- maximum number of moled of substrate than can be processed in a unit of time; mol s-1
what is Km? (2)
- [S]; the michaelis constant required to achieve half the maximum velocity
- gives an indication of how tightly the enzyme binds to its substrate
what is the Km value for a weak substrate?
- large Km as a high concentration of substrate is needed to achieve Vmax/2
what is an inhibitor?
- a compound that binds to an enzyme and interferes with its activity by preventing the formation of the ES complex
what two types are reversible inhibitors classified into? (2)
- competitive
- non-competitive
what is a competitive inhibitor and how does it work? (3)
- a competitive inhibitor competes directly with the natural substrate for the enzyme active site
- the inhibitor only binds to the free enzyme in the active site (which is the only binding site)
- therefore the amount of free enzyme available for substrate binding is reduced (if the inhibitor binds tightly to the enzyme and remains in the active site)
what can competitive inhibitor be overcome by?
- by increasing the substrate concentration
what are the kinetics of competitive inhibition? (3)
- the inhibitor (I) and substrate (S) are competing for the active site (E)
- greater the [I] the more (S) needed to achieve saturation
- greater [S] needed to achieve Vmax there Km increase
when a competitive inhibitor is added what happens to Vmax and Km on a Lineweaver Burk plot? (3)
- steepness increases
- Vmax remains unchanged
- Km increases as [I] increases
what can a non-competitive inhibitor bind to? (2)
- free E
- ES
what is a non-competitive inhibitor? (3)
- they generally do not resemble the natural substrate of the target enzyme (as they are bonding at an alternate site)
- inhibition can’t be overcome by increasing the substrate concentration
- acts by decreasing the turnover number of an enzyme
what are the kinetics of non-competitive inhibition? (3)
- EI and ESI are inactive forms of the enzyme
- saturation of E with S can occur but is inactivated by I therefore Vmax is reduced
- [S] required to saturate E does not change since the substrate is free to interact with the active site alone
when a non-competitive inhibitor is added what happens to Vmax and Km on a Lineweaver Burk plot? (3)
- gradient increases
- Km remains unchanged
- Vmax decreases as [I] increases
what is allopurinol? (3)
- competitive inhibitor of xanthine oxidase
- enzyme xanthine oxidase produces gout
- blocking production of uric acid
what is captopril? (3)
- competitive inhibitor of angiotensin converting enzyme (ACE)
- an enzyme that controls blood pressure and volume
- enzyme binds to captopril
what do kinase enzymes catalyse the transfer of? (2)
- phosphate groups between proteins
- kinase use ATP as a substrate and a source of the phosphate group (cofactor used to transfer phosphate to target molecule)
how do irreversible inhibitors form bonds with the enzyme?
- they form strong covalent bond
what does penicillin inhibit?
- transpeptidase
what is transpeptidase?
- an enzyme involved in the synthesis of bacterial peptidoglycan cell wall synthesis
how do penicillins work? (3)
- beta-lactam ring on penicillin molecule is responsible for antibacterial activity
- ring is highly reactive and forms a covalent bons with the enzyme
- bond is irreversibly bound
what are prostaglandins? (2)
- hormones that regulate inflammation and pain
- eg aspirin irreversibly inhibits prostaglandin synthesis by the trans-acetylation of a serine in the active site
