Properties of enzymes Flashcards
What are enzymes
Biological catalysts that speed up the rate of a reaction without altering the final equilibrium between products and reactants.
What are the two types of specificity that an enzyme can show?
Group specificity for example alcohol dehydrogenase oxidises primary alcohols to aldehydes; works on methanol, ethanol, propanol etc. because of the -OH group.
Absolute specificity, will only act on one substrate (or one stereoisomer of a substrate only)
What are the classes of enzymes
Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases
What is an oxidoreductase? Give an example
Oxidoreductases catalyse transfer of H and electrons.
For example, lactate dehydrogenase:
Pyruvate + NADH -> L-lactate + NAD
What is a transferase? Give an example
Transferases swap groups between molecules.
For example, alanine aminotransferase:
Pyruvate + glutamate -> L-alanine + a-ketoglutarate
What is a hydrolase? Give an example
Hydrolyses a covalent bond
An example is trypsin:
Gly-Lys-Val-Ala + water -> Gly-Lys + Val-Ala
What is a lyase? Give an example
Lyases are involved in the cleavage of bonds - forms double bonds by the removal of groups
For example, ATP-citrate lyase:
citrate + ATP oxaloacetate + acetate + ADP + Pi
What is an isomerase? Give an example
Isomerases swap groups within molecules (creating an isomer of the original molecule)
For example, phosphoglucose isomerase
glucose-6-phosphate fructose-6-phosphate
What is a ligase? Give an example
Ligases use ATP to produce a covalent bond (kinda the opposite of a lyase)
An example is DNA ligase (sticks two complementary strands of DNA together using ATP)
What does chymotrypsin do?
Chymotrypsin is a hydrolase and uses water to hydrolyse the peptide bond on the carboxyl side of tyrosine, tryptophan, phenylalanine and methionine.
What enzyme/s use Cu2+ as a cofactor?
Cytochrome oxidase
What enzyme/s use Fe2+/3+ as a cofactor?
Cytochrome oxidase, catalase, peroxidase
What enzyme/s use K+ as a cofactor?
Pyruvate kinase
What enzyme/s use Mg2+ as a cofactor?
Hexokinase, G-6-phosphatase, pyruvate kinase
What enzyme/s use Ni2+ as a cofactor?
Urease
What enzyme/s use Se as a cofactor?
Glutathione peroxidase
What enzyme/s use Zn2+ as a cofactor?
Carbonic anhydrase, alcohol dehydrogenase
What is an isoenzyme and give an example
Isoenzymes are enzymes with different protein structures which catalyse the same reaction. Hexokinase and glucokinase are isoenzymes.
What can effect the rate of an enzyme catalysed reaction?
Amt of substrate/enzyme; temp; pH; presence of cofactors; amount of metal ions.
What assumptions are made when working under the Michaelis-Menton reaction model?
- [S]»_space; [E]
- [ES] does not change as it is formed at the same rates as it is used up or at the same rate at which the backwards reaction occurs.
- Initial velocities used (t=0); [P] is small therefore the back reaction can be ignored.
When can Km be used as a measure of the affinity of an enzyme for a substrate
When k2 «_space;k1; the formation of the product from the ES complex can be ignored and so the Km value reduces to the dissociation constant of the initial forward reaction of the formation of the ES complex
How can the measurement of the activity of an enzyme be used clinically?
Lactate dehydrogenase (LDH) and creatine kinase 2 present (CK2) in blood following a myocardial infarction as endothelial cells rupture releasing their contents into bloodstream.
What are the types of inhibitors for an enzyme?
Competitive (blocks active site)
Non-competitive (Interferes in another way with catalytic mechanism)
How does a competitive inhibitor affect the Km and Vmax of an enzyme?
It lowers Km, does not change Vmax
How does a non-competitive inhibitor affect the Km and Vmax of an enzyme?
It lowers Vmax, does not change Km
Describe the inhibition of angiotensin production.
Prevents conversion of AT1 to AT2, done either by reversible or irreversible inhibition.
Inhibition of this process prevents formation of AT2 which can lead to peripheral vasoconstriction.
What is allosteric regulation of an enzyme?
A substrate binds to an enzyme and causes a conformational change in it, so makes it easier for another substrate to bind to it in the future.
What amino acids can have phosphate groups added/removed?
Ser, thr, tyr, his
How does phosphorylation be used to regulate the synthesis and breakdown of glycogen
Via adrenaline and glucagon.
Two enzymes involved: glycogen phosphorylase (degrades glycogen) activity increased by phosphorylation.
And glycogen synthase (synthesises glycogen) activity reduced by phosphorylation.
How can the amount of an enzyme released be regulated?
An example is that high blood sugar leads to an increase in insulin production and so in turn that leads to an increase in the synthesis of other enzymes involved in glucose metabolism: glucokinase, phosphofructokinase and pyruvate kinase.
Give an example of reversible inhibition of an enzyme
Inhibition of a Mg2+ requiring enzyme with EDTA/chelation
Give an example of irreversible inhibition of an enzyme
Inhibition of cholinesterase by organophosphate
