Enzymes Flashcards
What are enzymes?
Biological catalysts
What does an enzyme do?
Increase rate of reaction by providing a pathway of lower activation energy to get reactants to products
What does lysozyme do?
Catalyses the cutting of polysaccharide chains
What happens when you increase substrate concentration?
Reaction velocity increases
What is the maximum rate of reaction called?
Vmax
What is Km?
The substrate concentration required for half maximum velocity
What is PHOSPHO1?
Found in osteoblasts and chondrocytes
What are the two classifications of enzyme inhibitors?
Irreversible and reversible
What are irreversible enzyme inhibitors called?
Inactivators
What are reversible enzyme inhibitors called?
Competitive and allosteric
Describe irreversible inhibition?
React with the enzyme and form a covalent adduct with the proteins
What is the primary mechanism of action of diisopropyl fluorophosphate?
Inhibition of acetylcholinesterase (AChE)
What does AChE do?
Degrades the neurotransmitter ACh
What happens if there is too many ACh?
Overstimulation of receptors ion the post synaptic membrane
What is aspirin?
Antipyretic, anti-inflammatory and analgesic
What does aspirin do?
Irreversibly inhibiting cylooxygenase-1 (COX-1)
What does COX-1 do?
Catalyses the conversion of arachidonic to prostaglandin H2 (precursor for synthesis of inflammatory mediators)
Where does aspirin bind?
On the serine residue close to the active site preventing the substrate arachidonic acid from binding
Describe competitve inhibition
Competes for active site of the enzyme
Like a key that gets through the keyhole but cannot unlock the door
What is 4-aminobenzoic caid?
What folic acid is synthesized from
What is used to competitively inhibit the synthesis of folic acid?
Sulphonamides
What happens to Km when you introduce a competitive inhibitor?
Km increases
Describe allosteric inhibition
Never bind to the active site
Change in conformation, substrate can longer bind
What happens to Vmax and Km in allosteric inhibition?
Vmax decreases
Km often (but not always) increases
What are the two types of allosteric inhibition?
Mixed and non-competitive
What happens to the Vmax and Km in mixed allosteric inhibition?
Vmax decreases
Km increases
What happens to the Vmax and Km in non-competitive allosteric inhibition?
Vmax decreases
Km is unchanged
What does phophofructokinase do?
Catalyses transfer of phosphate from ATP to fructose 6-phosphate
What happens when ATP is not needed?
The inhibitory site of PFK will be filled
