enzymes 1 Flashcards
are enzymes chemically altered in a reaction?
no
how do enzymes increase the rate of a reaction?
by providing an alternative reaction pathway with a lower activation energy
what conditions do enzymes work under?
physiological conditions (moderate temperature, around neutral pH, low concentrations of substrate, aqueous environment)
what is the active site?
enzymes work by forming complexes with their substrate by binding to them at the active site, providing a unique microenvironment for the reaction to proceed. Very high specificity for reaction catalysed AND substrate used.
as the substrate concentration is increased what happens to the velocity of the reaction?
the velocity increases
what is increased steadily until a maximum rate of reaction is reached?
the rate of a reaction increases as the substrate concentration increases until Vmax is reached
what type of graph can be plotted to calculate the Vmax?
a Lineweaver-Burke Plot
what is the first michaelis-menten equation?
K-1 + K2/K+1 = Km
where K+1 is the rate of formation of the complex, K-1 is the rate at which the complex changes back into substrates and K2 is the rate of formation of end products
what is the second michaelis-menten equation?
Vo = Vmax [S]/Km + [S]
where Vo is the initial reaction velocity, [S] is the substrate concentration and Vmax is the maximum reaction velocity
what is Km?
Michaelis constant; it is the substrate concentration required for half maximum velocity
what are irreversible enzyme inhibitors?
substances that react with the enzyme to form a covalent adduct with the protein.
what does diisopropyl fluorophosphate (DIPF) do?
this is an organophosphate pesticide which inhibits the enzyme acetylcholinesterase (AChE) which breaks down the neurotransmitter acetylcholine into choline and acetic acid.
how does DIPF inactivate AChE?
by phosphorylating the serine hydroxyl group located at the active site of the enzyme. This results in an accumulation of ACh throughout the nervous system, resulting in overstimulation of receptors.
what are the functions of aspirin? (acetylsalicylic acid)
it is an antipyretic, anti-inflammatory and analgesic
what enzyme does aspirin inhibit?
cyclooxyrgenase-1 (COX-1) which catalyses the conversion of arachidonic acid (AA) to prostaglandin H2 (PGH2) which is a precursor for synthesis of inflammatory mediators
how does aspirin inhibit COX-1?
by reacting with a serine residue close to the active site which prevents the substrate from binding.
what is a competitive inhibitor?
a competitive inhibitor is a drug that can compete with the substrate for the active site of the enzyme. Similar structure to the substrate and leaves the active site unchanged.
how is the action of an enzyme affected by a competitive inhibitor?
the action of the enzyme is slowed down.
what is the name of the chemicals that competitively inhibit the enzyme bacteria use to synthesise folic acid?
sulphonamides which are similar in structure to the substrate, 4-aminobenzoic acid
what is needed to reach the Vmax for a competitively inhibited reaction?
a higher substrate concentration, Vmax is unchanged. Results in an increase in Km
what type of graph can competitive inhibition be shown on ?
a line weaver-burke plot. The enzymes with a higher concentration of inhibitor have a steeper gradient.
what are allosteric inhibitors?
inhibitors that bind to the enzyme away from the active site and changes the conformation of the enzyme, meaning that the substrate cannot bind to the enzyme anymore
what happens to Vmax inn allosteric inhibition?
VMax decreases
what often (but not always) happens to Km with allosteric inhibition?
Km increases
