enzymes 1 Flashcards
enzyme definition
globular proteins that lower activation energy and speeding up rate of chemical reactions by stabilising transition states
enzymes can be referred to biological catalysts. how do they differ from chemical catalysts?
- Catalyse very high reaction rates
- Shows great reaction specificity
– Work in mild temperature/pH conditions
– Can be regulated
define co factor
non-protein compound or ion
aid catalysis by transferring functional groups or electrons
either organic (derived from vitamins) or inorganic (metal ions)
define co enzyme
type of co-factor
organic molecule
define prosthetic group
cofactor that is covalently bound or very tightly associated with he enzyme
define apoenzyme
protein component of an enzyme containing a cofactor
define holoenzyme
“whole enzyme”
apoenzyme + cofactor(s)
define substrate
molecule acted on by the enzyme
define active site
part of the enzyme in which the substrate binds and is acted upon
reaction type of oxidoreductases (1)
transfer electrons
reaction type of transferases (2)
group transfers
reaction types of hydrolyases (3)
hydrolysis (transfer chemical groups to water)
reaction type of lyases (4)
form, or add group to double bonds
reaction type of isomerases (5)
transfer group within molecules (form isomers)
reaction type of ligases (6)
formation of C-C, C-S, C-O and C-N bonds (coupled to ATP cleavage)
function of enzymes:
- increase the rate of spontaneous reactions
- lower activation energy of biochemical reactions
- accelerate movement towards react equilibrium
how do enzymes reduce activation energy?
- entropy reduction
- desolvation
- induced fit
entropy reduction
Molecules in free solution will only react by “bumping” into one another
Enzymes “force” the substrate(s) to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed
desovlation
- weak bonds between the substrate and enzyme replace most or all of the H-bonds between substrate and aqueous solution
induced fit
- conformation changes occur in protein stature as substrate binds
techniques used to understand enzyme function
- enzyme kinetics
- mutagenesis
- 3D structure
energy barrier definition
the minimal amount of energy that is necessary to launch a chemical reaction
explain concentrations of hexokinase and glucokinase post meal
- post meal = high [blood glucose]
- glucokinase activity inc as repsonse in inc bg
- hexokinase already at Vmax and so stays at constant rate
- allows glucokinase to respond proportionally to [bg]
explain concentrations of hexokinase and glucokinase at low [blood glucose]
- gluconeogenesis releases glucose from liver
- glucokinase cannot catalyse glucose to G6P when [gb] low
- this prevents glucose phosphorylation allowing glucose to be available for immediate use and not trapped in liver
isoenzyme definition
different proteins but catalyse same reaction
In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the:
intercept on the
1/[S] axis
Km increases because the inhibitor competes with the substrate to bind to the enzyme’s active site
so intercept on the axis shifts right, indicating an increase in Km
.
increase in km means:
High values of KM = low enzyme affinity for substrate (it takes more substrate to get to Vmax )
Low KM values = high affinity for substrate.
heterotrophic modulator of allosteric protein
external molecule or ligand that binds to a regulatory site on the protein, inducing a conformational change that alters the protein’s activity.
homographic modulator of allosteric protein
a molecule that acts as both a substrate for the enzyme’s catalytic reaction and as a regulatory molecule that affects the enzyme’s activity through binding to its allosteric site(s).
Which statement is correct about the Michaelis-Menten parameters Vmax and KM? a. KM = Vmax when V0 = 1/2 Vmax b. Vmax is attained when [S] «_space;KM c. Vmax does not depend on the total enzyme concentration in the reaction. d. A compound that exhibits mixed inhibition will both decrease Vmax and increase KM.
d
