3- enzymes Flashcards
What are enzymes
Biological catalysts
Proteins
Speed up the rate of chemical reaction, without being changed at the end of the reaction
Most enzymes are HIGHLY specific
Alcohol intolerance
DEFECTIVE enzyme
Problem in aldehyde dehydrogenase ( ALDH enzyme )
ethanol= aldehyde = acetic acid
ALDH has a higher Km - enzyme works slower and cant clear the aldehyde
How do enzymes work ? general in terms of reaction energy etc
LOWER the activation energy of a reaction
HIGHER activation energy = slower rate of reaction
Overall energy for reaction(delta G) is NOT changed by enzymes
Haven’t changed how likely it is for reaction to precede , just made it happen more quickly
How do enzymes work with substrates to form product
Bind substrate in their active site
Active site is COMPLEMENTARY to substrate
LOCK and KEY
Enzyme is unchanged and recycled
Enzyme substrate complex and enzyme product complex
What is enzyme activity effected by
Temperature, pH , conc of enzyme, conc of substrate
How does temp effect rate of reaction when enzymes are present
As temp increases, rate Increases UP TO A POINT( optimum temperature )
After then, rate decreases as enzymes denature
How does pH effect rate of reaction when enzymes are present>
Similar to temp, increases up to a point
When pH changes from optimum, structure of the enzyme and therefore active site is altered,
But if it returns to optimum pH ,protein will resume shape = RENATURATION
BUT if pH is changed significantly and structure is irreversibly altered = denaturation
How does substrate and enzyme conc effect reaciton rate
Increase up to a point , then plateaus
Michanelis menten curve
Shows the effect of substrate conc on reaction rate
Vmax ( michaenlis menten curve )
MAX possible rate
All enzyme active sites are full with substrate = enzyme saturated
Estimated from the plateau of curve where reaction is plotted against conc
Km ( michaelis constant )
Substrate conc at which the rate is half V max
The michaleis menten reaction
V( rate of reaction )= Vmax * {S} / KM + {s)
S= substrate
What is the michaelis menten equation used for
To compare enzyme action in different substrate levels
As Km and Vmax stay the same
Only applies to a reaction with a single substrate
Km
What does LOW Km mean
What does HIGH Km mean
A measure for affinity of the enzyme for its substrate
LOW Km = enzyme binds substrate TIGHTLY and will work fast even at low substrate conc. Only a low conc of substrate is required to saturate the enzyme
HIGH KM = Enzyme binds substrate WEAKLY and required high substrate to work fast
Allosteric effectors
Molecule that binds to an enzyme and causes allosteric effects. Positive allosteric effects involve “activation” of the enzyme - increasing its activity. Negative allosteric effects involve “inhibition” of the enzyme - decreasing its activity.
