Q/A Session 3 Flashcards
Vo/Vi
- Initial reaction rate
- Velocity of reaction measured at time 0 at a particular substrate concentration
Vmax
- Maximum velocity
- Velocity of reaction when enzyme is saturated
Km
- An inverse measure of the affinity of the enzyme for substrate
- Defined as substrate concentration required for the reaction to proceed at 1/2 Vmax
What is the Michealis constant?
- Km
- Measure of how well the enzyme binds to its substrate
What does a low Km show?
Tight binding
What does a high Km show?
Bad binding
At low substrate concentration (enzyme is unsaturated)
- Reaction order
- Rate
- Velocity
- First order reaction
- Rate depends on substrate concentration
- Velocity increases linearly with increased substrate concentration
At high substrate concentration (enzyme is saturated)
- Reaction order
- Rate
- Velocity
- Vmax
- Zero order reaction
- Rate is independent of substrate concentration
- No increase in velocity with increase of substrate concentration
- Vmax is reached
What is kcat?
Catalytic rate constant (turn over number)
The Lineweaver Burk Plot refers to
How much Substrate (moles) is converted to product (moles) per enzyme (moles) per unit time when enzyme is saturated with substrate
Enzymes efficiency is
How quickly the substrate can be converted to product (kcat) RELATIVE TO how well the enzyme binds to substrate (Km)
What’s the equation for enzyme efficieny?
kcat/km
What are the two types of inhibition?
- Reversible
2. Irreversible
What are the two types of Reversible inhibition?
- Competitive
2. Non-competitve
What happens in Competitive inhibition?
-Inhibitor competes with the substrate for the active site on E
(CI) Will reaction occur when inhibitor binds to active sit/
No. Inhibitor binding does affect S binding
(CI) How can inhibition be overcome?
Increasing substrate concentation
(CI) What happens to Vmax and Km?
Vmax stays the same
Km increases
(CI) Describe the plot on LWBP
Km line is closer to 0, the Vmax intercept stays the same. Line comes out above Non inhibitor
(CI) Describe the plot on MM
Km point decreases, reaches vmax. Line in below Non inhibitor
What happens in PURE Non-Competitive inhibition?
-Inhibitors binds to other site on enzyme than the substrate (allosterically)
(PNCI) Does inhibitor binding effect S binding
No it doesn’t. The enzyme cannot work when inhibitor is bound
(PNCI) What happens to Vmax and Km?
Vmax decreases
Km stays the same
(PNCI) Describe the plot on LWBP
Km point stays the same. The Vmax intercept increases (because it’s inverse). Line is above non-inhibitor
(PNCI) Describe the plot on MM
Reaches same Km spot, Vmax is lower. Line is underneath non inhibitor
What happens in MIXED Non-Competitive inhibition?
-Inhibitor binds to other side on enzyme than substrate (allosterically)
(MNCI) Does inhibitor binding have an effect on substrate binding?
Yes it does.
Enzyme cannot work when inhibitor is bound
(MNCI) What happens with Vmax and Km?
Vmax decreases
Km increases
(MNCI) Describe the plot on LWBP
The Km intercept shifts closer towards 0
The Vmax intercept increases (inverse)
Line is above the non-inhibitor
(MNCI) Describe the plot on MM
Much lower for both than the non-inhibitor
What occurs in irreversible inhibition?
Inhibitors bind covalently to the enzyme, irreversibly inactivating them
Do allosteric enzymes in enzyme kinetics follow MM kinetics?
No
What shape do allosteric enzymes follow?
Sigmoidal rather than hyperbolic
Activators stabilise what state?
R state (high affinity for the molecule it binds configuration)
In the presence of activator what degree of cooperativity do enzymes show?
Low, as they are already in the high affinity configuration
What effect does low degree of enzyme cooperativity have on the curve?
What way does the curve shift?
The curve is more hyperbolic and less sigmoidal.
The curve shifts LEFT
Inhibitors stabilise what state?
T state (low affinity for molecules it binds configuration)
In the presence of inhibitors what degree of cooperativity do enzymes show?
More cooperativity, because they are not in the high affinity configuration
What effect does high degree of enzyme cooperativity have on the curve?
What way does the curve shift?
The curve is less hyperbolic and more sigmoidal.
Curve shifts RIGHT
