lecture 6 - enzymes Flashcards
What are cofactors?
metal ions
What are coenzymes?
organic molecules
What is the difference between cosubstrates and prosethetic groups?
cosubstrates are transiently associated with the enzyme whereas cofactors are associated with the enzyme
What is a holoenzyme
catalytically active enzyme - cofactor complex
What is a apoenzyme
inactive enzyme (absence of the cofactor)
where can we get cofactors?
The vitamins we eat
what are the units to measure specific enzyme activity?
Umol/min/mg protein
enzyme unit
amount which gives 1 Umol product/ min
Katal (SI unit)
Amount which gives 1Mol/sec
What is the Michaelis - Menton equation?
Vmax(S) / Km +(s)
What is an assumption of the steady state diagram?
K-1 is greater than k2. Therefore there is an equilibrium between (ES) and (E) + (S)
What is Km?
The substrate concentration at which the reaction rate is half of the maximal value
Unit for Km?
M
What is Vmax?
Reaction rate when the enzyme is fully saturated by the substrate
What is the units for Vmax?
Umol/min
What is Kcat?
Equal to K2. It measures. the number of substrate molecules “ turned over” by enzyme per second
what is the unit for Kcat?
1/second
What can be inferred when an enzyme has a small Km?
Achieves maximal catalytic efficiency at low substrate concentrations
What is Kcat equal to?
K2
What does K2 measure?
number of molecules ‘turned over’
What is Ks
The dissociation constant
What is the formula for KS?
k-1 divided by K1
This equals; Enzyme times substrate divided by the enzyme substrate complex.
What does Vo represent on a Michaelis Menton equation?
The initial rate
What can we assume due to the steady state assumption?
The rate of change of The enzyme substrate complex = 0
How to measure assays ?
rate of initial product// disappearance of substrate
What is a discontinuous assay?
reaction stopped and another enzyme added
What is a direct assay?
Real time detection
What are coupled assays?
measure a reaction which is easy to measure which links it to the main reaction which cannot be measured
What is the rate of product creation equal to?
= K2 times the concentration of the Enzyme substrate complex
What is the dissociation constant assuming?
The enzyme substrate complex does not change over the Time of the assay
What is Km known as?
The Michaelis constant
what happens when the substrate concentrations are low
substrate concentration small relative to Km.
simplified to V = Vmax/Km ( linear relationship)
What happens when substrate concentrations are high?
Km is relatively small , compared to substrate concentrations. v = Vmax.
When does Km differ?
- Differ with enzyme type
- differs with temp and ph
How can we consider Km?
When enzyme binds substrate tightly has a low Km value. Inverse affinity for the substrate.
How can we work out Vmax?
K2 times starting enzyme concentration// Kcat times starting enzyme concentration
What are the two graphs to analyse the Michaelis Menton equation?
Lineweaver burk plot and the Hanes Woolf equations
How to get the Lineweaver burk plot?
take the reciprocal of everything
Why is the line weaver burk plot not accurate ?
- Lots of incorrect crowded points and only one or two points at the top of the graph
what is the Hanes Woolf plot?
rearrangement of the Michaelis Menton equation
What are cofactors?
transiently associated with the enzyme
What are prosthetic groups?
associated with the enzyme
