5 - Enzymes Flashcards
What is the transition state?
- High energy intermediate between S and P
- E-S COMPLEX
How do enzymes increase the reaction rate?
- Lower activation energy
- Facilitate production of transition state
What are the important features of an enzyme?
- Highly specific
- Unchanged after reaction
- Do not affect equlibrium
- Increase rate of reaction
- Proteins
- May require cofactors
What is the active site?
A small part of the enzyme where the substrate binds, rest of the enzyme acts as scaffolding. Active site has clefts that exclude water to allow the reaction to occur
What is the induced fit model?
- Substrate not complementary to active site
- Binding of substrate causes conformational change and an induced fit
- Non covalent interactions between substrate and active site, e.g h bonds and electrostatic attractions
What is Km and what is Vmax?
Km - Substrate concentration that gives half Vmax
Vmax - Maximum rate of reaction if all active sites were saturated by substrate
What is the Michaelis-Menten Model?
A specific complex between enzyme and substrate is essential for catalysis
Predicts that the plot of Vo vs [S] will be rectangular parabola
What does a low Km mean?
HIGH AFFINITY FOR SUBSTRATE
How do you work out the rate of reaction using Michaelis-Menten?
What is the rate of reaction UNIT?
The amount of enzyme required to convert 1um of substrate into product per minute under standard conditions
Expressed per litre or gram
What is the Lineweaver-Burk Plot?
A way of rearranging the Michaelis-Menten so it is linear and Km and Vmax can be calculated
What is an irreversible and reversible inhibitor?
Irreversible: Binds tightly and forms covalent bonds
Reversible: Non-covalent. Competitive and non-competitive
How does competitive and non-competitive inhibition affect Km and Vmax?
Competitive: Vmax same, Km increases
Non-competitive: Vmax decreases, Km same
How would a Lineweaver Burk plot be affected by competitive and non-competitive inhibition?
What are the units for Km and Vmax?
Km (conc) = M
Vmax (rate) = M/min
What would these graphs look like if substrate was infinite?
