Enzymes Flashcards
What are enzymes
- Enzymes are catalysts
- Increase reaction rate
- Do not alter the equilibrium
of a chemical reaction - Accelerate attainment of
equilibrium - they lower the activation energy
What is the Transition state
This is the activation energy
What is the formation of an enzyme-substrate complex
- Binding of enzyme to a substrate is key to enzymatic catalysis
- Substrates bind to a specific region of an enzyme –
the active site
How is the active site formed
The active site is formed by amino acids from different parts of the primary sequence
How large is the active site
The active site occupies a small part of the enzyme
Where are active sites found in the enzyme
Why are they found there
Active sites are clefts (Between Subunits) or crevices (folds in the enzyme)
They are clefts or crevices so they can be hidden from water as water can cause problems for chemical reactions
What is the induced fit model
THE Active site of the enzyme is changed slightly to better fit the substrate after the substrate binds
This allows proper catalytic function
How are substrates bound to enzymes
Substrates are bound to enzymes by multiple weak bonds
NOT STRONG COVALENT INTERACTION
How are substrates bound to enzymes?
Substrates are bound to enzymes by multiple weak bonds
NOT STRONG COVALENT INTERACTION
Why do enzyme substrates have a weak bond
A weak bond so substrate can bind and product can be released effectively
How is the initial rate of reaction taken
V0 = initial rate of reaction
Rate is taken from Zero and Tangent is used.
How does substrate concentration affect the rate of reaction
The rate of reaction depends on the substrate concentration
Higher conc higher rate of reaction
What is the Michaelis-Menten equation
V0 = Vmax [S] / Km + [S]
Km = Michaelis constant (M)
Vmax = maximal velocity (mol/min)
[S] = concentration of substrate
What is Km
Km is the concentration of substrate which permits the enzyme to achieve half Vmax.
What does a Low Km Value mean
The lower the Km value the higher the affinity of the enzyme for the substrate
What is Vmax
the rate of the reaction at which the enzyme shows the highest turnover
What is “1 Unit”
1 unit = the amount of enzyme that produces 1mmol of product per min under standard conditions
* Often expressed as a standardised rate
e.g. per litre (L) of serum or per gram (g) of tissue
How is the rate of reaction affected by enzymes
The rate of an enzyme-catalysed reaction is proportional to the concentration of enzyme
* If you double the concentration of enzyme present then the measured rate of reaction doubles
How to make the
The Lineweaver-Burk plot
1/V0 = km/Vmax .1/(S) + 1/ Vmax = Y= mx + c
What is a competitive inhibitor
- Binds at the active site
- Reduces the proportion of enzyme molecules bound to a substrate
- Similar shape as substrate thus binds instead of substate.
What is a non-competitive Inhibitor?
- Binds at free enzyme away from the active site
- Changes the shape of the active site
- Decreases concentration of functional enzyme
What happens when more substrate is added to a competitive inhibitor
Adding enough substrate will always overcome the effect of the inhibitor, so no effect on Vmax
What happens to the Km and Vmax in competitive inhibitors when more substrate is added
Km increases; As higher CONC outcompetes inhibitor
Vmax is unaffected; Vmax doesn’t change
What happens when more substrate is added to a NON- competitive inhibitor
Inhibitor lowers the effective concentration of free enzyme so adding more substrate will not overcome the effect
What happens to the Km and Vmax in NON- competitive inhibitors when more substrate is added
Km unaffected; Adding more Conc won’t affect outcompete inhibitor
Vmax decreases; As the rate of reaction decreases
What is Enzyme Activity
Enzyme activity is measured in units which indicate the rate of the reaction catalysed by that enzyme expressed as micromoles of substrate transformed
