2 - Enzyme Kinetics Flashcards
What is the transition state of a chemical reaction?
The high energy intermediate between the substrates and products
What is the activation energy of a chemical reaction?
The minimum energy the substrates must have to allow the reaction to proceed
How can the rate of a chemical reaction be changed? How does these changes affect the activation energy and transition state?
Temperature increase - increases number of molecules with activation energy
Concentration increase - increases chance of molecular collisions
Addition of enzymes - biological catalysts that lower the activation energy and stabilise the transition state
Give some key features of enzymes that are important for their function
Proteins
Highly specific
Unchanged after the reaction
Don’t affect reaction equilibrium
Increase rate of reaction
May require associated cofactors
What is the active site of an enzyme?
Where the substrates bind and the chemical reaction occurs. They are clefts or crevices that usually exclude water and have complementary shape to the substrates.
What are the ‘lock and key’ and ‘induced fit’ hypotheses of enzymes?
Lock and key - active site is complementary to the substrates
Induced fit - binding of substrates changes the conformation of the enzyme to tightly bind and begin the reaction
What factors can affect the rate of an enzyme reaction?
Temperature
pH
Substrate and enzyme concentration
Addition of activators or inhibitors
In michaelis-menten kinetics, what shape is the [S] against rate curve?
Rectangular hyperbola
What is the Vmax of an enzyme reaction?
The maximal rate when all the enzyme active sites are saturated with substrate
What is the Km of an enzyme reaction?
Substrate concentration giving half the maximal rate (Vmax)
A low Km means an enzyme has a ……….. ………… for its substrate
High affinity
When measuring Vmax or V0 what is one unit?
How is this expressed as standardised rate?
The amount of enzyme that converts 1 micromol of product per minute under standard conditions.
Expressed standardised by units per litre of serum or gram of tissue.
What are the different types of enzyme inhibitors?
- irreversible (very tight binding - covalent)
- reversible competitive (at active site - affects Km)
- reversible non-competitive (at another site - affects Vmax)
What affect does competitive inhibition have on Km and Vmax?
Km increases, Vmax unaffected
Adding enough substrate will always overcome the effect of the inhibitor
What effect does a non-competitive inhibitor have on Km and Vmax?
Km unaffected, Vmax decreases
Binds an alternative site and decreases turnover number. Cannot be outcompeted with more substrate
An enzyme kinetics curve can be made linear using 1/V and 1/[S], what is this called?
Lineweaver-Burk plot
