Enzymes Wk 3 Flashcards
What do enzyme do
Catalyse biochemical reactions but changing substrates into products but without changing themselves
What does the tertiary structure in enzymes dictate
The active site where the substrate binds
What binds in allosteric sites on enzymes
Regulatory molecules
Isoenzymes
Causes by coding gene variants and have different physical properties
Isoforms
Due to post translational modifications but same genetic coding
When are enzymes released in the plasma
In cellular degradation
After tissue injury
Are enzymes specific to plasma or tissues
Enzymes can be specific to plasma like coagulation factors or present in one or more tissues
How are enzymes measured
By the production or consumption of a measurable substance so it is not direct
What is the point of a indicator reaction
To use the product from the assay reaction to form another produce which is easy to measure
What is in the assay reaction
The enzyme we are interested in
The product of this reaction is used as a substrate in the indicator reaction
Why are enzymes helpful energy wise
Substrates need a lot of energy to become a product
When combined with an enzyme the amount of total energy needed is less to get to the same product so the rate of reaction is increased
What does Vmax mean
Maximum velocity of the reaction
All of the enzyme is saturated with substrate, adding more substrate will not do anything
What does Vmax depend on
The affinity between the substrate and the enzyme
What is the Km
The substrate conc where the reaction velocity if half the maximum
A measure of substrate binding affinity
What does first order kinetics depend on
The rate depend on the substrate conc
Increase substrate = increase speed as the reagent is limiting
What does the rate of zero order kinetics depend on
The rate is independent of the substrate conc
Reaction is as fast as it can be, increase the substrate concentration will do nothing for speed
3 patterns for enzyme reactions
- Linear, proportional increase as rate is constant
- Decreases over time
- Lad phase, linear, curves off
When should you measure absorbance in a linear graph
End point assay
Velocity = max rate (k) so can use any two points
When should you measure abs in a decreasing graph
Velocity never reaches a maximum
Need to optimise reaction by changing temp, changing buffer, adding more substation conc, secondary reactions to get rid of inhibitory products
When to measure absorbance in sigmoidal curve with a lag phase
Max rate is in the middle
Continuous assay - measure linear part
Most classic curve
What happens in the lag phase
First reaction in the coupled ones are happening so forming the needed substrate
Waiting for optimal temp and pH
What are cofactors
Non protein molecules or irons that activate or enhance enzyme function
Cofactor examples
Mg2+
NAD+
ATP
What is a coenzyme
Organic non protein molecules that bind with the protein to form an active enzyme
Co enzyme example
Vitamins
Apoenzyme and holoenzyme define
Proteins are apoenzymes
Holoenzymes are activated enzymes made when the coenzyme bind with the apoenzyme
What are activators
Small regulatory molecules or ions that increase reaction rate
What do activators promote
Formation if the most active state of the enzyme/substrate by binding to a different site (allosteric)
What can inhibit activators
Additives like Mg/cofactors
What are inhibitors
Small regulatory molecules or ions that decrease reaction rate
Competitive inhibitors
Competes with the substrate for active site binding
Non competitive inhibitors
Allosteric
Binds to a different site on the substrate, not the active site and prevents the enzyme from releasing products
