Enzyme Kinetics Flashcards
What are enzymes and some features associated
Catalysts
Mostly proteins except form some ribozymes (rna)
Efficiently work at body temperature and near neutral
Have specific range of substrates (distinguish between stereoisomers)
Potent
What is the general concept of enzyme action
Enzymes specifically bind and stabilise the transition state
Transition state is reaction intermediate species which has the greatest free energy
Enzymes reduce the activation energy by providing an alternative pathway
How to describe enzyme behaviour
To understand how enzyme works need to know how the concentration of the substrate affects the rate of the catalysed reaction
Use the parameters Vmax and Km
What is the Vmax and Km
Vmax –> maximum rate of catalytic activity - velocity
Km –> Michelis constant, point when catalytic activity if 50% of Vmax
What is the Michelis constant equation and the symbol meanings
Km = k(-1)+k(2)/k(1)
K(1) - forward constant rate for enzyme association with the substrate
K(-1) - backwards rate constant for dissociation from the substrate
K(2) - forward rate constant for enzyme conversion of sub to product
How to measure Vmax and Km
Measure initika velocity Vo at a known sub concentration and repeat this at increasing substrate concentrations
Initial velocity rates plotted as a function of sub concentration
Reaction velocity never quite reached Vmax
Not linear graph not accurate to measure Vmax and Km
How can we achieve a line weaver burk plot
Instead of plotting V against S we plot 1/V and 1/S - a double reciprocal
Vmax - intersection of y axis
Km - intersection of x axis
What is the difference between a high and low Km
High Km - enzyme needs a lot of substrate to work at half maximal rate
Low Km - enzyme only needs a little substrate to work at half maximal rate
What are some clinical examples of using Vmax and Km
Glucose homeostasis - low Km maintains energy production in rbcs by glycolysis even if glucose levels fall dramatically
Maturity onset diabetes of the young - high Km enables glucose sensing and homeostasis abundance regulated in liver, excess is metabolised
What are the types of reversible inhibition
Competitive - inhibitor binds to the active site and blocks substrate access (orthosteric - at same place)
Non-competitive - inhibitor binds on to another site other than the catalytic centre inhibits enzyme by changing its conformation (allosteric - at different place)
What is an example of irreversible inhibition
Non-competitive - inhibition cannot be reversed usually involves formation or breakage of covalent bonds in the enzyme complex
What does competitive inhibition do to the Vmax and Km
Vmax - does not change
Km - varies
What does non competitive inhibition do to the Vmax and the Km
Vmax - varies
Km - does not change
What is feedback inhibition
Inhibition of rate limiting enzymes by end products is a common mechanism of allosteric control
What pathway do allosteric enzymes follow
Not michaelis-menten
Increasing substrate concentration results in sigmoidal curve instead of hyperbola
Shows cooperative behaviour
Can be controlled by allosteric inhibitors and allosteric activators
