PoH: Enzymes Flashcards
Define enzyme
A protein molecule that catalyses chemical reactions without being altered or destroyed
Name the 6 classes of enzymes
· Oxidoreductase – transfer e
· Transferase – group transfer
· Hydrolase – hydrolysis (transfer groups to water)
· Lyase – form or add groups to double bonds
· Isomerase – transfer groups within molecules (form isomers)
· Ligase – from C-C, C-S, C-O and C-N bonds
Enzymes reduce activation energy for reactions to proceed. In what 3 ways do they do this?
Entropy reduction - they force substrate to be oriented correctly
Desolvation - weak bonds between substrate and enzyme replace H-bonds between substrate and aqueous solution
Induced fit - changes in enzyme’s structure when substrate binds
What graph/equation shows the rate of reaction of enzymes?
Michaelis-Menten Plot
Michaelis-Menten Equation
What does Km show on a Michaelis-Menten Plot? What does it mean if Km is low? What if Km is high?
Affinity - how specific the enzyme is for a substrate
Low Km = good fit
High Km = poor fit
What does Vmax show on a Michaelis-Menten Plot?
Vmax is how fast a reaction is proceeding when enzymes are saturated with substrate
It’s also called the Michaelis constant
Name the old-fashioned graph for analysing Michaelis-Menten equations to determine Km and Vmax
Lineweaver-Burk Plot
Define Michaelis constant
It’s Km. Affinity. It’s the substrate concentration that’s half of Vmax
How can we experimentally calculate the Michaelis constant
By performing experiments to find the rate of reaction at various substrate concentration.
Then using the Michaelis-Menten equation to calculate Km
Define non-competitive inhibitor and describe its relationship to Vmax and Km
An inhibitor which binds to a secondary site of an enzyme. It changes the shape of the active site and prevents the substrate from binding.
Vmax - decreases
Km - stays the same
Define competitive inhibitor and describe its relationship to Vmax and Km
An inhibitor which binds to the active stie of an enzyme and prevents the substrate from binding there
Vmax - unchanged
Km - increases (it takes more substrate to overcome the inhibitor)
Why may we need to understand enzyme activity in a clinical setting?
· Detection of suspected disease at pre-clinical stage
· Confirmation of suspected disease and assessing severity
· Localisation of disease to organs
· Characterisation of organ pathology
· Assessing the response to therapy
· Organ function assessment
· Assessing genetic susceptibility to drug side effects
· Detection of inherited metabolic disease
Detection of vitamin deficiencies
Describe changes to Vmax in competitive and non-competitive inhibitors
Comp - unchanged
Non-comp - decreases
Describe changes to Km in competitive and non-competitive inhibitors
Comp - unchanged
Non-comp - increases
What 5 factors affect enzyme reactions?
· Enzyme concentration
· Substrate concentration
· Temperature
· pH
Inhibitors
