Unit 2 - Enzymes Flashcards
what are enzyme commission numbers?
classification of enzymes based on reaction catalysed - 4 numbers
1st - general type of reaction catalysed
2nd - sub-class/ 3rd - sub-subclass - highlights compounds/groups/ bonds/ product involved in reaction
4th - serial identifier - highlights metabolites/ co-factors involved
apart from EC numbers what other names do enzymes have?
recommended name (everyday use)/ systematic name (substrate followed by enzyme specifying type of reaction catalysed
what are the defined conditions under which specified activity of catalytic proteins are measured?
temp/ pH/ buffer/ substrate/ co-enzyme concentration
what is the rate of an enzymatic reaction?
rate of conversion of substrate to product per unit of time
what does 1 IU equal?
amount of enzyme that catalyses conversion of 1 micromole of substrate to product per minute
what does 1 katal equal?
amount of enzyme that catalyses conversion of 1 mole of substrate to product per second
what unit given for specific activity?
IU/ mg
what is difference between holoenzyme and apoenzyme?
holoenzyme has non-/covalently bound enzyme but apoenzyme does not
distinguish between soluble co-enzymes/ prosthetic groups/ cofactors
soluble: bind reversibly to protein moiety of enzyme but during reaction they are modified, dissociated and recycled by another enzyme
prosthetic groups: covalently linked to enzyme and remain associated during entire catalytic cycle
co-factors: insoluble inorganic ions required for enzymatic activity
what are the assumptions for the michael-menten equation?
- E, S, ES in rapid equilibrium
- conversion of ES to E + P - rate-limiting step
- there are no other forms of the enzyme present apart from E and ES
what is Kcat?
turnover number - rate constant showing the number of substrate molecules converted to product per enzyme molecule per unit time
what is velocity limited by? - give an equation
limited by ratio of enzyme substrate complexes to total number of enzymes
equation: v= Kcat [ES]
what is Km
kinetic constant showing substrate affinity
- on graph it is point corresponding to 1/2 Vmax ([ES] = 1/2 [E]t)
what is the relationship of lineweaver-burk plot to michael-menten equation? what is the significance of this?
double reciprocal plot of the menten equation so puts the equation in form y = mx + c
-this makes it easier to obtain values for Vmax and K
what is represented by the following on a lineweaver plot: x y x- intercept y- intercept slope
x= 1/ [S] y = 1/ v x-intercept: -1/ Km y-intercept: 1/ Vmax slope: Km/ Vmax