Enzymes Flashcards
Define enzyme
One or more polypeptide chains forming a catalytic active site
Define substrate
Molecule which binds active site and undergoes a chemical reaction
Define product
The result of the enzyme action
What does a anabolic reaction mean?
Smaller reactants form larger products
What does a catabolic reaction mean?
Larger products from smaller products
What are the six classes of enzymes?
Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases
What 2 things does reaction rate depend on?
Speed of reaction / Rate constant k
Number of reactions happening
What are the advantages of enzymes?
Reusable
Specific
Efficient
Controllable
How do enzymes ‘speed up’ reactions?
By lowering the activation energy
What are the 2 proposed models for enzyme reactions?
Lock and Key- Fischer
Induced Fit -Koshland
Each change in activation energy of 5kJ/mol= how many times faster?
10x
What is the enzyme attachment theory?
Ogston’s 3 point binding theory
What 2 things determines reaction specficity?
3D arrangement of residues
Chemical properties of the residues
Define Co-Enzymes
Organic molecules which provide/remove groups for reaction
What 3 things can you compare enzymes via?
Turnover number
Efficiency
Potency
What is the catalytic triad?
Often only 3 amino acids perform the actual catalyst
What 3 things can an active site also contain?
Metal cofactors
COenzymes
Prosthetic groups
Define isozymes
Different enzymes same substrate
What does spectrophotometer measure?
Starting point is the measuring the change in [S] or [P] over the time after addition of enzyme
What is an indication of purity?
Enzyme activity/ total amount of protein
Describe what the role of an enzyme is ?
Provides an alternative route from substrate to products requiring less energy
So more molecules have that energy so more go from S to P per second and equilibrium is reached sooner
Reactions can be pushed backwards by what?
Increasing the [product]
Keq=
Keq= K forward/k reverse= [P]/[S]
V=
V= Vmax x [S] / Km + [S]
which is also equal to Kwd x [S]
Overall rate depends on rate constants and concentrations. Which equations explain this?
Ks->p x [s]
Kp->s x [P]
Usually Ksp . Kps
What 2 assumptions do we make about enzyme reactions?
[ES] constant
[s] >[E] so [S] is constant
Vmax is set by what?
Number of enzyme molecules not number of substrate molecules. It is the maximum rate when all is [ES]
What is the equation of the Dissociation constant/ affinity for substance Kd?
K-1/K1= [E] X[S]/[ES]
What does a small Kd mean?
high affinity
What is Micheals constant?
Km= K-1 +Kcat/ K1
How do you measure V max ?
You cant measure it as its infinity so you find 1/2 V max
What are the x and y on Lineweaver-Burk plot?
Whhat doeds intersection of the X and Y axis mean?
X= 1/[S] y= 1/V
Y intercept= 1/vmax
X intercept= -1/Km
State the equation for V max?
Vmax= Kcat x[E]
Define Km
What does a low Km mean?
Km is [S] when half molecules are ES and its at half maximum rate
Low Km means high affinity for the substrate
Kcat catalytic rate constant =
number of reactions per second
If Kcat/Km > 1x108 the V is limited by what?
Diffusion of the substrate to the enzyme not the ezyme itself
