Enzyme Kinetics

Question 1

Isoenzymes

Answer 1

Enzymes with different protein structures that catalyse the same reaction.
They are coded by different genes

Question 2

Enzyme Kinetics define

Answer 2

Study of enzymes by determining their reaction rates.

• How rate varies with different substrate concentrations, presence of inhibitors, different temperatures, presence of metal ions/co-factors.
• Initial reaction velocity = V0

Question 3

Michaelis-Menten model - hyperbolic kinetics

Answer 3

E+S <> ES <> E+P
E=enzyme
S=substrate
ES=enzyme-substrate complex
P=product
K1=forward rate constant
K-1=reverse rate constant

Question 4

Michaelis Menten Equation

Answer 4

Vo = (Vmax[S]) / (Km+[S])

When Vo=1/2 Vmax Km=[S]

Question 5

Lineweaver-Burke plot

Answer 5

1/Vo=Km/Vmax x 1/[S]
Forms straight line equation.
Y-intercept = 1/Vmax
X-intercept = -1/Km

Question 6

What does Km tell us about an enzyme?

Answer 6

Km = Substrate concentration at which the enzyme is 50% saturated with substrate.
Higher Km=lower affinity of enzyme for its substrate.
Lower Km=high affinity to substrate.

Question 7

Kcat is the Turnover number

Answer 7

Kcat = number of molecules of substrate converted to product by a molecule of enzyme at saturating levels of substrate per second.

Question 8

Specificity Constant

Answer 8

= Kcat/Km
Optimum enzyme function would have low Km(high affinity for substrate) and high Kcat(fast turnover speed)
Therefore most efficient enzymes will have a high specificity constant.