All Labs

Enzyme Activity Lab

Investigate how enzymes catalyze reactions by measuring reaction rates under different conditions. Vary substrate concentration, temperature, pH, and inhibitor presence to discover Michaelis-Menten kinetics experimentally.

Guided Experiment: Substrate Concentration and Reaction Rate

As substrate concentration increases, what do you predict will happen to the reaction rate? Will the rate increase linearly forever, or will it reach a maximum?

Write your hypothesis in the Lab Report panel, then click Next.

Controls

[S] Substrate5.0 mM
Noise Level5%

Results

v=Vmax⁡⋅[S]Km+[S]=100.00⋅5.005.00+5.00=50.00v = \frac{V_{\max} \cdot [S]}{K_m + [S]} = \frac{100.00 \cdot 5.00}{5.00 + 5.00} = 50.00
[S] Substrate
5.0 mM
Temperature
37°C
pH
7.4
Measured Rate
—
Vmax/2 reference
50.00 μmol/min (at [S] = Km = 5.00 mM)

Reaction Rate vs Substrate Concentration

Data Table

(0 rows)
#Trial[S](mM)Rate(μmol/min)1/[S](1/mM)1/Rate(min/μmol)
0 / 500
0 / 500
0 / 500

Reference Guide

Michaelis-Menten Equation

The fundamental equation describing enzyme kinetics relates reaction rate to substrate concentration.

v=Vmax⁡⋅[S]Km+[S]v = \frac{V_{\max} \cdot [S]}{K_m + [S]}

Where v is the reaction rate, Vmax is the maximum rate at enzyme saturation, [S] is substrate concentration, and Km is the Michaelis constant.

Determining Km and Vmax

Km is the substrate concentration at which the rate is half of Vmax.

When v=Vmax⁡2,[S]=Km\text{When } v = \frac{V_{\max}}{2}, \quad [S] = K_m

The Lineweaver-Burk (double reciprocal) plot linearizes the MM equation. The slope equals Km/Vmax, the y-intercept is 1/Vmax, and the x-intercept is -1/Km.

1v=KmVmax⁡⋅1[S]+1Vmax⁡\frac{1}{v} = \frac{K_m}{V_{\max}} \cdot \frac{1}{[S]} + \frac{1}{V_{\max}}

Temperature Effects

Below the optimal temperature, increasing temperature increases molecular kinetic energy, raising the rate according to the Arrhenius equation.

k=A⋅e−Ea/RTk = A \cdot e^{-E_a / RT}

Above the optimal temperature, the enzyme denatures. The protein unfolds, destroying the active site shape and causing a rapid loss of activity.

pH Effects

Each enzyme has an optimal pH where its activity is highest. Changes in pH alter the ionization state of amino acid residues in the active site.

At extreme pH values, the enzyme loses its native conformation and activity drops sharply. The result is a bell-shaped activity curve centered at the optimal pH.

For example, pepsin works best near pH 2 (stomach acid), while trypsin is optimal near pH 8 (small intestine).