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3.2 Basic Kinetics
# 3.2 Basic Kinetics

### Chemical Reaction Equation 1:

A --> B

The rate equation for a first order reaction, such as this one, is:

(k1 is negative because A is disappearing)

### Chemical Reaction Equation 2:

A + B --> C

The rate equation for a second order reaction such as this one is:

### An enzymatic reaction:

- The symbols represent (in our example):
- E enzyme (b-galactosidase)
- S substrate (lactose)
- ES enzyme-substrate complex
- P product (glucose or galactose)

First consider the initial velocity of the reaction. In this case,
there will be a negligibly small amount of product present ( [P]<5% of
[S] is considered negligible). Under these conditions, the back
reaction is negligible, that is, k-2[P]= 0 (approximately). The initial
velocity is simply:

** Vo = k2[ES] (1)
**

The problem with this equation is that the quantity [ES] cannot be measured. However,

[S] (the initial concentration of substrate) is known,

[P] (product produced) can be measured, and

[E]tot (the amount of enzyme added to the reaction) is known.
Now what we can do is use the rate equations plus a few other
assumptions to derive an expression for [ES] (which we cannot measure)
in terms of quantities which we can measure ([S], [P], and [E]tot).
Okay, here we go . . .

shanec@mit.edu