An introduction to enzyme kinetics | Chemical Processes | MCAT | Khan Academy

Summary

This video explains enzyme kinetics, focusing on how enzymes speed up reactions by lowering activation energy. The enzyme binds with the substrate to form an enzyme-substrate complex, which then forms a product. The video covers reaction rates, the concept of Vmax (maximum reaction speed), and how enzyme concentration and substrate concentration influence reaction rates. It also assumes ideal conditions, including constant enzyme concentration and environmental factors. The two key steps in enzyme catalysis are the binding of the substrate to the enzyme and the conversion of substrate to product, each with its own distinct rate.

Takeaways

• 😀 Enzymes speed up reactions by lowering the activation energy or delta G of the transition state.
• 😀 Enzymes bind to substrates (S) to form the enzyme-substrate complex (ES) before transforming them into products (P).
• 😀 Enzymes are not consumed in the reactions they catalyze and are available to continue catalyzing multiple reactions.
• 😀 Enzyme kinetics involves understanding the rate of reaction and how it changes with concentration.
• 😀 The rate of a reaction can be calculated as the product of the rate constant (K) and the concentration of the starting material (A).
• 😀 The reaction sequence E + S → ES → E + P involves two reactions, each with its own rate equation (Rate 1 and Rate 2).
• 😀 The rate of a reaction is the speed at which the reaction occurs and can be represented as V, the change in product concentration over time.
• 😀 To increase the reaction rate, you can increase the substrate or enzyme concentration, assuming the rate constant (K) remains unchanged.
• 😀 The maximum rate (Vmax) is reached when enzymes are saturated with substrates and cannot work faster, even if more substrate is added.
• 😀 A plot of reaction rate (V) versus substrate concentration will level off at Vmax, indicating that the reaction rate has reached its limit.
• 😀 Ideal conditions are assumed for enzyme kinetics, including constant enzyme concentration and a fixed rate constant, with no external factors affecting the reaction.

Q & A

What is the role of enzymes in biochemical reactions?

Enzymes speed up reactions by lowering the activation energy or the delta G of the transition state, making the reaction occur faster without being consumed in the process.

What is the enzyme-substrate complex?

The enzyme-substrate complex (ES) is formed when the substrate (S) binds to the enzyme (E) before being converted into the product (P).

How do enzymes affect the reaction rate?

Enzymes increase the rate of reaction by lowering the activation energy. This leads to a faster conversion of substrate to product.

What is the relationship between substrate concentration and reaction rate?

Increasing substrate concentration can increase the reaction rate until the enzyme becomes saturated. Beyond this point, further increases in substrate concentration won’t affect the rate, as the enzyme is working at maximum capacity (Vmax).

What is the rate equation for enzyme reactions?

The rate equation for an enzyme reaction is typically written as rate = k * [substrate], where 'k' is the rate constant and [substrate] is the concentration of the reacting substrate.

What is the significance of Vmax in enzyme kinetics?

Vmax represents the maximum rate of reaction that can be achieved when all enzyme active sites are saturated with substrate. It signifies the enzyme’s maximum efficiency under optimal conditions.

What assumptions are made in enzyme kinetics models?

Three main assumptions are made: the solutions behave ideally, enzyme concentration remains constant, and the rate constant (k) does not change due to environmental factors.

What does it mean when the reaction rate levels off at high substrate concentrations?

When substrate concentration is high, the enzyme becomes saturated with substrate, and the reaction rate reaches a plateau. At this point, increasing substrate concentration will not increase the rate, as the enzyme is working at its Vmax.

Why is it assumed that enzyme concentration is constant in enzyme kinetics?

It is assumed that enzyme concentration remains constant because factors like protein synthesis and degradation are not significant enough to affect the enzyme concentration in the time frame of the experiment.

Why is the formation of product without the enzyme considered negligible?

In enzyme kinetics, it’s assumed that the formation of product without the enzyme is negligible because enzymes speed up the reaction to a degree that the rate of product formation without them is insignificant.