77 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.4 Enzymes And Biological Reactions) Flashcards
The progress of an enzyme-catalysed reaction for a given concentration of substrate can be followed by measuring either the formation of product or the disappearance of substrate.
Draw a graph showing the formation of product over time
Explain the shape of the following graph?
The shape of the graph may be explained as follows:
- The line goes through the origin, because at zero time, no reaction has happened yet.
- When the enzyme and substrate are first mixed together, there are many substrate molecules.
- Both enzyme and substrate molecules are in constant motion and collide.
- Substrate molecules bind to the active sites of the enzyme molecules.
- In a ‘successful’ collision, substrate is broken down and products are released.
- More active sites become filled with substrate molecules.
Initially, the rate of the reaction depends on the number of free active sites, if all other conditions are optimal and there is excess substrate.
The enzyme concentration is the limiting factor because it controls the rate of the reaction.
As the reaction proceeds there is less substrate and more product.
The enzyme concentration is constant.
The substrate concentration is the limiting factor because it controls the rate of the reaction.
Eventually, all the substrate has been used and no more product can be formed so the line plateaus.
What is the:
Mass of product at 5 minutes
Mass of product at 15 minutes
Mass increase
% increase in mass
Initial rate of reaction
What is the initial rate of reaction?
The curve is steepest at the start of the reaction.
Its gradient there is the initial rate of reaction.
What should you remember when you need to read off a graph?
When you have to read off a graph, draw on it, using a pencil and ruler, making sure the line you draw is parallel with the graph’s grid lines.
