Chapter 4: Enzymes Flashcards
Define enzyme.
Enzymes are proteins that function as a biological catalyst. They catalyse or speed up the rate of chemical reactions. They remain chemically unchanged at the end of a reaction.
What is a catalyst?
A substance that alters or speeds up a chemical reaction, being chemically unchanged at the end of the reaction.
What is activation energy?
The minimum amount of energy needed to start a chemical reaction
What is an anabolic reaction?
The building up of complex substances.
e.g.Protein synthesis, photosynthesis (synthesising glucose)
What is a catabolic reaction?
The breakdown of complex substances.
e.g. Decomposition of hydrogen peroxide, respiration (breakdown of glucose), hydrolytic reactions (e.g. in digestion)
[Application]
Are enzymes only involved in digestion?
No, they are also involved in many chemical reactions, e.g. photosynthesis, respiration etc.
Answer structure to Lock-and-Key hypothesis qns?
- Identify lock (enzyme) and key (substrate)
- The [key] with a 3-D shape complementary to the active site of [lock] binds to [lock]
- to form an enzyme-substrate complex.
- [Lock] then catalyses the breakdown of [key], and [key] is then broken down into {products}.
{Products} then detach from the active site of [lock].
[Lock] remains chemically unchanged at the end of the reaction, and its active site is then available for another [key] to bind to it.
Characteristics of enzymes?
-Speed up chemical reactions
-Specific in action
-Required in small quantities, remain chemically unchanged at the end of the reaction
-Affected by temperature
-Affected by pH
How do enzymes speed up chemical reactions?
By lowering activation energy
What does it mean for an enzyme to be specific in action?
-Enzyme molecule has a specific 3D shape
-Only a substrate that has a shape complementary to the enzyme’s active site will be able to bind with the enzyme and cause a chemical reaction
Why are enzymes only required in small quantities?
Since enzymes remain chemically unchanged at the end of a reaction, its active site is free to bind to another substrate molecule. This means that enzymes can be reused and hence are required only in small quantities.
How does temperature affect enzymes?
At low temp,
Enzymes are inactive, so chances of substrate molecules colliding with enzymes are very low.
As temp increases,
Enzyme activity increases, increasing chances of substrate molecules colliding with enzymes, increasing the rate of formation of enzyme-substrate complex.
At optimum temp,
Enzyme is most active, rate of reaction is the highest
Beyond optimum temp,
Enzyme activity slowly decreases to zero, as high temp breaks peptide bonds within the enzyme and changes its 3D shape. The active site of the enzyme is no longer complementary to the substrate, and enzyme is denatured.
How does pH affect enzymes?
Extreme acidity or alkalinity causes enzymes to denature.
Describe what happens to its function when an enzyme is denatured.
When an enzyme is denatured,
1. There is loss or change of its active site.
2. The substrate can no longer fit into the enzyme’s active site as it is no longer complementary to it
3. and no reaction can take place
