Enzymes
Learning objective: to examine what enzymes are and
describe how they work.
What are they?
Enzymes
Why do we need them?
Name some examples ?
Enzymes
Globular proteins that catalyse chemical reactions in living organisms
Properties
Enzymes
Globular proteins that catalyse chemical reactions in living organisms
Specific
Properties
Enzymes
Globular proteins that catalyse chemical reactions in living organisms
Specific
Properties
Increase rate of the reaction
Enzymes
Globular proteins that catalyse chemical reactions in living organisms
Specific
Properties
Increase rate of the reaction
Unchanged at the end of the reaction
Enzymes
Globular proteins that catalyse chemical reactions in living organisms
Specific
Properties
Increase rate of the reaction
Unchanged at the end of the reaction
Need them
Enzymes
Globular proteins that catalyse chemical reactions in living organisms
Specific
Properties
Increase rate of the reaction
Unchanged at the end of the reaction
Reactions too slow to maintain life
Need them
Can’t increase temperatures/pressure in cells (fatal)
Enzymes Are Proteins
The enzyme binds to the substrates by its active site
The active site is a pocket formed by the folding of the protein
where the substrates bind.
Enzymes Are Proteins
The enzyme binds to the substrates by its active site
The active site is a pocket formed by the folding of the protein
where the substrates bind.
Active site
The active site involves a small number of key residues that actually bind the
substrates
The rest of the protein structure is needed to maintain these residues in position
How do enzymes work?
An Example
An Example
Sucrose + H2O
Glucose + Fructose
An Example
Substrates
Sucrose + H2O
Glucose + Fructose
Products
For a reaction to occur the sucrose
and water would have to collide with
enough energy to break and form bonds
For a reaction to occur the sucrose
and water would have to collide with
enough energy to break and form bonds
This is the activation energy
Sucrose + H2O
+
Substrates
Glucose + Fructose
+
Products
Energy
Progress of reaction
Energy
Substrates
Progress of reaction
Energy
Substrates
Progress of reaction
Products
High energy
intermediate
Energy
Substrates
Progress of reaction
Products
High energy
intermediate
Activation energy
Energy
Substrates
Progress of reaction
Products
The minimum amount of energy needed to start
the reaction, leading to the formation of a high
energy intermediate
= The Activation energy
High energy
intermediate
Activation energy
Enzymes reduce the
height of the energy
barrier
Energy
Substrates
Progress of reaction
Products
Questions
Read page 165-66
1. Write a definition for the following:
Active Site
Substrate
Products
2. Explain how the structure of the protein is linked to its ability to act
as an enzyme?
3. How does heating a mixture increase the chance that a chemical reaction
Will occur? Why can’t this approach be used in cells?
4. Write a paragraph in your own words describing how enzymes act as
catalysts by lowering activation energy.