Transcript ENZYMES and METABOLIC REACTIONS

ENZYMES and
METABOLIC
REACTIONS
ENZYMES and METABOLIC
REACTIONS
 How


do reactions occur in cells?
Molecules are in constant motion
Collisions between molecules allow
reactions to occur
ENZYMES and METABOLIC
REACTIONS
 Enzymes

Are protein catalysts that allow chemical
reactions to take place in our body without
increasing the temperature

Usually end with the suffix ‘-ase’
Examples: urease, amylase, sucrase

Catalysts
 Control
the speed of reactions without
changing the products formed

They do this by reducing the activation
energy
Enzymes…
 Work

on molecules called the substrate
Can be anything
Enzymes…
 Work

on molecules called the substrate
Can be anything
 Are
substrate-specific
Enzymes…
 Work

on molecules called the substrate
Can be anything
 Are
substrate-specific
 Alter the substrate in some way
Substrate
approaches an
enzyme
The enzymesubstrate
complex is
formed
Reaction is complete.
Enzyme remains
unchanged.
Products are formed.
Enzymes Models
 Where
the substrate
joins the enzyme is
called the active
site
 ‘Lock and Key
Model’
 The
active site of an
enzyme is a perfect
match to a specific
substrate
Enzymes Models
 ‘Induced-Fit
Model’
 The
active site
changes shape
slightly when the
E-S complex join
together
 Makes a tighter fit
Factors that Affect Enzymes
1. Temperature
 Reaction
rates increase
as temperature
increases
 Peaks at ~ 37 - 40°C
then drops rapidly
 Why?
 E.g.
egg frying
 What
happens at
cooler temperatures?
Factors that Affect Enzymes
2. pH
 Enzymes
function within an optimal pH range
 Stomach
pH
 Small intestine pH
Factors that Affect Enzymes
3. Concentration of Substrate Molecules


Reaction rate increases as the substrate
concentration increases up to a point
The limiting factor in the reaction may be
the amount of substrate or the amount of
enzyme available
4. Inhibitor molecules


Molecules that attach to the enzyme
and reduce its ability to bind substrate
There are two types of inhibitors
Competitive inhibitors
Non-competitive inhibitors
4. Inhibitor molecules
a. Competitive inhibitors
•
•
•
Attach to enzyme’s active site
Shape is similar to substrate
Compete with the substrate
E.g. drugs and
poisons
- CO
- Cyanide
4. Inhibitor molecules
b. Non-competitive inhibitors
•
•
•
Attach elsewhere on the enzyme (not the active site)
Attachment changes the 3D shape of enzyme
Reaction still occurs, but is inhibited