ENZYMES
BIOLOGY
MODULE 2
OCR A
Enzymes are globular proteins that act as biological catalysts and speed up the rate of
metabolic reactions by lowering the activation energy, remaining unchanged by that
reaction
intracellular enzymes:
Catalase in liver cells
● Breakdown of Hydrogen peroxide into oxygen and water by hydrolysis
extracellular enzymes:
Amylase made in pancreatic cells but secreted to the digestive system
● Breakdown of starch to maltose in small intestine
Trypsin made in pancreas but operates in the small intestine
● Hydrolysis of peptide bonds in proteins into smaller peptides
Enzyme action
Reaction:
- Molecules must collide with enough activation energy in the correct orientation
Enzymes increase the likelihood of successful collisions and reduce activation energy
1
, Specificity: enzymes can only bind to 1 substrate b/C they are complementary to the shape
of the substrate
Lock and key
Shape of active site is fixed
= only 1 substrate is complementary
- Form ES complex = reaction
- ED complex = products then leave the active site
Induced fit model
Shape of active site goes through a conformational change (changes slightly) to fit the
shape of the substrate more closely/perfectly
Temperature
Increases:
1. Molecules gain kinetic energy and vibrate more
2. Increased collision frequency btw substrate and active site
3. More ES complexes formed = more product made in a given time
Rate of reaction increases up to optimum where :
- Molecules gain too much kinetic energy and vibrate too much
- Strained hydrogen and ionic bonds in the tertiary structure of the enzyme break
- Active site changes shape and the enzyme denatures so is no longer complementary
to the shape of the substrate
- Substrate cannot bind to the active site
- No enzyme-substrate complexes form = no product made
- Rate of reaction rapidly decreases
2
BIOLOGY
MODULE 2
OCR A
Enzymes are globular proteins that act as biological catalysts and speed up the rate of
metabolic reactions by lowering the activation energy, remaining unchanged by that
reaction
intracellular enzymes:
Catalase in liver cells
● Breakdown of Hydrogen peroxide into oxygen and water by hydrolysis
extracellular enzymes:
Amylase made in pancreatic cells but secreted to the digestive system
● Breakdown of starch to maltose in small intestine
Trypsin made in pancreas but operates in the small intestine
● Hydrolysis of peptide bonds in proteins into smaller peptides
Enzyme action
Reaction:
- Molecules must collide with enough activation energy in the correct orientation
Enzymes increase the likelihood of successful collisions and reduce activation energy
1
, Specificity: enzymes can only bind to 1 substrate b/C they are complementary to the shape
of the substrate
Lock and key
Shape of active site is fixed
= only 1 substrate is complementary
- Form ES complex = reaction
- ED complex = products then leave the active site
Induced fit model
Shape of active site goes through a conformational change (changes slightly) to fit the
shape of the substrate more closely/perfectly
Temperature
Increases:
1. Molecules gain kinetic energy and vibrate more
2. Increased collision frequency btw substrate and active site
3. More ES complexes formed = more product made in a given time
Rate of reaction increases up to optimum where :
- Molecules gain too much kinetic energy and vibrate too much
- Strained hydrogen and ionic bonds in the tertiary structure of the enzyme break
- Active site changes shape and the enzyme denatures so is no longer complementary
to the shape of the substrate
- Substrate cannot bind to the active site
- No enzyme-substrate complexes form = no product made
- Rate of reaction rapidly decreases
2
