1. Enzymes – protein catalysts
The active site can lower an EA barrier by
orienting substrates correctly
straining substrate bonds
providing a favorable microenvironment
directly participating in the reaction

2. Induced Fit of Substrate e.g. carboxypeptidase
3D structure and the amino acids present at the binding site determine which substrates bind
binding of substrate can induce changes in the structure of the enzyme to enhance binding and the catalytic process – induced fit
carboxypeptidase is synthesized in the pancreas and secreted into the small intestine
hydrolyzes the peptide bond between the last and second last amino acid in a peptide chain

3. Substate Active site Enzyme (a) (b)
Enzyme- substrate
complex
hexokinase

4. Zn2+ - an essential cofactor in carboxypeptidase
this shows the amino acids that are specifically involved in binding the zinc cofactor

5. Mechanism of action
mechanism of action – show website mechanism…

7. (b) Competitive inhibition
Competitive inhibitors
Bind to the active site of an enzyme, competing with the substrate
(b) Competitive inhibition
A competitive
inhibitor mimics the
substrate, competing
for the active site.
Competitive
inhibitor
A substrate can
bind normally to the
active site of an
enzyme.
Substrate
Active site
Enzyme
(a) Normal binding

8. (c) Noncompetitive inhibition
Noncompetitive inhibitors
Bind to another part of an enzyme, changing the function
Figure 8.19
A noncompetitive
inhibitor binds to the
enzyme away from
the active site, altering
the conformation of
the enzyme so that its
active site no longer
functions.
Noncompetitive inhibitor
(c) Noncompetitive inhibition

9. Examples of allosteric regulation: -phosphorylation -Ca2+/calmodulin
example is a tetramer – cleft between each pair is the regulatory site; then each subunit has an active site
tetramer goes back and forth between 2 conformations – active and inactive
binding of an activator or an inhibitor stabilizes a particular conformation
what will change in a cell is the level of the activator and inhibitor – the regulators
other possibility is that binding of the substrate to one active site, stabilizes the active form for the other subunits

10. Active site available
Isoleucine used up by cell
Feedback inhibition
Isoleucine binds to allosteric site
Active site of enzyme 1 no longer binds threonine; pathway is switched off
Initial substrate (threonine)
Threonine in active site
Enzyme 1 (threonine deaminase)
Intermediate A
Intermediate B
Intermediate C
Intermediate D
Enzyme 2
Enzyme 3
Enzyme 4
Enzyme 5
End product (isoleucine)

11. Cellular Respiration C6H12O6 + O2 ↔ 6CO2 + 6H2O
forward reaction: DG = -686 kcal/mol
reverse reaction: DG = 686 kcal/mol