Oxidation is loss of electrons Reduction is gain of electrons Oxidation is always accompanied by reduction The total number of electrons is kept constant Oxidizing agents oxidize and are themselves reduced Reducing agents reduce and are themselves oxidized

2. OXIDATION & REDUCTION
INVOLVES ELECTRON TRANSFER

3. Organic material
Burn
Single Step
Heat
Direct addition
of oxygen
Metabolism
Multiple Steps
Enzymes
No direct
addition of
oxygen
Cellular process Vs Burning

4. Oxidation - reduction
• Oxidation is loss of electrons
• Reduction is gain of electrons
– Oxidation is always accompanied by reduction
• The total number of electrons is kept constant
• Oxidizing agents oxidize and are themselves
reduced
• Reducing agents reduce and are themselves
oxidized

5. Follow the electrons

6. Combustion of sugar (or respiration).
• The number of electrons is conserved
• Oxidation and reduction always occurs
simultaneously
• Glucose reacts with molecular oxygen to produce
carbon dioxide and water.
• The carbon atoms in glucose are oxidized. That is,
they lose electron and go to a higher oxidation state.
• The oxygen atoms in molecular oxygen are reduced.
That is, they add electrons and go to a lower
oxidation state

7. Reaction

8. Formation of Polar Covalent Bond

9. Hydrogenation & Dehydrogenation
Increase C-H Bonds
(Hydrogenation/Reduction)
Decrease C-H Bonds
(Dehydrogenation/Oxidation)

10. HOW ENZYMES FIND THEIR SUBSTRATE:
THE ENORMOUS RAPIDITY OF
MOLECULAR MOTIONS

11. How do E & S find each other?
• Enzyme Substrate reaction rate = (1000 substrate
molecules/ Seconds )
• Thus Enzyme bind to substrate for a milliseconds
• High Molecular level motions due to heat energy
– Translational motion
– Vibration
– Rotations
Meaured by spectroscopic techniques

12. Diffusion & Random walk
• Molecules are also in constant translational motion,
which causes them to explore the space inside the cell
very efficiently by wandering through it-a process
called diffusion.
• Every molecule in a cell collides with a huge number
of other molecules each second. As the molecules in a
liquid collide and bounce off one another, an
individual molecule moves first one way and then
another, its path constituting a random walk

13. • Average net distance that each molecule travels (as
the crow flies) from its starting point is proportional
to the square root of the time
– 1second to travel 1 µm
– 4 seconds to travel 2 µm
– 100 seconds to travel 10 µm
• A small organic molecule, for example, takes only
about one-fifth of a second on average to diffuse a
distance of 10 pm
Random Walk

14. Rate of Encounter
• The rate of encounter of each enzyme molecule with
its substrate will depend on the concentration of the
substrate molecule. For example,
– some abundant substrates are present at a concentration of
0.5 mM. Since pure water is 55.5 M, there is only about
one such substrate molecule in the cell for every 10s water
molecules.
• Active site on an enzyme molecule that binds this
substrate will be bombarded by about 500,000
random collisions with the substrate molecule per
second.

15. Stronger the binding of the enzyme &
substrate, the slower their rate of
dissociation.
• Once an enzyme and substrate have collided and
smuggled together properly at the active site, they
form multiple weak bonds with each other that persist
until random thermal motion causes the molecules to
dissociate again
• when two colliding molecules have poorly matching
surfaces, they form few non-covalent bonds and their
total energy is negligible compared with that of
thermal motion. Two molecules dissociate as rapidly
as they come together, preventing incorrect Link
between an enzyme and the wrong substrate