1. Review Reaction mechanisms 2. Reducing sugars
3. Amino acid mutations and their effects
4. Lipids

2. Review Reaction mechanisms
Draw the catalytic amino acid side chains with an eye for geometry
Remember the substrate and products
Use arrows to move to another panel when you need to
For this class, focus on Attack!
Let’s go through the serine protease mechanism again.

3. Review Carbohydrates and Reducing sugars
What does a reducing sugar have? What makes non-reducing sugar?
When dealing with disaccharides or oligosaccharides, draw the monomers first and then connect them appropriately

4. Review Amino acid mutations What are the effect(s) of the mutation?
Which kinetic parameters change?
What does that tell you?
Can you relate it to what we already know about kinetics and inhibition?
You must think about the relationship between the actual mutation, the physical difference between the wild type and the mutant as well as the effect of this difference

5. Review Lipids As usual, FIND THE FUNCTIONAL GROUPS
Think about the role unsaturation plays in the behaviour of the molecule
Where/when would you want to change the saturation of the acyl chain?
What other types of linkage could you have in acylglycerides? What effect(s) would the different linkage have?

6. Electron Transfer Types of biological redox reactions
Direct electron transfer:
2. H atom transfer
3. H:- (hydride) ion transfer
4. Direct reaction with O2 in some form

7. Electron Transfer Direct electron transfer:
Fe+2 + Cu+3 --> Fe+3 + Cu+2
Oxidation Half Reaction: Fe+2 --> Fe+3 + 1e-
Reduction Half Reaction: Cu+3 + 1e- --> Cu2+
The 2 half reactions make a RedOx couple
We can combine 2 half reactions from the previous table and a reaction will occur as long as the E°’ is POSITIVE

8. Electron Transfer 2. Hydrogen atom transfer
A Hydrogen atom has a single electron:
AH2  A + 2e- + 2H+
AH2 is the hydrogen/electron donor
This is not an acid/base reaction, the H+ comes from the removal of a hydrogen atom with its electron, not just the proton
AH2 and A together constitute a conjugate redox pair that can reduce another compound, B, or redox pair (B/BH2) by transfer of hydrogen atoms:
AH2 + B  A + BH2

9. Electron Transfer 3. H:- (hydride) ion transfer
A hydride ion is a hydrogen atom with 2 electrons
Hydrides are transferred to NAD+ and FADH2
We’ll look at these in just a bit…

10. Electron Transfer 4. Direct combination with oxygen
Oxygen combines with an organic reductant and is covalently incorporated into the product
Example: Oxidation of a hydrocarbon to an alcohol
R-CH3 + 1/2 O2 --> R-CH2OH
The hydrocarbon is the electron donor and the oxygen atom is the electron acceptor

11. Electron Carriers in Biological Systems
In Many biological reactions, electrons are transferred as hydrides to a Carrier Molecule
Nicotinamide adenine dinucleotide (NAD+) and Flavin Adenine Dinucleotide (FAD2+) are the 2 primary electron carrier molecules in cells

12. Nicotinamide adenine dinucleotide
NAD+, Nicotinamide Adenine Dinucleotide, is an electron acceptor in catabolic pathways.
The nicotinamide ring, derived from the vitamin niacin, accepts 2 e- & 1 H+ (a hydride) in going to the reduced state, NADH.
NADP+/NADPH is similar except for Pi. NADPH is e- donor in synthetic pathways.

13. NAD+/NADH The electron transfer reaction may be summarized as :
NAD+ + 2e- + H+  NADH
It may also be written as:
NAD+ + 2e- + 2H+  NADH + H+

14. FAD (Flavin Adenine Dinucleotide), derived from the vitamin riboflavin, functions as an e- acceptor.
The dimethylisoalloxazine ring undergoes reduction/oxidation.
FAD accepts 2 e- + 2 H+ in going to its reduced state:
FAD + 2 e- + 2 H+  FADH2

15. Enzymes involved in RedOx Reactions
Enzymes that catalyze RedOx reactions are generally called Oxidoreductases
This includes : Oxidases, Dehydrogenases, Hydroperoxidases and Oxygenases.
Oxidases use oxygen as an electron acceptor
Dehydrogenases can’t use as an electron acceptor
Hydroperoxidases use H2O2 as a substrate
Oxygenases catalyse the direct transfer of O2 into the substrate
Oxidases & dehydrogenases are involved in respiration; hydroperoxidases neutralize free radicals & oxygenases are involved in biotransformation

16. Oxidases
Catalyze the removal of hydrogen from a substrate with the involvement of oxygen as a Hydrogen acceptor
Exist in two different forms :
some of them are copper containing as, Cytochrome oxidase - the terminal component of ETC which transfer the e - to O2.
Other are flavoproteins such L – aminoacid oxidase, xanthine oxidase

17. Dehydrogenases Perform 2 main functions:
Transfer hydrogen from one substrate to another in a coupled RedOx reaction
As components of Electron transport chain Dehydrogenases use coenzymes – nicotinamides & riboflavin to carry hydrogens

18. Haloperoxidases Includes 2 sets of enzymes : Catalase and Peroxidases
Peroxidases reduce H2O2 at the expense of several other substances
H2O2 + AH2  2H2O + A
Catalase uses H2O2 as electron acceptor & electron donor
2H2O2  2H2O
Peroxisomes are rich in oxidases and catalases

19. Oxygenases Catalyse the incorporation of O2 into subtrates in 2 steps
Oxygen is bound to the active site of the enzyme
The O2 is then reduced or transferred to the substrate
Consists of two sets of enzymes
Dioxygenases : incorporate both atoms of oxygen into the substrate
A + O2  AO2
Monooxygenases : incorporates one atom of oxygen into the substrate & the other is reduced to water
AH + O2 + ZH2  AOH + H2O + Z