Molecules of Biological Redox Reactions & Activated Carrier Molecules

Biological Reactions of Reduction and Oxidation

• Are coupled

• Something gets reduced while something gets oxidized

• X- + Y → X + Y-

NAD+

• Without the H+

• Nicotinamide adenine dinucleotide – oxidized

NADH + H+

• With the H+

• Nicotinamide adenine dinucleotide – reduced

• has stereoisomers

• can be oxidized

Nicotinamide

Derived from niacin – (aka, vitamin B3)

Reduction

NAD + + 2H + + 2e- → NADH + H

Oxidation

NADH + H + → NAD + + 2H + + 2e-

Reduction of acetaldehyde by alcohol dehydrogenase:

• The aldehyde group is reduced to yield a hydroxyl group

• The reaction is reversible

Flavin Adenine Dinucleotide (FAD)

Riboflavin (aka, vitamin B2 )

FAD and FMN

Act as coenzymes in metabolic reactions

Pantothenate Unit

Vitamin B5

Coenzyme A (CoA)

Includes a β-Mercapto-ethylamine unit and a Pantothenate unit (B5)

• oxygen esters are stabilized by resonance structures not available to thioesters

Thiamine (B1)

• Coenzyme: Thiamine pyrophosphate

• Reaction type: Aldehyde transfer

• Can cause Beriberi if deficient

Riboflavin (B2)

• Coenzyme: FAD

• Reaction type: Oxidation-reduction

• Can cause Cheliosis and angular stomatitis if deficient

Pyridoxine (B6)

• Coenzyme: Pyridoxal phosphate

• Reaction type: group transfer to or from amino acids

• depression, confusion, and convulsions are possible consequences of deficiency

Nicotinic Acid (Niacin, B3)

• Coenzyme: NAD+

• Reaction type: oxidation-reduction

• Pellagra is a possible consequence of deficiency

Pantothenic Acid (B5)

• Coenzyme: Coenzyme A

• Reaction type: acyl-group transfer

• can cause hypertension if deficient

Biotin (B7)

• Coenzyme: Biotin-lysine adducts

• Reaction type: ATP-dependent carboxylation and carboxyl-group transfer

• deficiency can cause a rash around the eyebrows, muscle pain, and fatigue (rare)

Anabolic Outcomes of Glucose Metabolism

• extracellular matrix and cell wall polysaccharides (synthesis of structural polymers)

• glycogen, starch, sucrose (storage)

Catabolic Outcomes of Glucose Metabolism

• Ribose 5-phosphate (oxidation via pentose phosphate pathway)

• Pyruvate (oxidation via glycolysis)

Glycolysis

1. Trapping and preparation phase:

• Traps glucose in the cell

• Forms fructose-1,6-bisphosphate: Cleaved into two 3-carbon molecules

• ATP is used twice

2. Payoff phase:

• Uses glyceraldehyde-3-phosphate

• Forms pyruvate

• 4 ATP and 2 (NADH + H+) are generated

Select active carriers in metabolism:

• NADH

• NADPH

• FMNH2

• FADH2

• Coenzyme A