Bioenergetics

Bioenergetics

The application and transformation of energy in living systems; biochemistry focuses on ΔG for cellular processes

ΔG = ΔH – TΔS

Mathematical relationship between free energy

Enthalpy (ΔH)

Heat content change; ΔH < 0 favorable (makes bonds)

Entropy (ΔS)

Disorder change; ΔS > 0 favorable

ΔG < 0

Exergonic and spontaneous; products favored

ΔG = 0

Equilibrium; no net change

ΔG > 0

Endergonic and non-spontaneous; reactants favored

ΔG and spontaneity notes

ΔG does not indicate reaction speed; ΔG relates to Keq by ΔG = –RT ln Keq

Metabolism

Series of linked and regulated reactions converting substrate → product

Stages of Catabolism

1) Digestion 2) Formation of acetyl-CoA 3) ATP production via oxidation

Catabolism

Breakdown pathway; oxidative; produces ATP and reducing equivalents (NADH

Anabolism

Synthesis pathway; reductive; requires ATP and reducing power

Oxidation

Loss of electrons/H+

Reduction

Gain of electrons/H+

Bioenergetics definition

Transformation of energy in living systems; fuels → ATP

Phototrophs

Obtain energy from sunlight

Chemotrophs

Obtain energy by oxidizing carbon fuels

Carbon oxidation and energy

More reduced carbons release more energy when oxidized; fats > sugars

Insulin

Released when blood glucose is high; lowers blood glucose

Glucagon

Released when blood glucose is low; raises blood glucose

Epinephrine

Released during fight/flight; mobilizes sugar for rapid ATP production

Metabolic regulation

Controlled by enzyme amount

Reaction coupling

Unfavorable (+ΔG) reactions driven by coupling to favorable ones

ATP hydrolysis

Highly favorable reaction (ΔG = –30.5 kJ/mol) used to drive pathways

Criteria for metabolic pathways

Steps must be specific and overall pathway must be thermodynamically favorable

Coupling example

A→B with +16.7 + ATP hydrolysis –30.5 → net –13.8 kJ/mol (favorable)

ATP importance

Primary energy currency; ATP must be continually recycled

ATP synthesis

Catabolic reactions or light energy make ATP

ATP hydrolysis

Drives anabolic reactions; exergonic due to unstable phosphoanhydride bonds

Why ATP releases energy

Charge repulsion + resonance stabilization + hydration stabilization

Mg²⁺ role

Helps stabilize ATP phosphoanhydride bonds

Fat calories

9 kcal/g

Carbohydrate calories

4 kcal/g

Protein calories

4 kcal/g

Cofactor

Non-protein molecule aiding enzyme catalysis; often metal ions

Coenzyme

Organic cofactor; regenerated after reactions

NADH

2-electron carrier; NAD⁺ gains 2 e⁻ (hydride transfer)

FADH₂

1 or 2-electron carrier; FAD gains 2 H atoms

Coenzyme A (CoA)

Acyl/acetyl carrier; thioester bond makes transfer highly exergonic

Vitamins

Essential because many coenzymes are derived from them

B Vitamins

B1 Thiamine; B2 Riboflavin; B3 Niacin; B5 Pantothenic acid; B6 Pyridoxine; B7 Biotin; B9 Folate; B12 Cobalamins