Metabolism and Energetics

Release of energy from food

coupled reactions

free energy

DF for oxidation of 1 mol glucose = 686 kcal

Role of ATP in metabolism

at STP ~-bond DF = 7.3 kcal, but 12 kcal at body conditions

Role of glucose in carbohydrate metabolism

Transport of glucose through the cell membrane

facilitated diffusion

active sodium cotransport

GI cell membrane

renal tubule membrane

facilitation of glucose transport by insulin

phosphorylation of glucose

glucokinase in liver

hexokinase elsewhere

Storage of glycogen in liver and muscle

glycogenesis

g6p ® g1p ® UDPg

sources include convertible monosaccharides

lactic acid, glycerol, pyruvic acid, some amino acids

glycogenolysis

activation of phosphorylase by Epi and glucagon

increase of cAMP

Release of energy from glucose molecule by the glycolytic pathway ¹

glucose + 2 ADP + 2 PO₄^3- ® 2 pyruvic acid + 2 ATP + 4 H

amount of energy lost from glucose, 56 kcal, efficiency 43%

Conversion of pyruvic acid to acetyl-CoA

2 pyruvic acid + 2 CoA ® 2 Acetyl-CoA + 2 CO₂ + 4 H

Citric acid cycle ²

2 Acetyl-CoA + 6 H₂O + 2 ADP ® 4 CO₂ + 16 H + 2 CoA + 2 ATP

Formation of ATP by oxidative phosphorylation ³

chemiosmotic mechanism of the mitochondria

ionization of hydrogen

2 H + NAD⁺ ® NADH + H⁺

electron transport chain

flavoprotein, ubiquinone, cytochromes

cytochrome A₃, cytochrome oxidase

ATP synthase

Control of glycolysis and oxidative phosphorylation by ATP and ADP

allosteric inhibition of phosphofructokinase

excess citrate

Anaerobic glycolysis

formation of lactic acid

reconversion of lactic and pyruvic acids to glucose

expenditure: 6 ATP

Phosphogluconate pathway

glucose + 12 NADP⁺ + 6 H₂O ® 6 CO₂ + 12 H + 12 NADPH

5 for 6

Transport of lipids in the blood

lipoproteins

Protein metabolism

nonessential and essential amino acids

ATP

synthesis of cellular components

muscular contraction

membrane active transport

glandular secretion

nerve conduction

Phosphocreatine and ATP

~-bond contains 8.5 kcal at STP, 13 kcal at body conditions

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