Nutrient Role in Bioenergetics

Chapter 4 Part 2

Bioenergetics-Glycolysis

Carbohydrates primary function Energy for cellular work.

Breakdown of 1 mole of glucose liberates 686 kCal of energy.• 233 kCal (34%) usable• The remainder dissipated as heat.

Bioenergetics

Glucose Degradation - glycolysis Occurs in two stages:

• 1. Anaerobic: Glucose breaks down relatively rapidly to 2 molecules of pyruvate → lactate

• 2. Aerobic: Pyruvate degrades further to carbon dioxide and water.

Glycolysis

Occurs in cytoplasm Enzymes

ATP required as phosphate donor Glucose → glucose-6-phosphate

ATP required as phosphate donor Fructose 6-phosphate

Glycogenolysis

Catabolism of muscle glycogen Glycogen phosphorylase

Glucose-6-phosphate Epinephrine

Glycolysis

Glycolysis

Hydrogen ions released during glycolysis NAD → NADH Additional 5 ATP molecules (ETC)

Bioenergetics

Aerobic glycolysis C3H4O3 – pyruvic acid Rest, light to moderate levels Hydrogen + Oxygen → H2O

Bioenergetics

Anaerobic NAD availability Lactate formation C3H4O3 + 2H+ → C3H6O3

Pyruvic Lactic Acid Acid

Bioenergetics

Aerobic C3H4O3 + 2H+ C3H6O3

Pyruvic Lactic Acid Acid

The Cori Cycle: Lactate As a Fuel Source

Fig 4.16

Bioenergetics

Citric Acid Cycle (Krebs cycle). The second stage of carbohydrate

breakdown Pyruvate converts to acetyl-CoA, degrades

Carbon dioxide and hydrogen atoms-mitochondria

Most important function Generate H ions for Electron Transport Chain

(ETC)

Bioenergetics

Bioenergetics

Stored fat Largest source of potential energy.

Supplies fatty acid molecules

Energy sources for fat catabolism include: • Triacylglycerol

Muscle fiber - stored Lipoprotein complexes - circulating Free fatty acids - circulating

Bioenergetics

Energy metabolism – lipolysis FFA + glycerol

Form intracellular triglycerides Bind with intramuscular proteins

Bioenergetics

Adenosine 3’,5’-cyclic monophosphate Cyclic AMP -

Hormonal effects Epinephrine, norepinephrine, glucagon,

and growth hormone

Bioenergetics

Bioenergetics

Glycerol• Provides carbon skeletons for glucose

synthesis Fatty acids

• Beta (ß)-oxidation converts a free fatty acid to multiple acetyl-CoA molecules.

• Hydrogen ions oxidized through the respiratory chain.

Bioenergetics

Fats in CHO Flame

FA breakdown requires CHO breakdown Intermediates of citric acid cycle

Oxaloacetate (pyruvate) Malate

Bioenergetics

Lipogenesis The formation of fat

Cytoplasm of liver cells Excess glucose or protein not metabolized

Converted into stored triacylglycerol

The lipogenic process requires: ATP energy B vitamins

Biotin, niacin, and pantothenic acid.

Bioenergetics

Protein Energy substrate

Endurance activities Heavy trainings.

Deamination: Nitrogen removed from amino acid Pyruvate FA synthesis

Bioenergetics

Protein Catabolism facilitates water loss. The amine group of protein breakdown

must be eliminated. “Obligatory” water as the waste products

of protein catabolism leave the body dissolved in fluid (urine).

Bioenergetics

Bioenergetics

Metabolic Mill The citric acid cycle

Link Food energy and the chemical energy of ATP.

Intermediates Mitochondrial membrane into the cytosol to

synthesize bionutrients.

Metabolic Mill