BIOENERGETICS – Part 2HOW THE BODY CONVERTS FOOD TO ENERGY

Geromil J. Lara, RMT, MSMT

GLUCONEOGENESIS

• Production of glucose from non-carbohydrate sources– Lactate – All amino acids except leucine and lysine– Glycerol from fats

• Amino acids and glycerol are used only under starvation conditions

• Occurs primarily in the liver

CORI CYCLE

GLYCOGENESIS

• Formation of glycogen from glucose

• Occurs in the liver

• Influenced by insulin – Inhibits glycogen phosphorylase– Stimulates glycogen synthase and

glucokinase

GLYCOGENOLYSIS

• Breakdown of stored glycogen to form glucose

• Influenced generally by glucagon and epinephrine in response to low blood glucose levels

• Glycogen phosphorylase is activated• Glycogen synthase is inhibited

(2) CITRIC ACID CYCLE

• Also known as the Kreb’s Cycle• Final stage of the breakdown of

carbohydrates, fats, and amino acids.

• Series of enzymes involved

KETONES

• Formed from beta-oxidation pathway of fatty acid metabolism due to low level of glucose (starvation and fasting)

• Low glucose supply slows down citric acid cycle– No glycolysis– No PEP production– Greatly reduced oxaloacetate production

• As a result, acetyl CoA builds up in the body

(3) OXIDATIVE PHOSPHORYLATION

• Is a series of reactions which couples the oxidation of NADH and FADH2 to the phosphorylation of ADP to generate ATP

• NADH = used to produce 3 ATPs• FADH2 = used to produce 2 ATPs

NUMBER OF ATP PRODUCED BY THE COMPLETE OXIDATION OF ONE MOLECULE

OF GLUCOSEGlycolysis

– Substrate-level Phosphorylation 2 ATP– 2 NADH x 2 ATP/cytoplasmic NADH 4

ATP

Conversion of 2 pyruvate molecules to 2 acetyl CoA molecules– 2 NADH x 3 ATP/NADH 6 ATP

Citric Acid Cycle– 2 GTP x 1 ATP/GTP 2 ATP– 6 NADH x 3 ATP/NADH 18 ATP– 2 FADH2 x 2 ATP/FADH2 4

ATP

CATABOLISM OF THE NITROGEN OF AMINO ACIDS

• Dietary proteins are hydrolyzed to amino acids in digestion

• Amino acids are primarily used to synthesize new proteins

• Cannot be stored, so excess amino acids are catabolized for energy production in the liver1. Transamination

2. Oxidative Deamination

3. Urea Cycle

TRANSAMINATION

• Amino acids transfer their amino group to alpha-ketoglutarate

OXIDATIVE DEAMINATION

• Oxidative deamination of glutamate

UREA CYCLE

• Ammonia is converted to urea

CATABOLISM OF HEME

• Red Blood Cells– 80 – 120 days life span– Destroyed by the phagocytic cells– Hemoglobin is metabolized

• Globin is hydrolyzed to amino acids• Heme is oxidized to biliverdin and

finally reduced to bilirubin• Bilirubin enters the liver• Iron is preserved in ferritin and reused

NEXT ON BIOCHEMISTRYNUTRITION: AN INTRODUCTION