METABOLISM
The chemical changes that occur in living
organisms
The Principal Organs:
 Digestive Organs
 Liver
 Pancreas
 Heart and Blood Vessels
 Kidneys

Energy Metabolism Centers on 4 Basic Units:
 From Carbohydrate – glucose
 From Lipids – glycerol and fatty acids
 From Protein – amino acids
Metabolic pathways break down
compounds (CATABOLIC) or build more
complex compounds (ANABOLIC)
 Metabolic pathways are never completely
inactive

IMPORTANT METABOLIC
COMPOUNDS
ATP – adenosine triphosphate
 A high energy compound that is the main
direct fuel for cells
 Production of ATP is the fundamental goal
of metabolism’s energy producing pathway

BREAKDOWN and RELEASE of
ENERGY - CARBOHYDRATE

1. Glycolysis: the anaerobic metabolic
pathway that breaks down glucose into two
molecules of pyruvate
BREAKDOWN and RELEASE of
ENERGY - CARBOHYDRATE



2. Pyruvate to Acetyl CoA: an aerobic reaction
If oxygen is unavailable, this reaction cannot
occur and lactate is formed
Lactate is an alternative fuel that muscle cells can
use, or liver cells can convert to glucose
BREAKDOWN and RELEASE of
ENERGY - CARBOHYDRATE

3. Citric acid cycle/Kreb’s Cycle/Tricarboxylic
Acid Cycle: a circular metabolic pathway
BREAKDOWN and RELEASE of
ENERGY - CARBOHYDRATE

4. Electron Transport Chain: This pathway produces
most of the ATP available from glucose
END PRODUCTS
When completely broken down, each
glucose molecule yields carbon dioxide,
water, and ATP
 30-32 ATP are formed by the complete
break down of glucose

BREAKDOWN and RELEASE of
ENERGY - FATS
To begin breaking down fat, the body
breaks triglycerides into glycerol and fatty
acids
 Most of the energy is stored in the fatty
acids (glycerol can be converted to glucose
or pyruvate)
 Fatty acids usually produce substantially
more ATP than glucose (16 carbon fatty
acid = 129 ATP)

BREAKDOWN and RELEASE of
ENERGY - PROTEIN
Protein is only used for energy in the
absence of carbohydrate or fat
 Carbon skeletons: are formed by the
deamination of amino acids and can enter
the metabolic pathways at several points
depending on their structure (# carbons)

BREAKDOWN and RELEASE of
ENERGY - PROTEIN
Glucogenic Amino Acids: become pyruvate
or a citric acid cycle intermediate
 Ketogenic Amino Acids: become acetyl
CoA
 The carbon skeleton’s point of entry
determines the amount of ATP produced

FEASTING
FASTING
FASTING
Figure 6-5 (continued fasting).