Triglycerides: Types & Formation

Before entering the triglyceride pathway, a phosphate is added to the glycerol molecule creating glycerol-3-phosphate. The synthesis of triglycerides can be thought of as occurring in four basic steps - fatty acid activation, phosphatidic acid formation, diacylglycerol formation and finally, triglyceride formation.

• The fatty acids are combined with a sulfur-containing coenzyme derived from vitamin B5, and known as coenzyme A.
• Once activated by coenzyme A, the fatty acids can be converted to phosphatidic acid, a phosphate-containing lipid that is a precursor for many metabolites.
• The phosphate from phosphatidic is removed and it is converted into another important metabolite called diacylglycerol.
• The final fatty acid is added to form a triglyceride.

Functions of Triglycerides

The major function of triglycerides centers around energy creation and energy storage. The long hydrocarbon tails of the esterified fatty acids are an enormous source of stored energy for the human body.

• When energy is needed, the fatty acids are freed from glycerol in the small intestine by an enzyme called pancreatic lipase.
• Two carbon units of the fatty acid tail are removed at a time and converted to acetyl coenzymeA, a very important intermediate that can feed directly into the Krebs cycle.
• The Krebs cycle produces several molecules of nicotinamide and flavin adenine dinucleotides, which then enter the electron transport chain and result in the generation of ATP.
• One molecule of glucose may yield as much as 36 ATP. A triglyceride like tripalmitin yields over 125 molecules of ATP, a number which is over three times larger.

Where are Triglycerides Stored?

The major site for triglyceride storage in the human body is within specialized cells called adipocytes.

• Adipose tissue is located under the skin below the dermis layer, around certain vital organs like the liver, intestines and kidneys, and in the bone marrow.
• Although not technically a storage site, triglycerides can also be found circulating in blood plasma as part of lipoprotein particles like chylomicrons and very low-density lipoproteins.
• Because the typical American diet is high in fat, triglycerides can also accumulate in the liver.
• Recent evidence suggests that triglycerides are also stored within skeletal muscle.

Importance of Triglycerides

Triglycerides are important macromolecules because they give the body a way to store energy-rich fatty acids.

• When the triglycerides are broken down, the energy that they provide ensures that vital functions like metabolism or skeletal contraction can occur with constant regularity.

The fatty acids of triglycerides are also precursors for lipoprotein particles and cell membrane components.

• Lipoproteins are the vehicles through which the large, water-insoluble fatty acids can circulate to tissues like the liver and skeletal muscles.

Finally, there is a delicate balance between too few triglycerides and too many triglycerides.

• Both conditions underlay some of the most important and commonplace diseases that the human body is forced to endure.

Lesson summary

• Triglycerides are lipids that contain glycerol and fatty acids.
• Triglycerides can be solids fats or liquid oils at room temperature depending on their fatty acid makeup.
• These colorless, odorless and tasteless macromolecules are consumed in the diet or synthesized in the body.
• The human body stores triglycerides for future use in specialized cells called adipocytes.
• Adipocytes make up adipose tissue that is concentrated underneath the skin, around or in visceral organs and in the bone marrow of long bones.
• When needed for energy, the fatty acids are enzymatically released from glycerol, efficiently feed into the Krebs cycle and will eventually provide large amounts of energy to support the body until another carbohydrate-rich meal is found.
• As lipids, triglycerides represent some of the most important biochemicals in the body.
• Triglycerides are a storage form for energy, a back form of energy and a precursor for molecules like lipoproteins and cell membrane components.