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What are Triglycerides?

Shawn Millinder, Mary Ellen Ellis
  • Author
    Shawn Millinder

    Shawn Millinder PhD has taught both Biology and Chemistry at the College level and at the secondary level for the last 25 years. She has a doctoral degree in Molecular Biology from USC (1991) and a BS degree in Bio-veterinary Science / Biology from Utah State University (1986). Doc is also dual-certified in Biology and Chemistry (grades 7-12) by the PA Department of Education.

  • Instructor
    Mary Ellen Ellis

    Mary Ellen is a science and education writer with a background in chemistry. She holds an M.S. in analytical chemistry and has worked as a high school science teacher.

What are triglycerides? Learn the triglycerides definition, their importance, types of triglycerides, triglyceride formation, and various properties. Updated: 08/12/2021

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What are Triglycerides?

Triglycerides belong to a structurally-diverse class of macromolecules that includes some of the most important biochemicals in the human body.

Triglycerides are:

  • lipids and they should be thought of as the molecules the body uses as a backup source of energy;
  • a large part of the typical American diet and are ingested in the foods that we eat; and
  • used for the physical protection of vital organs like the kidneys and the liver.

When the amount triglycerides exceeds what the body needs, triglycerides are stored in adipose tissue, in the liver, and can be found circulating in blood plasma.

  • High plasma levels of triglycerides are associated with serious human diseases like cardiovascular disease, diabetes and obesity.

Triglycerides Examples

In everyday life, triglycerides are called fats or oils.

  • Fats are solids and oils are liquids at room temperature.
  • Fats include butter and lard and oils include olive oil and vegetable oil.

The fatty acids of triglycerides are also described with words like saturated, monounsaturated and polyunsaturated.

  • These three terms refer to the degree to which each carbon atom is surrounded by hydrogen atoms.
  • The carbon atoms in saturated fatty acids are connected to one another by single bonds and are saturated with hydrogen.
  • Unsaturated fatty acids typically have at least one double bond connecting some of the carbon atoms. These atoms are not saturated with hydrogen.
  • Monounsaturated means there is only one double bond present whereas polyunsaturated means that there are multiple double bonds present.

Another way to think about triglycerides is based on the types of fatty acids present in them. For example, triglycerides can be simple or mixed in their fatty acid composition.

Examples of simple triglycerides include tristearin, triolein and tripalmitin.

  • Tristearin is used in soap, candles and adhesive paste;
  • triolein is found in olive oil and a component of a fatty acid mixture used to treat an inherited disorder of the nervous system; and
  • tripalmitin is used for the preparation of leather dressings, soap and some cosmetics.

Mixed triglycerides contain one saturated fatty acid and two unsaturated fatty acids. Examples of mixed triglycerides include:

  • oleo-distearin,
  • dioleo-palmitin, and
  • stearo-oleo-palmitin.

These mixed triglycerides are components of animal tallow, cacao butter and lard.

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  • 0:00 What Are Triglycerides?
  • 1:00 The Chemistry of Triglycerides
  • 2:02 Triglycerides and Health
  • 3:05 Monitoring Triglyceride Levels
  • 4:02 Lesson Summary
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Structure of Triglycerides

There are three important parts to a triglyceride molecule,

  • the glycerol backbone,
  • the ester linkage and
  • the esterified fatty acids.

Triglycerides contain three fatty acids esterified to glycerol through an ester linkage.

Example of a triglyceride.

Glycerol is a small 3-carbon molecule that bears three alcohol (-OH) groups.

  • The fatty acids contain between 12 and 20 carbon atoms with a carboxylic acid (-COOH) at one end.
  • The fatty acids are enzymatically attached to the carbons of glycerol via a condensation reaction that occurs between the alcohol groups of glycerol and the carboxylic acid group of the fatty acid.
  • When the condensation reaction is complete, one molecule of water has been removed for each fatty acid that is added and a new functional group, called the ester, is formed.

The fatty acids that attach to the alcohol groups of glycerol can be saturated or unsaturated.

Saturated fatty acids contain only single carbon to carbon bonds in the hydrocarbon portion of the molecule.

  • The most common saturated fatty acids are named lauric acid, myristic acid, palmitic acid and stearic acid and contain between 12 and 18 carbons.

Unsaturated fatty acids contain at least one double carbon to carbon bond in their hydrocarbon chains.

  • The common unsaturated fatty acids are oleic acid, linoleic acid, linolenic acid, and arachidonic acid.
  • Oleic, linoleic, and linolenic acids each contain 18 carbons each. Linolenic acid contains 20 carbon atoms.

Triglycerides,

  • are white or colorless;
  • are tasteless and odorless;
  • are solids at room temperature;
  • are insoluble in water; and
  • exhibit melting points that are atypical.

If the triglyceride contains saturated fatty acids, the long nonpolar tails can pack tightly together and result in a higher than expected melting and boiling point. If the triglyceride contains unsaturated fatty acids, the melting point and boiling point are lower because the hydrocarbon tails cannot pack as tightly due to a structural "kink" that results from the presence of the double carbon to carbon bond.

For example,

  • tristearin, a plant and nematode metabolite, contains three esterified stearic acids and has a melting point of 55.0 degrees Celsius;
  • oleo-distearin contains one esterified oleic acid and two esterified stearic acids. The melting point of oleo-distearin is 40.5 to 42.0 degrees Celsius.

Both of these triglycerides contain the same number of carbon and oxygen atoms a have a very similar number of hydrogen atoms. The fact that oleo-distearin contains a double bond in the attached oleic acid lowers the melting point significantly.

Triglyceride Formation

From the structure of a triglyceride, it is obvious that both glycerol and fatty acids are required to synthesize the molecules.

Sources of glycerol include our diets, a carbohydrate pathway known as glycolysis and a pathway known as glyceroneogenesis.

  • Glycolysis is the first stage of cellular respiration, the main pathway by which ATP will be generated.
  • Glyceroneogenesis uses amino acids and intermediates of the Krebs cycle to produce glycerol.

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Frequently Asked Questions

What are the 3 types of triglycerides?

Triglycerides are composed of glycerol and fatty acids. They exist as solid fats or liquid oils at room temperature. They are classified as simple or mixed triglycerides based on they type of fatty acid that is present in the molecule.

How triglycerides are formed?

Formation of a triglyceride requires glycerol and three fatty acids. Glycerol can be ingested through the diet or synthesized from intermediates in the glycolysis pathway. The liver synthesizes the fatty acid and the glycerol phosphate combines the glycerol and fatty acids to create the triglyceride.

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