Lipids in Medical Biochemistry

Study Notes

Lipids

Lipids are a heterogeneous group of compounds formed by mainly carbon and hydrogen atoms.
They are insoluble in water but soluble in non-polar solvents such as ether, chloroform, and benzene.
Lipids are important dietary constituents due to their high energy value, fat-soluble vitamins, and essential fatty acids.

Properties of Lipids

Lipids are characterized by low solubility in water, making them relatively hydrophobic.
They have a high energy value, making them a good source of energy.

Biological Functions of Lipids

Storage of energy: lipids provide a lot of available energy due to their good packing and low thermal conductivity.
Insulation from the environment: lipids provide mechanical protection, prevent excessive wetting, and prevent loss of water via evaporation.
Membrane structure: lipids are the main structure of cell membranes.
Cofactors for enzymes: lipids act as cofactors for enzymes, such as vitamin K and coenzyme Q.
Signaling molecules: lipids act as signaling molecules, such as paracrine hormones, steroid hormones, growth factors, and vitamins A and D.
Pigments: lipids are responsible for the color of certain fruits and vegetables.
Antioxidants: lipids, such as vitamin E, act as antioxidants.

Classification of Lipids

Lipids can be classified into three categories: simple lipids, complex lipids, and isoprene-derived lipids.
Simple lipids include fatty acids, triglycerides, and waxes.
Complex lipids include phospholipids, glycolipids, and lipoproteins.
Isoprene-derived lipids include terpenes and steroids.

Fatty Acids

Fatty acids are carboxylic acids with hydrocarbon chains containing between 4 to 36 carbons.
Almost all natural fatty acids have an even number of carbons.
Most natural fatty acids are unbranched.
Fatty acids can be classified as saturated, monounsaturated, or polyunsaturated based on the number of double bonds in the chain.

Important Fatty Acids

Palmitic acid: 16 C, saturated
Palmitoleic acid: 16 C, a single double-bond, mono-unsaturated
Stearic acid: 18 C, saturated
Oleic acid: 18 C, a single double-bond, mono-unsaturated
Linoleic acid: 18 C, two double-bond, polyunsaturated
Linolenic acid: 18 C, three double-bond, polyunsaturated
Arachidonic acid: 20 C, four double-bond, polyunsaturated

Essential Fatty Acids

Essential fatty acids cannot be synthesized in the body and must be obtained through the diet.
Linoleic acid, linolenic acid, and arachidonic acid are essential fatty acids.

Solubility and Melting Point of Fatty Acids

Solubility of fatty acids decreases as the chain length increases.
Melting point of fatty acids decreases as the chain length decreases and as the number of double bonds increases.

Conformation of Fatty Acids

Saturated fatty acids tend to adopt extended conformations.
The double bonds in natural unsaturated fatty acids are commonly in cis configuration, which kinks the chain.

Description

This quiz covers the biological roles, structure, and properties of different types of lipids, including storage, membrane, and signaling lipids. Understand the common properties of lipids and their importance in medical biochemistry.