Biochemistry

TLO: Identify the different types of lipids.

Do you still remember about the cell membrane structure that you have learned from Anatomy and Physiology? Do recall, the main structure of our cellular membrane is made of phospholipid—which is made of lipid or also known as fat. Due to its water-insolubility properties, this give them the ability to control what comes in and out of the cell—thus, achieving homeostasis.

            Let’s get to know more about lipid. Lipids are fatty, waxy, or oily compounds that are soluble in organic solvents and insoluble in polar solvents such as water. Lipid is the second most important group of organic compounds in the body. It makes up 18-25% of body mass in lean adults. Similar like carbohydrate, lipids also contain carbon, hydrogen, nitrogen and oxygen. The difference between these two organic compounds is the lipid do not have a 2:1 ratio of hydrogen to oxygen.

            Most lipids are hydrophobic which means they are insoluble in polar solvent like water. They are non-polar—meaning that the charge distribution is evenly distributed and the molecules does not have positive or negative charge ends. As a result of their hydrophobic nature, only the smallest lipids (some fatty acids) can dissolve in watery blood plasma. In order to become more soluble in plasma, other lipid molecules join with hydrophilic protein molecules resulting in a formation of lipid-protein complexes known as lipoprotein. Lipoproteins are soluble because the lipid is coated by protein from outside.

Figure 1 Lipoprotein is soluble in plasma because inner hydrophobic core is coated by protein.