[STPM] [BIOLOGY] [NOTES] CHAPTER 1 : BASIC CHEMISTRY OF A CELL (PART 3.2)
Monday, May 12, 2014 | 9:21 PM | 0 comments
Fatty acids
Fatty acids can be divided into saturated fatty acids and unsaturated fatty acids.
Saturated fatty acids contain the maximum number of H atoms and do not have any double bond.
Unsaturated fatty acids contain at least one double bond. It is called “unsaturated” because the fatty acid can be still inserted some more H atoms to make it saturated.
Triglyceride formed from saturated fatty acids is normally solid at room temperature due to its compact shape and it is called fat.
Triglyceride formed from unsaturated fatty acids is liquid at room temperaturedue to the kinks caused by double bond and prevent triglyceride to form compact shape. It is called oil.
Oil can be converted to fat by the process of hydrogenation.
Phospholipids
Cells could not exist without another type of lipid – phospholipids.
Phospholipids are essential for cells because they make up cell membranes.
Phospholipids contain one glycerol and two molecules of fatty acid and a phosphate group.
Additional small molecules, which are usually charged or polar, for example choline, can be linked to the phosphate group to form a variety of phospholipids.
Lecithin is the common phospholipid which forms the cell membrane.
The two ends of phospholipids show different behaviour toward water.
The hyrocarbon tails are hydrophobic and are excluded from water while the phosphate groups and its attachments form a hydrophilic head that has an affinity for water.
When phospholipids are added to water, a micelle is formed where all the hydrophobic tails point to a point.
If phospholipids is in excess, a phospholipid bilayer is formed that shield their hydrophobic portions from water.
Steroids
Many hormones, as well as cholesterol are steroids which are lipid characterized by a carbon skeleton consisting of four fused rings.
Different steroids vary in the chemical groups attached to this ensemble of rings.
Cholesterol is a common component of animal cell membranes and is also the precursor from which other steroids are synthesized.
In vertebrates, cholesterol is synthesized in the liver.
Many sex hormones are steroids produced from cholesterol.
By : Gemini
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