STPM Biology - chapter 1: Revision essay question 6

6.  Fats, Oils, Fatty Acids, Triglycerides are lipids. Explain and describe.

Lipids consist of numerous fat like chemical compounds that are insoluble in water but soluble in organic solvents. Lipid compounds include monoglycerides, diglycerides, triglycerides, phosphatides, cerebrosides, sterols, terpenes, fatty alcohols, and fatty acids. Dietary fats supply energy, carry fat-soluble vitamins (A, D, E, K), and are a source of antioxidants and bioactive compounds. Fats are also incorporated as structural components of the brain and cell membranes.

 Fatty acids consist of the elements carbon (C), hydrogen (H) and oxygen (O) arranged as a carbon chain skeleton with a carboxyl group (-COOH) at one end. Saturated fatty acids (SFAs) have all the hydrogen that the carbon atoms can hold, and therefore, have no double bonds between the carbons.Monounsaturated fatty acids (MUFAs) have only one double bond. Polyunsaturated fatty acids (PUFAs) have more than one double bond.

Butyric Acid

Butyric acid (butanoic acid) is one of the saturated short-chain fatty acids responsible for the characteristic flavor of butter. This image is a detailed structural formula explicitly showing four bonds for every carbon atom and can also be represented as the equivalent line formulas:

CH₃CH₂CH₂COOH    or    CH₃(CH₂)₂COOH

The numbers at the beginning of the scientific names indicate the locations of the double bonds. By convention, the carbon of the carboxyl group is carbon number one. Greek numeric prefixes such as di, tri, tetra, penta, hexa, etc., are used as multipliers and to describe the length of carbon chains containing more than four atoms. Thus, "9,12-octadecadienoic acid" indicates that there is an 18-carbon chain (octa deca) with two double bonds (di en) located at carbons 9 and 12, with carbon 1 constituting a carboxyl group (oic acid). The structural formula corresponds to:

CH₃CH₂CH₂CH₂CH₂CH=CHCH₂CH=CHCH₂CH₂CH₂CH₂CH₂CH₂CH₂COOH

9,12-octadecadienoic acid   (Linoleic Acid)

which would be abbreviated as:

CH₃(CH₂)₄CH=CHCH₂CH=CH(CH₂)₇COOH

Fatty acids are frequently represented by a notation such as C18:2 that indicates that the fatty acid consists of an 18-carbon chain and 2 double bonds. Although this could refer to any of several possible fatty acid isomers with this chemical composition, it implies the naturally-occurring fatty acid with these characteristics, i.e., linoleic acid.  Double bonds are said to be "conjugated" when they are separated from each other by one single bond, e.g., (-CH=CH-CH=CH-). The term "conjugated linoleic acid" (CLA) refers to several C18:2 linoleic acid variants such as 9,11-CLA and 10,12-CLA which correspond to 9,11-octadecadienoic acid and 10,12-octadecadienoic acid. The principal dietary isomer of CLA is cis-9,trans-11 CLA, also known as rumenic acid. CLA is found naturally in meats, eggs, cheese, milk and yogurt.

CH₃(CH₂)₅CH=CH-CH=CH(CH₂)₇COOH

9,11-Conjugated Linoleic Acid

 Assignment submitted by L.Y., Kong,  S. H., Lim, S. C., Soo, C. W. Tan and C.C.,Teh 2011/2012 (IBM)