[STPM] [BIOLOGY] [NOTES] CHAPTER 1 : BASIC CHEMISTRY OF A CELL (PART 3.1)
Sunday, May 11, 2014 | 9:55 PM | 0 comments
After part 1 and 2, finally here's the part 3~ So in part 3, we're gonna learn about lipids.
Before we start, let's revise something we've learnt during our Chemistry in SPM.
Well, lipids are organic compounds which are made up of hydrogen, carbon and oxygen atoms. The only difference between lipids and carbohydrates I think is that the ratio of C:H is not the same. Not only that, some lipids even contain phosphorus and nitrogen. Since it's organic compound, it can only dissolve in organic solvent like acetone, benzene etc.
And here, we are going to learn 3 types of lipids : -
3 types of lipids : - Triglycerides | Phospholipids | Steroids.
First, let's go to the triglyceride. We've learnt about that last year. A triglyceride is an ester formed from condensation of 1 molecule of glycerol and 3 molecules of fatty acid. [Reaction: Esterification]
Now let's go through a bit details on the reaction esterification. So, during this esterification, glycerol with 3 carbon atoms, each bearing a hydroxyl group (-OH) will neutralise with 3 molecules of fatty acids (RCOOH), each containing the carboxyl functional group (-COOH).
[R represents H or alkyl groups.]
Extra :-
Water is formed when fats are oxidised. This metabolic water can be very useful to some desert animals like camels, which store fat in their humps for this purpose.
The long and hydrophobic alkyl group forms the hydrocarbon chain of fatty acids and in most naturally occuring ones, the number of carbon atoms are even between 14 and 22.
Here's a little comparison between saturated and unsaturated fatty acid.
First, saturated fatty acid is a straight molecule while unsaturated one is a bent molecule. Why does it bend? Its due to the presence of one or more double bonds. The kinks where double bonds located prevent unsaturated fat molecules from packing together closely enough. And that's why unsaturated fat is usually in liquid form.
Fatty acids are required in very small qtt. But, if we lack of this substance, it results in :
- deterioration of nerve cells
- failure of certain groups of cells to function properly and death
Triglycerides are non-polar thus they don't form hydrogen bonds with water molecules. So, this explains why they are hydrophobic.
Some major functions of triglycerides : -
- act as energy stores : have higher calorific value than carbohydrates
- serves as an insulator : extensive in mammals living in cold climates
Plants usually store oils rather than fats. Fruits and seeds are often rich in oils.
Ohoho~~ So, finally we conclude our part 3.1, that is our triglyceride~
For the upcoming part 3.2, we are going to going for phospholipids and hopefully together with steroids :-]
Notes by WanQing
