The Molecules for life (the small ones) part 2

Now onto the organic and fatty acids!
Organic acids are very important due to their roles in complex chemical reaction, although not being very exciting chemicals themselves. If the cell is not supplied with them and with sugars, it soon is not able to sustain its protein and lipid organelles.
Some examples: (Using common names)
Acetic acid

Acetic Acid

Succinic acid

Fumaric acid

Citric acid

Pyruvic acid

Fatty acids are also vital for the structural role they have within the cell, specifically in cell membranes.They act as a barrier to polar substances in the membranes, as they are relatively long hydrocarbon chains with only a small acidic COOH group on the end. This makes them non-polar, and therefore hydrophobic, themselves, which is very useful to ensure that water levels inside and outside of the cell can be carefully controlled.
The acidic group is also important, as it allows the fatty acid to combine easily with other organic molecules, e.g. to make lipids!
Their long hydrocarbon chain parts can also be unsaturated (contain a carbon-carbon double bond):

  If they are unsaturated however it means that their can be two molecular configurations surrounding the double bond:

Top - cis
Bottom - trans

 This determines how straight the fatty acid is, as in the trans position the symmetry of the molecule keeps it straight, but in the cis position the chain becomes bent and changes direction. This then determines the fluidity of the fatty acids, which also plays an important role in controlling membrane stability.

Source: The Chemistry of Life by Steven Rose