Fatty acids

The basic characteristics of fatty acids (FA)

The basic characteristics of fatty acids (FA), which determine their physical, chemical und biological properties, are:

Biogennous role

Organisms synthesize FA in specialized cells; there are however certain fatty acids that cannot be synthesized and the only source for organisms to obtain them is through a nutrition. FA play two major roles for the animals:

• Energetic - energy storage and energy release
• Structural - synthesis of vital substances

Energetic Role

Organisms synthesize FA as a way to store energy at the time of energy surplus. FA cover for example in the case of mammals 30% of total energy demand when the muscle is relaxed, which increases up to 90% at muscle contraction. Not all cells are however capable to use FAs as an energy source – the brain cells for instance depend completely on carbohydrates (glucose to be more precise).

Organisms store energy in the form of triglycerides – molecules consisting of one glycerol and three fatty acid molecules. Triglycerides contain about 6 times as much energy as carbohydrates of the same weight. When organisms need energy they have to break down the triglycerides enzymatically into glycerol and unbound fatty acids. Free FA are consequently oxidized in three steps, which finally lead to the formation of ATP (adenosintriphosphate) - the cells’ primary energy source.

Structural Role

For living organisms the FA are precursors of phospholipids synthesis (fats which are main constituents of cell membranes), as well as components of the myelin sheath of the nerve cells and precursors for the synthesis of hormone-like substances, which serve a number of functions relating to immunity, activity of the central nervous system, organism reaction to injuries etc.

Utilization of free FA

Marine invertebrates’ primary source of fatty acids is macromolecular organic food, as well as marine water itself. The latter contains a certain amount of free dissolved fatty acids, however in very low concentrations. The manner in which crustaceans uptake FA from marine water has been studied primarily on annelids, brittlestars and sea urchins with the following results:

• The accumulation and metabolization of free FA directly from seawater
  by marine invertebrates has been scientifically proven
• The FA uptake takes place directly across the invertebrates’ body wall,
  not through a water filtration within alimentary tract
• The rate of FA accumulation was in most tests directly dependent
  on the FA concentration in the medium
• In natural oceanic ecosystems direct FA uptake can probably support
  not more than a few percent of the organisms’ metabolism

Graph no. I

This graph shows the uptake of linoleic acid by sea worm Nainereis dendritica as a function of incubation time in medium. The quantity of accumulated FA grows linearly in time, thus longer the animal is exposed to the dissolved fatty acid, the more will by uptaken.

Graph no. II

This graph shows the uptake velocity of palmitic acid (in 10-9mol g-1 hod-1) by sea worm Stauronereis rudolphi as a function of molar concentration of FA in substrate. It can be stated the uptake velocity grows with FA concentration, although in the certain concentration interval is almost constant.

Literature