1. Fatty Acid Synthesis

5. Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. The term "essential fatty acid" refers to fatty acids required for biological processes but does not include the fats that only act as fuel.
Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).
Some other fatty acids are sometimes classified as "conditionally essential," meaning that they can become essential under some developmental or disease conditions

8. Metabolism (synthesis)
of fatty acids
Acyl-CoA is a group of coenzymes involved in the metabolism of fatty acids. It is a temporary compound formed when coenzyme A (CoA) attaches to the end of a long-chain fatty acid inside living cells.
The compound undergoes beta oxidation, forming one or more molecules of
acetyl-CoA. This, in turn, enters the citric acid cycle, eventually forming several molecules of ATP.
General chemical structure of an acyl-CoA, where R is a fatty acid side chain

9. Acetyl-CoA
is an important molecule in metabolism, used in many biochemical reactions
UPAC name
S-[2-[3-[[(2R)-4-[[[(2R,3S,4R,5R)-5-(6-aminopurin-9-yl)-4-hydroxy-3-phosphonooxyoxolan-2-yl]methoxy-hydroxyphosphoryl]oxy-hydroxyphosphoryl]oxy-2-hydroxy-3,3-dimethylbutanoyl]amino]propanoylamino]ethyl] ethanethioate

10. Fatty acid metabolism
In animals, acetyl-CoA and other acyl-CoA coenzymes are essential to the balance between carbohydrate metabolism and fat metabolism (see fatty acid synthesis). In normal circumstances, acetyl-CoA from fatty acid metabolism feeds into the citric acid cycle, contributing to the cell's energy supply. In the liver, when levels of circulating fatty acids are high, the production of acetyl-CoA from fat breakdown exceeds the cellular energy requirements. To make use of the energy available from the excess acetyl-CoA, ketone bodies are produced, which can then circulate in the blood.
In some circumstances, this can lead to the presence of very high levels of ketone bodies in the blood, a condition called ketosis, which is different from ketoacidosis, a dangerous condition that can affect diabetics.

11. citric acid cycle

12. Fatty acid synthesis is the creation of fatty acids from acetyl-CoA and malonyl-CoA precursors through action of enzymes called fatty acid synthases. It is an important part of the lipogenesis process, which – together with glycolysis – functions to create fats from blood sugar in living organisms.

13. Acetyl-CoA Carboxylase catalyzes the 2-step reaction by which acetyl-CoA is carboxylated to form malonyl-CoA.
As with other carboxylation reactions, the enzyme prosthetic group is biotin. 
ATP-dependent carboxylation of the biotin, carried out at one active site 1 , is followed by transfer of the carboxyl group to acetyl-CoA at a second active site 2 .

14. The overall reaction, which is spontaneous, may be summarized as:
HCO3- + ATP + acetyl-CoA  ADP + Pi + malonyl-CoA

15. Biotin is linked to the enzyme by an amide bond between the terminal carboxyl of the biotin side chain and the e-amino group of a lysine residue.
The combined biotin and lysine side chains act as a long flexible arm that allows the biotin ring to translocate between the 2 active sites.

16. Biotin, also known as vitamin H or coenzyme R, is a water-soluble B-vitamin (vitamin B7).
It is composed of a (tetrahydroimidizalone) ring fused with a tetrahydrothiophene ring. A valeric acid substituent is attached to one of the carbon atoms of the tetrahydrothiophene ring. Biotin is a coenzyme for carboxylase enzymes,
involved in the synthesis of fatty acids, isoleucine, and valine, and in gluconeogenesis.
Names
IUPAC name
5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoic acid