This post will seem out of context, but I wanted to post some definitions to be able to link to in the future for when some of these terms are used incorrectly.  (Note, let's ignore for simplicity diacylglycerides etc.)

Lipolysis:  This is the breakdown of a TAG/triglyceride, three fatty acids attached to a glycerol backbone -- into the component parts, e.g. glycerol + free fatty acids.  Lipolysis is often referred to in the context of mobilizing stored fats, but is also involved in the digestion of dietary fats.

Free Fatty Acids / Non-Esterified Fatty Acids (FFA/NEFA) :  Usually used to refer to the long chain fatty acids (LCFA) consisting of a carbon-hydrogen "chain" with a carboxyl (COOH) terminal end (sometimes referred to as the "head") .   FFA's can pass through cell membranes by facilitated diffusion (often get some "help" and move from areas of high concentration to low concentration).  FFA's are also the form of lipids that are fed into metabolic pathways to produce energy.  If the CH "tail" of the molecule contains only single bonds, this is a saturated fatty acid (SFA), if it contains one double bond it is a monounsaturated FA (MUFA), and if it contains multiple double bonds it is a polyunsaturated FA (PUFA).

Triglycerides / Triacylglycerols (TAGs):  This is the esterified or "bundled" lipid form consisting of three fatty acids attached to a glycerol backbone.  This form is too bulky to pass through cell membranes.  It is the form that fats are stored in adipose and other tissues.  This is therefore the form of most dietary fat, be it animal fat or fruit or seed oils.

Lipases:  Enzymes that facilitate lipolysis.
   1. Lipoprotein Lipase (LPL) acts outside the cells in capillary beds
   2. Hormone Sensitive Lipase (HSL) acts within the cells (adipose and other types)

Esterification:  The "packaging" of fatty acids into triglycerides by attaching 3 fatty acids to a glycerol backbone.

Acyl Transferases:  Enzymes that facilitate triglyceride synthesis

Acylating Stimulating Protein:  Protein that stimulates/facilitates esterification in adipose tissue.

Lipogenesis:  The synthesis of a lipid from smaller precursor molecules.  In the metabolic context this refers to de novo lipogenesis (DNL) from acetyl CoA.

Acetyl CoA Carboxylase:  The first enzyme in the DNL pathway.

Lipid Oxidation:  (aka beta-oxidation, the Fatty Acid Spiral - FAS)  The breaking down of fatty acids to produce energy.  Each "turn" of the cycle/spiral produces an Acetyl CoA molecule and a shortened fatty acid moiety.

Thiolase:  The enzyme actually involved in the oxidation step (there are other enzymes involved in getting a FFA into the FAS, etc.)

{last updated 12/14/2010 7:45am EST}


David Isaak said…
For clarity, you may want to spell out acronyms. Just a suggestion...
CarbSane said…
Hi David, I fixed a few and would add that FFA = free fatty acid aka NEFA = non-esterified fatty acid. Also, TAG in TAG/triglyceride is triacylglyceride.
Moran Bentzur said…
Hi, new reader here. great blog. small typo correction:
"Hormone Sensitive Lipase (HSL) acts with the cells" should probably be "within the cells".
CarbSane said…
Welcome MB! Good catch! Yep, a typo. I'm going to change that now.