Lipids

Classes of lipids: 

 

Storage lipids: 

Storage lipids are used for energy. They contain more energy than carbohydrates as they are more reduced and have more electrons per carbon molecule. 

 

• Triacylglycerides: Triacylglycerides contain a glycerol backbone and three fatty acids. They are stored in adipocytes. 

• Fatty Acids: Fatty acids are either saturated (no double bonds, solid at room temp), unsaturated (double bonds, liquid at room temp), or trans (double bond in trans formation instead of cis)

Omega 3s are an essential fatty acid that humans cannot make. They have anti-inflammatory roles. 

 

Structural lipids: 

Structural lipids are used in membranes. 

 

• Glycerophospholipids: Contain a glycerol, 2 fatty acids, a phosphate, and a head group

• Sphingolipids: Sphingosine backbone, FA, and head group

• Sterols: rigid 4 ring structure that is important for fluidity of cell membranes and precursor to steroids

• Glycolipids: membrane lipid with sugar attached

 

Others: 

• Fat soluble vitamins (A, D, E, K)

• Pigments

• Electron carriers

• Signaling molecules

• Steroid hormones

 

Lipid metabolism: 

 

In mitochondria fatty acids are broken down into acetyl CoA which enters the Krebs cycle and generates energy. 

 

To synthesize fatty acids acetyl CoA is converted into malonyl CoA which builds palmitate and fatty acids. This occurs in the cytosol. 

 

Cholesterol is synthesized from four key precursors. 

• Acetyl-CoA → Mevalonate → Isoprenes → Squalene → Cholesterol. 

• This then can be converted to steroid hormones or added to membranes

• Cholesterol at low temp maintains fluidity and at high temp prevents fluidity

 

LDL vs HDL 

 

Lipoproteins LDL (low density lipoprotein) and HDL (high density lipoprotein) transport cholesterol. LDL delivers cholesterol from liver to tissues. High amounts can lead to plaque buildup (atherosclerosis) or risks of heart disease and strokes. HDL removes cholesterol from tissues and transports it back to the liver. This recycles the cholesterol or produces bile acid. HDL can prevent plaque buildup.