Lipids

Lipids

1. Classes

   • Fatty acids
     • Carboxylic acids. Have a terminal carboxyl group (moiety) (-COOH)
     • LOng saturated or unsaturated alkyl (hydrocarbon) chains
       • Can be 4 to 36 carbons
       • Most commonly have an even number of carbons between 12 and 24
       • Most natural fatty acids are unbranched
       • Saturated chains of fatty acids can adopt extended conformations due to unrestricted rotation about single bonds
         • More orderly stacking
       • Unsaturated chains of fatty acids (in cis configuration) are more limited in their conformation due to restriction about double bond (usually cis configuartion)
         • Less orderly stacking
     • Metabolic fuel
     • Precursors to other lipids (e.g., triglycerides)
     • Saturated
     • unsaturated (mono and poly)
       • Double bonds are almost always in cis configuratuib
   • Glyceryl esters
     • Fatty acids esterified to a trihydric glycerol molecule
       • Acylglycerols
       • Phosphoglycerides
     • Storage
     • Structure
   • Sphingolipids
     • Fatty acids plus sphingosine
       • Sphingosine is a long chain alcohol with an amino group (-NH2)
     • Membrane structure
     • INtracellular modulators
   • Sterolsn and sterol derivatives
     • Tetracyclic ring structure (2 fused cyclohexanes, 1 cyclohexene, and 1 cyclopentane, ABCD)
     • Structure (cholesterol with membrane fluidity)
     • Digestion
     • Signaling/regulation
   • Terpenes
     • Polymers of isoprene subunits linked head-to-tail
     • COmprise natural products
     • Vitamins
     • Singaling/regulation

2. Nomenclature

   • Position of carbon atoms in a fatty acid chain is endicated by methyl or caboxy end
     • If methyl, omega-n
     • If carboxy end, C-n (starting at carboxyl carbon being C1)

3. Roles

   • Membrane structure: main components of membranes
     • Phospholipids
     • Glycolipids
   • Signalling/communication and regulation
     • Hormones
       • Paracrine hormones (local effect)
       • Endocrine hormones (systemic effect)
       • Vitamins A &D (hormone precursors)
     • Secondary messengers
     • Growth factors
       • "naturally occurring regulatory molecules, which bind to receptors on the cell surface. They stimulate cell and tissue function through influencing cell differentiation by changing their biochemical activity and cellular growth, and regulating their rate of proliferation" https://www.sigmaaldrich.com/technical-documents/articles/biofiles/growth-factors-in.html
   • Fuel
     • Energy storage
   • Molecular recognition
     • Acylation of proteins
     • Targeting of proteins to membrane and/or organelles
   • Cofactors for enzymes (assist in enzymatic reaction)
     • Metal ions (inorganic)
     • Organic Chemicals
       • CoQ10
       • Vitamins, such as Vitamin K
   • Pigments
     • Provide color to tomatoes, pumpkins, some birds, etc.
   • Antioxidants
     • Vitamin E

4. Features

   • All are water-insoluble

5. All types of lipids commonly contain fatty acids as a component

6. Physical properties

   • Solubility
   • Melting point
     • Increases as chain length increases
     • Decreases as chain length decreases
     • Decreases as # double bonds increases
     • Increases as # double bonds decreases
     • Increases as amount of saturated fat (# single bonds) increases