From Biolk483



  • These are the major components of membranes.
  • They are built out of glycerol, phosphate, 2 fatty acids and one alcohol.
  • Six different alcohols can be attached to one end of the glycerol, plus one diglyceride makes seven major phospholipids
    • Some have specific functions

Phosphatidic acid (PA)

  • All seven phospholipids can fit in membrane
  • If we make pH 7.2, charge would be -1.5
  • So we would have large negative charge density
    • This is important because many proteins need negative environment to work.
    • This is an example of a specific function of a phospholipid.
  • A typical membrane has 1500 different lipids.
  • Specific functions of phosphatidic acid
  1. ?
  2. ?

Phophatidyl Ethanolamine (PE)

  • When in pH 7, we have slight negative charge because the amine will be almost a full positive charge while the OH group on the phosphate group will have a full -1 charge.
  • Egg yolk has lots of phophatidyl choline and cholesterol
  • Phophatidyl ethanolamine has a small head area, so when lots of it is side by side it forms a curve.
    • This is called nom lameller phase.
    • This phase makes hydration hard (the water molecules have a hard time lining up to the surface) so there is a little dry spot on the surface of the membrane where there is much phosphatidyl ethanolamine: a place of weakness.

Phosphatidyl choline (PC)

  • This molecule is just like PE only methylated 3 times via s-adenosyl methionine.
  • We have more PC than any other phospholipid
  • PC has a big head, is easily hydrated, and is can-shaped.
    • Because of these features this phospholipid forms membranes perfectly.
  • The old name of PC is lesophin.
  • At biological pH (7.0), the OH group on the phosphate has a formal -1 charge and the amine group has a formal +1 charge, so there is a formal charge distribution over the head of the phospholipid.

Phosphotidyl Serine (PS)

  • This phospholipid has the amino acid serine on it.
  • At biological pH, the OH group on the phosphate group has a -1 charge (pKa 2.1), the NH3 group has a +1 charge (pKa 9.1) and the carboxyl group will have a -1 charge (pKa 2.1) thus having a net -1 charge.
    • This phospholipid provides a negative density at biological pH.
  • At pH 2.1: -0.5, -0.5, +1 = 0. When acitic, these have not charge, think of stomach lining: cells on wall of the stomach will have phospholipids with differing properties on the exterior layer of the bilipid layer verses those of the inner layer.
  • Many proteins require phosphotidyl Serine.
  • Less than 10% of our phospholipid material is phosphotidyl serine.
  • All of our PS is on the interior layer of the bilipid layer. We have flipases to put them on inside whenever they happen to get to the outside layer.
    • PS on the outside can trigger apoptosis
    • PS on the outside is seen in aging and disease states.

Phosphatidyl Inositol (PI)

  • Inositol is a sugar we aren't good at digesting, so it is often put in sugar-free candy because we don't digest it.
    • It is not a complete sugar.
  • None of the OH on this ring are dissociable at reasonable pH levels.
  • Net charge is -1 at 7.2pH because of the OH group on the phosphate group (with pKa 2.1)
  • This is the best example of phospholipids responsible for lipid diversity.
  • There are unique functions for phophatidyl Inositol
    • Can be an anchor in membrane for classes of proteins
      • A lipid anchor in the membrane.
      • Example: alcoline phophatase -> a protein that anchors on GPI
      • So these kinds of proteins are called GPI anchored proteins.
        • GPI = Glycosil phosphatidyl inositol
    • Hormonal Role
      • PI + Phospholipase-c -> diacylglicerol (amphipathic and membrane bound) and the phosphate connected to the inositol (very water soluble, binds with signal proteins).
      • Both these products are activators to mechanisms.

Phosphatidyl glycerol (PG)

  • At pH 7 there is a -1 net charge because of the OH group with pKa 2.1 on the phosphate group.
  • These are found in plants and prokaryotes.
  • There are two optically active carbons on this phospholipid.

Cardiolipid (CA)

  • The old name for this phospholipid is diphosphatidyl glycerol
  • At pH 7, there is a net -2 charge from the OH on each of the two phosphate groups (pKa 2.1); each has a -1 charge.
  • This phospholipid has 4 acyl chains and two formal charges, therefore it pretty much looks like two phospholipids stuck together.
  • This phospholipid is found in the mitochondrial inner membrane, therefore it probably has something to do with the electron transport chain and oxidative phosphorylation (the ability to make ATP).

Phospholipids: Prokaryotes vs. Eukaryotes

  • Eukaryotes have Sphingo myelin, Phosphatidyl choline, and Phophatidyl Ethanolamine.
  • Prokaryotes have Phophatidyl Ethanolamine and Phosphatidyl glycerol.

Thylocoid Phospholipids

  • These are phospholipids found in the thylecoid of plants.
  • They are used for photosynthesis:
    • CDG = monogalactacyl diacylglycerol: the major photosynthesis phospholipid.
    • CDCG = digalactacyl diacylglycerol
    • Sophogweno-vacyl (sp?)
    • Phosphatidyl glycerol
  • We drew the structure of PG, a monogalactycil diacylglycerol, to show each component.
    • We also noted that it is the most common monogalactacyl diacylglycerol on the planet.

Phospholipid misc

  • A note on ether bonds in phospholipids
    • There are two types alkyl and alkenyl
  • Ether links cannot be undone by hydrolysis
  • Ether linkage found at SN-1
  • Ester linkage found at SN-2.
  • Examples: ethylolamine or choline.
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