SR: What determines the solubility of a fatty acid?
VP: Saturated fatty acids tend to be solid at room temperature, because their carbon tails have a standard, monotonous, up and down pattern, that enables them to interdigitate closely, with each other.
Double bonds are normally in cis configuration. Cis double bonds cause a BIG BEND in the carbon tail. This big bend “pushes away” other fatty acids – like in a plasma membrane fatty acid bilayer – so that the membrane is “fluidized.”
The more double bonds, the more likely the fatty acid is oil = liquid.
The longer the fatty acid – ie. the more carbons in the tail – the more likely it is solid.
The effect of double bonds can “overpower” the effect of fatty acid length; EPA and DHA are liquid at body temperature. That’s how “fish oil” helps prevent the fish from freezing in cold temperatures.
SR: What is a phospholipid?
VP: A phospho-lipid contains phosphate and lipid. The phosphate is just a phosphate. The lipid is a Di-Acyl Glycerol. Phospholipids are the second most common type of dietary fat.
Pmp: Di-Acyl Glycerol (DAG) + Phosphate is called Phospha-Tidic Acid (PTA). PTA is the “building block” for most phospholipids.
Membrane phospholipids are made by starting with PTA and adding a “head group” like choline, or serine, or inositol, or ethanolamine.
For example: PhosphaTidic Acid + Choline = PhosphaTidyl Choline. PhosphaTidyl Choline is the most common membrane phospholipid in mammals.
SR: What is CARDIOLIPIN?
VP: Cardiolipin is a unique fatty acid. Cardiolipin is a “giant size” phospholipid. Cardiolipin consists of 2 PTA’s connected by a glycerol. Cardiolipin is mostly found in the inner mitochondrial membrane.
The fatty acid tails on cardiolipin are often PUFA’s. The fact that cardiolipin has several PUFA type fatty acid tails, and it is located on the inner mitochondrial membrane – the hot spot in the human body for the production of reactive oxygen, free radicals – makes it obvious that cardiolipin is highly vulnerable to lipid peroxidation!!16
SR: What about lipid peroxidation?
VP: Lipid peroxidation is a major problem with PUFA’s (PolyUnsaturated Fatty Acids). A PUFA is any fatty acid with two or more double bonds.
A methylene group is a CH2 group. The methylene bridge carbon – the single bonded carbon, between a pair of double bonds – has only a “weak” grip on its hydrogen – and is vulnerable to lipid peroxidation.
Lipid peroxidation is a chain reaction that progresses like a stack of dominoes, to destroy lots of other lipids.
Lipid peroxidation can be very damaging to plasma membranes, and to mitochondrial membranes. Cardiolipin is especially vulnerable to lipid peroxidation. The brain has a relatively large amount of PUFA’s in its cell membranes, and this makes the brain more vulnerable to oxidative stress, and lipid peroxidation.
Pmp: With lipids, there’s always more details to talk about.
VP: The key point is to minimize dietary lipids! There are no “good fats.” FAT IS BAD! The way to minimize dietary lipids is to eat a low fat, plant based diet.
SR: What is the difference between cholesterol and a steroid?
VP: Cholesterol has 4 rings of carbon – labeled A, B, C, D – and a total of 27 carbons. Cholester-OL has a hydroxy group at the C3 position (on the A ring).
The steroid nucleus also has 4 rings of carbon, based on the 4 rings of cholesterol.