I. Theoretical part

1. Lipids metabolism

Lipids are a group of substances widespread in living organisms. They are water-insoluble; soluble in non-polar solvents. Lipids serve in an organism as an energy source, carry out thermo-isolation function, function of the protection against mechanical influences, affect the permeability of bio-membranes, they are involved in nervous impulse conduction.

1.1. Classification of lipids

A. Simple lipids are complex esters of fatty acids with various alcohols.

1. Triglycerides or fats are located in an organism in the form of the protoplasmic fat contained in tissues in certain quantity, and the reserve fat the quantity of which can change considerably. Fatty acids can be saturated and unsaturated. All of them contain an even number of carbon atoms, as a rule ranging from 12 to 24. Palmitic, stearic and oleic acids are founded most often.

2. Waxes are esters of the higher fatty acids and monatomic or diatomic alcohols with the number of carbon atoms from 16 to 22.

B. Complex lipids are esters of fatty acids with alcohols, additionally containing other groups.

1. Phospholipids: contain the phosphoric acid residual:

a) glycerophospholipids

Phosphatidylcholines (lecithines) contain nitrogen base of choline

[НО—СН₂—СН₂—N⁺(CH₃)₃]

Phosphatidylethanolamines include nitrogen base ethanolamine

(НО–СН₂–СН₂–N⁺H₃):

Phosphatidylserines contain the residual of serine amino acid

(НО–СН₇–СН(СОО^-)–NH⁺₃).

Of all the lipids glycerophospholipids possess the most expressed polar properties. Phosphatidylcholine and phosphatidylethanolamine are the main lipid components of cell membranes.

Phosphatidylinositols have a cyclic alcohol inositol as a radical (R₃).

b) sphingolipids (sphingophospholipids) containan alcohol sphingosine. They are located basically in cell membranes, especially in nerve tissue. The most common are sphingomyelins. They contain the residues of fatty acid, diatomic unsaturated alcohol sphingosine, nitrogen base (most often choline) and phosphoric acid.

choline

sphingosine

fat acid

phosphoric

acids

sphingomyelin

2. Glycolipids (basically glycosphingolipids).

Are widely presented in tissues, especially nerve tissue. Contain ceramide, consisting of sphingosine alcohol and fat acid residual, and the rests of carbohydrates (more often galactoses – galactosylceramide or glucoses – glucosylceramide):

sphingosine

fatty acid

(e.g., cerebronic acid)

galactose

Galactosyl ceramide

Derivatives of galactosylceramide – cerebrosides – can carry out receptory functions.

3. Steroids belong to un-saponificated fraction of lipids. Cholesterol, steroid hormones, bile acids, group D vitamins are among them:

Cholesterol

Each cell contains cholesterol as part of cell membranes. Together with phospholipids and proteins it provides selective permeability of a cellular membrane and influences the activity of the enzymes bound to it.

B. Predecessors and derivatives of lipids: fatty acids, glycerine, fat soluble vitamins, hormones etc.