lipids

 lipids 

BIOMEDICAL IMPORTANCE

• The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, that are related more by their physical than by their chemical properties.
• Lipids have the common property of being:

1. relatively insoluble in water .
2. soluble in non polar solvent such as either and chloroform . 

• Lipids are important dietary constituents because:

1. high energy value .
2.  fat soluble vitamin (  A,D,E,K ) .
3.  essential fatty acids .

Functions of lipids :

• Fat is stored in adipose tissue, where it also serves as a thermal insulator in the subcutaneous tissues and around a certain organ.
• nonpolar lipids act as electrical insulators ( myelinated nerve).
• lipoprotein serve as a mean transporting lipids in the blood.

Biomedical Problems that are associated with lipids :

• diabetes mellitus 
• obesity

• atherosclerosis . 

Lipids are classified as simple or complex :

• Simple lipids

• Complex lipids

• Precursor and derived lipids

1. Simple lipids: 

• Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state.
• Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols.

2. Complex lipids: 

• Esters of fatty acids containing groups in addition to alcohol and a fatty acid.
• Phospholipids: Lipids containing, in addition to fatty acids and an alcohol, a phosphoric acid residue. They frequently have nitrogen-containing bases and other substituents, eg, in glycerophospholipids the alcohol is glycerol and in sphingophospholipids the alcohol is sphingosine.
• Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine, and carbohydrate.
• Other complex lipids: Lipids such as sulfolipids and aminolipids. Lipoproteins may also be placed in this category.

3. Precursor and derived lipids: 

• These include fatty acids, glycerol, steroids, other alcohols, fatty aldehydes, ketone bodies, hydrocarbons, lipid-soluble vitamins, and hormones.

Fatty acids:

• these are aliphatic carboxylic acids
• occur mainly as esters in natural fats and oils but do occur in the unesterified form as free fatty acids, a transport form found in the plasma.
• that occur in natural fats are usually straight-chain derivatives containing an even number of carbon atoms.
• The carbon atoms adjacent to the carboxyl carbon (Nos. 2, 3, and 4) are also known as the α, β, and γ carbons, respectively, and the terminal methyl carbon is known as the ω or n-carbon.
• Saturated acids end in –anoic (no double bond)
• Unsaturated acids with double bonds end in -enoic.

Unsaturated Fatty Acids Contain One or More Double Bonds

1. Monounsaturated (monoterpenoid, monoenoic) acids, containing one double bond.
2. Polyunsaturated (polyenoic) acids, containing two or more double bonds.
3. Eicosanoids: These compounds, derived from eicosa (20-carbon) polyenoic fatty acids, comprise the prostanoids, leukotrienes (LTs), and lipoxins (LXs). Prostanoids include prostaglandins (PGs), prostacyclins (PGIs), and thromboxanes (TXs).

• Most naturally occurring unsaturated fatty acids have cis double bonds

• Double bonds in naturally occurring unsaturated longchain fatty acids are nearly all in the cis configuration.

• Trans fatty acids are present in certain foods, arising as a by-product of the saturation of fatty acids during hydrogenation, or "hardening," of natural oils in the manufacture of margarine ( increased risk of diseases including cardio-vascular disease and diabetes mellitus).