LIPIDS

• Lipids


  are organic substances insoluble in water, but soluble in organic solvents such as ether, chloroform, benzene, acetone, etc.
• Lipids

  Chemically they are all esters of glycerol with higher fatty acids and utilizable by living organisms.
• Lipids includes fats, oils, waxes and related compound. An oil is liquid at ordinary temperature.
• What is common for LIPIDS?

  • Hydrophobic
  • Non-polymeric structure
• Important dietary constituents on account of their high calorific value and fat soluble vitamins and essential fatty acids contained in them.
• Lipids are superior to carbohydrates, bec. It can stored in the body in unlimited quantities and produce more energy per gram (9.5 c/gm) as compared to carbohydrates 4 c/gm).
• It serves as thermal insulator in the subcutaneous tissues and around certain internal organs like kidneys.
• Nervous tissue is rich in lipids and are essential for proper functioning of nervous system.
• It provides building blocks for building biologically active subtances. Ex. Acetic acid (acetyl coA) is used in the synthesis of cholesterol, which in turn can be utilized for the synthesis of certain hormones.
• Lipids supply essential fatty acids which cannot be synthesized in the body and are essential in the diet for normal health and growth.
• Some vitamins like A, D, E and K are fat soluble, hence lipids are necessary for these vitamins.
• Lipoproteins are carriers of triglycerides, cholesterol, etc. in the body.
• Lipoproteins and phospholipids are important constituents of many cell membranes and cell organelles like mitochondrion.
• CLASSIFICATION OF LIPIDS

  • Simple lipids
  • Compound lipids or complex lipids
  • Derived lipids
• SIMPLE LIPIDS - are esters of fatty acids with different alcohols and do not carry any other group.
• Neutral fats or triglycerides or triacylglycerols neutral fats are esters of fatty acids wit glycerol. A fat in the liquid state at room temperature is known as oil.
• Waxes – are solid esters of fatty acids with monohydroxy aliphatic alcohols other than glycerol. In the human body the most common waxes are the cholesterol esters.
• Bees wax- palmitic acid ester of mycricyl alcohol
• Lanoline – (woolfat) palmitic, oleic or stearic acid ester of cholesterol.
• Spermaceti – palmitic acid ester of acetyl alcohol from the head of the sperm of whale.
• Compound Lipids or Complex Lipids – are fatty acid esters of different alcohols. But in addition, they carry other groups like carbohydrates, phosphate, nitrogeneous bases and proteins.
• Phospholipids – are fatty acid esters of glycerol carrying in addition a phoshoric acid residue, a nitrogeneous base and other substituents. They are classified into three groups:

  • Glycerophosphatides
  • Phosphoinositides
  • phosphosphingosides
• Glycolipids ( glycosphingosides) – lipids containing carbohydrate moiety are called glycolipids. They contain a special alcohol called sphingosine or sphingol and nitrogenous base in addition to fatty acids. But does non contain phosphoric acid or glycerol. The two types:

  • Cerebrosides
  • Gangliosides
• Lipoproteins – are complexes of proteins and lipids. The lipid part consists of fats, phospholipids, cholesterol and its esters, and free fatty acid. They are found in cell membranes, milk, egg yolk, etc.
• Sulfolipids (sulfatides) – lipids possess sulfate groups, largely found in white matter of brain and to a less extent in liver, kidney, salivary gland, testis, etc.
• Amino Lipids (Proteolipids) – lipids possess protein group.
• DERIVED LIPIDS – are derived from simple or compound lipids by their hydrolysis. These include fatty acids, glycerol, sterols and steroids, alcohols, fatty aldehydes and ketone bodies.
• Fatty Acids

  • Primary fat stored in the body
  • Long chain of carboxylic acids
  • Maybe saturated or unsaturated
• fatty acid

  A) carboxylic head

  B) hydrocarbon tail

  
• Triglycerides

  • Stored form of fatty acids
  • Glycerol + fatty acids linked by ester bond
  • Composed of two building blocks of proteins (fatty acids and glycerol)
• Steroids

  • Polycyclic lipids
  • Ring structure is attributed for hydrophobicity
  • Steroid hormones are present in the body in only small quantities
• Cholesterol

  • Most abundant steroid in the body
  • Component of the cell membrane and is the raw material of Vit. D , steroid hormones and bile salts.
  • Precursor of steroid hormones and bile salts
• Cholesterol - A waxy substance found in the blood; the body needs cholesterol to build healthy cells, but high levels of cholesterol can risk of heart disease.
• High cholesterol – develop fatty deposits in the blood vessels; deposits grow making it difficult for enough blood to flow in the arteries.
• Cholesterol is carried through the blood, attached to proteins.
• The combination of proteins and cholesterol is called lipoprotein.
• Types of cholesterol:

  LDL – bad cholesterol

  HDL – good cholesterol
• High-Density Lipoprotein – picks up excess cholesterol and takes it back to liver.
• Low Density Lipoprotein – transports cholesterol particles throughout the body. LDL builds up in the walls of the arteries making them hard and narrow.
• Having a high triglyceride level can increase risk of heart disease.