Lipid

From The School of Biomedical Sciences Wiki
Jump to: navigation, search

A lipid is a "water-insoluble biomolecule that is highly soluble in organic solvents" by definition[1]. Their molecules tend to stay together to form droplets and bilayers[2]. The lipid's we come across most often are those which play the most important role in forming the lipid bilayer membranes around cells, these are phospholipids. They (like all lipids) contain a hydrophobic, long hydrocarbon chain 'tail', they also contain a hydrophilic 'head'. In phospholipids the main component of this 'head' is a phosphate, it is also formed from an alcohol and a platform bonded to the phosphate creating the hydrophilic part of the lipid. Lipids are amphiphatic, they have both a hydrophilic and a hydrophobic part.

Contents

Fatty Acids and Triacylglycerols (Triglycerides)

A good place to start thinking about lipids is the fatty acids. A fatty acid has the chemical formula CH3(CH2)nCO2-, where n can be anything from 1 to 20 or more[3]. Triglyceride molecules are composed of a glycerol (glycerol backbone) and three fatty acids. The glycerol backbone is always constant but fatty acids that are attached to the backbone may differ[4].

Long fatty acid chains arrange themselves into a spherical globule called a micelle form which are achieved by the hydrophobic chains associating together while their hydrophilic heads face outwards, interacting with the water; such structures can act as various detergents or soaps[5].

Triacylglycerols are referred to as 'natural fats' and their molecules tend to cluster together to form droplets and keep away from water[6]. The fact that they isolate themselves as hydrophobic droplets makes storage easy, for example, storage of energy in cells which can be released when required via enzyme action. Triacylglycerols also can act as thermal and mechanical insulators and in aquatic animals, can supply buoyancy[7].

Phospholipids

Phospholipids are a group of compounds that are similar to triacylglycerols except that one of the fatty acid chains is instead replaced by a phosphate group; several other varying small molecules may be attached to the phosphate giving a group of different structures[8]. The phospholipids position themselves in a bilayer; the hydrophobic groups in contact with each other on the inside of the bilayer and the hydrophilic groups on the outsides of the bilayer. The role of phospholipid bilayer is to allow the conditions inside the cell to be different to those outside and to control the movement of substances into and out of the cell. It is the phospholipids in the membrane that control the movement of the substances into and out of the cell. As only lipid-soluble molecules to pass through them therefore entering and leaving the cell and water-soluble molecules cannot pass through therefore are prevented from entering and leaving the cell[9].

Cholestrol

Cholesterol is another group of lipid which contains different and unique structure. It consists of a short hydrocarbon chain with 4 linked hydrocarbon rings and a hydroxyl group. It shares the same properties as phospholipids which is amphipathic (contain both hydrophobic and hydrophilic regions)[10].

References

  1. Berg, JM. (2006) "Biochemistry" 6th Ed. p329, New York, W.H. Freeman and company
  2. Wood, E., Smith, C. A., and Pickering, W. R. (1997 ). Life Chemistry and Molecular Biology .
  3. Wood, E., Smith, C. A., and Pickering , W. R. (1997 ). Life Chemistry and Molecular Biology .
  4. http://www.differencebetween.com/difference-between-triglycerides-and-phospholipids/
  5. Wood, E., Smith, C. A., and Pickering, W. R. (1997 ). Life Chemistry and Molecular Biology .
  6. Wood, E., Smith, C. A., and Pickering, W. R. (1997 ). Life Chemistry and Molecular Biology .
  7. Wood, E., Smith, C. A., and Pickering, W. R. (1997 ). Life Chemistry and Molecular Biology .
  8. Wood, E., Smith, C. A., and Pickering, W. R. (1997 ). Life Chemistry and Molecular Biology .
  9. AQA As level biology textbook, page 52
  10. Albert et al. (2008) 'Molecular Biology of The Cell' -- Fifth Edition. New York, Garland Science.
Personal tools
Namespaces
Variants
Actions
Navigation
Toolbox