The Biological Importance of Lipids Lipids are organic compounds found in all types of plant and animal cells. They always contain carbon, hydrogen and oxygen, however the relative amount of oxygen is less than the amount of carbohydrates in lipids. Lipids are polymers and the long chains of repeating units are joined together in a condensation reaction where water is also produced. The most common types of lipids are triglycerides, phospholipids and waxes. Triglycerides are formed by three fatty acids and glycerol linked together by an ester bond.
The three fatty acids that make up the triglyceride bond may be identical but a mixture of fatty acids is possible therefore many different triglycerides structures can be formed and this means that they have a range of functions (1).
Saturated fats contain single bonds between carbon atoms and they are usually solid at room temperature. Unsaturated fats such as vegetable oils are liquid at room temperature and have many double bonds between carbon atoms. Lipids form excellent energy storage molecules for example as fats in seeds, lipid deposits in the stroma of the chloroplast and adipose tissue of vertebrates.
In addition oxidation of lipids yields more ATP than the oxidation of carbohydrates and therefore they are high-energy molecules, which are important for fruits or seeds to be dispersed. This is because just as the oxidation of glucose, acetylcoenzyme A is produced in the first stage, but so are many molecules of NAD and FAD. In lipids these are reoxidised in the electron transport chain and that’s why they provide more than twice the energy as the same mass of carbohydrate.
Review Chapter 8 and pages 160–162 of Chapter 9 in Biology, 7th edition. Then complete the discussion by supplying or choosing the appropriate terms. To maintain life, organisms must be able to convert energy from one form to another. For example, in the process of photosynthesis, algae, plants, and photosynthetic prokaryotes use the energy from sunlight to convert carbon dioxide and water to ...
Also saturated fats contain more energy that unsaturated fats there are more Hydrogen’s, therefore more to reduce the NAD/FAD during the respiration process (1).
There is no osmotic effect in lipids so they cannot diffuse away and this helps them to be am excellent storage molecule. Furthermore another major biological function of lipids is that they are used for structural components in cells. For example phospholipids make up 40% of cell membranes and as they have an amphipathic nature (having polar and non-polar end) allows the automatic formation of the bilayer.
Phospholipids are made up of two fatty acid molecules and one phosphate molecule. The fatty acid molecules repel water and form a hydrophobic tail, which turns itself away from water but mixes readily with fats (2).
The phosphate molecule attracts water and forms a hydrophilic head that interacts with water but not with fats. This means that when the phospholipid molecules are placed in water they orientates themselves so that the hydrophilic head is as close towards any aqueous medium and the hydrophobic tails are as far away from aqueous medium.
Thus making the phospholipid bilayer a selectively permeable membrane and only allows certain substances to enter or leave the cell and are therefore essential components of cell and organelle membranes. Moreover the complex lipid cholesterol is also amphipathic and is present in cell membranes between phospholipid molecules. This is thought to make the membranes stronger and less flexible, but may also reduce permeability. Cholesterol forms the basis of all steroids and also is a precursor of bile salts and sex hormones such as oestrogen, testosterone etc.
Glycolipids (molecular complexes of lipid and polysaccharides) form hydrogen bonds with water molecules outside the cell membrane, which helps to stabilise the membrane (2).
... Membrane Fatty acid molecules are perfect as a cell membrane. Protection is provided by the hydrophilic and hydrophobic parts of the lipid molecule ... removed from a glyceride molecule, dehydration synthesis occurs and a water molecule is taken away. ... A. (N.D.). Three Functions of Body Fat. Retrieved from Healthy Eating: http://healthyeating.sfgate.com/three-functions-fat-body-3402.html National ...
The carbohydrate portion of the Glycolipid is involved in cell-to-cell recognition and communication, particularly during growth and development, also the carbohydrate part of the glycoprotein may be ‘recognised’ by antibodies, hormones, etc. Lipoproteins transport lipids in the blood; low-density lipoproteins transport cholesterol from cells into the blood.
High- density lipoproteins remove cholesterol from the blood. Terpenes are hydrocarbon chains of alternating double and single bonded carbon atoms. Many are important plant defensive compounds. For example, the smell of pine trees and the sticky sap that pine trees give off are largely mixtures of terpenes. Steroids are built of simple three carbon terpene units called isoprene units. Gibberellin is a type of plant hormone, which regulates growth.
Plants produce these hormones naturally through biosynthesis as they grow, ensuring that they have the hormones they need to develop normally. Gibberellin can also influence sex expression, and they can break dormancy and promote germination of seeds. In addition lipids provide insulation this is because fats conduct heat slowly and when stored beneath the body surface help to retain body heat and are important for maintaining optimum temperature for metabolism. Also some types of phospholipids such as Sphingomyelin are electrical insulators (3).
For example Sphingomyelin is a specialized phospholipid in the myelin sheet of the nerve axons that provides electrical insulation. Another major biological function of lipids is that it provides mechanical protection. Fat is stored around delicate organs such as the kidneys, heart etc. Additionally lipids are insoluble in water and therefore they are suitable for waterproofing. Both plants and animals of waxy cuticles that conserve water, but mammals produce an oily secretion from the sebaceous, and also in insect exoskeletons.
Also the presence of waxy suberin in the casparian strip of endodermal cells in the plant roots forces water into the symplast pathway that is controlled by the nucleus (3).
The strip gives the plant control over substances entering the xylem. Also lipids provide buoyancy since fat is less dense than water, fat reserves therefore provide buoyancy for aquatic life. Surfactant is a naturally occurring substance made of six lipids (fats) and four proteins that are produced in the lungs; it can also be manufactured synthetically.
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Surfactant reduces the surface tension of fluid in the lungs and helps make the small air sacs in the lungs (alveoli) more stable. This keeps them from collapsing when an individual exhales. In preparation for breathing air, feotuses begin making surfactant while still in the womb. Referencing: 1. http://en. wikipedia. org/wiki/Lipid (12 October 2012) 2. http://biology. clc. uc. edu/courses/bio104/lipids. htm (12 March 2011/J. Stein Carter) 3. http://www. infoplease. com/cig/biology/lipids. html (January 2004/ Glen E. Moulton)