BIO MOLECULES Pt 4 (Lipids)

• Source of energy - can be respired
• Energy storage
• All biological membranes made from lipids
• Heat/electrical insulation - eg. blubber in whales, electrical insulation around nerve cells
• Protection - eg. cuticle on plant leaves protected from drying out
• Some hormones (steroid hormones) are lipids

• Carbon, hydrogen & oxygen. (oxygen small proportion)
• Lipids insoluble in water.

Glycerol and fatty acids

• Glycerol molecule is always the same.
• Fatty acid molecules can differ significantly.

• Fatty acids that animals cannot make and therefore an essential part of their diet.
• Very much like essential amino acids.

• An acid group at one end (same as amino acid)
• Rest of the molecule consists of a hydrocarbon chain (can be anything from 2-20 carbons)

• Monounsaturated - one C=C bond
• Polyunsaturated - more than one C=C bond

C=C bonds changes the shape of the hydrocarbon chain (fatty chain), making the chain "kink" at the position of double bond, making the molecules in a lipid push apart, making them more fluid.

Consists of one glycerol molecule bonded to three fatty acid molecule.

By condensation reaction between the acid group of the fatty acid and one of the OH (hydroxyl) groups of the glycerol molecule forms a covalent bond. (Water molecule is also produced).

• Ester bond
• Produces a monoglyceride
• (two more condensation reactions with the other OH groups and two more fatty acid molecules will produce a triglyceride molecule).

• They are insoluble in water. (hydrophobic)
• Because the charges on the molecule are evenly distributed around the molecule and thus it cannot form hydrogen bonds with the water molecules.

• In phospholipids, the third fatty acid is not added to the glycerol molecule, and instead a phosphate group is covalently bonded to the third OH group by condensation.
• Phosphate head is hydrophilic and fatty acid tails are hydrophobic.

• The fatty acids can be saturated or unsaturated.
• An organism living in colder climates will have increased number of unsaturated fatty acids in their phospholipid molecules, making membrane more fluid because of the "kink" in their shape.

• First requires hydrolysis of the ester bonds
• Both the glycerol and the fatty acids can then be broken down completely into CO2 and H2O to release energy which is used to generate ATP.
• Advantages: respiration of one gram of lipid gives roughly twice as much as respiration of one gram of carbohydrate.
• They can be stored without affecting water potential for they are insoluble.
• Respiration of lipid gives out much more water than carbohydrate. (metabolic water vital for some organisms in extreme climates)

• It is a lipid, but not formed from fatty acids and glycerol.
• Small, narrow molecule made from 4 carbon-based rings.

• All biological molecules have cholesterol.
• Its small, narrow structure and hydrophobic nature allow it to sit between phospholipid hydrocarbon tails and help regulate fluidity and strength of membrane.
• Steroid hormones (eg. testosterone, oestrogen, vitamin D) are made from cholesterol. Its lipid nature allows it pass straight through phospholipid bilayer and nuclear envelope to reach target receptor.

• In bile, cholesterol can stick together to form lumps called gallstones.
• In blood, cholesterol can be deposited in inner lining and cause atherosclerosis.