Lipids

Triglycerides Protection- Humans have fat around delicate organs , such as their kidneys , to act as a shock absorber. The peptidoglycan cell wall of some bacteria is covered in a lipid-rich outer coat

Triglycerides Protection

Triglycerides Buoyancy- Because fat is less dense than water , it is used by aquatic animals to help them stay afloat

Triglycerides Buoyancy

Phospholipid -When surrounded by water , the phosphate group has a negative charge , making it polar(attracted to water) and the fatty acid tails are nonpolar and so are repelled by water. So the head is hydrophilic and the tail is hydrophobic , which means the phospholipid molecule is amphipathic. Phospholipids may form a layer on the surface of the water with heads in the water and tails sticking up out the water. They may also form micelles which are tiny balls with the tails tucked away inside , and the heads pointing outwards into the water.

Structure Of Phospholipids

Glycerol - It is a alcohol - 3 Carbon atoms - 3 -OH groups

The Structure Of A Glycerol

Phospholipids -Same structure as triglycerides except that one of the fatty acids is replaced by a phosphate group.

The Structure Of A Phospholipid As An Example Of A Macromolecule

Cholesterol is a steroid alcohol and is a type of lipid which is not made of glycerol or fatty acids. It is made from four carbon based rings. Small and hydrophobic molecule which means that it can sit in the middle of the hydrophobic part of the bilayer and they can pass through the hydrophobic part of the cell membrane and any other membrane inside the cell. It regulates the fluidity of the membrane , preventing it from becoming too fluid or stiff. Cholesterol can form vitamin D , and steroid hormones such as testosterone , oestrogen The steroid hormones testosterone, oestrogen and vitamin D are made from cholesterol Waterproofing for the skin It is mainly made in the liver of animals and in plants cholesterol is derivative in their membranes. It is called stigmasterol , and is different from cholesterol as it has a double bond between carbon 22 and carbon 23.

Cholesterol

Fatty Acids -Have a carboxyl group (-COOH) on the end , attached to a hydrocarbon tail, made of only Carbon and Hydrogen atoms -2-20 carbons long -The tails are hydrophobic(they repel water). These tails make lipids insoluble in water -Carboxyl group ionises into H+ and -COO_ This structure is therefore an acid because it can produce free H+

The Structure Of A Fatty Acid

Triglyceride -Consists of one glycerol molecule bonded to 3 fatty acids

The Structure Of A Triglyceride As An Example Of A Macromolecule

Triglycerides Energy Store-Because triglycerides are insoluble in water , they can be stored without affecting the water potential of the cell. Mammals store fat in adipose cells under the skin. One gram of fat releases twice as much energy as 1 gram of glucose. This is because lipids have a higher proportion of hydrogen atoms than carbohydrates , and almost no oxygen atoms.

Triglycerides Energy Store

Triglycerides Insulation- Adipose tissue is a storage location for lipids in whales , acting as a heat insulator. Lipid in nerve cells act as an electrical insulator. Animals preparing for hibernation store extra fat

Triglycerides Insulation

The synthesis and breakdown of triglycerides by the formation (esterification) and breakage of ester bonds between fatty acids and glycerol.

A triglyceride consists of one glycerol molecule bonded to three fatty acids. A condensation reaction happens between the -COOH group of the fatty acid and the -OH group of the glycerol. Because there are three -OH groups , three fatty acids will bond , hence the name triglyceride. Because it is a condensation reaction , a water molecule is produced , and the covalent bond formed is known as an ester bond.

Amphipathic ( Both Hydrophobic And Hydrophilic Elements) - phospholipids are excellent at forming membranes around cells and organelles. Inside and outside a cell membrane is an aqueous solution. The phospholipids form a bilayer , with two rows of phospholipids , tails pointing inwards and heads pointing outwards into the solution The individual phospholipids are free to move around in their layer , but will not move into any position where their hydrophobic tails are exposed to water. This gives the membrane some stability .

Phospholipids Are Amphipathic ( Contains Both Hydrophobic And Hydrophilic Elements)

The membrane is selectively permeable and the centre of the bilayer is hydrophobic. It is only possible for small and non-polar molecules to move through the tails in the bilayer, such as oxygen and carbon dioxide. This lets the membrane control what goes in and out of the cell, and keeps it functioning properly because it acts as a barrier to water-soluble substances

Phospholipids Selectively Permeable Membrane

If a fatty acid is saturated this means that there are no C=C bonds in the molecule. If a fatty acid is unsaturated , there is a double bond between two of the Carbon atoms , which means that fewer hydrogen atoms can be bonded to the molecule. A single C=C bond makes a fatty acid monounsaturated , e.g oleic acid. More than one C=C bond makes it polyunsaturated , e.g linoleic acid. Having one or more C=C bonds changes the shape of the hydrocarbon chain , giving it a kink where the double bond is. Because these kinks push the molecules apart slightly , it makes them more fluid. Animal lipids contain lots of saturated fatty acids , which are often solid at 20°C. If there are more unsaturated fatty acids , the melting point is lower.

To include an outline of saturated and unsaturated fatty acids.

Triglycerides Energy Source- Triglycerides can be broken down in respiration to release energy and generate ATP. The first step is to hydrolyse the ester bonds , and then both glycerol and the fatty acids can be broken down completely to carbon dioxide and water . Respiration of a lipid produces more water than respiration of a sugar.

Triglycerides Energy Source