lipids Flashcards
lipids
-macromolecules which contain carbon, hydrogen and oxygen atoms
-contain a lower proportion of oxygen
-non polar + hyrophobic (insoluble in water)
2 groups of lipid:
triglycerides (main component of fats and oils)
phospholipids
triglycerides
-non-polar, hydrophobic molecules
-monomers are glycerol and fatty acids
glycerol
alcohol (an organic molecule that contains a hydroxyl group bonded to a carbon atom)
fatty acids
-methyl group at one end of a hydrocarbon chain known as the R group (chains of hydrogens bonded to carbon atoms, typically 4 to 24 carbons long) and at the other is a carboxyl group
- shorthand chemical formula for a fatty acid is RCOOH
fatty acids can vary in 2 ways
-Length of the hydrocarbon chain (R group)
-The fatty acid chain (R group) may be saturated (mainly in animal fat) or unsaturated (mainly vegetable oils, although there are exceptions e.g. coconut and palm oil)
Unsaturated fatty acids can be mono or poly-unsaturated:
-If H atoms are on the same side of the double bond they are cis-fatty acids and are metabolised by enzymes
-If H atoms are on opposite sides of the double bond they are trans-fatty acids and cannot form enzyme-substrate complexes, therefore, are not metabolised. They are linked with coronary heart disease
how are tryglicerides formed
-esterification
-ester bond forms when a hydroxyl (-OH) group on glycerol bonds with the carboxyl (-COOH) group of the fatty acid
-H from glycerol + OH from fatty acid= H20 (condensation)
-3 fatty acids+1 glycerol= triglyceride
-1 triglyceride= 3 H2O molecules released
triglyceride storage and function
-long hydrocarbon chains contain many carbon-hydrogen bonds with little oxygen (triglycerides are highly reduced)
-when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP
triglyceride enegy storage
-store more energy per gram than carbohydrates and proteins (37kJ compared to 17kJ)
-hydrophobic so do not cause osmotic water uptake in cells so more can be stored
-Plants store triglycerides, in the form of oils, in their seeds and fruits, generally liquid at room temp due to presence of double bonds which add kinks to the fatty acid chains altering their properties
-Mammals store triglycerides as oil droplets in adipose tissue to help them survive when food is scarce (e.g. hibernating bears)
-The oxidation of the C-H bonds releases large numbers of water molecules (metabolic water) during cellular respiration
-Desert animals retain this water if there is no liquid water to drink
-Bird and reptile embryos in their shells also use this water
tryglyceride insulation
- part of the composition of the myelin sheath that surrounds nerve fibres and provides insulation which increases the speed of transmission of nerve impulses
-compose part of the adipose tissue layer below the skin which acts as insulation against heat loss (eg. blubber of whales)
tryglyceride buoyancy
- less dense than water = buoyancy of aquatic animals
tryglceride protection
-adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage
H
compare phospholipids and triglyerides
-glycerol backbone
-may be attatched to a mixture of saturated, monounsaturated and polyunsaturated fatty acids
- contain C, H, O
-formed by condensation reactions
contrast phospholipids and triglycerides
phospholipids:
-2 fatty acids+ 1 phosphate group
-hydrophillic head+ hydrophobic tail
-used primarily in membrane formation
triglycerides
-3 fatty acids
-entire molecule is hyrophobic
-used primarily as a storage molecule (oxidation releases energy)
