Lipids Flashcards
What are they constructed out of?
Always contain atoms of carbon, hydrogen and oxygen like carbohydrates.
What are lipids (general)
Oils (liquid at room temperature) and fats (solid at room temperature).
What are their functions (in order of importance)?
1 - energy storage
like polysaccharides they are insoluble in water but contain much more energy than polysaccharides.
2 - Waterproofing
i.e the waxy cuticle on plants, the wax layer on the exoskeleton of insects and the oil (sebum) excreted by the skin of mammals.
3 - heat insulation in birds and mammals
4 - Structural functions e.g phospholipids in cell membranes.
5 - metabolic functions e.g steroids such as oestrogen and testosterone.
6 - buoyancy and protection for internal organs.
What is a triglyceride formed out of?
A glycerol molecule (C3-H8-O3 no isomers) and three fatty acids.
What is the region responsible for the differences between fats and oils and different oils and different fats?
As there is only a single isomer of glycerol the variations above stated are down to the fatty acids.
What are the two types of fatty acids?
Saturated fatty acids such as stearic acid (C17-H36-O2) which have no double bonds.
And Unsaturated fatty acids have double bonds such as Linoleic acid (C17-H36-O2) Which has two double bonds
What state do lipids with unsaturated fatty acids tend towards?
The liquid state so are often oils.
What state do lipids with saturated fatty acids exist at at room temperatures?
The solid state and are fats or waxes.
Describe the general structure of a fatty acid.
They have a methyl (C-H3) group at one end and a Carboxylic acid group at the other (C-O-OH) with a hydrocarbon chain in the middle of variable length and degree of saturation.
Are fatty acids water soluble?
Yes due to hydroxyl group the Carboxylic acid.
What does the viscosity of a lipid depend on?
The degree of saturation and length of the hydrocarbon chains in the fatty acids of the lipid.
How are triglycerides synthesised?
Through a condensation reaction between the hydroxyl group of the carboxylic acid portion of the fatty acid and one of the hydroxyl groups on the glycerol molecule. This forms an ester (C-O-C) linkage which releases a water molecule. This occurs three times for each fatty acid releasing a total of three water molecules.
What are the advantages of storing energy as fat?
They store approximately double the energy of carbohydrates and release a lot of metabolic water when created which is useful for desert animals and some species rely upon this to get the water they need I.e caterpillars.
How are triglycerides broken apart?
Through a process called hydrolysis carried out in the human gut by an enzyme called lipase. This splits triglycerides into three fatty acids and a glycerol molecule by replacing the three water molecules. These components are then all water soluble and so can be absorbed by the cells lining the gut.
Describe the structure of a phospholipid.
These have the same structure as a triglyceride except that the third hydroxyl is bonded to a phosphate group which is hydrophilic and so gets wrapped up in the glycerol molecule in an attempt to avoid the hydrophobic fatty acids. This creates a two tailed molecule with a hydrophilic head and hydrophobic tail.
