Lipids Flashcards
What are lipids?
Lipids contain less oxygen molecules than carbohydrates
They are non-polar & hydrophobic (insoluble in water)
There are two groups
Triglycerides - the main component of fats & oils
Phospholipids
Non-polar molecule
When electrons are shared equally, so the molecule is not charged
Triglycerides have two monomers:
Glycerol is an alcohol (C - OH)
Fatty acids contain a methyl group (-CH3) at one end of the chain, and a carboxyl group at the other end (-RCOOH)
Fatty acids can vary in length and saturation
Saturated triglyceride
Hydrocarbon chain is saturated (single bonds of carbon)
Monounsaturated triglyceride
1 double bond of carbon in hydrocarbon chain
Polyunsaturated triglyceride
More then 1 carbon double bond in the hydrocarbon chain
How are triglycerides formed?
By esterification - an ester bond forms when a hydroxyl (-OH) group on glycerol bonds with the carboxyl (-COOH) group of the fatty acid
Three fatty acids join to one glycerol molecule to form a triglyceride
Triglyceride function
Protection - triglycerides within adipose tissue protects organs from the risk of damage
Insulation - triglycerides are used to insulate nerve fibres & within adipose tissue below the skin
Buoyancy - the low density of fat tissue helps animals to float more easily
Energy storage - the many C-H bonds can be oxidised in cellular respiration to release lots of energy → used to produce ATP
Plants store triglycerides in the form of oils (within seeds & fruit)
Mammals store triglycerides as oil droplets in adipose tissue (a reserve energy source)
The structure of phospholipids
Phospholipids have only two fatty acids
The third has been replaced by a phosphate ion (PO4 3-)
The structure of phospholipids
As the phosphate is polar, it is soluble in water (hydrophilic)
The fatty acid ‘tails’ are non-polar and insoluble in water (hydrophobic)
Phospholipids are therefore amphipathic - contains both hydrophobic & hydrophilic parts
What does the structure of phospholipids form?
In the presence of water due to the hydrophobic and hydrophilic parts phospholipids will form monolayers or bilayers.
Phospholipid function
Phospholipids are the building block of cell membranes
They act as a barrier to water-soluble molecules & can control what substances enter and leave the cell
Different compositions of phospholipids helps to change the fluidity of the cell membrane
Mainly saturated fatty acids - membrane will be less fluid
Mainly unsaturated fatty acids - membrane will be more fluid
Phospholipids also control the orientation of proteins present in the cell membrane
Weak hydrophobic interactions hold proteins in place, but still allow them to move