What is the Difference between saturated and unsaturated fatty acids?

 Firstly, saturated fatty acids are where all the carbon atoms have single bonds between them making the lipid saturated as no more hydrogens can be added. Having no double bond means the fatty acid is straight, and so they can pack closely together (e.g. in triglycerides and phospholipids) meaning they are usually solid at room temperature and are called fats. These usually have a higher melting point as the van der waals forces between them are stronger as they are closer together, meaning it takes more energy to break the bond/ force. On the other hand, unsaturated fatty acids are where there is a double bond between one or more of the carbon atoms in the hydrocarbon chain. This leads to them being unsaturated as the double bond can effectively ‘fold out’ so another hydrogen is able to be added to the molecule. Having one double bond means that the fatty acid is monounsaturated, having many means it is polyunsaturated. These double bonds cause the fatty acid chain to ‘kink’ meaning the fatty acids can’t pack as closely together, which results in more fluidity. This causes the triglycerides to be liquid at room temperature, thus an oil. Having the bend in the hydrocarbon chain means there are weaker van der waals forces between the molecules, and so leading to a lower melting point.