Lipids Flashcards
Describe the structure of a simple lipid
Simple lipids consist of an alcohol (usually glycerol) linked to one or more fatty acids via an ester linkage
Describe the structure of glycerol and its properties
A molecule of glycerol has the molecular formula C3H8O3 and is a three-carbon alcohol, with each carbon bearing a hydroxyl (OH) group.
It is soluble in water because of its polar –OH group.
Describe the structure of fatty acid and its properties
Fatty acids are carboxylic acids composed of an acidic carboxyl (COOH) functional group at one
end and an attached hydrocarbon chain
Fatty acids possess long carbon skeletons (between 12-20 carbons) with each carbon joined to hydrogen atoms. The abundance of these non-polar C-H bonds results in the hydrophobicity of fats.
Describe the formation of an ester bond between glycerol and a fatty acid
The formation of each ester linkage between a hydroxyl (OH) group of glycerol and the carboxyl (COOH) group of a fatty acid is a condensation reaction, where one molecule of water is lost.
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Describe the structure of a triglyceride
A triglyceride refers to a glycerol molecule that has formed ester linkages to three fatty acids
Explain why the melting point of fats increases with hydrocarbon length
The longer the hydrocarbon chains, the more extensive the hydrophobic interactions between the chains, and the higher the melting points (as more thermal energy is required to break the bonds).
**Hydrophobic interaction is a weak bond that exists between hydrophobic molecules.
Explain the effect of the degree of saturation of fatty acid tails on the melting point of fats
The melting point of fats decreases as the degree of unsaturation of fatty acids tails increases.
This is because the kinks where the double bonds are located prevent the molecules from packing closely. When the fatty acids tails are less closely packed, hydrophobic interactions are less extensive. Hence, less thermal energy is required to break enough of these interactions to liquefy the triglycerides
Describe the structure of a phospholipid
Phospholipids consist of one glycerol and two fatty acids. The third OH group of glycerol is joined to a negatively-charged phosphate group. Additional small molecules, usually charged or polar (e.g. serine, choline and inositol) can be linked to the phosphate group to form a variety of phospholipids
Explain the behaviour of phospholipids towards water
Phospholipids show ambivalent behaviour towards water, as it has both hydrophobic and hydrophilic regions, thus it is amphipathic. The two fatty acids that comprise the hydrocarbon tails are non-polar and are hence hydrophobic while the phosphate group and its attachments form a polar/charged hydrophilic head that has an affinity for water.
How does the amphipathic structure of phospholipids relate to its function?
Phospholipids each have 2 non-polar, hydrophobic fatty acids ‘tails’ and a charged, hydrophilic phosphate ‘head’.
Phospholipids form a selectively permeable cell
membrane where hydrophilic heads are exposed to the aqueous medium while the hydrophobic tails are in contact with those of neighbouring molecules but excluded from the aqueous medium in the non-polar interior of the bilayer. This forms an effective barrier/boundary between the cell and its external environment
