Lipids 1.1 Flashcards
What are the main structural differences between a phospholipid and a triglyceride?
A phospholipid has a phosphate group and a hydrocarbon tail made of two fatty acids, whereas a triglyceride has no phosphate group and three fatty acids in its hydrocarbon tail.
What is the general chemical formula of a fatty acid? What does the term variable group refer to?
RCOOH.
The variable group refers to the hydrocarbon tail, noted in the formula as R.
Describe how a triglyceride is formed.
A triglyceride is formed in three separate condensation reactions between a glycerol molecule and three fatty acid molecules. In each reaction, an ester bond is formed and a molecule of water is released.
- Identify which types of fatty acids are shown in the diagrams A and B. Explain how you know.
Fatty acid A is is a saturated fatty acid, as it does not have any double bonds between it’s carbon atoms.
(saturated with hydrogen bonds)
Fatty acid B has at least one double bond between its carbon atoms, so it’s an unsaturated fatty acid.
A student is testing foods to find out if they contain any fat. He performed the emulsion test on a sample of butter and a sample of carrot. He results showed that his butter sample contained more fat than his carrot sample.
Describe the emulsion test and explain how the student would have come to this conclusion.
the emulsion test involves shaking the test tube containing the sample and ethanol for around one minute and then pouring the solution into water. If a lipid is present, it will show as a milky emulsion. The greater the concentration of the lipid sample, the more noticeable the the milky colour will be.
Therefore in the student’s test, the milky colour will have been more noticeable when testing the butter sample compared to the butter sample.
In cells, triglycerides are used as energy storage molecules and phospholipids make up the bilayer of the cell membrane. Suggest which properties of triglycerides and phospholipids make them suitable for their functions and explain how these properties related to their functions.
e.g. the long hydrocarbon tails of fatty acids contain lots of chemical energy (which is released when they are broken down). Triglycerides have 3 fatty acids so are able to store lots of energy.
Triglycerides are also insoluble due to their hydrophobic tails - this makes them suitable for storage as they don’t affect the water potential of the cell.
Phospholipids have a hydrophobic tail and a hydrophilic head so they form a double layer with their heads facing out. This allows them to form membrane that acts as a barrier against water soluble substances, as these substances can’t easily pass through the hydrophobic centre.
This allows them to form a membrane that acts as a barrier to water soluble substances, as these substances can’t easily pass through the hydrophobic centre.
Diagram of a phospholipid
