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Sunday, July 16, 2017

Introduction to Biochemistry - Quiz 2.5.1

We are starting a whole new topic on lipids now.


Lipids encloses aqueous cytosol of an animal cell in a bilayer (not a monolayer) - the monolayer is used to enclose triacylglycerols in adipocytes.

Lipids are not polymers.

Sphingolipid have peptide bonds, but most other don't.

Therefore the correct answer is:

Lipids all have a large hydrophobic region.


Sphingosine has a amine group, not a nitrogen group. I don't know if the term "nitrogen group" exists or not, the closest I can think of is cyanide, which is highly toxic.

The molecule drawn has a double bond in it, so it is not saturated.

Lipid formed with sphingosine, such as sphingomyelin, are often structural lipid, not storage lipid.

Therefore the correct answers are:

Sphingosine already contains one hydrocarbon 'tail', and
Sphingosine serves as a backbond, like glycerol.


Each of the 3 hydroxyl group of glycerol and the carboxylic acid group of the fatty acid reacts to form ester bonds, that's how triacylglycerols are formed. Therefore, the correct answer is:

... a fatty acid is esterified to each hydroxyl group of glycerol.


The key intermolecular interaction force between lipid molecules is Van der Waal's force. Molecule A, a saturated lipid is more regular and can be closely packed, therefore it will have more Van der Waal's force. On the other hand, molecule B will have less and therefore easier to boil, and theerfore it is more likely to be liquid at room temperature.

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