Biochemistry : Identifying Specific Lipid Functions

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Identifying Specific Lipid Functions

Which of the following sphingolipids is also a phospholipid? 

Possible Answers:

Ceramide

Ganglioside

Cerebroside

Sphingomyelin

Correct answer:

Sphingomyelin

Explanation:

Spinghomyelin has a head group of phosphotidylcholine, which makes sphingomyelin a phospholipid. None of the other lipids have phosphates, and therefore are not phospholipids. 

Example Question #2 : Identifying Specific Lipid Functions

After a serum test, it is observed that a patient has very low levels of a substance. Nuclear magnetic resonance (NMR) and infrared (IR) analysis reveal that the substance has a three-carbon backbone that has two, long hydrocarbon chains and a phosphate group attached. Which of the following structures is most likely compromised in this patient?

Possible Answers:

Cytoskeleton

Plasma membrane

Ribosomes

Chromatin

Correct answer:

Plasma membrane

Explanation:

To answer this question we need to recall the structure of the different macromolecules. Proteins are made up of amino acids, nucleic acids are made up of nitrogenous bases, phosphate groups and 5-carbon sugars, carbohydrates are made up of monosaccharides, and most of the lipids are made up of a three-carbon glycerol molecule attached to varying numbers of fatty acids and other molecules. If there are three fatty acids attached to three of the carbons of glycerol, then it is classified as a triglyceride. If there are two fatty acids and a phosphate group, then it is a phospholipid; therefore, the molecule mentioned in this question is phospholipid. Recall that phospholipids are mainly found in cellular membranes, such as plasma membrane.

Note that certain lipids such as cholesterol and sphingolipids don’t have 3-carbon backbone molecule with fatty acids. They are organized in a different manner. Cholesterol is a ring structure with four rings and hydroxyl group whereas sphingolipids are synthesized from sphingosine.

Example Question #3 : Identifying Specific Lipid Functions

Which of the following functions is not compromised due to low levels of lipids?

Possible Answers:

Elimination of free radicals

Rate of absorption of vitamin D

Vision

Clotting cascade

Correct answer:

Rate of absorption of vitamin D

Explanation:

Recall that there are four main nonpolar vitamins (lipids): vitamins A, D, E, and K. Vitamin A is an important vitamin for proper functioning of eye and can be found in foods containing carotene, such as carrots. Vitamin D is involved in the absorption of key minerals such as iron, calcium, and phosphate. It is usually obtained through sun exposure. Vitamin E is an antioxidant and is used to prevent the effects of reactive oxygen species (free radicals). Finally, Vitamin K is a clotting factor that is essential to repair and clot damaged endothelial walls and tissue.

Decreased levels of lipids will actually increase the absorption of these essential lipid vitamins. The body will try to absorb even the slightest amount of vitamins in diet to compensate for the depletion of these vitamins; therefore, the rate of absorption of Vitamin D will increase.

Example Question #4 : Identifying Specific Lipid Functions

What type of lipid structure requires a phosphate group, and what is the most common use of this lipid structure in a cell?

Possible Answers:

Triacylglycerides, fats

Phospholipids, ATP

Free floating fatty acids, acetyl-CoA

Phospholipids, cell membranes

Steroids, cholesterol

Correct answer:

Phospholipids, cell membranes

Explanation:

Phospholipids, as the name implies, require a phosphate head group attached to two fatty acid tails. Their polar phosphate head groups and non-polar fatty acid tails are perfect for a bi-layer membrane, where 2 layers of phospholipids are arranged such that their non-polar tails face each other and their polar phosphate head groups face outwards.

Example Question #5 : Identifying Specific Lipid Functions

Which type of lipid is both an important component of cell membranes and the precursor of steroid hormones?

Possible Answers:

Triacylglycerols

Fatty acids

Phospholipids

Sterols

Acetyl-CoA

Correct answer:

Sterols

Explanation:

The correct answer is "sterols." The most common sterol in animals is cholesterol, which is an important structural component of cell membranes and the precursor to steroid hormones. Acetyl-CoA is not a lipid but is a precursor to cholesterol itself. The other answers are lipids with other functions. While phospholipids are an important part of cell membranes, they are not precursors to steroid hormones.

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