Biochemistry : Lipid Catabolism Regulation

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Lipid Catabolism Regulation

Why does consuming alcohol (ethanol) promote storage of fatty acids in the form of triglycerides (fatty tissue), especially in the liver?

Possible Answers:

The free radicals produced in this process directly inhibit enzymes which oxidize fatty acids

The acetaldehyde produced from ethanol directly inhibits enzymes which oxidize fatty acids

Ethanol directly inhibits the enzymes which oxidize fatty acids by binding to their active sites

The  produced from ethanol oxidation to acetaldehyde inhibits fatty acid oxidation, causing them to be stored as triglycerides

The  produced from ethanol oxidation to acetaldehyde inhibits fatty acid oxidation, causing them to be stored as triglycerides

Correct answer:

The  produced from ethanol oxidation to acetaldehyde inhibits fatty acid oxidation, causing them to be stored as triglycerides

Explanation:

The oxidation of ethanol to acetaldehyde in the liver produces , leading to an elevated  ratio. Multiple enzymes responsible for fatty acid oxidation are under control of this ratio; they are active when there is more  an inactive when there is more . Thus, they become inactivated, and fatty acids are stored in the liver as triglycerides - this is why alcoholism leads to fatty liver disease. Free radicals can damage the liver and other tissues but do not directly inhibit these enzymes; neither does the ethanol molecule itself nor acetaldehyde

Example Question #2 : Lipid Catabolism Regulation

In the presence of insulin, cells alter the activity of a key enzyme in fat metabolism. This enzyme is called acetyl-CoA carboxylase. How does insulin signaling affect the activity of this enzyme, and what changes does this have on fat metabolism?

Possible Answers:

Acetyl-CoA becomes inhibited and the breakdown of fatty acids is activated

Acetyl-CoA becomes activated and the breakdown of fatty acids is activated

Acetyl-CoA becomes activated and the breakdown of fatty acids is inhibited

Acetyl-CoA becomes inhibited and the breakdown of fatty acids is inhibited

Correct answer:

Acetyl-CoA becomes activated and the breakdown of fatty acids is inhibited

Explanation:

For this question, we're going to need to know a few things right off the bat.

First, it's important to know what the general "mission" of insulin is. Generally speaking, insulin is a hormone that helps the body out when there is ample energy available. For example, right after eating a meal, blood sugar levels are going to be fairly high. Thus, the body is in a state where it doesn't want to be breaking things down to provide energy. Rather, it wants to store the energy that it has just been given. This storage generally comes in the form of glycogen and fat.

Next, it's important to understand what acetyl-CoA carboxylase (ACC) does. As its name would suggest, it adds a carboxyl group onto acetyl-CoA. By doing so, it generates malonyl-CoA. This is a very important molecule that is used in the synthesis of fatty acids. Thus, when there is a lot of malonyl-CoA in the cell, it's likely that the cell wants to use it up to create fatty acids. Furthermore, in order to ensure that fatty acids aren't being broken down at the same time (which would be wasteful), malonyl-CoA also blocks the breakdown of fatty acids.

Equipped with this information, we can go ahead and piece together the facts as though it were a story. Insulin wants the body to store energy. It activates cellular receptors, which causes a downstream signaling event. Ultimately, this results in the activation of the enzyme ACC. This, in turn, generates a high amount of malonyl-CoA. The presence of high amounts of malonyl-CoA inside the cell gives the signal to make fatty acids and to also block their breakdown. So, all in all, acetyl-CoA becomes activated and the breakdown of fatty acids is inhibited.

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