Cholesterol and cholate are sterols with very similar structures. However, the roles they play in the body are different: Cholate is an emulsifier, whereas cholesterol plays an important role in membrane structure. Identify the small differences in their structures that make them well suited to their jobs in the body. Given their similar structures, can the roles of these molecules be reversed?

Question

Cholesterol and cholate are sterols with very similar structures. However, the roles they play in the body are different: Cholate is an emulsifier, whereas cholesterol plays an important role in membrane structure. Identify the small differences in their structures that make them well suited to their jobs in the body. Given their similar structures, can the roles of these molecules be reversed?

Accepted Answer

Hello, everyone. Let's take a look at the next problem which of these statements is true. And we have four statements. And below this, we have two structures drawn one for cate and one for cholesterol. So our statements are number one cate a bile acid anion and cholesterol have similar structures and fulfill the same functions in the body. Number two Coates, hydrophilic groups allow it to play an important role in membrane structure similar to cholesterol. Number three cholesterol with its hydroxyl group and hydrophobic tail serves as an emulsifier like cate or number four, Kate has additional carboxyl and hydroxyl groups compared to cholesterol making it effective as an emulsifier rather than a membrane component. So let's look at these two structures and compare them and see which of these statements is the true one. So we can see that the steroid ring structure in these two molecules is very similar and is largely hydrophobic. But there's a pretty big difference here on the bright side of the structures, we see that Kate has a carboxylate group. Whereas cholesterol just has this hydrocarbon chain here. So that's a big difference between a nonpolar hydrocarbon chain in the same region as a negatively charged very reactive carboxylate portion. In addition, while both Kate and cholesterol have an alcohol group down in the lower left of this structure, uh coming off the steroid ring cate has two additional alcohol groups and they're kind of in the middle of the structure. So you have two polar and fairly reactive groups right in the middle of the structure. So let's think about this and think about our statements and evaluate them. So number one says that the two of these have similar structures and to fill the same functions, they do have similar structures. That is true, but they do not fill the same functions due to the fact that the differences in our structures are quite significant as we discussed. So number one would not be a true statement. Number two says Kate's hydrophilic groups allow it to play an important role in membrane structure similar to cholesterol. But what do we call about membrane structure? We have this, these hydrophilic heads that make the two outsides of the double layered membrane and the whole interior of the membrane is hydrophobic. Well, what does our cate look like? It has polar hydroxyl groups in the middle and it's got three extra polar groups compared to cholesterol. That's too many hydrophilic groups. It is incompatible with the hydrophobic interior of the membrane. So number two is not going to be our true statement. Then number three says cholesterol with its hydroxyl group and hydrophobic tail serves as an emulsifier like Kate. Well, what's the purpose of an emulsifier? It can help you mix fats and water. And it does that by having both hydrophobic and hydrophilic portions that allow it to form my cells around fat droplets that allow it to be mixed in to an aqueous solution. Cholesterol. On the other hand, just has a single alcohol group as its only polar functional group. So that is not going to be enough to allow it to act as an animals fire. So try three, not correct. So we've just got one statement left by process of elimination. This must be our true statement. But let's look at it cate has additional carboxy and hydroxyl groups correct compared to cholesterol making it effective as an emulsifier. Yes, with those hydrophilic and hydrophobic parts rather than a membrane component. And yes, this is correct. While cholesterol with its mostly nonpolar structure is very effective as a membrane component. It does just fine in the interior of a membrane colate is not but colate is an effective emulsifier. So choice four that Kate is effective in emulsifier rather than a membrane component due to those additional polar functional groups is our true statement. See you in the next video.

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Key Concepts

Sterol Structure

Function of Cholesterol

Function of Cholate