Functional Groups: Study with Video Lessons, Practice Problems & Examples

Functional groups are specific groups of atoms that confer reactivity to biomolecules, typically extending from a carbon backbone. Key functional groups include the methyl group (–CH₃), hydroxyl group (–OH), carbonyl group (C=O), carboxyl group (–COOH), amino group (–NH₂), phosphate group (–PO₄), and sulfhydryl group (–SH). Understanding these groups is essential for recognizing their roles in various biomolecules, such as lipids and carbohydrates, and their significance in biological processes.

Functional Groups

In this video, we're going to begin our lesson on functional groups. Now, functional groups, as their name implies, are really just groups of atoms that are reactive or functional, and they're also commonly found together within biomolecules. And so, moving forward in our course, when we're talking about different classes of biomolecules, we're going to see lots and lots of functional groups appear, and so it's important to get to know these functional groups pretty well. Now, the functional groups are typically going to extend off of the carbon backbone of a molecule, and so notice down below in our image we're going to represent the carbon backbones of the molecules by using these squiggly lines throughout which again represent the carbon backbone of the rest of the molecule, and so the functional group is always going to be extending off of some type of carbon backbone. Now, throughout all of biology, there are a lot of different types of functional groups. However, in a typical biology course like yours, you're likely only going to need to know 7 functional groups that are pretty common in biology. And so notice down below in our table, we have these 7 functional groups for you all, to know. And so the very first functional group that you all should know is the methyl group. And the methyl group is just when you have a carbon atom branching off of a carbon backbone, and this carbon atom is covalently attached to 3 other hydrogen atoms. And so that's it for the methyl group over here. And typically these methyl groups, what we'll see is that they're going to be found in lipids and things like that. So we'll be able to see those a little bit later in our course. Now, the second functional group that you all should know is the hydroxyl group. And the hydroxyl group, as you can kind of see with its name, it has the "oxy" in here for an oxygen atom and it has the "hydro" in here for the hydrogen atom, and that's exactly what it is. The hydroxyl group is going to have an oxygen atom branching off of a chain that's also bound to a hydrogen atom. And so an OH group like what you see here is going to represent the hydroxyl group, and we'll see hydroxyl groups in lots of different types of molecules, including carbohydrates. Now, over here what we have is the 3rd class of the functional group or the 3rd functional group, and that is the carbonyl group. And the carbonyl group is whenever you have a carbon atom that is double bonded, has a double bond to an oxygen atom. And so whenever you have a carbon atom double bonded to an oxygen atom that is a carbonyl group. And so once again these are fairly common throughout different types of biomolecules. Now, over here the 4th functional group that we have here is going to be the carboxyl group. Now I admit, at first glance, the carbonyl and the carboxyl sound very, very similar. However, the carboxyl, what can help you remember is that boxes like this box over here are used to store things and really the carboxyl is a combination of the hydroxyl group and the carbonyl group as well. And so, it's going to be, a combination of both. So, notice that the carbonyl group is present here in the carboxyl because there's a carbon double bonded to an oxygen just like what we saw over here. But in addition to the carbonyl group, there's also a hydroxyl group over here within this carboxyl group and so there's an OH over here as well. And so when you see a carbon double bonded to an oxygen and then that same carbon is bonded to a hydroxyl group, together we refer to this entire thing as a carboxyl group. And so, the 5th functional group that we have down below here is going to be the amino group. And so the amino group, you can think has this "n" in it, and really that's representing the nitrogen atom that is found within the amino groups. And so this is an example of an amino group. Now the 6th functional group that we have here is going to be the phosphate group, and the phosphate group looks pretty complex here. However, it's pretty easily identifiable because it's the only one of the 7 that has a phosphorus atom like what we see here. And so, this is it for the phosphate group. And once again, we'll see these functional groups throughout many different types of biomolecules moving forward in our course. And then the 7th and final functional group that you all should be aware of is the sulfhydryl group. And so the sulfhydryl group, as its name implies, with the "sulf" here, it's going to have a sulfur atom. And the "hydra" prefix here is going to have a hydrogen atom. And that's exactly what the sulfhydryl group is, a sulfur and a hydrogen atom just like what we see here. And so these are the 7 functional groups that would be good to commit to memory because moving forward in our course, we're going to be able to refer to all of these different functional groups. Now some of them you might need to commit to memory in terms of the structures, but others you might need to commit to memory just in terms of being able to identify or recognize them. For example, the phosphate group might be one that you would just need to identify and recognize, but you'll have to ask your professor to figure out exactly which functional groups they want you to be aware of. Now, this here concludes our introduction to functional groups and we'll be able to get some practice applying the concepts that we've learned in our next few videos. So I'll see you all there.

Functional Groups Example 1

Alright. So here we have an example problem that's asking which functional group listed down below over here is not present in this molecule over here. And so notice that the very first functional group listed is carboxyl, and recall that the carboxyl has the box in it which we know is going to store 2 other functional groups, the carbonyl group and the hydroxyl group. And so notice over here we have a carbon double bonded to an oxygen, and we also have a hydroxyl group branching off. And so together when we see this format like this, we refer to it as a carboxyl group. So the carboxyl group is present here and we can go ahead and cross it off and label it, as we see right here. Let's label this as carboxyl.

Then moving on, what you'll also notice is that we have an OH group extending off of a carbon. And so the OH, recall, is going to be the hydroxyl group because it has the oxy in it for the oxygen and the hydro for the hydrogen. And so, this here is going to be a hydroxyl group. And so because a hydroxyl group is here, we can go ahead and cross off option c as well.

And then recall that amino groups are going to have a nitrogen atom in them, and so notice that the nitrogen atom is right here and this here represents the amino group. And so the only one that is not present here is going to be the sulfhydryl group, which recall has a sulfur atom and a hydrogen atom. But there are no sulfur atoms at all throughout here, so this is going to be the one that is not present in the molecule. So we can go ahead and indicate that b here is the correct answer for this example and that concludes this example, so I'll see you all in our next video.

What is the name of the functional group shown in the figure?

a) Carbonyl.

b) Ketone.

c) Carboxyl.

d) Methyl.

e) Phosphate.

• A. Carbonyl.
• B. Ketone.
• C. Carboxyl.
• D. Methyl.
• E. Phosphate.

All of the following are examples of functional groups in biology except:

a) -CH₃.

b) -COOH.

c) -H₂O.

d) -NH₂.

e) -OH.

• A. -CH₃
• B. -COOH
• C. -H₂O
• D. -NH₂
• E. -OH

Here’s what students ask on this topic:

What are functional groups in organic chemistry?

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They typically extend from a carbon backbone and confer specific reactivity and properties to the molecule. Common functional groups include the methyl group (–CH₃), hydroxyl group (–OH), carbonyl group (C=O), carboxyl group (–COOH), amino group (–NH₂), phosphate group (–PO₄), and sulfhydryl group (–SH). Understanding these groups is essential for recognizing their roles in various biomolecules, such as lipids and carbohydrates, and their significance in biological processes.

Why are functional groups important in biology?

Functional groups are crucial in biology because they determine the properties and reactivity of biomolecules. They play a key role in the structure and function of molecules like proteins, nucleic acids, carbohydrates, and lipids. For example, the hydroxyl group (–OH) is important in carbohydrates, while the amino group (–NH₂) is essential in amino acids, the building blocks of proteins. Functional groups also participate in chemical reactions that are vital for life, such as enzyme catalysis, energy transfer, and cell signaling.

What is the difference between a carbonyl group and a carboxyl group?

The carbonyl group (C=O) consists of a carbon atom double-bonded to an oxygen atom. It is found in aldehydes and ketones. The carboxyl group (–COOH) is a combination of a carbonyl group and a hydroxyl group (–OH) attached to the same carbon atom. It is found in carboxylic acids and is important in amino acids and fatty acids. The carboxyl group can donate a proton (H⁺), making it acidic, whereas the carbonyl group does not have this property.

How do you identify a phosphate group in a molecule?

A phosphate group (–PO₄) is identifiable by the presence of a phosphorus atom bonded to four oxygen atoms. It is unique among common functional groups because it contains phosphorus. Phosphate groups are crucial in energy transfer molecules like ATP (adenosine triphosphate) and in the backbone of nucleic acids like DNA and RNA. They often participate in energy transfer and signaling processes within cells.

What role does the amino group play in proteins?

The amino group (–NH₂) is a fundamental component of amino acids, which are the building blocks of proteins. In amino acids, the amino group is attached to the alpha carbon along with a carboxyl group (–COOH), a hydrogen atom, and a variable R group (side chain). The amino group can act as a base, accepting a proton (H⁺), which is important for the protein's structure and function. It also participates in peptide bond formation during protein synthesis.