Functional Groups - Online Tutor, Practice Problems & Exam Prep

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. 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. The functional groups are typically going to extend off of the carbon backbone of a molecule. 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, so the functional group is always going to be extending off of some type of carbon backbone. 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. Notice down below in our table, we have these 7 functional groups for you all to know. The very first functional group that you all should know is the methyl group. 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. That's it for the methyl group over here. Typically, these methyl groups, what we'll see, is that they're going to be found in lipids and things like that. We'll be able to see those a little bit later in our course.

The second functional group that you all should know is the hydroxyl group. The hydroxyl group, as you can kind of see with its name, has the oxy in here for an oxygen atom and 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.

Now over here, what we have is the third class of functional group, and that is the carbonyl group. The carbonyl group is whenever you have a carbon atom that is double-bonded to an oxygen atom. So when you have a carbon atom double-bonded to an oxygen atom, that is a carbonyl group.

The fourth 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. 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 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.

The fifth functional group that we have down below here is going to be the amino group. 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.

The sixth 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.

The seventh and final functional group that you all should be aware of is the sulfhydryl group. The sulfhydryl group, as its name implies, with the 'sulf' here, is going to have a sulfur atom. 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.

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. 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. 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 a 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 the seven common functional groups in biology?

The seven common functional groups in biology are the methyl group (–CH₃), hydroxyl group (–OH), carbonyl group (C=O), carboxyl group (–COOH), amino group (–NH₂), phosphate group (–PO₄), and sulfhydryl group (–SH). These groups are essential for the reactivity and function of biomolecules, often extending from a carbon backbone. Understanding these groups helps in recognizing their roles in various biological processes and molecules, such as lipids and carbohydrates.

How does the carboxyl group differ from the carbonyl group?

The carboxyl group (–COOH) is a combination of a carbonyl group (C=O) and a hydroxyl group (–OH). In the carboxyl group, a carbon atom is double-bonded to an oxygen atom (carbonyl) and also bonded to a hydroxyl group. In contrast, the carbonyl group consists only of a carbon atom double-bonded to an oxygen atom. The carboxyl group is more reactive and commonly found in organic acids, while the carbonyl group is found in aldehydes and ketones.

What is the significance of the phosphate group in biomolecules?

The phosphate group (–PO₄) is crucial in biomolecules due to its role in energy transfer and storage. It is a key component of ATP (adenosine triphosphate), which is the primary energy carrier in cells. The phosphate group is also involved in the formation of DNA and RNA, where it links nucleotides together. Its presence in phospholipids is essential for the structure and function of cell membranes.

Where can hydroxyl groups be commonly found in biomolecules?

Hydroxyl groups (–OH) are commonly found in carbohydrates, such as sugars and alcohols. They are also present in some amino acids and nucleotides. The presence of hydroxyl groups makes molecules more soluble in water due to their ability to form hydrogen bonds. This property is crucial for the function and interaction of biomolecules in aqueous environments.

What role does the amino group play in proteins?

The amino group (–NH₂) is fundamental in proteins as it is part of the structure of amino acids, the building blocks of proteins. Each amino acid has an amino group and a carboxyl group attached to a central carbon atom. The amino group can act as a base, accepting a proton (H⁺), which is essential for the formation of peptide bonds during protein synthesis. This group also contributes to the overall charge and reactivity of amino acids.