Tertiary Protein Structure - Online Tutor, Practice Problems & Exam Prep

The tertiary structure of a protein is its overall three-dimensional shape, resulting from the folding of a peptide chain stabilized by interactions among R groups. Key interactions include hydrophobic (water-repelling), hydrophilic (water-attracting), hydrogen bonds, ionic bonds (salt bridges), and covalent disulfide bridges formed between cysteine residues. These interactions build upon the primary (amino acid sequence) and secondary (alpha helices and beta pleated sheets) structures, leading to a fully functional protein. Understanding these structures is crucial for grasping protein functionality and stability.

Tertiary Protein Structure Concept 1

Now we can say here that the tertiary structure of a protein is its overall three-dimensional shape, and it's a result from the twisting and bending of a peptide chain, and it's stabilized by interactions between R groups. It involves both the close and distant R groups. So, in terms of our journey to a fully functional protein, we had our primary structure, which is just amino acids connected to each other by peptide bonds. Then we moved to secondary structures, which can be alpha-helices or beta-pleated sheets. And now we're talking about a tertiary structure, which we can see as a folded peptide chain.

Now if we take a look here, in this, we have alpha-helices as well as beta-pleated sheets involved. Here, remember these blue arrows here represent our beta-pleated sheets, and then here we have our alpha-helix. Remember, in a polypeptide chain, we can have areas of multiple alpha-helices and beta-pleated sheets, not just one of each. Here we're going to say the folding of a peptide into a tertiary structure, it does not change its primary and secondary structure. Remember, this is kind of like a buildup, so we get to a fully functional protein.

We had our primary structure, that primary structure, if you look closely, parts of it can be alpha-helices, parts of it can have beta-pleated sheets. Tertiary structures is the continued folding of that polypeptide chain to give us this folded peptide look, which makes it one step closer to becoming a fully functional protein. We're not there yet, but we're on our way to that. So remember, it's just a buildup from primary to secondary to now tertiary. Getting to tertiary does not erase all the work done on the primary and secondary structures.

Okay? So they build on top of each other. So keep that in mind when we take a look at questions dealing with the tertiary structure of proteins.

Tertiary Protein Structure Example 1

Which of the following statements about primary, secondary, and tertiary protein structures is incorrect? The tertiary structure of a protein is stabilized by interactions between R groups of different amino acids. That's true. Remember, it's close and distant R groups that are helping with the stabilization. Now here the folding of a peptide into the tertiary structure destroys its secondary structure.

Remember, this is incorrect. The tertiary structure being formed does not erase the primary and secondary structures. It's just an evolution; it's becoming more complex in terms of the polypeptide chain. Okay? It's not undoing the primary and secondary structures.

Due to the folding of the peptide chain, distant R groups come close and interact with each other. That is true. With this folding in and moving and twisting, some R groups are going to have greater interactions than before. A folded peptide or protein can have alpha-helices and beta-pleated sheets at the same time. Yes.

These polypeptide chains can be many amino acids long; portions of it can contain alpha-helices, and portions of it can contain beta-pleated sheets at the same time. So this is indeed possible. So this is correct. The only statement here that is incorrect is option B.

Interactions within the Tertiary Structure Concept 2

In this video, we'll talk about the interactions with the tertiary structure itself. Now here, we're going to say that the tertiary structure mostly consists of noncovalent interactions. Here we'll talk about 4 of them. They are hydrophobic, afraid of water. The opposite of this is hydrophilic, the portions that like water.

Next, we have hydrogen bonding. And then a salt bridge; salts are terms we use for ionic compounds. So a salt bridge would be an ionic bond. Now here, if we take a look, let's not worry about the other ones for now. If we were to take a look at this portion of our peptide, we could say that this portion here, that has this hydrocarbon and this hydrocarbon are groups.

They are nonpolar in nature because they're hydrocarbons, so their interaction will be hydrophobic. Over here, we have this R-group which has an OH group, so it has similar intermolecular force as well as polarity as the water molecules around it. So it would not be afraid of water, it would love water. So it would be hydrophilic. Next, we have this R-group, which has an OH group, and this R-group, which has an OH group.

This would be hydrogen bonding. And then finally, we're talking about ionic bonds, so we're talking about charges, salts. Here's a negative charge attracted to this positive charge. This would be our ionic bridge. This leaves this last interaction.

So if we come back up here, we're going to say a covalent bond can help to hold the folded peptide in place. So kind of like ratchets it up and keeps it in place. We're going to say we have what's called a disulfide bridge. It forms when SH groups from 2 cysteine residues react to form a SS bond. So here, if we look, this would be our disulfide bridge.

So here we made a disulfide bond, these SS here that connect together. So this was a cysteine R-group and this was a cysteine R-group. They combined, meaning they lost their hydrogens and what's left behind is this disulfide bridge, this connection that's ratcheting up and connecting more strongly this alpha helix with this beta pleated sheet. So remember, these are the different types of interactions that can exist with the tertiary structure. 4 of them are noncovalent in nature and one of them, the disulfide bridge, is a covalent bond.

Tertiary Protein Structure Example 2

Which of the following interactions is the most likely to be found at the surface of a folded peptide? So if we're thinking about this, we have a folded peptide, and it's in an aqueous medium, so water. If we're talking about the surface of that peptide, we're talking about its outside. If you're going to be on the outside of the peptide, you have to make sure that you like water because water is going to be all around you. So it's safe to say here, the interaction most likely to be found on the surface of a folded peptide would have to be a hydrophilic interaction, the portion that likes water.

Now the least likely one to be found on the surface would have to be our hydrophobic interactions, and we know that one of the first actions in folding is for the hydrophobic or water-fearing portions to fold and go on the interior of this peptide chain. Alright? So just remember, hydrophobic portions are most likely to be found on the inside, hydrophilic are found on the surface of the peptide.

Which of the following amino acid pairs are the most likely to form hydrogen bonds?

• A. Cysteine – cysteine
• B. Lysine – glutamate
• C. Serine – threonine
• D. Leucine – valine

What type of R group interaction is the most likely between the alanine and isoleucine residues?

• A. Hydrogen bonding
• B. Hydrophobic interaction
• C. Disulfide bridge
• D. Salt bridge

Which of the following amino acid pairs can form a salt bridge?

• A. Cysteine – methionine
• B. Serine – glutamine
• C. Valine – isoleucine
• D. Lysine – glutamate