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 interactions, hydrogen bonding, ionic bonds (salt bridges), and disulfide bridges, which are covalent bonds formed between cysteine residues. This structure builds upon the primary (amino acid sequence) and secondary (alpha helices and beta sheets) structures, leading to a fully functional protein. Understanding these interactions 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. Now, 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 move 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. Now 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 structures. 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 are 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. 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 non-covalent interactions. Here we'll talk about 4 of them. They are hydrophobic interactions, so the portions that are 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 R groups, they are non-polar 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'd 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 bond, 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 gonna 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 gonna say we have what's called a disulfide bridge. It forms when SH groups from 2 cysteine residues react to form a S-S bond. So here, if we look, this would be our disulfide bridge. So here we made a disulfide bond, these S-S here that connect together. So this was a cysteine R group and this was a cysteine R group. Then combining 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 non-covalent 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 that 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 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

Here’s what students ask on this topic:

What is the tertiary structure of a protein?

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

How do hydrophobic interactions contribute to the tertiary structure of a protein?

Hydrophobic interactions play a crucial role in stabilizing the tertiary structure of a protein. These interactions occur between nonpolar R groups that are repelled by water. In an aqueous environment, these hydrophobic R groups tend to cluster together in the interior of the protein, away from the water. This clustering helps to minimize the exposure of hydrophobic residues to the aqueous environment, thereby stabilizing the folded structure of the protein. This is essential for maintaining the protein's functional three-dimensional shape.

What are disulfide bridges and how do they stabilize protein structure?

Disulfide bridges are covalent bonds that form between the sulfur atoms of two cysteine residues within a protein. These bonds are created when the thiol groups (–SH) of two cysteines oxidize to form a disulfide bond (–S–S–). Disulfide bridges play a significant role in stabilizing the tertiary structure of proteins by providing strong covalent links that hold different parts of the protein together. This stabilization is particularly important in extracellular proteins, which are exposed to more variable and potentially harsh conditions.

What types of bonds and interactions are involved in the tertiary structure of a protein?

The tertiary structure of a protein is stabilized by several types of bonds and interactions among the R groups of amino acids. These include:

• Hydrophobic interactions: Nonpolar R groups cluster together to avoid water.
• Hydrogen bonds: Form between polar R groups or between R groups and the backbone.
• Ionic bonds (salt bridges): Form between positively and negatively charged R groups.
• Disulfide bridges: Covalent bonds between the sulfur atoms of two cysteine residues.

These interactions collectively contribute to the protein's overall three-dimensional shape and stability.

How do hydrogen bonds affect the tertiary structure of a protein?

Hydrogen bonds significantly contribute to the stability of a protein's tertiary structure. These bonds form between polar R groups or between R groups and the peptide backbone. For example, an R group with an –OH group can form a hydrogen bond with another R group containing a carbonyl group (C=O). These interactions help to stabilize the folded structure by creating specific patterns of attraction between different parts of the protein. Hydrogen bonds are relatively weak individually, but collectively, they provide substantial stability to the protein's three-dimensional shape.