Summary of Protein Structure - Online Tutor, Practice Problems & Exam Prep

Proteins exhibit four levels of structural organization: primary, secondary, tertiary, and quaternary. The primary structure is the linear sequence of amino acids linked by peptide bonds. The secondary structure involves coiling into alpha helices or folding into beta pleated sheets, stabilized by hydrogen bonds. Tertiary structure refers to the overall 3D shape, maintained by hydrophobic interactions, hydrogen bonds, salt bridges, and disulfide bonds. Finally, the quaternary structure consists of multiple polypeptide chains forming a functional protein, stabilized by similar interactions as tertiary structure.

Summary of Protein Structure Concept 1

Hey, everyone. So in this video, we're going to take a look at a summary of our different protein structures. Now we're going to say that proteins are very complex molecules with 4 levels of structural organization. In the first one, we're going to talk about our primary structure. Now, remember, the characteristics of our primary structure is that it's just a sequence of our amino acids.

All these amino acids are linked together or stabilized by peptide bonds. Next, we move on to our secondary structure. We're still dealing with our same peptide chain, and we're going to say this peptide chain can basically coil upon itself to create alpha helices, or it can basically orient itself to create beta pleated sheets. Now, here we're going to say the characteristics here is that it's a spatial arrangement of the polypeptide chain. Here, we're going to see that it's stabilized by the fact that we have hydrogen bonds between the backbone atoms.

Next, we move on to our tertiary structure. Here we have our hydrophobic interactions that kind of cause the peptide chain to turn in on itself, where the hydrophobic portions will be on the interior of the chain. Now, here we're going to say the overall shape of the folded polypeptide chain is the characteristic when it comes to the tertiary structure. Now, here we're going to say that it's stabilized by four non-covalent interactions and one covalent bond. The four non-covalent interactions include hydrophobic interactions, as well as hydrophilic.

So the hydrophobic portions will orient themselves on the interior of our chain, and the hydrophilic portions, which like water, would orient themselves on the outside. Now in addition to this, we'd have hydrogen bonding involved, and then our salt bridge. Our covalent bond is when we have our disulfide bridge. Finally, we'd have our quaternary structure which is the most complex level of our protein structure. We're going to say this is the association of 2 or more subunits.

So remember, just think of the quaternary structure as building on top of the tertiary structure. We'd have multiple polypeptide chains coming together to form this fully functional protein. Now, here we're going to say because it is building off of the tertiary structure, we're going to say that it's stabilized by the same interactions as in the tertiary structure. So this is what we can say in summary when it comes to organizing proteins, all the way from the primary structure up to the quaternary structure.

Summary of Protein Structure Example 1

Here in this example question, it says, determine whether each of the following statements describes the primary, secondary, tertiary, or quaternary structure of a protein. For the first one, it says, side chains interact to form disulfide bonds. So remember, disulfide bonds are a key characteristic of a tertiary structure. So here, this represents a tertiary structure. Next, peptide bonds join amino acids into a polypeptide chain.

This is how we begin our journey towards a fully functional protein. This represents our primary structure. Remember, amino acids form these peptide bonds with one another, forming and linking together to form a long peptide chain. Next, 2 peptide chains are held together by hydrogen bonding. Alright.

So they're talking about 2 chains. Now here, that could be primary or secondary. Because remember, those happen amongst one chain. So, that means it's either going to be tertiary or quaternary. Here they're saying 2 polypeptide chains are held together by hydrogen bonding.

This has to be a tertiary structure, because here we can have these types of interactions that connect different chains with one another. Eventually, this will lead up to our quaternary structure later on. Next, hydrogen bonding between amino acids in the same polypeptide gives a coiled shape to the protein. Coiled shape is a reference to our alpha helices or alpha helix. Remember, that is indicative of a secondary structure.

So this will represent our different types of protein structures based on these four statements.

Determine which of the following statements describes a tertiary structure of a protein.

• A. Three polypeptide chains interact to form a biologically active protein. 
• B. Hydrogen bonds form between adjacent segments of the backbones of the same protein to form its creased structure.
• C. Nonpolar side chains are repelled by water and move to the interior of the protein.
• D. Amino acids react in a condensation reaction to form a peptide bond.

Indicate whether each of the following statements describes a primary, secondary, tertiary, or quaternary protein structure:                                                            

______ a) Hydrophobic R groups seeking a nonpolar environment move toward the inside of the folded protein.  

______ b) Protein chains of collagen form a polypeptide chain composed of 3 alpha helices. 

______ c) An active protein contains 4 tertiary subunits. 

______ d) Two polypeptide chains held together by disulfide bridges. 

Indicate whether each of the following statements describes a primary, secondary, tertiary, or quaternary protein structure. Hydrophobic R groups seeking a nonpolar environment move towards the inside of the folded protein. This involves hydrophobic interactions that help to give shape to the protein chain. This would represent a tertiary structure. Next, protein chains of collagen form a polypeptide chain composed of 3 alpha helices. Since it is only a single chain, it could not be tertiary or quaternary, because those involve multiple types of interactions besides these alpha helices, and quaternary involves more than one chain. Here, alpha helices are a key characteristic of a secondary structure. It could not be primary because primary only deals with peptide bonds. Now, an active protein contains 4 tertiary subunits. This indicates it is biologically operable as a protein, which suggests it is quaternary. Additionally, having many subunits together is a key characteristic of a quaternary structure as well. Finally, two polypeptide chains held together by disulfide bridges. Disulfide bridges are a key indicator of a tertiary structure. Therefore, this statement describes a tertiary structure.