Oxytocin is a small peptide that is used to induce labor by causing contractions in uterine walls. It has the primary structure Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gln. This peptide is held in a cyclic configuration by a disulfide bridge. Draw a diagram of oxytocin, showing the disulfide bridge.

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All right. Hi, everyone. So this question says that octreotide is a growth hormone inhibitor and it is used to treat disorders caused by excess growth hormone. It is a polypeptide with the primary structure of pheno alanine cysteine, pheno alanine tryptophan lysine thine cysteine and thine its structure has a cyclic configuration held by a disulfide bridge using their abbreviations show the structure of octreotide and show the disulfide bridge. And here we have four different answer choices labeled A through D that notably differ in the size of their ring structures. So let's go ahead and get started. The main part of this question or the most important piece of information given is the fact that we do have a disulfide bridge. If we consider all of the answer choices for one more. Second, notice that all of the ring structures have two sulfur atoms connecting to each other. This is called the disulfide bridge or disulfide bond. Now recall that a disulfide bridge is created between two residues of cysteine because Sistine, if you recall has a th group or an S group at the very end of its side chain. So when these two thy groups combine together, they create a new covalent bond between both sulfur atoms. Hence the term disulfide. Now recall also that Sistine is abbreviated using its first three letters or cys. So here the disulfide bond is going to form between the two cysteine residues found in the primary structure given. So what I'll do here is scroll down to show you the primary structure that I went ahead and rewrote. So in this case, we have a total of eight amino acids in the primary structure. Now, the two cysteine residues are the second and the seventh amino acids in this structure here, the primary structure. So the disulfide bridge is going to form in between these two cysteine residues. And if I count the number of residues in between both cysteine and including both cysteine, what I notice is that I count six amino acid residues, therefore, six amino acid residues are going to be inside of the ring in the structure of octreotide. So in this case, right, we're going to have six residues as part of the ring as well as the two atoms of sulfur from each cysteine residue. This means that our answer here must have an eight member ring in its structure because we have six amino acid residues and two sulfur atoms as part of the ring. This means that the first and the last amino acid residues, Beno alanine and thine respectively are going to be outside of the ring itself. So if I scroll up here one more time, only one of these answers has an eight member ring and that is option c in the multiple choice. So that is going to be our final answer and there you have it. So with that being said, thank you so very much for watching and I hope you found this helpful.

Oxytocin is a small peptide that is used to induce labor by causing contractions in uterine walls. It has the primary structure Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gln. This peptide is held in a cyclic configuration by a disulfide bridge. Draw a diagram of oxytocin, showing the disulfide bridge.

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Key Concepts

Oxytocin Structure

Disulfide Bridge

Peptide Diagramming