Question

RECALL Is it possible to form cyclic peptides without bonds between side chains of the component amino acids?

Short answer

Yes, it is possible to form cyclic peptides without bonds between side chains.

Step-by-step solution

- Understand Cyclic Peptides

Cyclic peptides are sequences of amino acids that form a closed loop. This means that the chain's terminal ends are connected forming a circle.

- Identify Bonds Typically Involved

Typically, cyclic peptides may involve two types of bonds. The peptide bond that links consecutive amino acids and disulfide bonds between cysteine residues in side chains.

- Consider Peptide Bonds Only

Examine if forming a loop using only peptide bonds (without involving side chains) is possible. Connecting the terminal amino group of the first amino acid to the carboxyl group of the last amino acid using regular peptide bonds will create a cyclic structure.

- Draw Conclusions

Since peptide bonds alone can create a cyclic structure, side chain bonds are not necessary for the formation of cyclic peptides. Therefore, it is indeed possible to form cyclic peptides without bonds between side chains of the component amino acids.

Key concepts

Peptide Bonds

Peptide bonds are special covalent bonds that connect amino acids in a chain. These bonds are formed through a dehydration reaction between the carboxyl group of one amino acid and the amino group of another. When the bond forms, a water molecule is released. It’s this process that creates a long chain of amino acids, forming a protein or peptide.

In the context of cyclic peptides, these peptide bonds can connect the terminal amino group of the first amino acid to the terminal carboxyl group of the last amino acid. This creates a ring structure without the need for any side chain interactions. Cyclic peptides are unique because their ends are joined, forming a closed loop. These bonds provide structural integrity and can be helpful in creating stable molecules for various biological functions.
By understanding peptide bonds, you can see how the basic building blocks of proteins are connected and how this process plays a crucial role in forming cyclic peptides.

Amino Acids

Amino acids are the building blocks of proteins and peptides. Each amino acid has a central carbon atom (the alpha carbon), to which an amino group, a carboxyl group, a hydrogen atom, and a distinctive side chain (R group) are attached. The side chain determines the characteristics and reactivity of each amino acid.

Special sequences of amino acids can fold or loop into particular shapes, and in the case of cyclic peptides, they loop into a ring. The variety in side chains allows for diverse functions and properties, but for cyclic peptides, the main focus is on the backbone structure created by peptide bonds.
It's essential to know that although side chains play important roles in protein structure and function, they are not always necessary for creating the basic cyclic structure via peptide bonds. This highlights how versatile amino acids are and how their different combinations can form both simple and complex structures.

Disulfide Bonds

Disulfide bonds are another type of covalent bond found within or between protein molecules. These bonds form between the sulfur atoms of cysteine residues. When two cysteine side chains come into proximity, their sulfur atoms can form a disulfide bond, which helps stabilize the protein’s structure.

In cyclic peptides, disulfide bonds can provide additional stability by linking cysteine residues in the peptide’s sequence. However, these bonds are not necessary to form the cyclic structure itself. The ring can be closed solely by peptide bonds between the terminal amino and carboxyl groups.
Disulfide bonds are especially important in the function of many proteins, influencing their folding and stability. But for basic cyclic peptide formation, understanding that peptide bonds alone can achieve the structure is key.
This simplifies the concept and demonstrates that while side chain bonds like disulfide bonds add to the stability, the essential cyclic form is maintained by the simpler peptide bonds.