Question

Using the four symbols shown to represent four different amino acids, draw structures four possible peptides for a four-member chain that can be made by linking them together in different orders $\begin{array}{ll}\text{ Amino acid }1:& \text{ Amino acid }3:\\ \text{ Amino acid }2:& \text{ Amino acid }4:\end{array}$

Short answer

Here are four example unique peptide combinations with different orders of amino acids: 1. Amino acid 1 - Amino acid 2 - Amino acid 3 - Amino acid 4 2. Amino acid 4 - Amino acid 3 - Amino acid 2 - Amino acid 1 3. Amino acid 1 - Amino acid 3 - Amino acid 2 - Amino acid 4 4. Amino acid 2 - Amino acid 4 - Amino acid 3 - Amino acid 1 Peptide structures can be represented as: 1. Amino acid 1 - (bond) - Amino acid 2 - (bond) - Amino acid 3 - (bond) - Amino acid 4 2. Amino acid 4 - (bond) - Amino acid 3 - (bond) - Amino acid 2 - (bond) - Amino acid 1 3. Amino acid 1 - (bond) - Amino acid 3 - (bond) - Amino acid 2 - (bond) - Amino acid 4 4. Amino acid 2 - (bond) - Amino acid 4 - (bond) - Amino acid 3 - (bond) - Amino acid 1

Step-by-step solution

Understand the problem

We are given four different amino acids, and we need to create peptides with four members in each chain. We need to find four possible unique combinations of these amino acids in different orders and draw their structures.

Determine the number of possible combinations

Since there are four different amino acids and four-member chains, there are a total of $4^4=256$ possible combinations. However, we only need to create and draw four possible unique peptides.

Create four unique peptide combinations

To create four unique peptides, we can simply use different orders of amino acids. Here are four example combinations: 1. Amino acid 1 - Amino acid 2 - Amino acid 3 - Amino acid 4 2. Amino acid 4 - Amino acid 3 - Amino acid 2 - Amino acid 1 3. Amino acid 1 - Amino acid 3 - Amino acid 2 - Amino acid 4 4. Amino acid 2 - Amino acid 4 - Amino acid 3 - Amino acid 1

Draw the structures of the four peptides

Since we have already listed four unique peptides, you can now draw them like the following: Peptide 1: - Amino acid 1 - (bond) - Amino acid 2 - (bond) - Amino acid 3 - (bond) - Amino acid 4 Peptide 2: - Amino acid 4 - (bond) - Amino acid 3 - (bond) - Amino acid 2 - (bond) - Amino acid 1 Peptide 3: - Amino acid 1 - (bond) - Amino acid 3 - (bond) - Amino acid 2 - (bond) - Amino acid 4 Peptide 4: - Amino acid 2 - (bond) - Amino acid 4 - (bond) - Amino acid 3 - (bond) - Amino acid 1 Please note that we have used a simple representation for the peptide structures using "-", "(bond)" and the amino acid names. You can also draw these structures using the specific amino acid symbols and peptide bonds.

Key concepts

Amino Acids

Amino acids are the building blocks of proteins. Each amino acid consists of a central carbon atom, known as the alpha carbon, attached to an amino group $-N{H}_2$, a carboxyl group $-COOH$, a hydrogen atom, and a distinctive side chain or R-group which differentiates one amino acid from another. In nature, there are 20 common amino acids combining different R-groups to provide variety in protein structures. The character and chemistry of the side chain can influence how an amino acid interacts with others:

• Acidic side chains (e.g., Aspartic acid)
• Basic side chains (e.g., Lysine)
• Neutral side chains that can be polar or non-polar (e.g., Glycine, Serine)

These interactions are crucial for the formation of complex proteins and peptides, which can have unique functional properties within the body.

Peptide Bonds

Peptide bonds are the special links that connect amino acids in a chain. When two amino acids come together, a chemical reaction takes place. The amino group $-N{H}_2$ of one amino acid reacts with the carboxyl group $-COOH$ of another, forming a covalent bond known as the peptide bond, along with a molecule of water as a by-product. The resulting structure, called a dipeptide, can further connect with additional amino acids through peptide bonds, forming long chains, known as polypeptides. This linear sequence determines the ultimate shape and function of the protein. The creation of a peptide bond is an example of a dehydration synthesis reaction, a type of condensation reaction that is vital for the development of the backbone of protein molecules.

Structural Representation

Structural representation of peptides involves illustrating the sequence of amino acids linked by peptide bonds. This is crucial for understanding how these molecules function in biological systems. Peptides can be represented:

• As a sequence of letters, each representing a specific amino acid (e.g., A-T-R for alanine-threonine-arginine pace).
• With 3D models showing the spatial arrangement of atoms.
• Using structural formulas that depict each atom and bond.

For learning purposes, simpler visual models like line drawings are often used, where each amino acid is denoted simply by its name or a letter, and connections between them are represented by dashes or lines. This helps in visualizing the sequential order and the bonding within the peptide chain, making it easier for students to comprehend complex molecular architecture.