Question

How many tripeptides can be made from three different amino acids? If the three are glycine (Gly), alanine (Ala), and phenylalanine (Phe), what are the structures of the possible tripeptides. (Hint: Gly-Ala-Phe is one structure.)

Short answer

There can be 27 different tripeptides made from the three amino acids. The structures include all permutations of Gly, Ala, and Phe in a sequence of three.

Step-by-step solution

Understanding the Problem

A tripeptide is a molecule formed by the combination of three amino acids. Since we have three different amino acids to choose from and we are forming a sequence of three, we will consider the permutations of these amino acids where the order matters and repetitions are allowed.

Calculating the Number of Possible Tripeptides

To calculate the total number of tripeptides possible with three different amino acids, each position in the tripeptide can be occupied by any of the three amino acids. Thus, the number of tripeptides is the number of permutations with repetitions allowed, which is calculated by raising the number of amino acids to the power of the number of positions: \( 3^3 = 27 \).

Listing All Possible Tripeptide Structures

We list all possible structures by considering each amino acid for each position in the tripeptide. We will have Gly, Ala, and Phe that could take each of the three positions, leading to 27 different combinations.

Key concepts

Amino Acids

Amino acids are the fundamental building blocks of proteins, which play crucial roles in virtually all biological processes. A standard amino acid contains a central carbon atom (the \(\alpha\)-carbon), a hydrogen atom, an amino group (\(-NH_2\)), a carboxyl group (\(-COOH\)), and a unique side chain or \(R\)-group, which determines the characteristics and properties of that particular amino acid.

There are 20 different standard amino acids that are encoded by the universal genetic code, and they can be linked together in varying sequences to form peptides or proteins. Some amino acids are produced by the human body, while others, known as essential amino acids, must be obtained through diet. Understanding amino acids is crucial in biochemical studies because of their versatility and their role in the synthesis of proteins.

In the context of the exercise regarding tripeptides, the specific amino acids concerned were glycine (Gly), alanine (Ala), and phenylalanine (Phe). Each has distinct side chains ranging from the simplest hydrogen side chain in glycine to the complex benzyl group in phenylalanine.

Permutations and Combinations in Chemistry

Permutations and combinations are concepts from mathematics, particularly the field of combinatorics, which are applied in chemistry to solve problems related to the arrangement and selection of molecules. A permutation is an arrangement of all or part of a set of objects, with regard to the order of the arrangement. For example, when considering the formation of tripeptides from three different amino acids, each position in the peptide chain can be occupied by any of the three amino acids, making order an important factor.

In cases where repetitions are allowed, as with tripeptides, the number of permutations of \(n\) different objects taken \(r\) at a time with repetition is denoted as \(n^r\). The exercise demonstrated this by calculating the possible tripeptides using \(3^3\), equating to 27 different tripeptides when three unique amino acids are available. In combinatorial chemistry, understanding permutations allows chemists to predict how many different molecules can be created in synthesis experiments or in biological systems.

Peptide Bond Formation

A peptide bond is a chemical bond that forms between two amino acids. When the carboxyl group of one amino acid reacts with the amino group of another, a molecule of water is released in a process called condensation or dehydration synthesis. The resulting bond is a covalent bond specifically called a peptide bond, and it joins the amino acids together in a peptide chain.

The formation of a tripeptide involves the linking of three amino acids via two peptide bonds. The sequential nature of peptide bond formation leads to a chain with a free amino group at one end, known as the N-terminus, and a free carboxyl group at the other end, the C-terminus. The sequence in which amino acids are joined determines the primary structure of the peptide or protein, and the eventual folding into secondary, tertiary, and quaternary structures dictates its biological function.

With respect to tripeptides like the ones composed of Gly, Ala, and Phe, understanding peptide bond formation is essential for appreciating how individual amino acids come together to form more complex structures with diverse biological activities.