Question

Proteins are naturally occurring polymers formed by condensation reactions of amino acids, which have the general structure In this structure, \(-\mathrm{R}\) represents \(-\mathrm{H},-\mathrm{CH}_{3},\) or another group of atoms; there are 20 different natural amino acids, and each has one of 20 different R groups. (a) Draw the general structure of a protein formed by condensation polymerization of the generic amino acid shown here. (b) When only a few amino acids react to make a chain, the product is called a "peptide" rather than a protein; only when there are 50 amino acids or more in the chain would the molecule be called a protein. For three amino acids (distinguished by having three different R groups, R1, R2, and R3), draw the peptide that results from their condensation reactions. (c) The order in which the R groups exist in a peptide or protein has a huge influence on its biological activity. To distinguish different peptides and proteins, chemists call the first amino acid the one at the \({ }^{\prime \prime} \mathrm{N}\) terminus" and the last one the one at the "C terminus." From your drawing in part (b) you should be able to figure out what "N terminus" and "C terminus" mean. How many different peptides can be made from your three different amino acids?

Short answer

In summary, a protein consists of multiple peptide chains bonded together, and a peptide with three unique amino acids (R1, R2, R3) can be represented as R1 – R2 – R3. N-terminus represents the end of the peptide with a free amino group (-NH2), and C-terminus refers to the end with a free carboxyl group (-COOH). There are six distinct peptides that can be formed from three unique amino acids.

Step-by-step solution

Draw the general structure of a protein

Proteins result from a condensation polymerization process between amino acids, which have a general structure in the form of an amino group (NH2), a carboxyl group (COOH) and an R group. In a condensation reaction, a water molecule is formed by removing one hydrogen atom from the amino group of one amino acid and a hydroxyl group from the carboxyl group of the other amino acid: Amino Acid 1: -NH2 – COOH Amino Acid 2: -NH2 – COOH Upon reaction, the following peptide bond is formed: (-NH2 – CO – NH – COOH) The general structure of a protein formed consists of multiple such peptide chains bonded together.

Draw the structure of a peptide formed from three different amino acids

First, let's define three different amino acids distinguished by different R groups R1, R2, and R3: Amino Acid 1: -NH2 – COOH (R1) Amino Acid 2: -NH2 – COOH (R2) Amino Acid 3: -NH2 – COOH (R3) Now, let's make a peptide from these three amino acids by going through the following condensation reactions: Amino Acid 1 + Amino Acid 2: -NH2 – CO – NH – COOH (R1 – R2) Amino Acids 1 & 2 + Amino Acid 3: -NH2 – CO – NH – CO – NH – COOH (R1 – R2 – R3) The resulting peptide can be represented as: R1 – R2 – R3

Understand N-terminus and C-terminus

N-terminus is the end of the peptide with a free amino group (-NH2), while the C-terminus is the end with a free carboxyl group (-COOH). In our R1 – R2 – R3 peptide, R1 would be the N-terminus, and R3 would be the C-terminus.

Calculate the number of different peptides

To find out the number of distinct peptides that can be formed from three different amino acids, we can use the permutation concept from combinatorics. The number of permutations for a set of three unique amino acids is 3! (factorial), which can be calculated as: 3! = 3 × 2 × 1 = 6 Thus, there are six distinct peptides that can be formed from the three unique amino acids.

Key concepts

Amino Acids

Amino acids are the building blocks of proteins and have a unique structure. Each amino acid includes an amino group \((\text{-NH}_2)\), a carboxyl group \((\text{-COOH})\), and a variable side chain known as the R group. The R group is what differentiates each of the 20 natural amino acids.
It can be as simple as a hydrogen atom or more complex, like a fully developed aromatic ring. The unique R group determines the properties and functions of the amino acid, which ultimately contributes to the protein's functionality in the body.
To understand amino acids deeply, it helps to:

• Recognize the basic structure of an amino acid.
• Know how the R group varies among different amino acids.
• Understand that amino acids link together to form proteins through condensation reactions.

Amino acids are vital for many biological processes and each has a specific role due to its unique R group. This role impacts how they interact with other molecules.

Condensation Polymerization

Condensation polymerization is the process by which amino acids are linked to form proteins. During this reaction, two amino acids join together, and a water molecule is released. This is why it's called a condensation reaction, as water is condensed out as a byproduct.
In this process, the amino group \((\text{-NH}_2)\) of one amino acid reacts with the carboxyl group \((\text{-COOH})\) of another. This reaction forms a special link known as a peptide bond, which is central to the structure of peptides and proteins.
Understanding condensation polymerization involves these key points:

• The nature of water release during the reaction.
• How peptide bonds form between amino acids.
• The repetitive linking of amino acids to create long protein chains.

By releasing a water molecule, a stable peptide bond forms, linking the amino acids in a potentially endless chain that becomes part of complex proteins. This process is essential for protein synthesis in living organisms.

Peptide Bonds

Peptide bonds are the links formed between amino acids in proteins. These bonds are crucial in biology as they connect amino acid sequences into stable structures.
When the amino group of one amino acid links with the carboxyl group of another, a peptide bond is formed through a condensation reaction, with water as a byproduct. This bond essentially connects the nitrogen atom of the amino group to the carbon atom of the carboxyl group.
Key aspects of peptide bonds include:

• The stability they bring to protein structures.
• The role of peptide bonds in forming long polypeptide chains.
• Understanding their influence on protein's three-dimensional shape.

Peptide bonds ensure that proteins can maintain their structure and function properly. The order in which amino acids are linked determines the protein's shape and activity, making peptide bonding fundamental in protein chemistry.