Question

Draw a representation of the peptide linkage that holds amino acids together in polypeptide chains.

Short answer

A peptide bond is formed between two amino acids when the amino group (NH₂) of one amino acid reacts with the carboxyl group (COOH) of the other amino acid through a dehydration synthesis reaction. The resulting peptide linkage can be represented as follows: AA-COOH + H₂N-BB → AA-CO-NH-BB + H₂O Here, `-CO-NH-` is the peptide linkage connecting the amino acids AA and BB in a polypeptide chain.

Step-by-step solution

Understand the structure of an amino acid

An amino acid consists of three main parts: a central carbon atom (C) bonded to an amino group (NH₂), a carboxyl group (COOH), and a side chain (R) which differs for each amino acid. We will represent amino acids as AABBs, with AA and BB representing two different amino acids.

Dehydration synthesis reaction

When two amino acids bond together, they undergo a dehydration synthesis (also called a condensation reaction). In this process, the amino group (NH2) of one amino acid (AA) reacts with the carboxyl group (COOH) of the other amino acid (BB), forming a peptide bond, which involves the removal of a water molecule (H2O).

Draw the peptide bond between two amino acids

Show the amino acids AABB and the peptide bond between them: AA-COOH + H₂N-BB → AA-CO-NH-BB + H₂O In this representation, `-CO-NH-` is the peptide linkage which connects the two amino acids (AA and BB) together in a polypeptide chain.

Key concepts

Amino Acids

Amino acids are the building blocks of proteins, like the individual bricks in a wall. Each amino acid contains a central carbon atom, known as the $\alpha$-carbon, to which an amino group ($-N{H}_2$), a carboxyl group ($-COOH$), a hydrogen atom, and a distinctive side chain (represented as $-R$ in chemistry) are attached.

The side chain $R$ is what makes each amino acid unique, with properties that can be acidic, basic, hydrophobic, or hydrophilic. These properties influence how amino acids interact with each other and the environment within a protein's structure, ultimately determining the protein's function and shape. Magnificently, there are 20 different amino acids in the human body that combine to form a myriad of proteins, each serving a specific role in our physiological functions.

For students learning about amino acids, it's essential to recognize their general structure to understand how they connect and interact to form proteins. Picturing them as individual beads on a string can help visualize how they come together to create more complex structures like polypeptide chains.

Polypeptide Chains

Polypeptide chains are the strings of beads where amino acids are the beads. Imagine each amino acid connecting one after another in a long, sometimes complex, strand. These polypeptide chains fold and curl into specific three-dimensional structures, which are the functional proteins.

The order of amino acids in a polypeptide chain is determined by the genetic code, and this sequence is crucial because it dictates the protein's structure and function. Proteins can consist of one or multiple polypeptide chains that twist and coil around each other. For instance, some proteins are like little machines within cells, with sections that move to perform tasks such as muscle contraction or transporting substances across cell membranes.

Students might find it useful to liken the formation of a polypeptide chain to assembling a model kit where each piece has to be in a certain place for the final product to work. Remembering that sequence and structure go hand-in-hand can clue students into understanding how changes at the genetic level can greatly impact a protein's function or lead to diseases.

Dehydration Synthesis

Dehydration synthesis, also known as a condensation reaction, is the process by which two molecules are joined together with the removal of water. In the case of amino acids, this is how they connect to form the polypeptide chains.

To visualize this process, think of two amino acids approaching each other, with one carrying a flag labeled $-OH$ (from the carboxyl group) and the other waving a flag labeled $-H$ (from the amino group). When they get close enough, they shake hands, and the $-OH$ and $-H$ flags combine to form $H_{2}O$—water, which is then released. This 'handshake' is the peptide bond forming, and it's this linkage that connects all amino acids in a polypeptide chain.

For students, it's important to understand that each peptide bond formation releases a molecule of water, indicating why the process is termed 'dehydration' synthesis. Grasping this concept is foundational in biochemistry, where dehydration synthesis is a frequent and essential type of chemical reaction. Appreciating the simplicity—and the necessity—of losing a molecule of water to build larger structures can make learning the intricacies of biochemistry much more approachable.