Question

The amino acid glycine can be condensed to form a polymer called polyglycine. Draw the repeating monomer unit.

Short answer

The repeating unit of polyglycine is "-NHCH_2CO-".

Step-by-step solution

Understand the Structure of Glycine

Glycine is the simplest amino acid with the chemical formula \( NH_2CH_2COOH \). It consists of an amino group \( (NH_2) \), a single hydrogen as the side chain (\( H \)), and a carboxyl group \( (COOH) \).

Recalling Polymerization

Polymerization involves linking monomers by forming bonds, releasing a small molecule such as water. For glycine, polymerization involves the amino and carboxyl groups reacting with each other.

Form the Peptide Bond

During polymerization to form polyglycine, a peptide bond is formed between the amino group of one glycine and the carboxyl group of another. This is done by a condensation reaction.

Draw the Repeating Unit

The repeating monomeric unit for polyglycine is a segment of the polymer chain in which one glycine's carboxyl group is connected to the next glycine's amino group through a peptide bond. The structure of one repeating unit, which is "-NHCH_2CO-", shows the formation of a peptide bond by the removal of \( H_2O \).

Key concepts

Amino Acid

Amino acids are the building blocks of proteins and play a crucial role in the structure and function of living cells. They are organic compounds characterized by the presence of two functional groups: an amino group (-NH₂) and a carboxyl group (-COOH). The core structure of an amino acid includes a central carbon atom, known as the alpha carbon ( (C _α), to which an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group) are attached.

The R group varies between different amino acids and is responsible for the unique characteristics of each one. Amino acids are essential for life as they are involved in various metabolic pathways, and are key components in the synthesis of neurotransmitters and hormones.

• There are 20 standard amino acids commonly found in proteins.
• The side chain (R group) dictates the properties and functions of the amino acid.

Peptide Bond

A peptide bond is a special kind of covalent chemical bond that forms between two amino acids. This bond is essential for protein synthesis as it connects amino acids in a linear sequence to form polypeptides or proteins. The formation of a peptide bond occurs through a reaction between the amino group of one amino acid and the carboxyl group of the adjacent amino acid.

This reaction results in the release of a water molecule ( (H₂O)), which is characteristic of a condensation reaction. The newly formed peptide bond is represented in chemical notation as (-C(=O)NH-), indicating a linkage between the carbonyl and nitrogen atoms.

Useful points to remember about peptide bonds include:

• They are rigid and planar due to partial double-bond character, providing structural stability.
• Peptide bonds are central to forming the primary structure of proteins, which is the linear sequence of amino acids.

Glycine

Glycine is one of the simplest and smallest amino acids in existence, with the chemical formula (NH₂CH₂COOH). It has a straightforward structure, consisting of an amino group, a carboxyl group, and a single hydrogen atom as its side chain, making its R group just hydrogen. This simplicity lends glycine unique properties, such as being achiral, since it does not have four different substituents attached to its central carbon.

Despite its simplicity, glycine plays a significant role in the structure and function of proteins. It contributes to the flexibility of collagen and is involved in various biological processes. Some key features of glycine include:

• It is non-polar and therefore hydrophobic, though it can fit into tight spaces in proteins due to its small size.
• Glycine is often found in flexible regions of proteins, adding flexibility to their structure.

Condensation Reaction

A condensation reaction is a fundamental type of chemical reaction that involves the joining of two molecules (or functional groups) with the concurrent loss of a small molecule, which is often water. In the context of amino acid polymerization, condensation reactions play a pivotal role in forming peptide bonds.

During peptide bond formation, the carboxyl group (COOH) of one amino acid reacts with the amino group (NH₂) of another. This reaction eliminates a water molecule and establishes a robust, covalent peptide bond, integral to constructing polypeptides or proteins.

Condensation reactions are vital not only for forming peptide bonds but also in various other polymerization processes and biological mechanisms, such as the synthesis of nucleic acids and other biopolymers. It's essential to grasp the importance of these reactions as they underpin many synthetic processes in biochemistry.