Macromolecules

In one of the previous lessons, we discussed how atoms bond with other atoms to form molecules, and we also discussed four classes of organic molecules: proteins, carbohydrates, nucleic acids, and lipids. All these organic molecules are macromolecules.

Organic macromolecules play a critical role in cellular processes and perform other important functions. As the name suggests, a macromolecule is a large molecule formed by repetitively linking smaller subunits called monomers. A monomer is defined as a molecule that can bond with identical molecules to form larger molecules. These subunits join together through chemical bonds, creating long chains or complex structures. The number of molecules in a macromolecule can vary depending on its specific structure and composition. The number of monomers within a macromolecule determines its size and molecular weight.

In the case of proteins, the macromolecule is composed of chains of amino acids. The number of amino acids in a protein can range from a few dozen to several thousand, with each amino acid representing a molecule within the protein chain. Consequently, a protein macromolecule can consist of hundreds or thousands of individual amino acid molecules.

Similarly, nucleic acids like DNA or RNA are composed of linear chains of nucleotide monomers. A typical DNA molecule may contain millions to billions of nucleotides, resulting in a vast number of individual nucleotide molecules within the macromolecule. Carbohydrates and polysaccharides form macromolecules by linking monosaccharide units. The size and complexity of these molecules can vary greatly, with some polysaccharides consisting of hundreds or thousands of monosaccharide molecules.

The specific number of molecules within a macromolecule depends on factors such as the length of the chain, the type of monomers, and the overall structure of the macromolecule.

1. Proteins: As discussed previously, proteins are macromolecules made up of amino acids. Amino acids are organic compounds that consist of an amino group (-NH ₂), a carboxyl group (-COOH), and a unique side chain
(-R group). There are 20 different amino acids commonly found in proteins, each with its own specific properties. Proteins are involved in a wide range of functions, including enzymatic reactions, structural support, transport, and signaling. The human body is mainly made up of proteins. Proteins are also responsible for the transportation of small molecules within the body. For example, hemoglobin is a protein present in red blood cells that transports oxygen from the lungs to every single cell inside the body. Proteins also transport small water-soluble molecules into or out of cells.

2. Nucleic Acids: Nucleic acids are responsible for storing and transmitting genetic information. There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA contains the instructions for building and maintaining an organism, while RNA plays a crucial role in protein synthesis.

3. Carbohydrates: Carbohydrates are macromolecules composed of carbon, hydrogen, and oxygen. They come from food and mainly serve as a primary energy source for humans. Examples of carbohydrates include bread, pasta, rice, or sugar. Carbohydrates can exist as simple sugars (monosaccharides), such as glucose and fructose, or as complex structures (polysaccharides), such as starch and cellulose.

4. Lipids: Lipids are a diverse group of macromolecules that are hydrophobic (repel water). They include fats, oils,

phospholipids, and steroids. Lipids serve as energy stores, insulation, and structural components of cell membranes.

Macromolecules are essential for the structure, function, and regulation of cells and organisms. The specific arrangement and interactions between their subunits give rise to their unique properties and capabilities. Understanding macromolecules and their functions is not only crucial in the field of medicine but also important in other fields such as biochemistry and molecular biology. It helps unravel the complexities of life and opens avenues for research and innovation.