For each of the four major classes of organic compounds, identify the subunits. Describe the general process by which all of these subunits are joined together to form larger molecules.

The four major classes of organic compounds are carbohydrates, lipids, proteins, and nucleic acids. Each class has its unique subunits that are joined together to form larger molecules.

1. Carbohydrates: The subunits of carbohydrates are monosaccharides, which are simple sugars such as glucose, fructose, and galactose. These monosaccharides can join together through a process called dehydration synthesis or condensation reaction. During this reaction, a water molecule is removed, and a glycosidic bond is formed between the subunits, resulting in the formation of larger carbohydrates such as disaccharides (e.g., sucrose, lactose) or polysaccharides (e.g., starch, cellulose).

2. Lipids: Lipids are composed of different subunits based on their specific type. The subunits can include glycerol and fatty acids for triglycerides, phosphoric acid, glycerol, and fatty acids for phospholipids, and cholesterol for steroids. Lipids are formed through the process of esterification or condensation reaction. In this process, a carboxyl group of a fatty acid reacts with an alcohol group of a glycerol or another molecule, creating an ester bond and forming larger lipid molecules.

3. Proteins: Proteins are made up of subunits called amino acids. There are 20 different amino acids that can be combined in various sequences to form proteins. The process by which amino acids are joined together is called peptide bond formation or a condensation reaction. During this reaction, the carboxyl group of one amino acid reacts with the amino group of another amino acid, releasing a water molecule and forming a peptide bond. These peptide bonds link amino acids together, and the sequential arrangement of amino acids results in the formation of polypeptide chains, which then fold and interact to form functional proteins.

4. Nucleic Acids: Nucleic acids are composed of subunits called nucleotides. Nucleotides consist of three components: a sugar molecule (ribose in RNA or deoxyribose in DNA), a phosphate group, and a nitrogenous base (adenine, thymine/uracil, guanine, or cytosine). The nucleotides are linked together through a process called phosphodiester bond formation or condensation reaction. In this reaction, the phosphate group of one nucleotide bonds with the sugar molecule of another nucleotide, forming a phosphodiester bond and creating a backbone structure. The sequence of the nitrogenous bases along the backbone forms the genetic information stored in nucleic acids.

In summary, the joining of subunits in organic compounds involves condensation reactions where a small molecule, such as water, is removed. This process allows for the formation of larger molecules like disaccharides, polysaccharides, triglycerides, phospholipids, polypeptides, and nucleic acids with their respective subunits.