Molecular Heredity: Carbon, Carbohydrates, and Proteins
Molecular Basis of Heredity
Carbon: The majority of the primary constituents of organisms are composed of carbon atoms. Carbon forms almost 18% of living matter. Compounds that have carbon are called organic compounds. In nature, carbon is associated with hydrogen (H), nitrogen (N), and oxygen (O). It has a valency of 4. The organic compounds are found in cells and tissues, affect metabolism, and are a source of energy in biological processes. Carbon has two reasons to form a variety of compounds:
- The ability to form stable chains, since carbon atoms joined by single bonds are very strong.
- The ability to form multiple bonds.
Polymers or macromolecules: Consist of structural units (monomers), which are repeated with a predetermined pattern, therefore they are called polymers. They possess a high molecular mass (10,000 amu) as they consist of thousands of atoms, so they are called macromolecules.
Biopolymers are those polymers that are found in nature (wood, latex, cotton). These are also known as polysaccharides, proteins, and nucleic acids. Biopolymers (except for most carbohydrates) have monomers with unequal structures. Humans have created synthetic polymers, but these differ from biopolymers in structure. Synthetic polymers have one or two repeating monomer units along the chain. The thousands of organic compounds that make up living things are composed of at least 40 small and simple monomers.
Carbohydrates
Carbohydrates are called so since most of them have the general formula (CH2O)n. They are also known as glycosides or sugars. The smallest carbohydrates have 3 to 7 carbon atoms. They are known as monosaccharides. The most important are the pentoses (ribose and deoxyribose) and hexoses (glucose and fructose). The union of two monosaccharides results in a disaccharide by glycosidic bonds (sucrose or table sugar). When more than two monosaccharides are involved, they are called polysaccharides.
Glucose
Glucose is the monomer in the three most important polysaccharides: cellulose, starch, and glycogen.
- Cellulose: A linear chain polymer consisting of 3,000 glucose units, it is the component of the plant wall and is the most widely used composite in the wood and cotton industries.
- Starch is found in two forms:
- Amylose: Small, unbranched molecules with 60 to 300 glucose units.
- Amylopectin: Branched molecules with 300 to over 5,000 glucose units.
- Glycogen: A branched macromolecule consisting of glucose units, it stores energy in animals and accumulates in organs like the liver and muscles.
Functions of Carbohydrates
Carbohydrates provide energy to cells (e.g., DNA). In plants and insects, they fulfill structural functions.
Note: Humans do not have enzymes that degrade chitin and cellulose (insoluble polysaccharides) but do have some that degrade starch (soluble polysaccharides).
Proteins
Bacteria have approximately 3,000 proteins, whereas humans have approximately 30,000 proteins. These are macromolecules formed by monomeric units (amino acids). Amino acids have a carboxyl group (COOH) and an amino group (NH2) bound to the same carbon. To be assimilated, proteins should be degraded into their constituent amino acids. Of all amino acids, only 20 are part of proteins. Of these 20, only 10 are considered non-essential because they can be synthesized by the body and do not need to be included in the diet.
- Non-essential amino acids: Alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine.
- Essential amino acids: Arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine.