Biochemistry is the study of chemical processes that occur within living organisms. It explains how cells, tissues, and organs function at the molecular level. The field includes several major branches such as structural biochemistry, metabolic biochemistry, molecular biology, enzymology, and clinical biochemistry. Understanding biochemistry is important because it helps explain disease mechanisms, supports drug development, guides nutrition and agriculture, and forms the foundation of biotechnology and forensic science.
Biomolecules are the substances that make up living cells, and they fall into four major categories: carbohydrates, proteins, lipids, and nucleic acids. Carbohydrates serve as the main energy source in the body and exist as simple sugars such as glucose and fructose, double sugars like sucrose and lactose, and complex carbohydrates such as starch, glycogen, and cellulose. Proteins are composed of amino acids and have four levels of structure—primary, secondary, tertiary, and quaternary. They carry out essential functions such as catalysis of reactions by enzymes, transport of gases (hemoglobin), structural support (collagen), defense (antibodies), and hormonal regulation.
Lipids are hydrophobic molecules including fatty acids, triglycerides, phospholipids, and steroids. They store long-term energy, form cell membranes, insulate the body, and act as precursors for hormones such as testosterone and estrogen. Nucleic acids, which include DNA and RNA, store genetic information and control the synthesis of proteins. DNA carries the hereditary code, while RNA helps convert genetic information into proteins.
Water is a critical biological solvent. Its key properties include high heat capacity, high surface tension, cohesion, adhesion, and its ability to dissolve many substances. Biological systems rely on a stable pH environment. The pH scale measures acidity, and buffers such as the bicarbonate buffer system help maintain constant pH levels in the body to prevent harmful fluctuations.
Enzymes are biological catalysts that speed up chemical reactions without being consumed in the process. They are highly specific, function best at optimal pH and temperature, and can be inhibited by competitive or non-competitive inhibitors. Enzyme kinetics involves understanding Vmax (maximum reaction rate) and Km (substrate affinity). A low Km means the enzyme has high affinity for its substrate.
Metabolism refers to the sum of all chemical reactions in the body. It is divided into catabolism, which breaks down molecules to release energy, and anabolism, which builds complex molecules using energy. ATP is the cell’s main energy currency and is produced during glycolysis, the Krebs cycle, and the electron transport chain. Glycolysis occurs in the cytoplasm and converts glucose to pyruvate while producing small amounts of ATP. The Krebs cycle takes place in the mitochondria and produces NADH and FADH₂. The electron transport chain generates most of the ATP through oxidative phosphorylation.
Protein metabolism includes processes such as transamination, deamination, and the urea cycle, which help manage amino acids and remove toxic ammonia. Lipid metabolism involves β-oxidation, the process of breaking fatty acids into acetyl-CoA for energy, and lipogenesis, which is the synthesis of fats mainly in the liver. Nucleic acid metabolism covers DNA replication, transcription, and translation. Replication is semi-conservative and involves enzymes like helicase and DNA polymerase. Transcription converts DNA into mRNA, and translation converts mRNA into protein at the ribosomes.
Vitamins act as cofactors for biochemical reactions. Vitamin C supports collagen formation, B-complex vitamins assist enzymes in metabolism, vitamin D regulates calcium absorption, and vitamin K plays a role in blood clotting. Hormones such as insulin, glucagon, steroid hormones, and neurotransmitters help regulate biological processes through cell-signaling pathways.
Laboratory techniques commonly used in biochemistry include spectrophotometry, chromatography, electrophoresis, centrifugation, titration, and microscopy. These techniques help scientists analyze molecules and understand biochemical reactions. Biochemistry has many applications including medical diagnostics, treatment of diseases, nutrition science, agriculture, forensic investigations, and biotechnology such as vaccine development and genetic engineering.