# 2.1 BIOCHEMISTRY / MOLECULAR BIOLOGY The study of the chemical basis of life, encompassing the composition, structure, and chemical processes of living organisms. ## Biochemistry Biochemistry is the study of the *composition* and *structure* of different chemical compounds found in living organisms and the chemical processes that occur within them. It is a sub-discipline of both **biology** and **chemistry**. Biochemistry applies the principles and techniques of chemistry to understand and solve biological problems. All living organisms are composed of specific chemical compounds, which can be classified into two main groups: 1. **Organic Compounds:** Carbohydrates, proteins, lipids, and nucleic acids. 2. **Inorganic Compounds:** Water, acids, bases, and salts. ### Chemical Composition of Cells The chemical composition of a cell varies between different types of organisms, such as bacteria and mammals, though water remains the most abundant component in both. | Component | Bacterial Cell (%) | Mammalian Cell (%) | | :--- | :--- | :--- | | Water | 70 | 70 | | Proteins | 15 | 18 | | Carbohydrates | 3 | 4 | | Lipids | 2 | 3 | | DNA | 1 | 0.25 | | RNA | 6 | 1.1 | | Other organic molecules | 2 | 2 | | Inorganic ions | 1 | 1 | ### Metabolism The sum total of all chemical reactions taking place within a cell is called **metabolism**. It consists of two coordinated processes: * **Anabolism:** The synthesis of complex molecules from simpler ones, usually requiring energy (e.g., photosynthesis). * **Catabolism:** The breakdown of complex molecules into simpler ones, usually releasing energy (e.g., cellular respiration). ## Molecular Biology Molecular biology is a specialized branch of biochemistry that focuses on the molecular basis of biological activity. This includes the study of the structure, function, and interactions of macromolecules like DNA, RNA, and proteins. These macromolecules carry out genetic processes in living organisms. While sometimes used interchangeably, molecular biology is considered a more focused field *within* the broader scope of biochemistry. It provides essential evidence for the unity of life and evolution. ## Comparison Table | Feature | Biochemistry | Molecular Biology | | :--- | :--- | :--- | | **Primary Focus** | The chemistry of biological processes and molecules (metabolism, enzymes, etc.). | The structure and function of macromolecules (DNA, RNA, proteins) and their role in genetic processes. | | **Scope** | Broad; covers all chemical reactions in living organisms. | Specialized; focuses on the flow of genetic information. | | **Relationship** | Molecular biology is a specialized sub-field of biochemistry. | | ## Importance of Carbon Carbon is the basic element of organic compounds. Due to its tetravalent nature, it can form stable covalent bonds with other carbon atoms, hydrogen, oxygen, nitrogen, and sulfur, creating the complex "backbone" of life's molecules.