Unit 1: Chemistry of Life

Topic 1.1: Structure of Water and Hydrogen Bonding

Water is a fundamental molecule for life, and its unique properties arise from its molecular structure and hydrogen bonding. These properties are essential for the biological functions of cells and organisms.

• Polarity of Water: Water is a polar molecule, meaning it has a partial positive charge on one side (hydrogen atoms) and a partial negative charge on the other (oxygen atom). This polarity allows water to form hydrogen bonds with other water molecules and with other polar substances.

• Hydrogen Bonding: The attraction between the slightly positive hydrogen atom of one water molecule and the slightly negative oxygen atom of another creates hydrogen bonds. These are weaker than covalent bonds but are crucial for water's properties.

• Cohesion and Adhesion: Cohesion refers to water molecules sticking to each other, while adhesion refers to water molecules sticking to other substances. Both are due to hydrogen bonding.

• Surface Tension: The cohesive forces at the surface of water create a 'film' that allows small objects to rest on the surface without sinking.

• Biological Importance: Water's properties support processes such as nutrient transport, temperature regulation, and chemical reactions in living organisms.

Topic 1.2: Elements of Life

Living organisms are composed of a limited set of elements, with carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur being the most important for biological molecules.

• Macromolecules: Large molecules required by living organisms, including carbohydrates, proteins, lipids, and nucleic acids.

• Essential Elements:

  • Carbon: Forms the backbone of biological molecules; found in carbohydrates, proteins, lipids, and nucleic acids.

  • Nitrogen: Essential for building proteins and nucleic acids.

  • Phosphorus: Found in nucleic acids and certain lipids.

• Exchange with Environment: Organisms must obtain atoms and molecules from their environment to grow, reproduce, and maintain organization.

Unit 2: Chemistry of Life

Topic 1.3: Introduction to Biological Macromolecules

Biological macromolecules are large, complex molecules essential for life. They are formed by the polymerization of smaller subunits called monomers.

• Monomers and Polymers: Monomers are small molecules that can join together to form polymers through covalent bonds.

• Hydrolysis and Dehydration Synthesis:

  • Dehydration Synthesis: The process of joining two monomers by removing a water molecule.

  • Hydrolysis: The process of breaking a covalent bond in a polymer by adding a water molecule.

• Types of Macromolecules: Carbohydrates, proteins, nucleic acids, and lipids (though the molecular structure of specific lipids is often outside the introductory scope).

Topic 1.4: Properties of Biological Macromolecules

The structure and function of biological macromolecules are determined by the properties of their monomers and the bonds that connect them.

• Nucleic Acids: Polymers of nucleotide monomers. Each nucleotide consists of a five-carbon sugar (deoxyribose or ribose), a phosphate group, and a nitrogenous base (adenine, thymine, guanine, cytosine, or uracil). DNA and RNA differ in structure and function.

• Proteins: Polymers of amino acids. The sequence and chemical properties of amino acids determine the protein's structure and function. Amino acids have an amino group, a carboxyl group, and a variable R group.

• Carbohydrates: Polymers of sugar monomers. The structure of the sugar monomers determines the properties and functions of the carbohydrate.

• Lipids: Not true polymers, but large molecules assembled from smaller components. The degree of saturation of fatty acids affects the structure and function of lipids.

• Phospholipids: Contain polar regions that interact with water and nonpolar regions that are hydrophobic, important for cell membrane structure.

Topic 1.5: Structure and Function of Biological Macromolecules

The function of a biological macromolecule is directly related to its structure, which is determined by the sequence and chemical properties of its monomers.

• Directionality: Polymers such as nucleic acids and proteins have directionality, meaning they have distinct ends (e.g., 5' and 3' ends in nucleic acids, N-terminus and C-terminus in proteins).

• Nucleic Acids: DNA and RNA are synthesized by adding nucleotides to the 3' end of the growing strand. DNA is double-stranded and antiparallel, with base pairing (A-T, G-C) via hydrogen bonds.

• Proteins: The primary structure is the sequence of amino acids. Higher levels of structure (secondary, tertiary, quaternary) arise from folding and interactions between amino acids, determining the protein's function.

• Carbohydrates: Polysaccharides can be linear or branched. The structure affects their function (e.g., cellulose vs. starch vs. glycogen).

Topic 1.6: Nucleic Acids

Nucleic acids, including DNA and RNA, store and transmit genetic information. They have both structural similarities and differences.

• Components: Both DNA and RNA are composed of a sugar, a phosphate group, and a nitrogenous base. Nucleotides are joined by covalent bonds to form a sugar-phosphate backbone.

• Structural Differences:

  • DNA contains deoxyribose; RNA contains ribose.

  • DNA uses thymine; RNA uses uracil.

  • DNA is usually double-stranded and forms a double helix; RNA is usually single-stranded.

  • DNA strands are antiparallel in directionality.

• Functional Differences: DNA stores genetic information; RNA is involved in protein synthesis and gene regulation.

Table: Comparison of DNA and RNA