Biochemistry

Biochemistry is a fundamental area of biology that examines the chemical reactions of biological molecules. It focuses on the sum total of all chemical reactions within a living organism, known as metabolism. A key characteristic of biochemistry is the close link between the structures of molecules and their functions. The sources emphasize that while there is a vast variety of life, the biochemical basis of life is similar for all living things, suggesting a common ancestor and providing evidence for evolution.

The main groups of biological molecules that make up all cells and organisms, as covered in biochemistry, include carbohydrates, lipids, proteins, and nucleic acids. Water and inorganic ions are also crucial components.

• General Principles

  • Most large biological molecules are polymers, which are molecules made from a large number of repeating monomers (smaller units) joined together.

  • These monomers are joined by condensation reactions, which form a chemical bond and eliminate a molecule of water.

  • The reverse process, hydrolysis reactions, breaks bonds by adding water, converting polymers back into their monomers.

  • Macromolecules are very large molecules (1000 or more atoms), which can include polymers like polysaccharides, proteins, and nucleic acids. Lipids, while large, are typically not described as macromolecules or polymers in the same way as their subunits are not repeating identical units.

• Carbohydrates

  • Elements and Formula: Contain carbon, hydrogen, and oxygen, with hydrogen and oxygen in a 2:1 ratio (as in water), often represented by Cₓ(H₂O)ᵧ.

  • Monomers: The simplest carbohydrates are monosaccharides, such as glucose, fructose, and galactose.

  • Polymers:

    • Disaccharides are formed from two monosaccharides joined by a glycosidic bond (e.g., maltose, sucrose, lactose).

    • Polysaccharides are formed from many monosaccharides joined by glycosidic bonds.

  • Examples and Functions:

    • Starch (amylose and amylopectin) and glycogen are energy storage materials in plants and animals, respectively. Their branched structures allow for quick glucose release.

    • Cellulose is a major component of plant cell walls, providing structural support due to its structure formed from beta-glucose units.

  • Biochemical Tests: The Benedict's test is used for reducing sugars (color change from blue to green, yellow, orange, or red precipitate for positive results). The iodine test is used for starch (blue-black indicates positive).

• Lipids

  • General Characteristics: Insoluble in water due to hydrophobic hydrocarbon tails.

  • Types and Structure:

    • Triglycerides consist of one glycerol molecule with three fatty acids attached via ester bonds. They are non-polar.

    • Phospholipids have a glycerol molecule, two fatty acids, and a phosphate group. The phosphate head is hydrophilic (polar) and the fatty acid tails are hydrophobic (non-polar).

  • Functions:

    • Triglycerides are used for energy storage, insulation, and buoyancy.

    • Phospholipids are vital for forming the bilayer of cell membranes, acting as a barrier to water-soluble substances and allowing for compartmentalization within cells.

  • Biochemical Test: The emulsion test (shaking with ethanol, then adding to water; a milky white emulsion indicates lipid presence).

• Proteins

  • Elements: Contain carbon, hydrogen, oxygen, and nitrogen, and usually sulfur.

  • Monomers: Amino acids are the monomers from which proteins are made. There are 20 common amino acids, differing only in their side (R) group.

  • Formation: Amino acids join together by condensation reactions to form peptide bonds, creating dipeptides (two amino acids) or polypeptides (many amino acids). A functional protein may contain one or more polypeptides.

  • Protein Structure (Four Levels):

    • Primary structure: The unique sequence of amino acids in the polypeptide chain.

    • Secondary structure: Regular coiling (α-helix) or folding (β-pleated sheet) of the polypeptide chain, held by hydrogen bonds between amino acids.

    • Tertiary structure: The complex 3D folding of the polypeptide chain, held by hydrogen bonds, ionic bonds, and disulfide bridges (covalent bonds between cysteine R groups). This structure determines the protein's specific shape and function.

    • Quaternary structure: The association of two or more polypeptide chains to form a functional protein (e.g., hemoglobin).

  • Types and Functions: Proteins have a huge variety of functions, including acting as enzymes (biological catalysts), hormones (e.g., insulin), structural components (e.g., collagen, keratin), transport molecules (e.g., hemoglobin), and antibodies for defense.

  • Biochemical Test: The Biuret test is used for proteins (blue indicates negative, purple indicates positive).

• Nucleic Acids (DNA and RNA)

  • Monomers: Made from nucleotides, which consist of a pentose sugar, a phosphate group, and a nitrogenous base. Phosphate ions are important components of DNA and ATP.

  • Functions: DNA (deoxyribonucleic acid) holds genetic information in all living cells, while RNA (ribonucleic acid) transfers genetic information from DNA to the ribosomes for protein synthesis.

  • Differences from DNA: RNA has ribose sugar instead of deoxyribose, uracil instead of thymine, and is typically single-stranded, whereas DNA is a double helix.

• Water

  • Properties: Water is a polar molecule due to uneven distribution of charge, leading to the formation of hydrogen bonds between water molecules. These bonds give water properties like high specific heat capacity, high latent heat of vaporisation, and good solvent action.

  • Roles in Organisms: Essential as a solvent for transport of substances (e.g., in blood plasma and tissue fluid), for temperature regulation through sweating and transpiration, and for turgor in plant support.

• Inorganic Ions

  • Definition and Occurrence: Ions that do not contain carbon and occur in solution in the cytoplasm of cells and body fluids.

  • Specific Roles: They have specific roles depending on their properties. Examples include iron ions in hemoglobin for oxygen transport, hydrogen ions and pH regulation for enzyme activity, sodium ions in glucose and amino acid co-transport, and phosphate ions as components of DNA and ATP.

• Enzymes (As a central component of biochemistry)

  • Enzymes are globular proteins that act as biological catalysts.

  • They speed up metabolic reactions without being permanently changed themselves.

  • Enzymes have a specific active site where substrate molecules bind to form an enzyme-substrate complex, which lowers the activation energy of the reaction.

  • Their high specificity is due to their tertiary structure.

  • Enzyme action can be intracellular (within cells) or extracellular (outside cells).

  • Factors like temperature, pH, substrate concentration, and inhibitors affect enzyme activity.