Chemistry of Life

Structure of Water and Hydrogen Bonding

Water is essential for life due to its unique chemical properties, which arise from its polarity and ability to form hydrogen bonds. These properties influence biological functions and interactions within living systems.

• Polarity: Water molecules are polar because of the unequal sharing of electrons between hydrogen and oxygen atoms, resulting in partial positive and negative charges. This polarity enables water to form hydrogen bonds with other molecules.

• Hydrogen Bonding: Hydrogen bonds are weak attractions between the hydrogen atom of one water molecule and the oxygen atom of another. These bonds are responsible for many of water's unique properties.

• High Specific Heat Capacity: Water can absorb or release large amounts of heat with minimal temperature change, helping organisms maintain stable internal temperatures.

• High Heat of Vaporization: Water requires significant energy to evaporate, allowing for evaporative cooling (e.g., sweating in mammals).

• Cohesion and Adhesion: Hydrogen bonds cause water molecules to stick together (cohesion) and to other surfaces (adhesion), contributing to surface tension and capillary action.

Example: Water's cohesion enables the transport of water in plants through xylem vessels.

Elements of Life

Living organisms are composed of a limited set of elements, which are used to build macromolecules necessary for life. These elements are obtained from the environment and assembled into complex biological molecules.

• Major Elements: Carbon, hydrogen, and oxygen are the most abundant elements in biological molecules.

• Other Essential Elements:

  • Sulfur: Incorporated into certain amino acids in proteins.

  • Phosphorus: Found in phospholipids and nucleic acids.

  • Nitrogen: Present in amino acids and nucleic acids.

Example: Phosphorus is a key component of ATP, the energy currency of the cell.

Introduction to Macromolecules

Macromolecules are large, complex molecules essential for life. They are formed and broken down through specific chemical reactions involving water.

• Hydrolysis: A reaction in which water is used to break covalent bonds in polymers, resulting in smaller molecules. The hydrogen ion (H+) from water attaches to one monomer, and the hydroxyl group (OH-) attaches to the other.

• Dehydration Synthesis: A reaction in which two monomers are joined by removing a water molecule, forming a covalent bond. This process is also known as condensation and leads to polymerization.

Example: The breakdown of starch into glucose monomers during digestion involves hydrolysis.

Equation:

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components in living organisms.

• Monosaccharides: Simple sugars (e.g., glucose) are the monomers of carbohydrates.

• Polysaccharides: Complex carbohydrates formed by covalent bonds between monosaccharides. They can be linear or branched.

• Functions: Energy storage (starch in plants, glycogen in animals), structural support (cellulose in plants).

Examples: Cellulose, starch, and glycogen are common polysaccharides.

Lipids

Lipids are hydrophobic, nonpolar molecules that play diverse roles in biological systems. Their structure and function depend on the arrangement of their subcomponents, particularly fatty acids.

• Fatty Acids:

  • Saturated: Only single bonds between carbon atoms; typically solid at room temperature.

  • Unsaturated: At least one double bond, causing kinks in the chain; more unsaturated lipids are liquid at room temperature.

• Functions of Lipids:

  • Fats: Energy storage, insulation, and cell function.

  • Steroids: Hormones regulating growth, development, metabolism, and homeostasis.

  • Cholesterol: Structural stability in animal cell membranes.

  • Phospholipids: Form lipid bilayers in plasma and cell membranes.

Example: Phospholipids are the main component of cell membranes, forming a bilayer that separates the cell from its environment.

Proteins

Proteins are complex macromolecules composed of amino acids. They perform a wide range of functions, including catalysis, structural support, transport, and regulation.

• Amino Acid Structure: Each amino acid has a central carbon atom bonded to a hydrogen atom, a carboxyl group (−COOH), an amine group (−NH2), and a variable R group.

• Peptide Bonds: Amino acids are linked by peptide bonds formed between the carboxyl group of one amino acid and the amine group of another.

• R Group Properties: R groups can be hydrophobic/nonpolar, hydrophilic/polar, or ionic, influencing protein structure and function.

• Protein Structure Levels:

  • Primary Structure: Sequence of amino acids in a polypeptide.

  • Secondary Structure: Local folding into alpha-helices and beta-pleated sheets via hydrogen bonding.

  • Tertiary Structure: Three-dimensional shape formed by hydrogen bonds, hydrophobic interactions, ionic interactions, and disulfide bridges.

  • Quaternary Structure: Interaction between multiple polypeptide chains.

• Function: The structure at all levels determines the protein's function.

Example: Hemoglobin is a protein with quaternary structure, consisting of four polypeptide chains that transport oxygen in blood.

Additional info: Nucleic acids (DNA and RNA) are also macromolecules essential for information storage and transmission, though detailed structure is not covered in the provided content.