Chemistry of Life & Biological Molecules: Foundations of General Biology

Chapter 1 – Chemistry of Life & Biological Molecules

Elements of Life

Living organisms are composed of matter, which consists of elements essential for life. These elements combine to form molecules that carry out biological functions.

• Essential elements: Elements required by an organism to live a healthy life and reproduce (e.g., carbon, hydrogen, oxygen, nitrogen).

• Trace elements: Elements required in minute quantities (e.g., iron, iodine).

Structure of Atoms

Atoms are the basic units of matter, composed of three subatomic particles:

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles found in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

Atoms combine in fixed ratios to form molecules. The arrangement of electrons determines chemical bonding and reactivity.

Chemical Bonds

Chemical bonds store energy and determine the structure of molecules. The main types include:

• Ionic Bonds: Formed by the electrical attraction between oppositely charged ions (cations and anions).

• Covalent Bonds: Formed when two atoms share one or more pairs of valence electrons.

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

• Van der Waals Interactions: Weak electrical forces that attract molecules to one another; present in all atoms/molecules.

Bond Type	Strength	Example
Ionic	Strong (in dry conditions)	NaCl (table salt)
Covalent	Very strong	H2O (water)
Hydrogen	Weak (individually)	Between water molecules
Van der Waals	Very weak	Gecko feet adhesion

Water: Properties and Biological Importance

• Polarity: Water molecules are polar, with a partial negative charge near the oxygen atom and a partial positive charge near the hydrogen atoms.

• Hydrogen Bonding: Responsible for water’s unique properties, such as cohesion, adhesion, and high specific heat.

Key Properties of Water

• Moderation of Temperature: Water absorbs and releases heat slowly, helping to stabilize temperatures (first law of thermodynamics).

• Cohesion: The attraction between water molecules, allowing them to stick together (important for transport in plants).

• Adhesion: The clinging of water molecules to other substances (e.g., cell walls).

• Solvent of Life: Water dissolves many substances, making it an excellent medium for biochemical reactions.

Solution: A homogeneous mixture of two or more substances. Solvent: The dissolving agent (e.g., water). Solute: The substance dissolved.

Formation and Modifications of Biological Molecules

Organic molecules are based on carbon, which forms a variety of chain and ring structures. These molecules are essential for life’s complexity.

Major Classes of Biological Molecules

• Carbohydrates: Contain carbon, hydrogen, and oxygen in a 1:2:1 ratio. Include sugars (monosaccharides) and polymers (polysaccharides). Main function: energy storage and structural support.

• Lipids: Water-insoluble molecules composed mainly of hydrocarbons. Types include:

  • Fats: Store energy.

  • Phospholipids: Form cell membranes.

  • Steroids: Hormones that regulate cellular activity.

• Proteins: Polymers of amino acids that perform a wide variety of functions in organisms (e.g., enzymes, structural proteins).

• Nucleic Acids: Macromolecules assembled from nucleotides. Store and transmit hereditary information.

Amino Acids and Proteins

• All organisms use 20 different amino acids.

• Peptide Bonds: Covalent bonds that link amino acids to form proteins.

Nucleic Acids

• DNA (Deoxyribonucleic Acid): Stores hereditary information responsible for inherited traits in all living organisms.

• RNA (Ribonucleic Acid): Hereditary molecule of another large group of viruses; involved in protein synthesis and gene regulation.

Nucleotides

Nucleotides are the monomers of nucleic acids, each consisting of three covalently bonded parts:

• Nitrogenous base

• 5-carbon, ring-shaped sugar

• 1-3 phosphate groups

Molecule	Structure	Function
DNA	Double helix of two nucleotide chains wrapped around each other (resembles a twisted ladder)	Stores genetic information
RNA	Single-stranded polynucleotide chain; can fold back on itself to form double-helical regions	Protein synthesis, gene regulation

Example: The sequence of nucleotides in DNA determines the sequence of amino acids in proteins, which in turn determines protein structure and function.

Additional info: The properties of water and the diversity of carbon-based molecules are foundational to all biological processes, influencing everything from cell structure to metabolism.