From Atoms to Macromolecules

Atoms and Their Structure

Atoms are the fundamental units of matter, forming the basis for all chemical substances, including those essential to life and microbiology.

• Atom: The smallest unit of an element that retains the properties of that element. Atoms consist of three main subatomic particles:

  • Protons: Positively charged particles located in the nucleus.

  • Neutrons: Neutral particles also found in the nucleus.

  • Electrons: Negatively charged particles orbiting the nucleus.

• Atomic Number (Z): The number of protons in an atom's nucleus; determines the element's identity.

• Atomic Mass (A): The sum of protons and neutrons in the nucleus.

• Chemical Symbol: One- or two-letter abbreviation representing an element (e.g., H for hydrogen, C for carbon).

Example: Carbon has 6 protons, 6 neutrons, and 6 electrons. Its atomic number is 6, and its atomic mass is approximately 12.

Ions and Isotopes

Atoms can gain or lose electrons or neutrons, resulting in ions or isotopes, respectively.

• Anion: A negatively charged ion formed when an atom gains electrons.

• Cation: A positively charged ion formed when an atom loses electrons.

• Isotope: Atoms of the same element with different numbers of neutrons. Isotopes have the same atomic number but different atomic masses.

• Medical Importance: Some isotopes are radioactive and used in medical imaging and cancer treatment (e.g., Technetium-99m in diagnostic scans).

Molecules, Compounds, and Isomers

Chemical substances can be classified based on their composition and structure.

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: A molecule composed of atoms of different elements (e.g., H2O).

• Isomer: Molecules with the same chemical formula but different structural arrangements (e.g., glucose and fructose).

Organic vs. Inorganic Compounds

Compounds are classified based on the presence of carbon and their origin.

• Organic Compounds: Contain carbon-hydrogen bonds; typically found in living organisms (e.g., proteins, carbohydrates).

• Inorganic Compounds: Generally do not contain carbon-hydrogen bonds (e.g., water, salts).

Acids, Bases, and pH

Acids and bases influence the pH of solutions, which is critical for biological processes.

• Acid: Substance that donates protons (H+) in solution; increases hydrogen ion concentration.

• Base: Substance that accepts protons or donates hydroxide ions (OH-); decreases hydrogen ion concentration.

• pH: A measure of hydrogen ion concentration; calculated as .

• Effect: Acids lower pH (more acidic), bases raise pH (more basic/alkaline).

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds hold atoms together in molecules and compounds.

• Ionic Bond: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other (e.g., NaCl).

• Covalent Bond: Formed when two atoms share one or more pairs of electrons (e.g., H2O).

• Comparison: Ionic bonds are generally stronger in dry conditions but weaker in aqueous environments; covalent bonds are strong and stable in biological systems.

Polar Covalent and Hydrogen Bonds

Polarity and hydrogen bonding are essential for the structure and function of biomolecules.

• Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges (e.g., O-H bond in water).

• Hydrogen Bond: Weak attraction between a hydrogen atom (attached to an electronegative atom) and another electronegative atom (e.g., between water molecules).

• Importance: Hydrogen bonds stabilize DNA, proteins, and contribute to water's unique properties.

Hydrophobic, Hydrophilic, and Amphipathic Molecules

These terms describe how molecules interact with water, influencing cell structure and function.

• Hydrophobic: "Water-fearing"; molecules that do not interact well with water (e.g., lipids).

• Hydrophilic: "Water-loving"; molecules that readily dissolve in water (e.g., salts, sugars).

• Amphipathic: Molecules with both hydrophobic and hydrophilic regions (e.g., phospholipids in cell membranes).

Chemical Reactions

Reactants, Products, and Catalysts

Chemical reactions transform substances, often with the help of catalysts.

• Reactants: Starting materials in a chemical reaction.

• Products: Substances formed as a result of the reaction.

• Catalyst: Substance that speeds up a chemical reaction without being consumed (e.g., enzymes in biological systems).

Dehydration Synthesis and Hydrolysis

These are key reactions in the formation and breakdown of biological macromolecules.

• Dehydration Synthesis (Condensation): Reaction in which two molecules are joined by removing a water molecule; forms bonds such as peptide or glycosidic bonds.

• Hydrolysis: Reaction in which a molecule is split into two by the addition of water; breaks down polymers into monomers.

Activation Energy and Reaction Types

• Activation Energy: The minimum energy required to initiate a chemical reaction.

• Lowering Activation Energy: Catalysts (e.g., enzymes) lower activation energy, increasing reaction rates.

• Endergonic Reaction: Absorbs energy; products have more energy than reactants.

• Exergonic Reaction: Releases energy; products have less energy than reactants.

Biologically Important Macromolecules

Major Classes and Building Blocks

Four main groups of biomolecules are essential for life, each with specific building blocks and functions.

• Carbohydrates: Monosaccharides (simple sugars) are the building blocks.

• Lipids: Fatty acids and glycerol are the main components.

• Nucleic Acids: Nucleotides (composed of a sugar, phosphate, and nitrogenous base).

• Proteins: Amino acids are the monomers.

Key Bonds in Macromolecules

• Glycosidic Bond: Covalent bond joining two monosaccharides in carbohydrates.

• Peptide Bond: Covalent bond linking amino acids in proteins.

• Phosphodiester Bond: Covalent bond connecting nucleotides in nucleic acids.

Structural and Functional Characteristics

• Carbohydrates: Provide energy and structural support (e.g., cellulose in plants, peptidoglycan in bacteria).

• Lipids: Store energy, form cell membranes, and act as signaling molecules.

• Nucleic Acids: Store and transmit genetic information (DNA and RNA).

• Proteins: Serve as enzymes, structural components, and signaling molecules.

Deoxyribonucleotides vs. Ribonucleotides

Lipid Saturation and Properties

• Saturated Lipids: No double bonds; solid at room temperature (e.g., animal fats).

• Unsaturated Lipids: One or more double bonds; liquid at room temperature (e.g., plant oils).

• Impact: Saturation affects membrane fluidity and function.

Protein Structure Levels

• Primary Structure: Linear sequence of amino acids.

• Secondary Structure: Local folding into alpha-helices or beta-sheets.

• Tertiary Structure: Three-dimensional folding of a single polypeptide chain.

• Quaternary Structure: Association of multiple polypeptide chains.