Atoms and Elements

Atomic Structure and Properties

Atoms are the fundamental units of matter, composed of protons, neutrons, and electrons. The atomic number defines the element by indicating the number of protons in the nucleus, while the atomic mass is the sum of protons and neutrons. Elements are organized in the periodic table, which provides information about their atomic number, chemical symbol, and atomic mass.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle in electron shells.

• Atomic Number: Number of protons; determines element identity.

• Atomic Mass: Sum of protons and neutrons.

Ions and Isotopes

Ion Formation and Types

Ions are atoms with unequal numbers of protons and electrons, resulting in a net charge. Cations are positively charged (loss of electrons), while anions are negatively charged (gain of electrons).

• Cation: Atom loses electrons, becomes positively charged.

• Anion: Atom gains electrons, becomes negatively charged.

Isotopes

Isotopes are variants of elements with the same number of protons but different numbers of neutrons. Some isotopes are stable, while others are radioactive and decay over time. Isotopes are important in medicine for diagnostic and therapeutic purposes.

Molecules, Compounds, and Isomers

Definitions and Examples

Molecules are formed when two or more atoms bond together. Compounds are molecules composed of more than one element. Isomers have the same molecular formula but different structural arrangements.

• Molecule: Two or more atoms bonded together.

• Compound: Molecule with atoms from different elements.

• Isomer: Same formula, different structure (e.g., glucose, fructose, galactose).

Organic and Inorganic Molecules

Classification and Functional Groups

Organic molecules contain both carbon and hydrogen, while inorganic molecules may contain one or neither. Functional groups are specific groups of atoms within molecules that determine their chemical properties and reactivity.

• Organic: CH4, C6H12O6

• Inorganic: CO2, H2O, NaCl

• Functional Groups: Participate in chemical reactions; help classify organic molecules.

Solutions and Concentration

Solute and Solvent

The concentration of a solution is determined by the amount of solute dissolved in a specific volume of solvent. This is important for preparing laboratory solutions and understanding cellular environments.

• Solute: Substance dissolved.

• Solvent: Substance doing the dissolving (usually water).

• Concentration: Amount of solute per volume of solvent (e.g., mg/mL).

Acids, Bases, and Salts

Definitions and Effects on pH

Acids release hydrogen ions (H+), bases release hydroxide ions (OH-), and salts are formed from the reaction of acids and bases. These substances affect the pH of solutions, which is critical for biological systems.

• Acid: Increases H+ concentration.

• Base: Increases OH- concentration.

• Salt: Formed from acid and base reaction.

pH and Buffers

pH Scale and Biological Importance

pH measures the acidity or basicity of a solution, ranging from 0 (most acidic) to 14 (most basic). Buffers are compounds that stabilize pH by absorbing or releasing H+ ions, which is essential for maintaining homeostasis in biological systems.

• pH: Negative logarithm of H+ concentration.

• Buffer: Stabilizes pH in biological systems.

pH Indicators

pH indicators, such as phenol red, are used in laboratory media to visually detect changes in pH, which can indicate microbial metabolic activity.

• Phenol Red: Changes color based on pH.

Chemical Bonds

Valence Electrons and Bond Formation

Valence electrons are the outermost electrons involved in chemical bonding. The type of bond formed depends on how these electrons are shared or transferred.

• Ionic Bond: Electrostatic attraction between oppositely charged ions.

• Covalent Bond: Sharing of electron pairs between atoms.

• Electrolytes: Free ions in solution; important for cellular function.

Polar Covalent Bonds and Hydrogen Bonds

Polar covalent bonds result from unequal sharing of electrons, creating partial charges (dipoles). Hydrogen bonds are weak attractions between a hydrogen atom and an electronegative atom, important for the structure of water and biological macromolecules.

• Polar Covalent: Unequal sharing, creates dipoles.

• Hydrogen Bond: Weak attraction between molecules or within large molecules.

• Van der Waals: Weak interactions between transient dipoles.

Hydrophilic, Hydrophobic, and Amphipathic Substances

Solubility and Micelle Formation

Hydrophilic substances dissolve readily in water, while hydrophobic substances do not. Amphipathic molecules contain both hydrophilic and hydrophobic regions, allowing them to form structures like micelles and lipid bilayers, which are essential for cell membranes.

• Hydrophilic: Water-loving, dissolves in water.

• Hydrophobic: Water-fearing, does not dissolve in water.

• Amphipathic: Both hydrophilic and hydrophobic regions.

Chemical Reactions

Types of Chemical Reactions

Chemical reactions involve making or breaking bonds. Synthesis reactions build molecules, decomposition reactions break them down, and exchange reactions swap components. Dehydration synthesis removes water to form bonds, while hydrolysis adds water to break bonds.

• Synthesis: Combines reactants to form products.

• Decomposition: Breaks down molecules into simpler components.

• Exchange: Swaps parts between molecules.

• Dehydration Synthesis: Removes water to form covalent bonds.

• Hydrolysis: Adds water to break covalent bonds.

Activation Energy and Reaction Types

Activation energy is the minimum energy required to start a reaction. Exergonic reactions release energy, while endergonic reactions require energy input. Some reactions are reversible and can reach equilibrium.

• Activation Energy: Energy needed to initiate a reaction.

• Exergonic: Releases energy; products have lower energy than reactants.

• Endergonic: Requires energy; products have higher energy than reactants.

• Reversible: Can proceed in both directions; equilibrium occurs when rates are equal.

Biological Macromolecules

Carbohydrates

Carbohydrates are composed of monosaccharides (simple sugars), disaccharides (two sugars linked by glycosidic bonds), and polysaccharides (many sugars). They serve as energy sources, structural components, and are involved in cell adhesion and communication.

• Monosaccharide: Glucose, fructose, galactose.

• Disaccharide: Sucrose (glucose + fructose).

• Polysaccharide: Glycogen, starch, cellulose, chitin, peptidoglycan.

Lipids

Lipids include fats, oils, waxes, and steroids. They are hydrophobic or amphipathic, serve as energy sources, structural components, and mediate cell signaling. Saturated lipids lack double bonds, while unsaturated lipids contain them, affecting their physical properties.

• Saturated: Solid at room temperature (e.g., butter).

• Unsaturated: Liquid at room temperature (e.g., olive oil).

• Phospholipids: Amphipathic, form cell membranes.

• Steroids: Four fused rings; sterols have alcohol groups (e.g., cholesterol).

Nucleic Acids

Nucleic acids include DNA and RNA, composed of nucleotide monomers. DNA contains deoxyribonucleotides (adenine, guanine, cytosine, thymine), while RNA contains ribonucleotides (adenine, guanine, cytosine, uracil). Nucleotides are linked by phosphodiester bonds, forming a sugar-phosphate backbone.

• DNA: Genetic blueprint; double-stranded.

• RNA: Protein synthesis; single-stranded.

• Phosphodiester Bond: Links nucleotides.

Proteins

Proteins are polymers of amino acids linked by peptide bonds. They have four levels of structure: primary (sequence), secondary (alpha-helices and beta-sheets), tertiary (3D folding), and quaternary (multiple polypeptides). Proteins serve as enzymes, structural scaffolds, transporters, and in cell communication.

• Amino Acid: Amine group, carboxyl group, variable R group.

• Peptide Bond: Links amino acids.

• Primary Structure: Linear sequence.

• Secondary Structure: Alpha-helix, beta-sheet.

• Tertiary Structure: 3D folding, disulfide bridges.

• Quaternary Structure: Multiple polypeptides.

Additional info: The notes above expand on brief points from the original material, providing definitions, examples, and context for each concept. This guide covers foundational biochemistry relevant to microbiology, including atomic structure, chemical bonding, macromolecules, and their biological functions.