Biochemistry Basics for Microbiology Students

Biochemistry Basics

Atoms and Elements

Atoms are the fundamental units of matter, forming the basis of all chemical substances. Understanding their structure is essential for grasping the molecular foundations of microbiology.

• Atom: The smallest unit of an element, which is a pure substance that makes up ordinary matter.

• Atomic nucleus: Contains protons (positively charged) and neutrons (neutral).

• Electrons: Negatively charged particles that orbit the nucleus in electron shells.

• Atomic number: Number of protons in the nucleus; defines the element.

• Atomic mass: Sum of protons and neutrons; electrons have negligible mass.

• Periodic table: Organizes elements by atomic number, symbol, and mass.

Ions and Isotopes

Atoms can exist in different forms, such as ions and isotopes, which are important in biological systems.

• Ion: An atom with unequal numbers of protons and electrons, resulting in a charge.

• Cation: Atom that has lost electrons; positive charge.

• Anion: Atom that has gained electrons; negative charge.

• Isotope: Atoms of the same element with different numbers of neutrons.

Molecules, Compounds, and Isomers

Molecules are formed when atoms bond together. Compounds are molecules made of more than one type of element, and isomers are molecules with the same formula but different structures.

• Molecule: Two or more atoms bonded together.

• Compound: Molecule with more than one type of element.

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

• Molecular formula: Indicates the ratio of elements in a molecule.

Organic vs. Inorganic Molecules

Biological molecules are classified as organic or inorganic based on their composition.

• Organic molecules: Contain both carbon and hydrogen.

• Inorganic molecules: May contain carbon, but lack associated hydrogen.

Acids, Bases, and Salts

Acids, bases, and salts play crucial roles in cellular chemistry, especially in aqueous solutions.

• Solvent: Dissolving agent (usually water in cells).

• Solute: Substance dissolved in the solvent.

• Acid: Adds hydrogen ions (H+) to solution.

• Base: Adds hydroxide ions (OH-) to solution.

• Salt: Formed when acids and bases react; composed of anions and cations.

Solution Concentration

The concentration of a solution is determined by the amount of solute dissolved in a specific volume of solvent.

• Concentration: Expressed as mass/volume or percentage.

pH: A Measure of Acidity

The pH scale measures the acidity or basicity of a solution, which is vital for microbial growth and cellular function.

• pH scale: Ranges from 0 (acidic) to 14 (basic); 7 is neutral.

• Logarithmic scale: Each unit represents a tenfold change in H+ ion concentration.

• Acidic: pH < 7; more H+ ions.

• Basic (alkaline): pH > 7; more OH- ions.

• Buffer: Compound that stabilizes pH by absorbing or releasing H+ or OH-.

Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules. The type of bond affects molecular properties and biological function.

• Valence electrons: Electrons in the outermost shell; participate in bonding.

• Ionic bond: Electrostatic attraction between oppositely charged ions; electrons are transferred.

• Covalent bond: Atoms share one or more pairs of electrons.

• Polar covalent bond: Unequal sharing of electrons, creating partial charges (dipoles).

• Hydrogen bond: Noncovalent attraction between molecules or within a molecule.

• Van der Waals interactions: Weak attractions due to temporary dipoles.

Hydrophobic, Hydrophilic, and Amphipathic Molecules

Molecules interact with water differently based on their polarity, affecting their biological roles.

• Hydrophilic: Water-loving; readily dissolve in water.

• Hydrophobic: Water-fearing; do not dissolve in water.

• Amphipathic: Have both hydrophilic and hydrophobic regions (e.g., phospholipids).

Biologically Important Macromolecules

Cells are built from four main classes of biomolecules: carbohydrates, lipids, nucleic acids, and proteins. Each has unique structures and functions.

• Carbohydrates: Simple sugars (monosaccharides), disaccharides, and polysaccharides; energy and structural roles.

• Lipids: Fats, oils, waxes, steroids; energy storage, membrane structure, signaling.

• Nucleic acids: DNA and RNA; genetic information and protein synthesis.

• Proteins: Polymers of amino acids; enzymes, structural scaffolds, transporters, cell recognition.

Biomolecule	Examples	Building Blocks	Notes
Carbohydrates	Glucose, Sucrose, Glycogen	Simple sugars	Monosaccharide, disaccharide, polysaccharide
Nucleic Acids	DNA, RNA	Nucleotides	Polymers of deoxyribonucleotides or ribonucleotides
Proteins	Enzymes, Antibodies	Amino acids	Catalysts, immune response
Lipids	Fats, Oils, Waxes, Steroids	Glycerol, fatty acids, alcohols, hydrocarbon rings	Energy, structure, signaling

Carbohydrates

Carbohydrates are organic molecules consisting of one or more sugar monomers. They serve as energy sources and structural components.

• Monosaccharides: Single sugar units (e.g., glucose).

• Disaccharides: Two monosaccharides linked by glycosidic bonds.

• Polysaccharides: Polymers of many monosaccharides (e.g., glycogen, cellulose, chitin, peptidoglycan).

• Glycosidic bond: Formed by dehydration synthesis; broken by hydrolysis.

Lipids

Lipids are hydrophobic biomolecules with diverse structures and functions, including energy storage and membrane formation.

• Saturated lipids: No double bonds; solid at room temperature.

• Unsaturated lipids: One or more double bonds; liquid at room temperature.

• Monounsaturated: One double bond.

• Polyunsaturated: Multiple double bonds.

• Fats and oils: Glycerol + up to 3 fatty acids (ester bonds).

• Waxes: Fatty acids + long-chain alcohol.

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

Nucleic Acids

Nucleic acids are polymers of nucleotides and serve as the genetic material of cells and viruses.

• DNA: Double-stranded; deoxyribonucleotides (adenine, guanine, cytosine, thymine).

• RNA: Single-stranded; ribonucleotides (adenine, guanine, cytosine, uracil).

• Phosphodiester bonds: Link nucleotides, forming sugar-phosphate backbone.

• ATP: Adenosine triphosphate; energy currency of the cell.

Proteins

Proteins are polymers of amino acids and are essential for nearly all cellular processes.

• Amino acids: 20 standard, 2 nonstandard; each has an amine group, carboxyl group, and R group.

• Peptide bonds: Covalent bonds linking amino acids.

• Protein structure: Four levels—primary (sequence), secondary (alpha-helices, beta-sheets), tertiary (3D folding), quaternary (multiple polypeptides).

• Chaperone proteins: Assist in proper protein folding.

Summary Table: Levels of Protein Structure

Level	Description
Primary	Linear sequence of amino acids
Secondary	Alpha-helices and beta-pleated sheets
Tertiary	3D folding due to interactions
Quaternary	Combination of multiple polypeptide chains

Protein functions: Structural scaffolds, enzymes, transporters, cell recognition, communication.