Chemistry of Microbiology

Matter and Atomic Structure

The study of microbiology requires an understanding of basic chemical principles, as all living organisms are composed of matter and atoms. Matter is anything that takes up space and has mass, and atoms are its smallest chemical units.

• Atoms consist of a nucleus (containing protons and neutrons) and electron shells surrounding the nucleus.

• Element: A substance composed of a single type of atom.

• Atomic number: Number of protons in the nucleus.

• Atomic mass: Sum of protons, neutrons, and electrons.

Periodic Table and Essential Elements

The periodic table organizes elements by their atomic number and properties. Only a subset of these elements are essential for life, with carbon, hydrogen, oxygen, and nitrogen making up the majority of living matter.

• About 25 out of 92 elements are essential to life.

• Trace elements are required in small amounts for proper cellular function.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons. They can be stable or unstable, with unstable isotopes releasing energy during radioactive decay.

• Stable isotopes: Do not change over time.

• Unstable isotopes: Undergo radioactive decay.

Electron Configuration and Chemical Behavior

Electrons occupy shells around the nucleus, and only the outermost (valence) electrons interact with other atoms, determining chemical behavior.

• Valence electrons: Electrons in the outermost shell.

• Atoms are most stable when their outer shell contains eight electrons (octet rule).

Chemical Bonds

Atoms combine by sharing or transferring valence electrons, forming chemical bonds. The main types are covalent, ionic, and hydrogen bonds.

• Covalent bonds: Sharing of electron pairs between atoms.

• Ionic bonds: Transfer of electrons, resulting in attraction between cations and anions.

• Hydrogen bonds: Weak attractions between partially charged hydrogen and other atoms.

Electronegativity and Bond Polarity

Electronegativity is the attraction of an atom for electrons. Atoms with similar electronegativities form nonpolar covalent bonds, while those with different electronegativities form polar covalent bonds.

• Nonpolar covalent bonds: Electrons are shared equally.

• Polar covalent bonds: Electrons are shared unequally, creating partial charges.

Ionic Bonds and Salts

Ionic bonds form when atoms with vastly different electronegativities transfer electrons, resulting in charged ions that attract each other. These typically form crystalline compounds known as salts.

• Cation: Positively charged ion.

• Anion: Negatively charged ion.

Hydrogen Bonds

Hydrogen bonds are weak but essential for stabilizing the three-dimensional shapes of large molecules, such as proteins and nucleic acids.

• Occur when polar covalent bonds are present.

• Important in DNA structure and protein folding.

Chemical Reactions

Chemical reactions involve the rearrangement of atoms to form new molecules. In biochemistry, these reactions are essential for life processes.

• Synthesis reactions: Formation of larger molecules (anabolism).

• Decomposition reactions: Breakdown of molecules (catabolism).

• Exchange reactions: Atoms are moved between molecules.

Water, Acids, Bases, and Salts

Water is the most abundant substance in organisms, with unique properties due to its polar covalent bonds. Acids and bases are defined by their ability to dissociate in water, affecting pH and cellular function.

• Acid: Dissociates into H+ and anions.

• Base: Binds H+ or dissociates into OH- and cations.

• Salt: Dissociates into cations and anions other than H+ and OH-.

• pH scale: Measures concentration of H+ ions.

Organic Macromolecules

Organic macromolecules are large molecules essential for life, including lipids, carbohydrates, proteins, and nucleic acids. They are composed of monomers and functional groups that determine their properties.

• Lipids: Hydrophobic molecules, including fats, phospholipids, waxes, and steroids.

• Carbohydrates: Composed of carbon, hydrogen, and oxygen; serve as energy sources and structural components.

• Proteins: Made of amino acids; perform structural, catalytic, regulatory, and defensive functions.

• Nucleic acids: DNA and RNA; composed of nucleotides.

Lipids

Lipids are not composed of regular subunits but are all hydrophobic. The four main groups are fats, phospholipids, waxes, and steroids.

• Fats (triglycerides): Formed by dehydration synthesis of glycerol and fatty acids.

• Phospholipids: Major component of cell membranes.

• Waxes: Used by certain bacteria for protection.

• Steroids: Have four fused carbon rings.

Carbohydrates

Carbohydrates are organic molecules with the formula (CH2O)n. They serve as energy sources, structural components, and are involved in cell interactions.

• Monosaccharides: Simple sugars like glucose.

• Disaccharides: Two monosaccharides joined together.

• Polysaccharides: Long chains of monosaccharides.

Proteins

Proteins are polymers of amino acids, which are joined by peptide bonds. They have diverse functions, including catalysis, regulation, transport, and defense.

• Amino acids: Monomers of proteins; 21 types used in organisms.

• Peptide bond: Covalent bond formed by dehydration synthesis.

• Protein structure: Includes primary, secondary, tertiary, and quaternary levels.

Nucleic Acids

Nucleic acids (DNA and RNA) are polymers of nucleotides, which consist of a phosphate group, a pentose sugar, and a nitrogenous base. They store and transmit genetic information.

• Nucleotide: Monomer of nucleic acids.

• Nucleoside: Nucleotide lacking phosphate.

• DNA structure: Double-stranded, complementary, and antiparallel.

• Hydrogen bonds: Form between bases (A-T, C-G).

Summary Table: Types of Chemical Bonds

The following table summarizes the main types of chemical bonds found in biological molecules:

Key Equations

• Atomic mass:

• pH calculation:

Additional info:

• Organic macromolecules are fundamental to microbial structure and function, influencing metabolism, genetics, and cellular processes.

• Understanding chemical bonds and molecular interactions is essential for studying microbial physiology and biochemistry.