Bacteria structure

Binomial Nomenclature

The system of giving every organism two names: the Genus (capitalized) and the specific epithet (species name, not capitalized)

Staphylococcus aureus (Name Meaning)

“Staphylo” describes clustered arrangement

Bergey’s Manual

The reference used for bacterial classification

Strain

A collection of cells derived from a single cell within a species

Phylogenetic Hierarchy (Order)

Species → Genus → Family → Order → Class → Division/Phylum → Kingdom → Domain

Procaryotes

Simple cells (bacteria and cyanobacteria) that exhibit all characteristics of life but lack a complex system of membranes and membrane-bound organelles.

Cocci Arrangements

Cocci that remain attached form: diplococci (pairs), streptococci (chains), tetrads (groups of 4), sarcinae (groups of 8), or staphylococci (clusters).

Bacilli Arrangements

Rod-shaped bacteria that appear in pairs are diplobacilli

Spiral Bacteria

Curved rods are vibrios

Monomorphic vs. Pleomorphic

Monomorphic bacteria always maintain the same shape

Peptidoglycan

A net-like polymer (sacculus) forming the bacterial cell wall, made of repeating N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) units linked by β-1,4 glycosidic bonds and cross-linked by short peptide chains.

Gram-Positive Cell Wall

Relatively thick (30–100 nm)

Gram-Negative Cell Wall

Thinner and more chemically complex than Gram-positive

Lipopolysaccharide (LPS)

A component of the outer membrane of Gram-negative bacteria

Plasma Membrane

Composed of phospholipids (with a polar hydrophilic phosphate head and hydrophobic fatty acid tails) and proteins

Fimbriae (Pili)

Hair-like proteinaceous structures (2–3 nm diameter, 0.1 µm to several µm long) projecting from Gram-negative cell surfaces

Flagella

Made of proteins called flagellins

Capsule (Slime Layer)

Composed of polysaccharide surrounding the bacterial cell

Plasmid

A short, usually circular, double-stranded DNA segment found in the cytoplasm separate from the main chromosome

Nucleoid

A region of the cytoplasm (not membrane-bound) where the bacterial chromosome (usually a single circular DNA strand) is located

Ribosomes (Bacteria)

Bacteria contain approximately 20,000 ribosomes per cell

Metabolism

The sum total of all chemical reactions taking place in a living cell

Catabolism

Energy-releasing reactions involving the breakdown of complex organic compounds into simpler ones (e.g., breakdown of sugars into CO₂ and H₂O)

Anabolism

Energy-requiring (biosynthetic) reactions that build complex organic molecules from simpler ones (e.g., proteins from amino acids, nucleic acids from nucleotides, polysaccharides from simple sugars).

ATP (Adenosine Triphosphate)

The energy currency of the cell

ATP–ADP Cycle

During catabolism, ATP loses a phosphate group to form ADP + energy

Activation Energy

The energy required to initiate a chemical reaction by enabling atoms, ions, or molecules to collide with sufficient impact

Enzymes

Biological catalysts that facilitate cellular chemical reactions without being consumed

Coenzymes (NAD⁺/NADH)

Small molecules that assist enzymes in transferring electrons and protons in redox reactions

Focal Metabolites

A few key precursor molecules from which biosynthetic building blocks and coenzymes can be traced