Bacteria: Prokaryotic Cells Overview

Study Notes

Bacteria are single-celled organisms capable of independent life.
They are much smaller than eukaryotes, measured in micrometers (µm).
Bacteria lack a true nucleus and complex organelles like mitochondria.
Bacteria have a large surface-to-volume ratio, allowing nutrients to quickly reach any part of the cell.
Bacteria have cell walls and plasma membranes.

Outer Layer: Contains a rigid cell wall (containing peptidoglycan) and a cytoplasmic (cell/plasma) membrane underneath.
Cytoplasm: Contains cytoplasmic inclusions, ribosomes, and a nucleoid region (containing DNA).
Additional Structures: Plasmid (extra circular DNA), slime layer, capsule (protection), flagella (movement), fimbriae/pili (attachment to other bacteria).

Bacteria are crucial due to rapid growth, reproduction, mutation rates, and ability to exist in adverse conditions.
The oldest known fossils, nearly 3.5 billion years old, are fossils of bacteria-like organisms.

These are a type of bacteria that are anaerobes (do not use oxygen).
Methanogens: Produce methane gas as a waste product. Found in swamps, sediments, sewage, and buried landfills.
Halophiles: Salt-loving bacteria. Thrive in environments like the Great Salt Lake or salt ponds, and can turn water dark pink. Use bacteriorhodopsin for a type of photosynthesis that does not produce oxygen.
Thermophiles: Thrive in hot springs and extreme temperatures. Some can survive above the boiling point of water.

Cyanobacteria: Perform "modern photosynthesis", creating oxygen from water. Found as single cells or chains, often as pond or aquarium "green slime". All plants inherited this process from cyanobacteria.
Other bacteria: Live symbiotically in animal guts (e.g., E. coli producing vitamin K for blood clotting); on plant roots converting atmospheric nitrogen into a usable form; help break down dead matter; form the base of food webs in many environments; give tang to yogurt and sourness to sourdough bread.

Shape: Coccus (spherical), bacillus (rod-shaped), spirillum (spiral-shaped).
Various arrangements of cocci include diplococci (pairs), streptococci (chains), and staphylococci (clusters).
Cell Wall Structure (Gram Staining): Gram-positive bacteria have thick peptidoglycan layers (stain purple); Gram-negative bacteria have thin peptidoglycan layers and a second outer membrane (stain pink).
Metabolism: Autotrophs (make their own food); heterotrophs (consume other organisms). Examples include photoautotrophs (e.g., cyanobacteria) and chemoautotrophs (use chemicals instead of light).
Endospore Formation: Certain bacteria form endospores, which are dormant, resistant structures allowing survival in harsh conditions and reviving later.

Bacteria reproduce asexually through binary fission (splitting into two).
Plasmids: small, circular, extra-chromosomal DNA that can be exchanged between bacteria during conjugation (a form of sexual exchange).
The process of exchanging genes during conjugation can help build antibiotic resistance in bacteria.

Bacteria have various ways of obtaining energy: photoautotrophic, chemoautotrophic, and heterotrophic.
Bacteria can be aerobes (require oxygen) or anaerobes (do not require oxygen). Facultative anaerobes can live with or without oxygen.