Prokaryotic Cell Structures

• Two of the three domains of life are prokaryotic, which are single-celled organisms lacking a nucleus and membrane-bound organelles.
• Prokaryotes can be found in diverse habitats like thermal vents, animal bodies, rocks, and the atmosphere.
• Archaea are more closely related to eukaryotes than bacteria, based on DNA evidence.
• Most prokaryotes are unicellular and significantly smaller than eukaryotes (10-100x smaller)
• Traditional classification is based on cell shape, structure, and metabolism.

Internal Structures

• The nucleoid is where the circular chromosome is located.
• Plasmids are small, circular DNA that contribute to virulence.
• All prokaryotic cells have ribosomes to produce proteins.
• Streptomycin kills bacteria by disrupting their ribosomes.
• Archaea and eukaryotes are not susceptible to streptomycin.

External Structures

• All prokaryotes possess a cell wall, though its composition varies.
• Most bacterial cell walls contain peptidoglycan
• Archaeal cell walls primarily comprise protein, thus penicillin is ineffective against them.
• Cell walls shape bacteria and aid in their identification.
• Arrangements of bacteria include clusters called staphylo- and chains called strepto-.

Gram Staining

• Gram-positive bacteria stain purple due to thick peptidoglycan trapping violet dye.
• Gram-negative bacteria stain red because they don't retain the violet dye due to a thin peptidoglycan layer and a larger outer membrane.
• Gram-negative bacteria are are more virulent and respond differently to antibiotics.

Pathogenic Bacteria

• The glycocalyx is a sticky outer layer made of proteins and polysaccharides that aids in protection and biofilm formation.
• Biofilms are surface coating colonies of prokaryotes that engage in metabolic cooperation.
• Endospores are dormant, thick-walled structures that protect bacteria from harsh conditions.
• Botulism and anthrax are caused by bacteria that produce endospores.
• Pathogenic bacteria produce Exotoxins, which are toxins secreted into their environment, and Endotoxins, which are components released upon bacterial death.

Metabolic Classification

• Organisms are classified by energy and carbon acquisition, using autotrophy vs heterotrophy (production of organic compounds from inorganic sources) and phototroph vs chemotroph (energy from sun vs chemicals).
• Oxygen needs for classification include obligate aerobes which require oxygen, obligate anaerobes for whom oxygen is toxic, and facultative anaerobes, which can live in both states.

Microbial Taxonomy

• Molecular data has triggered a revolution in microbial taxonomy.
• The analysis of rRNA (ribosomal ribonucleic acid) sequences reorganized living things into three domains.
• Prokaryotes use horizontal gene transfer in addition to vertical.
• Horizontal gene transfer complicates evolutionary relationships and aids in antibiotic resistence.

Bacteria

• There are 23 named phyla of bacteria.
• Attention is given to Proteobacteria, Cyanobacteria, and Chlamydiae.

Archaea

• Archaea are often found in extreme environments
• They are grouped by habitat, incuding Halophiles, Thermophiles, and Acidophiles.
• Classified into four superphyla, including Euryarchaeota (methanogens) and TACK (thermophiles).

Essential roles of Prokaryotes

• Most microbes are not harmful, serving instead in the carbon cycle and are required for photosynthesis and decomposition.
• They fix nitrogen, and can be found in soil and in nitrogen fixing nodules within plants.

Human Microbiome

• Bacteria helps to train the immune system and produces vitamins.
• They also help to outcompete disease-causing bacteria.
• No harmful archaea linked to human illness have been identified.

Prokaryotes At Work

• Many foods are the product of bacterial metabolism.
• Transgenic bacteria can produce human proteins such as insulin.
• Bioremediation uses organisms to remove pollutants.
• Decomposers digest organic matter and sewage treatment plants use biofilms to degrade organic waste.