Prokaryotes (Bacteria and Archea)

Prokaryote

Unicellular organism lacking a nucleus and membrane-bound organelles.

Prokaryotic vs. Eukaryotic cells

Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes possess them.

Archaea evolutionary relationship

Archaea share a more recent common ancestor with Eukarya than with Bacteria.

Last Universal Common Ancestor (LUCA)

The common ancestral cellular organism of Bacteria and Archaea.

Stromatolites

Layered sedimentary structures formed by ancient microbial communities ~3.5 billion years ago.

Great Oxidation Event

Major atmospheric oxygen increase ~2.4 billion years ago driven by cyanobacteria.

Basic prokaryotic cell components

Plasma membrane, cytoplasm, DNA in nucleoid region, and ribosomes.

Cocci

Spherical-shaped prokaryotic cells.

Bacilli

Rod-shaped prokaryotic cells.

Vibrios

Comma-shaped prokaryotic cells.

Spira

Spiral-shaped prokaryotic cells.

Diplo

Prokaryotic cells occurring in pairs.

Strepto

Prokaryotic cells arranged in chains.

Staphylo

Prokaryotic cells arranged in clusters.

Gram-positive bacteria cell wall

Characterized by a thick peptidoglycan layer. and will turn purple

Gram-negative bacteria cell wall

Characterized by a thin peptidoglycan layer surrounded by an outer membrane. and will turn pink

Binary fission

Asexual reproduction where a parent cell divides into two identical daughter cells.

Transformation

The uptake of free DNA from the surrounding environment by a prokaryote.

Transduction

The transfer of DNA between cells using bacteriophages.

Conjugation

Direct transfer of DNA between prokaryotic cells through physical contact.

Nitrogen fixation

Conversion of atmospheric nitrogen into bioavailable ammonia by certain prokaryotes.

Photoautotrophs

Organisms using light energy and inorganic carbon sources.

Biofilms

Microbial communities attached to surfaces embedded in a protective extracellular matrix.

Mutualism

Symbiotic relationship where both participating organisms benefit.

Chemotrophs

Organisms that obtain energy by a carbon source

Phototrophs

Organisms that obtain energy from sunlight

Heterotrophs

Organisms that obtain energy by consuming organic compounds

Autotrophs

Organisms that can produce their own organic food from light

Prokaryote

Unicellular organism lacking a nucleus and membrane-bound organelles.

Prokaryotic vs. Eukaryotic cells

Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes possess them.

Archaea evolutionary relationship

Archaea share a more recent common ancestor with Eukarya than with Bacteria.

Last Universal Common Ancestor (LUCA)

The common ancestral cellular organism of Bacteria and Archaea.

Stromatolites

Layered sedimentary structures formed by ancient microbial communities approximately $3.5$ billion years ago.

Great Oxidation Event

Major atmospheric oxygen increase approximately $2.4$ billion years ago driven by cyanobacteria.

Basic prokaryotic cell components

Plasma membrane, cytoplasm, DNA in nucleoid region, and ribosomes.

Cocci

Spherical-shaped prokaryotic cells.

Bacilli

Rod-shaped prokaryotic cells.

Vibrios

Comma-shaped prokaryotic cells.

Spira

Spiral-shaped prokaryotic cells.

Diplo

Prokaryotic cells occurring in pairs.

Strepto

Prokaryotic cells arranged in chains.

Staphylo

Prokaryotic cells arranged in clusters.

Gram-positive bacteria cell wall

Characterized by a thick peptidoglycan layer and will turn purple upon Gram staining.

Gram-negative bacteria cell wall

Characterized by a thin peptidoglycan layer surrounded by an outer membrane and will turn pink upon Gram staining.

Binary fission

Asexual reproduction where a parent cell divides into two identical daughter cells.

Transformation

The uptake of free DNA from the surrounding environment by a prokaryote.

Transduction

The transfer of DNA between cells using bacteriophages.

Conjugation

Direct transfer of DNA between prokaryotic cells through physical contact.

Nitrogen fixation

Conversion of atmospheric nitrogen into bioavailable ammonia by certain prokaryotes.

Photoautotrophs

Organisms using light energy and inorganic carbon sources.

Biofilms

Microbial communities attached to surfaces embedded in a protective extracellular matrix.

Mutualism

Symbiotic relationship where both participating organisms benefit.

Chemotrophs

Organisms that obtain energy from carbon

Phototrophs

Organisms that obtain energy from sunlight.

Heterotrophs

consuming organic compounds.

Autotrophs

produce their own food from carbon sources.

Archaea vs. Bacteria: Cell wall composition

Bacteria cell walls contain peptidoglycan, whereas Archaea cell walls lack peptidoglycan and often contain pseudopeptidoglycan, polysaccharides, or protein S-layers.

Archaea vs. Bacteria: Membrane lipid linkages

Bacteria possess ester linkages connecting glycerol to unbranched fatty acids, whereas Archaea possess ether linkages connecting glycerol to branched isoprene chains.

Archaea vs. Bacteria: Membrane lipid structure

Bacteria exclusively form lipid bilayers, whereas some Archaea form lipid monolayers that provide greater thermal stability.

Archaea vs. Bacteria: Initiator amino acid

Bacteria use formylmethionine ($\text{fMet}$) to initiate translation, whereas Archaea use methionine ($\text{Met}$).

Archaea vs. Bacteria: RNA polymerase complexity

Bacteria have a single simple RNA polymerase with $5$ subunits, whereas Archaea possess complex multi-subunit RNA polymerases structurally similar to eukaryotic RNA polymerase II.

Archaea vs. Bacteria: Histones and DNA packaging

Bacteria lack true histones, whereas many Archaea possess histones that wrap DNA into nucleosome-like structures.

Archaea vs. Bacteria: Antibiotic sensitivity

Bacteria are sensitive to traditional antibiotics targeting peptidoglycan synthesis or bacterial ribosomes, whereas Archaea are generally resistant to them.

Archaea vs. Bacteria: Presence of introns

Bacteria rarely possess introns in protein-coding genes, whereas Archaea possess introns in some of their transfer RNA ($\text{tRNA}$) and ribosomal RNA ($\text{rRNA}$) genes.

Archaea vs. Bacteria: Methanogenesis

Bacteria cannot perform methanogenesis, whereas certain Archaea (methanogens) uniquely produce methane as a metabolic byproduct.

Archaea vs. Bacteria: Flagellar structure and assembly

Bacterial flagella are hollow, assemble at the tip, and are powered by a proton gradient, whereas archaeal flagella (archaella) are solid, assemble at the base, and are powered by ATP.

Endospores

Dormant, highly resistant, and metabolically inactive structures produced by certain bacteria to survive extreme environmental stress.