27 - Bacteria and Archaea

Prokaryotes

organisms in the domains bacteria and archaea; lack a nucleus

unicellular

composed of a single cell; may form colonies

cell size (prokaryotes)

typically 0.5-5 µm

Prokaryotic shapes

spheres (cocci), rods (bacilli), and spirals (spirilli)

peptidoglycan

a polymer of sugars and amino acids found in bacterial cell walls

gram-positive bacteria

thick peptidoglycan layer, stains purple, simpler cell wall

gram-negative bacteria

thin peptidoglycan layer with outer membrane stains pink; more antibiotic resistant

capsule

sticky outer layer for protection and adherence; well organized

slime layer

similar to capsule but less organized

endospore

dormant, resistant cell formed by some bacteria to survive extreme conditions

fimbriae

short hairlike appendages for attachment to surfaces or cells

pili (singular pilus)

longer than fimbriae; used to pull cells together and transfer DNA

Flagella

tail-like structure for movement; made of motor, hook, and filament

Archaea cell wall

lacks peptidoglycan; made of polysaccharides and proteins

mycoplasma

smallest known bacteria; lack cell wall

nucleoid

region in prokaryotes where circular chromosome is located; no membrane

plasmids

small, independently replicating rings of DNA in prokaryotes

binary fission

asexual reproduction process where one cell divides into two identical cells

mutation in prokaryotes

occurs at low rate but accumulates rapidly due to fast reproduction

genetic recombination (horizontal gene transfer)

movement of genes between prokaryotic cells

transformation

uptake of foreign DNA from surroundings into a prokaryote

transduction

gene transfer via bacteriophages (viruses that infect bactera)

conjugation

direct transfer of DNA between prokaryotic cells via a pilus

mating bridge

structure formed during conjugation to transfer DNA between cells

autotrophs (prokaryotes)

use inorganic sources (light or chemicals) to produce their own energy

heterotrophs (prokaryotes)

obtain energy and carbon from organic compounds

obligate aerobes

poisoned by oxygen; survive via fermentation or anaerobic respiration

facultative anaerobes

can survive with or without oxygen

nitrogen fixation

conversion of atmospheric nitrogen (N₂) into ammonia (NH₃)

anabaena

filamentous cyanobacterium capable of nitrogen fixation

heterocysts

specialized cells in anabaena where nitrogen fixation occurs