Prokaryotes
• Lack nucleus• No organelles• Possess DNA, RNA,
and all other machinery
• Possess ATP synthesis• Two Domains
– Bacteria
– Archaea
Origins of Metabolism
• First prokaryotes - probably chemoheterotrophs– Easiest mode of acquiring nutrients as long
as nutrients present in environment
• ATP probably among those nutrients– Phosphorus limited and essential– ATP easily stores and releases energy
Origins of Metabolism
• Available ATP in environment would decline as numbers of prokaryotes increased
• Selection would favor prokaryotes that could synthesize their own ATP
• ADP + P + energy ATP
• Energy from organic molecules
Origins of Metabolism
• These steps probably lead to evolution of glycolysis
• Glycolysis is metabolic pathway for breaking down organic molecules
Why is Evolution of Glycolysis Significant?
• Provides cells with a means of acquiring and storing energy internally
• Glycolysis does not require oxygen
• Glycolysis and use of ATP as energy carrier found in prokaryotes and eukaryotes
Origin of Photosynthesis
• Abundance of organic molecules would become a problem
• Organisms capable of producing their own organic molecules would be at an advantage
• Light-absorbing pigments (chromophores) probably used early to absorb light energy
Origin of Photosynthesis
• First photosynthesizing prokaryotes probably had photosystems geared toward using hydrogen sulfide as a proton source
• Prokaryotes with metabolic machinery to use water would have a selective advantage
• Use of water significant because oxygen is a by-product
Symbiosis
• Prokaryotes rarely function singly in environment
• Often interact in groups with other prokaryotes or even eukaryotes with complimentary metabolisms
Symbiosis
• Symbiosis refers to ecological relationships between organisms of different species that are in direct contact
• Symbiotic relationships are varied– Mutualism +,+– Commensalism +,0– Parasitism +, -
Domain Archaea
• Prokaryotes but share features with Eukarya nucleus and cytoplasm
• Suggests common ancestry
• Number of unique features
• Ether linkages in membranes– Resistant to extreme conditions
Domain Archaea
• Found in extreme, hostile environments– “extremophiles” – acidic, basic, temperature,
methane
• Thermophiles – high temp. Hydrothermal vents in deep ocean (98°C)
• Halophiles – high salinity (evaporation ponds)
Domain Bacteria
• Very Diverse group (50+ Phyla)
• Table 27.1 – Examples of diversity
• Diversity is in metabolism – most unique to prokaryotes
• Cyanobacteria – photoautotrophs
• Proteobacteria – high diversity of metabolisms; medicine, ag, industry
Horizontal Gene Transfer
• Discussed earlier• Exchanges of genes between different
groups• Viruses can act as vector• Makes prokaryote phylogenetics
(ribosomal RNA)• Understanding to use in organismal
phylogenies
Figure 27.1
Evolutionary Concepts
• From information generated leading to development of Fig. 27.1
• Archaea and Bacteria evolved from common ancestor (see also commonalites in Table 26.1)
• Eukaryotic nucleus and cytoplasm likely arose from an archaeal organism
Evolutionary Concepts
• Mitochondria and plastids originated from proteobacteria and cyanobacteria – endosymbiosis (will discuss later)
• Contributed to gene transfer from bacteria to eukaryotes
GramNegative
GramPositive
Locomotion
• Many are non-motile• Several modes of
locomotion• One is flagella – a
solid fibril
Reproduction
• Binary fission• Transduction – viral• Transformation –
environment• Conjugation
Metabolism
•Obligate – something is required
•Facultative – can operate under broader range of conditions
•Obligate Anaerobe
•Facultative Anaerobe
•Obligate Aerobe
Metabolism
•Respiration – Oxygen used as an electron acceptor
•Anerobes use other molecules
•NOx or SOx molecules
•These metabolic pathways make bacteria important in global nutrient cycles
Nitrogen Cycle
Metabolism
•Cyanobacteria
•Important photosynthesizers
•Use mechanisms similar to plants (precursor)
Prokaryotes
•Limited structural diversity
•Limited genome – limited gene pool
•Why so diverse and successful?
–Mutations
–Horizontal gene transfer
–Transduction
–Transformation