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