Download Origins of Metabolism

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
– Parasitism
+,+
+,0
+, -
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
Gram
Positive
Gram
Negative
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