Origin of Life and Prokaryotes

BIOL 1407

Early Earth

• 4.6 billion years ago (bya)

• Early atmosphere:– No free oxygen– Primarily nitrogen and

carbon dioxide– High energy from

lightning, UV radiation• Photo Credit: Mount St. Helens, May 18, 1980, taken by

Austin Post, USGS

Conditions of Early Earth

• Intense volcanic activity

• Meteorite bombardment

• Warm environment

• Photo Credit: Courtesy of NASA @ http://origins.jpl.nasa.gov/habitable-planets/images/ra7in16-early-earth.jpg

Earliest Evidence of Life

• Oldest fossil organisms: photosynthetic cyanobacteria

• Western Australia

• 3.5 bya

Fossil Stromatolites

• Multiple layers of cyanobacteria

• Secreted CaCO3

dome-shaped structures

• First reefs

Living Stromatolites

• Shark Bay, Australia

• Hypersaline• Few

predators

Fossil vs. Living Cyanobacteria

Earliest Life

• Single-celled organisms probably evolved before 3.9 bya

• No 3.9 bya fossils• Photo Credit: Robert Simmon, 2008, NASA,

Wikimedia Commons

Jack Hills: Rock formation in Australia; rocks > 3.6 bya; 4.4 bya zircon crystal found in this formation

Why No 3.9 BYA Fossils?

• Few rocks date to 3.9 bya

• Tiny unicellular fossils are hard to find

• Photo Credit of Proterozoic Stromatolites: UNP, 2006, Wikimedia Commons

Molecular Fossils

• Chemical traces of biomolecules

• 3.9 bya evidence of prokaryotic lipids

• Photo Credit of Hopanoid Compound: MarcoTolo, 2006, Wikimedia Commons

Abiogenesis

• Origin of life from non-living components

• Photo of Stanley Miller: NASA, 1999, Wikimedia Commons

Four Steps of Abiogenesis

• Step 1: Synthesis of organic monomers from inorganic molecules

• Photo credit for amino acid, tryptophan: Boghog2, 2007, Wikimedia Commons

Four Steps of Abiogenesis

• Step 2: Organic Monomers Organic Polymers

• Catalysts?• Photo Credit for Kassinin: Edgar181,

2007, Wikimedia Commons

Four Steps of Abiogenesis

• Step 3: Protobionts form

• Protobiont = Organic molecules surrounded by membrane-like structure

Protobionts

• Life-like properties:– Reproduce– Simple

Metabolism– Membrane

potentials

Four Steps of Abiogenesis

• Step 4: Heredity• Pass instructions to

offspring• Controls protein

synthesis • 1st genetic material:

RNA?• Photo Credit of Hammerhead Ribozyme: William G.

Scott, 2007, Wikimedia Commons

RNA Self-Replication

Photo Credit: Campbell, 1999

DNA replaced RNA. Why?

Picture Credit: Figure 17-3, 8th ed. Campbell, modified from original

Where did Abiogenesis Occur?

• Hypotheses:– Hydrothermal vents– Tide pools– Panspermia: from

outer space• Photo Credit for Black Smoker: NOAA, 2006,

Wikimedia Commons

Evolution of Prokaryotes?

Photo Credit of Lassen Volcanic National Park Hot Springs: Walter Siegmund, 2005, Wikimedia Commons

Oxygen Revolution

• Oxygen accumulated

• Most anaerobes died

• Some survived in anaerobic habitats

• Photograph: Banded iron formations that indicate free oxygen in oceans (2.7 bya)

Oxygen Revolution

• Oxygen Evolution of aerobic respiration

• Increased ATP production More energy

• Photo Credit of Bacillus cereus on blood agar: CDC, 2006, Wikimedia Commons

Prokaryotic Cells

• Review – Prokaryotic

cell structure from BIOL 1406

– Cell wall present

Prokaryotic Cells

• Review – Circular

chromosome– Plasmids

Prokaryotic Cells

• Review – Reproduction

(binary fission)

– Membrane transport

• Gases• Water• Wastes• Ions

• Photo: Dr. Vincent A. Fischetti, Laboratory of Bacterial Pathogenesis and Immunology, Rockefeller University, Courtesy of NOAA

Prokaryotic Cell Shapes

Prokaryotic Nutrition

• Heterotrophs • Autotrophs

Heterotrophs

• Energy from:– Organic matter

• Chemoheterotroph– Light

• Photoheterotroph

Autotrophs

• Energy from:– Inorganic matter

• Chemoautotroph– Light

• Photoautotroph

Photoautotrophs

• Photoautotrophs can be:– Non-oxygenic– OxygenicPhoto: Cyanobacteria that uses oxygenic photosynthesis

Prokaryotic Domains

• Domain Bacteria

• Domain Archaea

Domain Bacteria

• Prokaryote• Cell wall contains

peptidoglycan• Circular

chromosome– No histones

• Photo: Beggiatoa, a sulfur bacterium. Granules contain elemental sulfur produced by the cell’s metabolism.

Domain Bacteria

• Five main clades of Bacteria

Clade Proteobacteria

Other Bacterial Clades

Domain Archaea

• Prokaryote• No peptidoglycan

in cell wall• Circular

chromosome– Histones

• Photo: Halobacterium, a salt-loving (halophile) archaean. Courtesy of NASA.

Archaeans

• Most known archaeans are extremophiles

• Picture Credit of Hydrothermal Vent Archeans, Extreme Thermophiles: Courtesy of NOAA

Halophiles

Left: Owen Lake, California

Right: Halobacterium Picture Credit: Courtesy of NASA

Extreme Thermophiles

Left: Hot Springs, Yellowstone

Right: Nevada Geyser

Methanogens

Left: Methanopyrus kandleri, 2006, PMPoon, Wikimedia Commons

Right: Methanothermobacter, Tashiror, 2006, Wikimedia Commons

Acidophiles

Left: Sulfolobus, Xiaoya Xiang,2007, Wikimedia Commons

Right: Acid mine drainage, Carol Stroker, 2005, NASA Wikimedia Commons

Archaeans in “Normal Environments”

• Oceans, soils,freshwater

Photo Credit of Worldwide View of Plankton, 1998-2004: NASA, Wikimedia Commons

Note: Archaeans are an important part of plankton. Up to 20% of world’s biomass may be archaeans.

Domain Archaea is Sister Taxon to Domain Eukarya

Lateral Gene Transfer

• Difficult to find universal ancestor

The End

Unless otherwise specified, all images in this presentation came from:

Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.