The Origin and Early History of Life Chapter 4

Outline Origin of Life Hypotheses Chemical Evolution Cell Origin Theories Bubble Theories Prokaryotic Cells Archaebacteria Bacteria Eukaryotic Cells Extraterrestrial Life

What do we know? ~ 1.5 Million species identified so far Many more remain unidentified

Are we alone? Yes No

Which one represents possible origin of life on earth? Extraterrestrial aliens brought it Came with meteors from other planets Some superhuman powers created it Chemicals from primordial soup combined to make life None of the above

What have we learned so far? Cell theory All living organisms are made of cells, and all living cells come from other living cells. Molecular basis of inheritance DNA encodes genes which make-up and control living organisms. Evolutionary change Life-forms have evolved varying characteristics to adapt to varied environments. Evolutionary conservation Some characteristics of earlier organisms are preserved and passed on to future generations.

Where the first cell came from? Or….Can life arise from non-life? Can we test this scientifically? Conditions on early earth Formation of organic molecules Chemical evolution Primitive cell Prokaryotes Eukaryotes Multicellular organisms

Conditions on Early Earth- Reducing Atmosphere Life most likely emerged under high-temperature conditions. Early atmosphere is often referred to as a reducing atmosphere. exact conditions unknown ample availability of hydrogen atoms very little oxygen

Origin of Life - Location Ocean’s edge bubble hypotheses Under frozen seas problematic due to necessary conditions Deep in Earth’s crust byproduct of volcanic activity Within clay positively-charged clay Deep-sea vents conditions suitable for Archaea

Miller-Urey Experiment Attempted to reproduce early reducing atmosphere and produce organic compounds from inorganic materials hydrogen-rich electrical discharges Produced amino acids carbohydrates lipids nucleotides

Chemical Evolution If life originally arose from non-life, how might this have happened? Consider the following scenario Synthesis and accumulation of small organic molecules Joining of these monomers into polymers Aggregation of these molecules into droplets to form localized microenvironments Origin of heredity

Polymer Formation Sidney Fox (University of Miami) demonstrated the abiotic polymerization of organic monomers Polymers were formed when dilute solutions of organic molecules were dripped onto hot sand, clay, or rock “Proteinoids” Clay can serve to concentrate these molecules Monomers bind to charged sites on clay particles Metal ions in clay have catalytic function

Which came first? DNA RNA Protein Most Likely DNA  RNA  PROTEIN (Genetic information) (Information and catalytic) (Catalytic and structural)

Abiotic RNA Replication Remember RNA enzymes?

Lets make something with those molecules Aggregations of abiotically produced molecules Preceded living cells Laboratory experiments have demonstrated their formation from organic compounds Protobionts and liposomes

Origin of protobiots Bubble theories (Oparin)

PROTO-CELLS Chemical evolution ultimately led to the formation of proto-cells Membrane-surrounded sacs containing genetic material and metabolically-active molecules Such structures have been experimentally produced From these proto-cells, cells ultimately arose

Microfossils have been found in rocks as old as 3.5 billion years old. Earliest Cells Microfossils have been found in rocks as old as 3.5 billion years old. resemble prokaryotes Stromatolites

EARLIEST LIFE The earliest cells were prokaryotic Lack a membrane-bound nucleus Early in the history of life, populations diverged into two major lineages  bacteria  archaea & eukaryotes

Archaebacteria Extreme-condition prokaryotes lack peptidoglycan in cell walls methanogens extreme halophiles extreme thermophiles thought to have split from Bacteria 2 bya.

Bacteria Second major group of prokaryotes strong cell walls simpler gene structure contains most modern prokaryotes includes photosynthetic bacteria cyanobacteria

EARLIEST LIFE How do we know that domain Eukarya is more closely related to domain Archaea than to domain Bacteria? Analysis of rRNAs and other highly conserved genes and proteins provide the strongest evidence

First Eukaryotic Cells Eukaryotes probably arose about 1.5 bya. Internal membrane-bound structures such as mitochondria and chloroplasts are thought to have evolved via endosymbiosis. Energy-producing bacteria were engulfed by larger bacteria. beneficial symbiotic relationship

First Eukaryotic Cells Sexual reproduction Eukaryotic cells can reproduce sexually, thus allowing for genetic recombination. Genetic variation is the raw material necessary for evolution. Multicellularity arisen many times among eukaryotes fosters specialization

Development of new branches on the TREE

TAXONOMY

Extraterrestrial Life Universe has 1020 stars similar to our sun. Conditions may be such that life has evolved on other worlds in addition to our own. ancient bacteria on Mars. largest moon of Jupiter, Europa, covered with ice. liquid water may be underneath

The Domains and Kingdoms

What they have and what they don’t

What about this group?

Summary Fundamental Properties of Life Origin of Life Hypotheses Chemical Evolution Cell Origin Theories Bubble Theories Prokaryotic Cells Archaebacteria Bacteria Eukaryotic Cells Extraterrestrial Life