BIO 140 - 2ND Module

• The Origin of the Universe (before life began)

  • About 14 BYA, the universe came into being (acc. to astronomers and physicists)

  • through an explosion from an infinitely dense point

  (“the big bang”)

  • Hydrogen was formed shortly after and gave rise to

  other elements
• • About 10 BYA, Milky Way Galaxy was formed from the collapse

  of a cloud of dust and gases

  • About 4.6 BYA, the Sun was formed as a second- or third-

  generation star from a stellar explosion (supernova) giving rise

  to the Solar System including the Earth

  ~ based on radiometric dating of meteorites and moon rocks

  • The Earth formed a solid crust as it cool and the oceans were

  formed about 4.5 BYA
• • About 4 BYA, small protocontinents may have arisen,

  leading to large landmasses by about 3 BYA

  • The oldest known rocks are younger ~3.8 BYO, only

  formed later from geological processes such as

  subduction of crust
• Primitive earth conditions:

  • Catastrophes

  • Volcanic eruptions

  • Boiling oceans

  • Lightning

  • UV radiation
• Pre-life:

  • Strongly reducing (oxygen-less) atmosphere

  • Common gases: methane, hydrogen, carbon dioxide,

  ammonia, etc.

  • Energy: Volcanic eruptions, storms, lightning charges

  • Oceanic world

  • These, along with sufficient time, provided the

  requirements for chemical evolution.
• General theories on the origin of

  life on earth:

  1. Special Creation Theory
  2. Spontaneous Generation
  3. Chemical Origin of Life
  4. Extraterrestial Origin
  5. Deep Sea Vents
• 1. Special Creation Theory

  • God made the Universe and the Earth in 7 days

  • “Big Bang” implied

  • 7 days= 7 Biblical days??

  • All organisms created simultaneously at the same

  point in time →→ no change ~ fixity of species
• Spontaneous generation

  • or ABIOGENESIS ~ life from non-life

  Examples:

  • Rats from dirty rags or

  shirt

  • Insects from rice grains

  • Flies or maggots from

  rotten meat
• Chemical origin of life

  • First living cell arose from aggregation of inorganic

  elements to form primitive organic molecules

  • Given the conditions of the primitive earth
• Life originated between 3.5 and 4.1 BY ago.

  • about the time at which the earth’s crust began to

  solidify

  • life arose by “spontaneous generation”

  • inorganic to organic molecules.. to cells....
• Raw materials :

  1. Water

  2. Nitrogen

  3. Ammonia

  4. Carbon dioxide

  5. Carbon monoxide

  6. Methane

  7. Hydrogen gas

  (Reducing atmosphere)
• Chemical evolution: 4 stages:

  1. Abiotic synthesis and accumulation of small organic molecules.

  2. Joining of monomers into polymers.

  3. Formation of protobionts (due to aggregation of abiotically produced molecules).

  4. Origin of heredity during or before protobiont appearance.
• • Oparin-Haldane Hypothesis (“Prebiotic/Primordial Soup”) – early atmosphere was a reducing environment

  • Reducing gases + heat and electricity = organic

  molecules (amino acids, sugars, fatty acids, etc.)

  • Molecules settled in the water or on rock or clay surfaces
• A.I. Oparin and J. B. S. Haldane (1920s)

  • postulated that the reducing atmosphere and greater

  UV radiation enhanced reactions

  • which joined simple molecules to produce the first organic molecules..

  • not possible today since Oxygen attacks chemical bonds.

  (Recall: aerobic respiration)
• About Oparin and Haldane Hypothesis...

  • However, the evidence is not yet convincing that the early

  atmosphere was in fact reducing

  • Instead of forming in the atmosphere, the first organic

  compounds may have been synthesized near submerged

  volcanoes and deep-sea vents

  • Alternative: Iron-Sulfur World Hypothesis: organic molecules

  produced at hydrothermal vents
• Stanley Miller and Harold Urey (1953)

  • tested the Oparin-Haldane hypothesis in the lab

  • made an apparatus with H2O, H2, CH4 and NH3 to create organic molecules

  • resulted to amino acids, sugars, lipids, ATP, purines and pyrimidines

  • lab experiments showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible
• The early biomolecules aggregated to form simple,

  “primitive” cells which were:

  1. Prokaryotic

  2. Heterotrophic

  The first cells may have been preceeded by protobionts
• Two examples of protobionts: (abiotically produced molecules)

  1. Proteinoids (microspheres) 2. Liposomes
• Proteinoids

  • abiotically synthesized polypeptides

  • can be made by dripping organic monomers

  onto hot sand, rock or clay
• Clay

  • substrate for abiotic synthesis of polymers since:

  1. Monomers bind to charged sites in clay.

  2. Metal ions in clay could act as catalysts of

  dehydration reactions.

  3. Binding sites in clay assisted in forming polymers.
• Iron Pyrite

  • or fool’s gold

  • consists of iron and sulfur

  • an alternative to clay as substratum of organic synthesis

  • provides a charged surface and electrons freed during its formation could support bonding between molecules.
• Laboratory evidence for protobionts:

  1. Proteinoids assemble into microspheres surrounded by a selectively permeable membrane.
  2. Liposomes can form spontaneously from phospholipids.
• Coacervates (named by Oparin)

  • one type of protobiont formed when a suspension of macromolecules is shaken

  • colloidal aggregates or droplets of polypeptides, nucleic acids and polysaccharides
• Coacervate droplets formed by interaction between gelatine

  and gum arabic. (A.I. Oparin)
• Origin of genetic information?

  • RNA- first genetic material

  • Amino acids aligned along RNA molecules by a primitive

  mechanism.

  • Proteins and enzymes evolved.

  • RNA chains base pair with each other to produce DNA.

  • DNA replaced RNA as the genetic material because it is more

  stable.
• Important features of RNA:

  1. RNA polymers can replicate
  2. RNA can serve as template on which polypeptides form.
• Several evidences suggest that RNA preceded DNA:

  1. Single-stranded RNA is simpler than DNA which is always double-stranded.
  2. RNA can take on many different structures depending on its nucleotide sequence.

  ~ some structural forms allow RNA to act as enzyme (or “ribozyme”),

  catalyzing biochemical reactions e.g. replication of RNA

  3. “Pre-biotic soup” experiments have readily yielded the nucleotide U rather than T.
• Transition from RNA to DNA

  • possibly because RNA has a high mutation rate

  • more complex life forms could not evolve until the

  mutation rate reduced

  • the evolution of DNA would have led to a reduction of

  mutation rate
• criteria for a living cell:

  1. It can capture energy from the environment.
  2. It can use that energy to replicate itself.
  3. It can carry out metabolism.
• In living organisms, the said functions are carried out by:

  • Nucleic acids – carry information which can be replicated

  • Proteins – help replicate nucleic acids, transduce energy, and generate / constitute the phenotype

  • Lipid membrane – hold the components together in compartments

  ~ “cells”
• Protobionts exhibit some life

  properties such as:

  1. Metabolism

  2. Self-replication

  3. Excitability

  4. Maintenance of an internal environment

  different from their surroundings
• Extraterrestial origin of life or PANSPERMIA

  Hypotheses:

  1. Through meteorites and comets
  2. Brought by intelligent extraterrestrial aliens
• Water dynamics in deep-sea vents

  1. Cold water seeps down into tiny fissures in an oceanic ridge.
  2. Hot rocks get shocked by the cold water and crack, causing little earthquakes to occur.
  3. Water in the cracks picks up heat from magma.
  4. Hot water forced through hydrothermal vents brings nutrients melted from the rock below.
• Stromatolites in Australia

  -These fossils appear to be photosynthetic; indicate that life evolved

  prior to the time of the “fossils”.
• Two models on the origin of eukaryotic cells

  1. The autogenous model – infolding of the plasma membrane → ER and nucleus
  2. The endosymbiotic model - engulfment of aerobic heterotrophic prokaryotes (mitochondria) and photosynthetic prokaryotes (chloroplast)
• Events associated with the evolution of eukaryotes:

  • Origin of the mitochondria and chloroplasts through endosymbiosis: strongly supported by:

  • Morphological similarity of the organelles to bacteria

  • Molecular evidence, i.e., the mitochondrial genes are more similar to free-living genes of bacteria than to nuclear genes
• Events associated with the

  evolution of eukaryotes:

  • Evolution of the nucleus

  • Evolution of mitosis and meiosis

  • Evolution of photosynthesis

  • Origin of multicellular life for more complex

  eukaryotes
• Inspite of the diversity of present-day organisms, there are certain universal features that point to a common ancestor, i.e., a monophyletic origin of all organisms:

  • Organisms synthesize and use only L isomers of amino acids as building block of proteins

  • Universality of the genetic code

  • Universality of the machinery of protein synthesis
• More scientific clues as to the actual origin of life are present in:

  1. Molecules
  2. Metabolic capabilities
  3. Anatomy of species
  4. Fossil records
• Proof of Panspermia: Earth's craters