Origin of Life to Cell Diversity

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Origin of Life to Cell Diversity

• Dr.Jessada Denduangboripant
• Department of Biology
• Faculty of Science
• Chulalongkorn University

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Origin of Life to Cell Diversity

• 1. Life and Genetic Information
• 2. From Chemistry to Heredity
• 3. From Heredity to Simple Cells
• 4. The Origin of Eukaryotic Cells

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1. Life and Genetic Information

• What is Life and the Nature of Life?
• The Major Transitions
• How did genetic information increase?

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What is Life the Nature of Life?

• There are 2 ways to define life.
• First - Something is alive if it has certain
  properties that we associate with living thing on
  Earth.
• E.g. if it has a complex structure, and grows or
  responds to stimuli.
• Or it has a metabolism (its atoms are not
  permanent parts, but taken in from the
  environment, combined to form chemical compounds,
  and excreted back to the environment).

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What is Life the Nature of Life?

• Or - if it has the properties of multiplication,
  variation, and heredity.
• A living thing multiplies can produce 2 or
  more similar entities.
• A living thing varies are not identical.
• A living thing have heredity tends to get rise
  to its like with occasional breakdown for
  variation.
• These properties are needed if the population is
  to evolve by natural selection.

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Can you distinguish between a living thing and an
artifact by that definition?
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The Major Transitions

• Q How the first life with multiplication,
  variation, and heredity could arise in the
  chemical environment of the primitive Earth?
• Evolution can lead simple life to have greater
  complexity by a number of major changes in the
  way in which genetic information is stored,
  transmitted translated - Major Transitions.

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Major Transitions

• Replicating molecules --gt Populations of
  molecules in protocells.
• Independent replicators --gt Chromosomes.
• RNA (as gene enzyme) --gt DNA protein.
• Prokaryote --gt Eukaryote.
• And so on . till human societies.

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How did Genetic Information Increase?

• Duplication divergence the duplication of a
  piece of DNA, from a single gene to a whole set
  of chromosomes, followed by minor divergence.
• Symbiosis 2 different kinds of individuals come
  to live together (mutualisitic symbiosis). The
  new individual has the sum of the information
  present in the 2 symbionts.

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2. From Chemistry to Heredity

• The Primitive Soup ( Pizza)
• The Origin of Replication
• RNA Worlds

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The Primitive Soup

• Miller (1953) passed an electric discharge
  through a chamber with water, methane (CH4),
  ammonia (NH3)
• --gt Various amino acids, sugars, purines
  pyrimidines were made.

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Primitive Soup

• But, the yield of ribose sugar (backbone of RNA
  DNA) was low.
• And the amino acids were linked together not only
  by peptide bonds.
• How polymers (proteins, nucleic acids) linked by
  specific chemical bonds, could have been formed?

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Primitive Pizza (Günter Wächtershäuser, late
1980s)

• Polymerization of those organic compounds took
  place while their (ve) charged ions (e.g.
  phosphate ions, PO43-) bonded to a (ve) charged
  surface of iron pyrite.
• Binding to a surface ensure that molecules were
  held in a correct orientation --gt be able to link
  together.
• Also increase local concentration of the
  interacting molecules --gt speed up the reaction.

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The Primitive Pizza
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The Origin of Replication

• Experimentally, a piece of 6 bp DNA can be
  replicated from a starting unit (two
  single-stranded molecules, each consisting of 3
  bases linked end to end) without enzymes.
• Moreover, if incubating a short primer RNA with 4
  RNA nucleotides and a replicase enzyme, the
  primer molecule will be replicated. ---gt RNAs
  1st role as a template.

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RNA Worlds

• The origin of life must have had RNA molecules to
  act not only as genetic-information carrying
  templates but also as enzymes.

• Problems of DNA-protien
• No enzymes can exist without long DNA molecules
  to code for them.
• But, no long DNA could be reliably copied without
  enzymes.

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RNA Worlds

• But, single-stranded RNA can fold to form a 2nd
  structures (e.g. hairpin loops) leading to a 3-D
  3rd structures (same as amino acid sequences) and
  could act as enzymes - Ribozymes.
• Moreover, primitive ribozymes acquired specific
  amino acids as cofactors to catalyze more
  efficiently --gt Code.

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RNA Worlds
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3. From Heredity to Simple Cells

• Why Cells?
• The Origin of Membranes and Cells

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Why Cells?

• To progress from simple replicating molecules to
  more complex, a web of co-operative interactions
  between genes had to evolve.

• One way to do that is to let all replicating
  molecules be enclosed within compartments or
  cells.

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Why Cells?

• The early cells must require
• a membrane (permit nutrients to pass through, but
  impermeable to metabolic molecules)
• building blocks for new membrane and new genetic
  materials
• and a collection of RNA-like genes acting as
  catalysts of various cellular processes.

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Origin of Membranes

• To form primitive membranes, fatty acids may have
  formed as a lipid-bilayer flat sheet on charges
  surfaces of minerals.
• Complex proteins (e.g. permease) could have been
  inserted into the membrane to increase its
  permeability for desirable compounds.

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Origin of Cells

• The first true cells with membranes were formed
  as semicells (minute semispherical vesicles) on
  surfaces.
• Semicells completely folded into a sphere to
  avoid the hydrophobic site of fatty acids to
  contact with water.

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4. The Origin of Eukaryotic Cells

• The Endomembrane System
• From Symbrionts to Organelles

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Origin of Eukaryotic Cells

• The transition from prokaryote to eukaryote is a
  complicated series of events
• 1. Loss of the rigid cell wall.
• 2. Acquisition of phagocytosis to feed on solid
  particles.
• 3. Origin of an internal cytoskeleton (actin
  filament microtubules) cell locomotion.
• 4. Appearance of an internal cell membranes,
  including the nuclear membranes.

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Origin of Eukaryotic Cells

• 5. Spatial separation of transcription and
  translation.
• 6. Evolution of rod-shaped chromosomes with
  multiple origins of replication --gt less
  limitation on genome size.
• 7. Finally, the origin of cell organelles, esp.
  mitochondria and plastids (in algae and plants).

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The Endomembrane System

• Nuclear membrane of eukaryotes consists of 2
  adpressed membrane, formed by flattening of
  spherical vesicles, to surround the nucleus.
• The same system as ER (endoplasmic reticulum) and
  other cell vesicles, e.g. food vesicles and
  lysosomes.
• It divides transcription process inside nucleus
  from translation in cytoplasm, but has nuclear
  pores for mRNA to pass out for replication
  transcription enzymes to pass into.

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From Symbrionts to Organelles

• Nowaday, mitochondrias and chloroplasts are
  believed to be descended from symbiotic purple
  bacteria and cyanobacteria.
• These eukaryotic organelles have two membranes
  and multiply within the cell by binary fission.
• Also have their own small circular chromosomes
  and small ribosomes, similar to those of
  bacteria, suggesting that they may be the
  descendants of formerly free-living bacteria with
  similar metabolic capacities.

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Finally, the last sentence of Charles Darwins
Origin of Species

• There is a grandeur in this view of life,
• with its several powers, being originally
  breathed into a few forms or into one
• and that,
• while this planet has gone cycling on according
  to the fixed law of gravity,
• from so simple a beginning endless forms most
  beautiful and most wonderful have been,
• and are being evolved