Origins of Life

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Transcript Origins of Life

Origins of Life
• The primitive earth
• The primitive atmosphere
• Theories on the origin of life
• Matter & Energy
• Cell surface-to-volume ratio
Let’s start at the beginning…
• Scientists believe the universe started with The Big
• Evidence for this comes from the fact that we know
the universe is always expanding
• According to second law of thermodynamics, the
universe is increasing in entropy (disorder) as time
goes on
• What we find is that life is becoming more and more
complex (orderly).
• We do this at the expense of our universe and ‘pay
for order’ in the form of energy
Two things keep us from being killed by the sun’s radiation
1. The magnetosphere formed by the movement of the iron core
2. The atmosphere
The Primitive Atmosphere
• The primitive atmosphere was made up of
hydrogen, ammonia and methane
• Nitrogen, carbon dioxide, sulfur dioxide, and
water vapor emitted from volcanoes replaced
the remaining primitive gases
• The earth is 4.6 billion years old
• The earth was too hostile for life until about
3.9 bya
• First fossils date back to 3.5 bya
Origin of life
What’s wrong with this
Origin of Life Overview
• Primitive Earth provided inorganic precursors from which organic
molecules could have been synthesized due to the presence of available
free energy and the absence of a significant quantity of oxygen
• In turn, these molecules served as monomers or building blocks for the
formation of more complex molecules, including amino acids and
• The joining of these monomers produced polymers with the ability to
replicate, store and transfer information.
• These complex reaction sets could have occurred in solution (organic soup
model) or as reactions on solid reactive surfaces.
• The RNA World hypothesis proposes that RNA could have been the earliest
genetic material
Evidence for the origin of life
• Geological
• Fossil record
• Chemical
• Miller-Urey experiment
• Molecular
• Shared genes
• Common characteristics for life
Geologic Time Scale
• No oxygen  oxygen
• No life  life
• Single-celled  multi-celled
• Prokaryote  eukaryote
(no nucleus  nucleus)
• Dating fossils
• Not ONE thing out of order
Miller-Urey Experiment
• Done in the 1950’s
• Abiogenesis: the creation of life (organic
matter) from non-life (inorganic matter)
• When they simulated the early
atmosphere they collected more complex
molecules and amino acids that had been
synthesized over time
• This was a sterile environment with NO
gaseous oxygen
Expanding upon the Miller-Urey
• His experiment is still going
• Now can find up to 25 different amino acids
• These amino acids are considered “old” in terms of ancient genes
• Other scientists who have repeated his experiment have found the
formation of nucleic acids (DNA & RNA)
Molecular Evidence
• We all came from a common ancestor
• Uses DNA and/or RNA to transmit information
between generations
• Uses proteins to carry our metabolic functions
• Uses ATP for energy
• Has a cellular membranes made up of a
phospholipid bilayer
• Undergo cell division
• You share 50% of your DNA with a banana
• If it were by chance, you would share 25% of your
DNA (because there are four letters in the genetic
Energy + Matter = Life
Need energy and matter for:
• Growth
• Homeostasis
• Reproduction
• In accordance with the laws of
thermodynamics, to offset entropy, energy
input must exceed energy lost from and
used by an organism to maintain order
• All of this takes a massive coordination
between obtaining energy and utilizing
• Getting energy
• Autotrophs: photosynthesis to capture free
energy from sun and turn it into sugars and CO2
• Heterotrophs: eat plants or animals & use the
carbon molecules they made already
• Using energy
• Cellular respiration (with oxygen) and
fermentation (without oxygen) harvest free
energy from sugars to produce free energy
carriers, including ATP.
• Storing energy
• fats
• Cells & organisms must exchange matter with the environment in
order to make complex molecules
• There are four macromolecules
The Big Picture
• Cells & organisms must exchange matter with the environment and all life
uses the same elements to build their macromolecules
Nucleic Acids
Cell Surface Area-to-Volume Ratio
• A cell is CONSTANTLY interacting
with their environment
• Cell MUST be able to bring stuff
into the cell (endocytosis) & get
waste out of the cell (exocytosis)
• As a cell grows, it’s volume
increases faster than it’s surface
area (decreasing SA-to-V ratio)
• If cell gets too big, the middle of
the cell becomes too disconnected
from the outside world