In such a problem as the spontaneous origin of life...time is on its side. However improbable we regard this event...given enough time it will almost certainly happen at least once...One only has to wait: time itself performs the miracles...This is by far our most significant conclusion--that life, as an orderly natural event on such a planet as ours, was inevitable. - George Wald

Origin of life


Audesirk, Audesirk & Byers Part of Chapter 17, selection from Chapter 1

Today's musical selection
Peter, Paul and Mary Puff the magic dragon

Personal reflection. When I was in 9th grade biology (1961-1962) I read a paper (The origin of life, Scientific American, August 1954) by George Wald (who won a Nobel Prize in 1967); reading that paper had a great impact on me.

Panspermia - seeds of life distributed everywhere
Extraterrestrial origin

Spontaneous generation discredited:

Figure E1-1 (scientific inquiry box chapter 1)
(1) Redi (1600's show maggots on meat need flies to lay eggs)

Figure 17-1
(2) Pasteur microorganisms

Universe 15 - 20 billion years old
Earth 4.6 billion
Earth has water as liquid, many heavy elements

Figure 17-2
Haldane = Oparin theory, Miller & Urey experiment to reconstruct synthesis of organic molecules using water, methane, hydrogen and ammonia.

Figure 17-3
Early atmosphere (there's still some debate): Nitrogen (N2), Hydrogen (reducing = build-up), Methane (for C, H), Ammonia (for N, H), Carbon dioxide (for C, O), Water (for H, O), also some Hydrogen - sulfide (S), CO (carbon monoxide)

No (or very little) Oxygen O2 (oxidizing = break-down) or Ozone O3 (block UV)

Now N2 78%, O2 21%, CO2 0.3% + others (Argon)

Primordial hot dilute soup
"chemical" vs. "biological" evolution
amino acids hook together with "geologically relevant" heating like lava
amino acids - proteins, nucleotides - RNA, DNA, ATP
Eventually, DNA became the major hereditary molecule because it is so stable.
Probably RNA was the first hereditary material.
Vesicles, protocells
In the laboratory, such protobionts have been made.
Prokaryotes 3 & 1/2 billion years ago

Figure 17-4
then Eukaryotes (1 & 1/2 billion years ago)
Origin of mitochondria and chloroplasts as endosymbionts

Ferment (energy and CO2) (anaerobic = w/o oxygen)

Photosynthesis 6 CO2 + 6 H2O -- C6H12O6 (glucose) + O2

Animals - motility, sensory

Respiration (metabolism, aerobic)

Ozone (O3) from O2
Prior to that, all life had to be in the sea for protection from ultraviolet light
(depletion with freon = fluorocarbons)

Invasion of land had special requirements:
(1) vascular system to transport nutrients, wastes, gasses and hormones for multicellular organisms, (2) support on land where gravity is more of a concern
(3) mating without water

Questions used in 2007 & 2008 relating to this outline

Spontaneous generation
*(a) is accepted as how life originated even though it was disproved in classic experiments by Redi (for flies) and Pasteur (for bacteria).
(b) relates to the observation that embryos have gill slits and tails while adults do not.
(c) is the expression used to describe continental drift.
(d) describes how mitochondria and chloroplasts originated in early eukaryotes.
(e) is a process in which the allele frequency changes if only a few individuals of the population mate.

The earliest heredity may have been based on
*(a) RNA.
(b) DNA.
(c) proteins.
(d) chloroplasts.
(e) autotrophs.

"Reducing atmosphere" refers to
(a) global warming.
*(b) hydrogen favoring constructive reactions.
(c) oxygen.
(d) depletion of ozone.
(e) nitrogen.

There is a consensus that (what gas?) was missing from or very low in the prebiotic atmosphere?
(a) water
*(b) oxygen
(c) ammonia
(d) methane
(e) hydrogen

Endosymbiotes relate to
(a) the Irish potato famine.
(b) the Hardy-Weinberg principle.
(c) the pollen tube.
(d) xylem and phloem.
*(e) organelles in eukaryotic cells.

In the history of life, the earliest nutrition for catabolism
(a) was provided by photosynthesis.
*(b) was anaerobic.
(c) was present in protostomes.
(d) was a product of mitochondria.
(e) required the use of oxygen.

Most scientists think that global warming results from
(a) freon leaking from air conditioners.
*(b) carbon dioxide from fossil fuels.
(c) abundance of the primordial "hot dilute soup."
(d) an asteroid impact.
(e) elimination of habitats.

Why is ozone depletion a big problem?
*(a) Ultraviolet light reaches Earth.
(b) Melting polar ice caps will inundate low altitude cities.
(c) Acromegaly results.
(d) Osteoporosis results.
(e) Diuresis results.

All experiments that simulate conditions in Earth's early atmosphere assume that it did NOT contain which gas?
A) water vapor
B) methane
*C) oxygen
D) hydrogen
E) carbon dioxide

Carbon dioxide
A) was the main ingredient in the "primordial hot dilute soup."
B) was responsible for the "reducing" reactions of the primordial atmosphere.
*C) is increasing in the atmosphere presently and is a greenhouse gas.
D) is created because of Freon leaking from air conditioners.
E) is offloaded from the blood to tissues in the systemic circulation.

Why was fermentation needed by the earliest organisms for energy production?
*A) Since photosynthesis had not yet evolved, there was no oxygen.
B) There were chloroplasts in cells, but there were not mitochondria yet.
C) The cells were autotrophs, and that's what autotrophs do for metabolism
D) Without ozone, there was no ultraviolet (UV) light.
E) With only a two-chambered heart, there was poor gas exchange in these organisms.

Louis Pasteur's experiment illustrated that
A) spontaneous generation does occur.
B) mitochondria were incorporated as endosymbiotes.
C) phospholipids will spontaneously form a bilayer in water.
D) some complex molecules associated with living organisms can be synthesized by heating and cooling a solution of simple molecules and providing an electric spark.
*E) microbes will not grow in a nutrient broth that has been sterilized unless they are allowed to enter by opening the vessel to the air.

It has been proposed that the first atmosphere of Earth had all the following gases EXCEPT
A) H2.
B) H2O.
*C) O2.
D) CH4.
E) water vapor.

A) was used in the metabolism of the earliest organisms, the autotrophs.
B) is a big problem because of the use of fossil fuels.
C) was the source of sulfur in the earliest organic molecules.
*D) could not have appeared in the atmosphere until after photosynthesis.
E) was incorporated into the earliest eukaryotic cells to become organelles.

In the most ancient life forms, what was hypothesized to be the first self-replicating hereditary molecule because it had some enzymatic capabilities?
C) protein
D) methane
E) carbohydrate

The scenario of prebiotic (chemical) evolution leading to the origin of life on Earth is plausible because
A) DNA was already present in the primordial atmosphere.
*B) there was a vast period of time for simple chemicals to form complex molecules that eventually became enclosed simple cells.
C) even today, the ocean is a hot dilute soup of organic molecules that form into cells.
D) Francesco Redi proved that spontaneous generation occurred.
E) extraterrestrial organic molecules were known to have arrived.

Questions used in 2002 relating to this outline (and other outlines)

Which gas was probably not abundant (during chemical and early biological evolution) until after the origin of photosynthesis?
*(a) ozone
(b) carbon dioxide
(c) methane
(d) nitrogen
(e) water vapor

Why was it important in an evolutionary context to have early reproducing molecules enclosed into coacervates?
(a) because nutrients were scarce
(b) to compete with the abundant chemiautotrophs
*(c) so that the peptides translated would reside near the RNA
(d) because aerobic processes were beginning to degrade RNA
(e) because DNA, unlike proteins, can have properties like enzymes

(a) was released when the Cambrian exploded.
(b) served as the energy source of ancient bacteria.
(c) causes programmed cell death.
(d) arrived on Earth from the asteroid that arrived at the end of the Cretaceous.
*(e) is used to date fossils.

Which form of life came into existence first?
(a) flowering plants
*(b) prokaryotes
(c) invertebrates
(d) eukaryotes
(e) reptiles

The first biological organisms
(a) were probably eukaryotes.
(b) were probably autotrophs.
*(c) were probably heterotrophs.
(d) probably used DNA as their hereditary molecule.
(e) were probably photosynthetic.

Organic compounds break down spontaneously in the presence of what substance? Hence, life probably never would have emerged if the atmosphere were the same billions of years ago as it is today.
(a) hydrogen
(b) water
(c) nitrogen
*(d) oxygen
(e) methane

Chemical evolution before the origin of life on Earth is believed to have taken place
(a) about 4000 years before Christ.
(b) about 10,000 years ago.
(c) about 1,000,000 years ago.
(d) about 1,000,000,000 years ago.
*(e) before any of the above.

The "atmosphere" in the Miller-Urey experiment was "reducing" because it contained what substance which would have promoted the formation of organic molecules through reduction reactions.
(a) Argon
(b) O2
*(c) H2
(d) N2
(e) CO2

Which would have come first?
(a) sexual reproduction
*(b) heterotrophic prokaryotes
(c) incorporation of bacteria (that eventually became mitochondria) into eukaryotes
(d) incorporation of photosynthetic bacteria (that eventually became chloroplasts) into the precursors of plant cells
(e) the invasion of land

Among his many contributions, Louis Pasteur is known for
*(a) a classic experiment disproving spontaneous generation.
(b) prosecuting the Scopes "monkey trial."
(c) publishing a theory much like Darwin's at about the same time.
(d) developing a way to distinguish bacteria with different cell wall-membrane geometry.
(e) visiting the Galopagos Islands.

About how long ago did the first cells appear?
(a) 3.5 million years
(b) 3.5 billion years
(c) after photosynthesis evolved
(d) not until there was sexual reproduction
(e) 1.5 billion years ago when eukaryotes came into existence

There are very few fossils, except for stomatolites (that are like current mats of prokaryotes)
(a) in the Jurassic period
(b) in the Permean extinction
(c) at the Cretaceous-Tertiary boundary.
(d) during the part of the Paleozoic era before the Carboniferous period.
(e) in the Precambrian

Why do scientists think RNA was the hereditary molecule in the earliest organisms?
(a) RNA is more stable than DNA.
(b) RNA has fewer nucleotides and thus it is simpler.
*(c) RNA has properties like enzymes (usually proteins).
(d) The earliest organisms were viruses, and these contain only RNA.
(e) It was not until later that proteins evolved to take over hereditary function.

Which is thought to have happened most recently?
(a) the first protobionts.
(b) the first heterotrophic prokaryotes
(c) oxygen production by photosynthesis.
(d) incorporation of bacteria that eventually became mitochondria into eukaryotic cells.
*(e) incorporation of bacteria that would eventually become chloroplasts into plant cells.

This page was last updated 8/3/09

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