2)Origin of Life

7/29/2019 2)Origin of Life

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The origin of life



The age of the Universe is aconcept that is not easily visualized.

The Cosmic Calendar is an analogythat can help us realize the concept

of “Deep Time”. This comparison

was devised by Carl Sagan.



Imagine that the age of the

Universe (~13.7 billion years) is

converted to one of our 365-day

years . . .

In this conversion, each month

would equal a little over a billionyears.

Here’s what this means . . .



January 1st The Milky Way Sun/planets Multicellular

The Big Bang forms form organisms

Life (on Earth)

appears

http://school.discovery.com

The Earth is formed

~ 4.6 BYA

First

worms

Firstamphibians

First truemammals



http://school.discovery.com

First

amphibians

First true

mammals



Another analogy:

If the Eiffel tower represents the history of

the Earth, the time

where we humans have

been around can be

shown as the coat of paint at the tower’s very

tip . . .

(This analogy was

presented by no other than Mark Twain).

Get the picture?



http://www.earthsci.org

This one is

just fun . . .



The Earth is about 4.6 billion years oldThe atmosphere of the early Earth is thought to have

included: CO2, H2O, CO, H2, NH3, H2S, CH4.

No free molecular oxygen (O2)!!!!!

Many sources of energy:Lightning

Volcanic activityRadiation (cosmic, UV)



Chemical evolution of life (Life from non-

life) – Different form biological evolution! For life to have arisen in this manner, it

is believed that four main conditions

were necessary:

• Little or no free oxygen

• Energy• Chemical building blocks (water, salts,

minerals, gases)

• Time



Based on those conditions (which we believe

we had on early Earth), organic chemicals,which are the essential components of life,

were synthesized.

There are two main models that try to explainhow this happened:

The prebiotic soup hypothesis

The iron-sulfur world hypothesis



The prebiotic soup hypothesis

States that the organic precursors formed near the Earth’s

surfaceIn the 1920s, two scientists, A. Oparin and

J. Haldane, independently proposed that organicmolecules such as simple sugars, amino acids and

nucleotide bases could form from basic rawMaterials.

In the 1950s Stanley Miller (a graduate student)and Harold Urey (his professor) designed an

experiment that simulated the early Earth’senvironment.

http://exobiology.arc.nasa.gov



What did the Miller-Urey experiments demonstrate?

• That biologically

important molecules ---

amino acids, nucleic

acids, sugars, lipids,

etc., can be formedfrom non-living

chemicals through

natural processes.

• This scenario could

work under various

atmospheric mixtures.



• It is currently accepted that the Earth, along with the rest of

the Solar System, originated approximately 4.6 billion years

ago.

• It is further argued, that for the next 600 million years,

meteors and comets blasted the planets. And yet,

apparently almost immediately (in geological terms) after

the last asteroid par-boiled the Earth's surface, life hadappeared.

• This has led some to suggest that life developed not on the

surface at all, but below the surface, perhaps in a super-heated environment like that which we find at the oceanicridge 'smokers.'

The iron-sulfur hypothesis.



The iron-sulfur world hypothesis

States that the organic precursors formedin hydrothermal vents at the ocean’s floor



Important questions about the origin of life in our planet:

Did life originate in a single setting or in several?

*

*

**



Where did the carbon come from?

http://exobiology.arc.nasa.gov/



Important questions about the origin of life in

our planet:

Did life’s building blocks come from different environments?

If life deterministic? In other words, is DNA inevitable?

What role did the environment play in life’s origin?

When did evolution start? (I can answer that!!!!)

Can the study of modern organisms give us

some clues into the origin of life?



All life on Earth is related

DNA is apparently the 'universal' basis for all

life on Earth.

Only 20 [known] amino acids are used in all

living things on Earth. L-amino acids

exclusively are used in all living things on

Earth.

ATP* is the 'universal' energy currency used in

all living cells.



The central dogma of molecular biology

DNA codes for RNA, which codes for proteins . . .

So far, so good, however, in order to synthesize DNA,we need specialized enzymes, which are proteins, but if

proteins need to be ultimately coded for by DNA, well . . .

What does this paradox reminds you of?



The RNA world hypothesis

RNA has the ability to act as both genes

and enzymes (ribozymes).

It has been suggested that RNA was the

first informational molecule, capable of self-replication.

DNA and proteins are thought to have

come later.

Recent developments have providedevidence for this hypothesis. RNA can

undergo directed evolution.



From Peretó, 2005



Most likely, the first living organisms on Earth

were heterotrophs and anaerobes.

Heterotrophs = obtained the molecules needed for

nourishment from the environment, instead of

synthesizing them directly. Autotrophs = Organisms capable of synthesizing their

required molecules using an external energy source

(sunlight, geotermal energy, etc.).

Anaerobes = Organisms that do not use oxygen in their

metabolic processes.

Aerobes = Organisms that use oxygen in their metabolic

processes.



Cells

Protobionts – assemblages organic polymers of non-biological origin

This is a good time to introduce

size scales:

1 meter (m) = 100 meters

1 centimeter = 10-2 meters

1 millimeter (mm) = 10-3 meters

1 micrometer (µm) = 10-6 meters

1 nanometer (nm) = 10-9 meters



Adapted form: www.urmc.rochester.edu/smd/mbi/grad2/pdf/gr03intr.pdf



www.sju.edu



T h e

o r i g i n

o f e u k a r y o

t e s



Dr. Xin Fan

PhD - UPenn

How can some bacteria cause disease?

Dr. Gus Mbuy

PhD - UCLA

Virology

Dr. Oné R. Pagán

PhD – Cornell

PharmacologyNeurobiology

Dr. Win Fairchild

PhD - Michigan

EcologyBiostatistics



Questions?

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