Copyright © 2005 Pearson Education, Inc. publishing as ... · Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Let’s try a practice question… • 1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


• Chemical and physical processes on early

Earth produced very simple cells through a

sequence of stages.

• Could this be true???? How could it happen??

• Let’s follow it step by step.

• Here are the objectives…


Describe a scientific hypothesis about the origin of life on Earth.

[LO 1.27,

Evaluate scientific questions based on hypotheses about the origin

of life on Earth. [LO 1.28, SP 3.3]

Describe the reasons for revisions of scientific hypotheses about

the origin of life on Earth. [LO 1.29, SP 6.3]

Evaluate scientific hypotheses about the origin of life on Earth. [LO

1.30, SP 6.5]

Evaluate the accuracy and legitimacy of data to answer scientific

questions about the origin of life on Earth. [LO 1.31, SP 4.4]

Justify the selection of geological, physical, and chemical data that

reveal early Earth conditions. [LO 1.32, SP 4.1]


Step One: Make Simple Organic Monomers

Earth formed about 4.6 billion years ago

– Along with the rest of the solar system

• Earth’s early atmosphere and oceans

contained water vapor and many chemicals

released by volcanic eruptions such as _____

and _____, but no _____.

• But how can these simple molecules become

complex molecules like proteins and DNA???


Figure 26.2

Electrode

Cooled water

containing

organic

molecules

H2O

Water vapor

CH4

CONCLSION

.

• Miller and Urey showed us one way.


Time for 6 minutes of Carl Sagan to show us how?

• Check it out on the Cosmos DVD: cosmic

Fugue, Ch. 10 – 12.

• To emphasize – a reducing atmosphere (no

molecular oxygen) was a key. What would

oxygen do to these chemicals that were

combining?


Let’s try a practice question…

• 1. By discharging electric sparks into a laboratory chamber atmosphere

that consisted of water vapor, hydrogen gas, methane, and ammonia,

Stanley Miller obtained data that showed that a number of organic

molecules, including many amino acids, could be synthesized. Miller

was attempting to model early Earth conditions as understood in the

1950s. The results of Miller’s experiments best support which of the

following hypotheses?

• (A) The molecules essential to life today did not exist at the time Earth

was first formed.

• (B) The molecules essential to life today could not have been carried to

the primordial Earth by a comet or meteorite.

• (C) The molecules essential to life today could have formed under

early Earth conditions.

• (D) The molecules essential to life today were initially self-replicating

proteins that were synthesized approximately four billion years ago.


• Instead of forming in the atmosphere, it could

have been deep sea vents, or maybe deep in ice.

Alkaline vents, not black smokers, seem to be the

current favorite (proton gradient handout)

Figure 26.3


Watch here. 4 min.

This is pretty good. 9 min. It starts with a decent

review of natural selection, and then starts to

compare chemical evolution to biological around

the 3 minute mark.

This is GOOD. Show this!

https://www.youtube.com/watch?v=mRzxTzKIsp8


Latest update. 2015

• Sutherland’s team reports that it created

nucleic acid precursors starting with just

hydrogen cyanide (HCN), hydrogen sulfide

(H2S), and ultraviolet (UV) light. What is more,

Sutherland says, the conditions that produce

nucleic acid precursors also create the starting

materials needed to make natural amino acids

and lipids. That suggests a single set of

reactions could have given rise to most of life’s

building blocks simultaneously.

http://www.nature.com/doifinder/10.1038/nchem.2202


Science – best explanation. Proof of how?

• Sutherland’s team argues that early Earth was

a favorable setting for those reactions. HCN is

abundant in comets, which rained down

steadily for nearly the first several hundred

million years of Earth’s history. The impacts

would also have produced enough energy to

synthesize HCN from hydrogen, carbon, and

nitrogen. Likewise, Sutherland says, H2S was

thought to have been common on early Earth,

as was the UV radiation that could drive the

reactions and metal-containing minerals that

could have catalyzed them.


Step Two: Make Polymers

• Now that you have small organic molecules,

they might polymerize when they are

concentrated on hot sand, clay, or rock. Or

maybe even in ice???

– Check out this 1:21 to see how fatty acids can

get made and concentrated, and then this :30

for nucleic acids.

– OR – here’s a link to the whole series.

../Animations/Origin of life videos/geyser.mov

../Animations/Origin of life videos/clayPolym.mov

http://exploringorigins.org/fattyacids.html


Step Three: Form Protobionts

• Now you are getting closer to something that is

almost a cell, a Proto – what???

– Check out this :25, and this :33 to see how

micelles and liposomes form naturally.

../Animations/Origin of life videos/FAdynamics.mov

../Animations/Origin of life videos/denovoVesicle.mov


Inside these membrane bound things, we get this.

20 m

(a) Simple reproduction. This lipo-

some is “giving birth” to smaller

liposomes (LM).

(b) Simple metabolism. If enzymes—in this case,

phosphorylase and amylase—are included in the

solution from which the droplets self-assemble,

some liposomes can carry out simple metabolic

reactions and export the products.

Glucose-phosphate

Glucose-phosphate

Phosphorylase

Starch

Amylase

Maltose

Maltose

Phosphate

Figure 26.4a, b


The “RNA World” and the Dawn of Natural Selection

• The first genetic material

– Was probably RNA, not DNA

– RNA can fold into a specific shape :25, and

catalyze like an enzyme. Where have we seen

RNA doing this?

../Animations/Origin of life videos/RNAfolding.mov


• Watch what ribozymes can do…

– Self-splicing watch :25

– Making complementary copies of short

stretches of their own sequence or other short

pieces of RNA :40

Figure 26.5

Ribozyme

(RNA molecule)

Template

Nucleotides

Complementary RNA copy

3

5 5

../Animations/Origin of life videos/nonEnzymaticPolym.mov

../Animations/Origin of life videos/ribozymeReplication.mov


How can these RNA’s get inside a liposome?

• If you are more efficient, natural selection will

take care of you watch :35

– Watch :35 to see how simple protocell division

can be.

– Watch for a good summary.

No, if there is time, which there never is, take a

look at a neat new finding on the evolution of

multicellularity.

http://elifesciences.org/content/5/e10147

../Animations/Origin of life videos/vesicleEntry.mov

../Animations/Origin of life videos/protocellDivision.mov

http://www.newscientist.com/article/dn17987-how-life-evolved-10-steps-to-the-first-cells.html

http://elifesciences.org/content/5/e10147


Extraterrestrial Sources of Organic Compounds

• How’s this for a crazy idea? Panspermia

• Let’s look at the Murchison meteorite.


But wait!!! Another new idea!!!! TNA world?

It differs from RNA and DNA in its sugar backbone:

TNA uses threose where RNA uses ribose and DNA deoxyribose.

That gives TNA a key advantage, says John Chaput of Arizona State University in Tempe:

it is a smaller molecule than ribose or deoxyribose,

possibly making TNA easier to form.

Chaput and his colleagues have now created a

TNA molecule that folds into a three-dimensional shape and clamps onto a specific protein.

These are key steps towards creating a TNA enzyme that can control a chemical reaction, just like RNA.

http://chemistry.asu.edu/faculty/J_chaput.asp


So let’s break down the steps

• If you want life to start, the first step is:

• Then…

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Copyright © 2005 Pearson Education, Inc. publishing as ... · Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Let’s try a practice question… • 1