Biology Now, 2e

42 ■ CHAPTER 03 Chemistry of Life

CELLS

At a crowded seminar, Miller presented his

results. Urey sat in the front row. Colleagues at

the meeting recalled that after the presenta-

tion, the famed physicist Enrico Fermi turned

to Urey and said, “I understand that you and

Miller have demonstrated that this is one path

by which life might have originated. Harold, do

you think it was the way?” Urey looked at Fermi

There are hundreds of known amino acids, but

only 20 are the building blocks for proteins, a

major class of molecules found in the cells of

living things. Of the five amino acids that Miller

isolated, three were part of that group of 20.

Thus, from a simple mixture of gases Miller had

indeed created some, but not all, of the amino

acids used in life on Earth.

Figure 3.2

Miller’s original spark discharge experiment

When Stanley Miller zapped a mixture of methane (CH 4 ), ammonia (NH 3 ), hydrogen (H 2 ), and water vapor (H 2 O) with electrical sparks,

he produced compounds called amino acids.

Q1: Before the experiment was run, the apparatus was sterilized and then carefully sealed. Why was this an important

thing to do?

Q2: Why is inclusion of methane in the gas flasks an essential part of the hypothesis that complex organic molecules

were formed in the early atmosphere of Earth? (Hint: What makes a molecule organic?)

Q3: Answer this question after reading about Miller’s “steam injection” experiments: Where was the steam injected in the

experimental apparatus?

1aWater is poured

into the apparatus

and heated.

1bGases are added

into this chamber

of the apparatus.

(^3) An electrical spark
continuously fires
during the
experiment.
(^2) The water
becomes vapor
and travels to the
flask containing
the gases.
5 Samples of the
water/organic
compound “soup”
are removed here.
(^4) The water cools and becomes liquid as it
moves through the apparatus, carrying
organic compounds created by chemical
reactions in the chamber above.