CLASSWORK: ORIGINS OF CELLS PERIOD:

NAME: DATE:

MILLER & UREY EXPERIMENT

Could organic molecules assemble under conditions on early Earth? In 1953, chemists Stanley Miller and Harold Urey tried to answer that question.

They filled a sterile flask with water, to simulate the early oceans, and boiled it. To the water vapor, they added methane, ammonia, and hydrogen to simulate the gasses that they thought were in the early atmosphere. Then, as shown in the diagram, they passed the gasses through electrodes to simulate lightning. Next, they passed the gasses through a condensation chamber, where cold water cooled them, causing liquid droplets to form and return to the starting flask.

The liquid circulated through the experimental set up for 1 week. The results were spectacular. From these simple molecules, they produced 21 different amino acids – the building blocks of organic proteins.

1. Explain what each part of the experiment shown below represents. (Why did Miller & Urey include each component?)

Part of the Experiment: What it Represents/Why it was Included:

Heated Water

Mix of Gasses (Methane, Ammonia, & Hydrogen)

Electric Charge

2. What conclusions can Miller & Urey draw, based on their 1953 experiment?

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3. We can say that the proteins in this experiment “self-assembled.” Based on your understanding of this experiment, what do you think the term “self-assemble” means?

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4. We know now that the mix of gasses Miller & Urey used did NOT accurately represent the gasses that were present on early Earth. Was their experiment still valuable, even though parts of it were incorrect? Why or why not?

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5. Other scientists built on Miller & Urey’s work by trying similar experiments with more accurate starting gasses. In 1961, one such experiment by Juan Oro produced adenine, one of the bases in DNA & RNA. In 1995, Miller himself repeated the experiment with more accurate starting gasses and produced cytosine and uracil, two other bases in DNA & RNA. How would this add to the conclusions we can draw from these experiments?

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6. Scientists have found amino acids and other organic molecules in meteorites that have landed on Earth from outer space. What does this evidence add to our understanding of the origins of first cells?

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7. How does the Miller & Urey experiment, and its follow-up experiments, add to our understanding of macromolecules?

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