Fundamentals of Biology

DNA Structure, Classic Experiments

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Session Overview

This session will explain early experiments in Molecular Biology. Outlined are classic experiments by Avery, Griffith, Hershey, and Chase that demonstrated DNA was the hereditary material, background on Chargaff, Watson, Crick, and Franklin and how their discoveries contributed to the discovery of the structure of DNA, and details regarding how the semi-conservative model of DNA replication was shown by Meselson and Stahl. Learning Objectives To understand the basic outline of the Griffith, Avery, and Hershey/Chase experiments, and how these showed that DNA was the hereditary material. To understand the role Chargaff played in discovering the structure of DNA. To understand the roles Watson, Crick, and Franklin played in discovering the structure of DNA. To understand how the data obtained by Meselson and Stahl confirms the semi-conservative model of DNA replication. To draw a schematic of DNA that highlights the double-stranded nature, the polarity of each strand with respect to the other, and the base pairing between the strands.

Session Activities

Lecture Video

Watch the lecture video excerpt

• DNA Structure and Classic experiments, Excerpt 1

Check Yourself

Question 1

Cells can be fractionated into different chemical components. Both Griffith and Avery found cellular fractions that could transform non-disease causing bacteria into disease causing bacteria. In each case, the transforming fraction contained predominantly which of the following molecules?

carbohydrates close

lipids close

nucleic acid check

protein close

Check   Show Solution

Although the fractions were not completely pure, the fractions that had transforming abilities were greatly enriched for nucleic acid, specifically DNA.

Question 2

What functional group is found on the 3’ end of a nucleotide?

carboxyl close

hydroxyl check

nitrogenous base close

phosphate close

Check

Question 3

Which of the following is found in DNA but not in protein?

Carbon close

Nitrogen close

Oxygen close

Phosphorus check

Sulphur close

Check

Session Activities

Lecture Video

Watch the lecture video excerpt

• DNA Structure and Classic experiments, Excerpt 2

Check Yourself

Question 1

In density gradient centrifugation, which of the following DNA molecules will travel the farthest down the tube?

a 14N-14N duplex close

a 14N-15N duplex close

a 15N-15N duplex check

Check

Session Activities

Practice Problems

• Problems (PDF)
• Solutions (PDF)

Further Study

Suggested topics for further study in an introductory-level Biology textbook

• Classic experiments by Avery, Griffith, and Hershey/Chase
• Chargaff
• Watson, Crick, and Franklin
• Semi-conservative model of DNA replication

Useful Links

• Hershey and Chase Experiment
• Meselson and Stahl Experiment
• “Molecular Structure of Nucleic Acids” (The original Watson and Crick paper)

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