Question

Which of the following conclusions was drawn from the Avery-MacLeod-McCarty experiment related to bacterial DNA?

• A. \( \text{Proteins are the genetic material in bacteria.} \)
• B. \( \text{RNA is the genetic material in bacteria.} \)
• C. \( \text{DNA is the genetic material in bacteria.} \)
• D. \( \text{Lipids are the genetic material in bacteria.} \)

Hint:

The Avery-MacLeod-McCarty experiment provided strong evidence that DNA, rather than proteins or RNA, is the genetic material in bacteria. This discovery paved the way for the molecular understanding of heredity.

Answer 1

The Correct Option is C

The Avery-MacLeod-McCarty experiment, conducted in 1944, was groundbreaking in demonstrating that DNA, not proteins or RNA, is the genetic material responsible for heredity. Their experiment was a follow-up to Griffith's earlier work on bacterial transformation. Step 1: Griffith's Transformational Experiment.
Griffith's experiment showed that when non-virulent \( R \)-strain bacteria were mixed with heat-killed \( S \)-strain bacteria, the non-virulent bacteria were transformed into virulent bacteria. However, Griffith was unable to determine what the "transforming principle" was—whether it was proteins, RNA, or DNA. Step 2: The Avery-MacLeod-McCarty Experiment.
To identify the transforming principle, Avery, MacLeod, and McCarty isolated three types of macromolecules—proteins, RNA, and DNA—from the heat-killed \( S \)-strain bacteria. They then tested each type of macromolecule to see if it could still transform the non-virulent \( R \)-strain: The samples were treated with enzymes that broke down proteins (protease), RNA (RNase), and DNA (DNase). When proteins and RNA were destroyed, transformation still occurred, indicating that neither of these molecules were the genetic material. However, when DNA was destroyed by DNase, transformation was inhibited, suggesting that DNA was the "transforming principle." Step 3: Conclusion.
From these results, Avery, MacLeod, and McCarty concluded that **DNA is the genetic material** responsible for transformation in bacteria, thus directly establishing DNA as the molecule responsible for heredity. Thus, the correct answer is \( \mathbf{DNA \, is \, the \, genetic \, material \, in \, bacteria.} \)