Video Transcript
Which of the following is true about Griffith’s experiment? (A) Griffith’s experiment proved that bacteria can take up genetic material through a
process now known as bacterial transformation. (B) Griffith’s experiment proved that bacteria can obtain DNA through a process
called conjugation. (C) Griffith’s experiment proved that DNA consists of nucleotides. (D) Griffith’s experiment proved that DNA is a double helix.
This question asks us about an experiment conducted by Frederick Griffith in the
early 1900s, which contributed to our understanding of DNA as the genetic
material. His contributions were discovered using a type of bacteria called Streptococcus
pneumoniae. He used two particular strains of bacteria called the smooth strain, or S strain,
which was smooth in appearance, and the rough strain, or R strain, which was rough
in appearance. These strains are genetic variants of Streptococcus pneumoniae that differ in
their physical appearance as well as their virulence, or their ability to cause
disease.
Griffith went on to inject these strains of bacteria into mice. When a mouse is injected with the rough strain, the mouse did not develop pneumonia
and survived. However, when the mouse was injected with the smooth strain, it would develop
pneumonia and die. Griffith decided to try something. He exposed the smooth strain to heat before he injected the bacteria into mice. This killed the bacteria, and so the mice did not develop pneumonia and survived.
What he did next was the interesting part. Griffith noticed that if he combined the heat-killed smooth strain with the rough
strain and then injected this, the mouse would develop pneumonia and die. So the addition of the heat-killed S strain caused the nonvirulent R strain to become
virulent, just like the S strain. This is because the DNA from the heat-killed S strain was able to be taken up by the
R strain. This DNA gave the R strain its virulence and allowed it to infect the mouse cells and
cause pneumonia and death. The process of bacteria taking up genetic material is known as bacterial
transformation.
If we now go back to our question, the option that is true regarding Griffith’s
experiment is given by answer choice (A). Griffith’s experiment proved that bacteria can take up genetic material through a
process now known as bacterial transformation.
