Video Transcript
Griffith’s experiment demonstrated
that genetic material can be passed between the cells of different strains of
bacteria. What term is now given to this
process?
This question talks about an
experiment performed by Frederick Griffith in 1928. Griffith’s experiments and results
formed the basis from which other scientists were able to prove that DNA was the
genetic material, but he also demonstrated a biological process in bacteria that had
never been recorded before.
Our question mentions the term
strains of bacteria. Griffith used a bacterium called
Streptococcus pneumoniae in his experiments. He used two different strains, or
types, of this bacterium, one called the rough strain or the R strain and one called
the smooth strain or the S strain.
These two strains have two key
differences. The names of the two strains give
us a clue about the first difference. The rough strain bacteria have
rough surfaces, while the smooth strain bacteria have smooth surfaces. This is because the smooth strain
bacteria synthesize a smooth coating over their outermost layer. The second difference is that the
rough strain bacteria are nonvirulent, which means that they are not capable of
causing a harmful infection in other organisms. The smooth strain bacteria are
virulent, which means that they are capable of causing a harmful infection.
Now let’s come back to the
statements in our question. It says that Griffith’s experiment
proved that genetic material can be passed between the cells of different strains of
bacteria. How did he do this? Well, Griffith took one set of
rough strain bacteria and one of smooth strain bacteria. He used heat to kill the smooth
strain bacteria, which meant that they were no longer able to cause a harmful
infection. He then mixed these heat-killed
smooth strain bacteria with living rough strain bacteria. Remember, neither of these
should’ve been capable of causing any kind of infection. However, when he injected this
mixture into a group of mice, contrary to what he expected, the mice all developed
pneumonia and died.
Griffith examined the blood of
these dead mice and found living bacteria that had smooth surfaces, even though
these weren’t in the mixture he had injected. He predicted that a substance have
been passed from the heat-killed smooth strain bacteria into the rough strain
bacteria. The substance had caused the rough
strain bacteria to transform. They were now able to synthesize a
smooth protective coating and cause a harmful infection in mice.
We now know that this substance was
DNA, the genetic material. Griffith didn’t know what exactly
the substance was, and so he simply named it the transforming principle. The process by which one strain of
bacteria is transformed into another is now called bacterial transformation, and it
has several uses in genetic engineering.
Now we can answer our question
correctly. The term now given to the process
by which genetic material can be passed between the cells of different strains of
bacteria is bacterial transformation.
