Bio Chapter 12 Clean Study Guide - Chapter 12 Section 1...

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Chapter 12 Section 1: Identifying the Substance ofGenesHow do genes work?To answer that question, the first thing you need to know is what genes are made of.How would you go about figuring out what molecule or molecules go into making a gene?What clues did bacterial transformation yield about the gene?By observing bacterial transformation, Avery and other scientists discovered that the nucleic acid DNA stores and transmits genetic information from one generation of bacteria tothe next.To truly understand genetics, scientists realized they had to discover the chemical nature of the gene.If the molecule that carries genetic information could be identified, it might be possible to understand how genes control the inherited characteristics of living things.The discovery of the chemical nature of the gene began in 1928 with British scientist Frederick Griffith, who was trying to figure out how certain types of bacteria produce pneumonia.Griffith isolated two different strains of the same bacterial species.Both strains grew very well in culture plates in Griffith’s lab, but only one of the strains caused pneumonia.The disease-causing bacteria (S strain) grew into smooth colonies on culture plates, whereas the harmless bacteria (R strain) produced colonies with rough edges.When Griffith injected mice with disease-causing bacteria, the mice developed pneumonia and died.When he injected mice with harmless bacteria, the mice stayed healthy.Perhaps the S-strain bacteria produced a toxin that made the mice sick? To find out, Griffith ran a series of experiments.First, Griffith took a culture of the S strain, heated the cells to kill them, and then injected the heat-killed bacteria into laboratory mice.The mice survived, suggesting that the cause of pneumonia was not a toxin from these disease-causing bacteria.In Griffith’s next experiment, he mixed the heat-killed, S-strain bacteria with live, harmless bacteria from the R strain and injected the mixture into laboratory mice.The injected mice developed pneumonia, and many died.The lungs of these mice were filled with the disease-causing bacteria. How could that happen if the S strain cells were dead?Griffith reasoned that some chemical factor that could change harmless bacteria into disease-causing bacteria was transferred from the heat-killed cells of the S strain into the live cells of the R strain.He called this process transformation, because one type of bacteria had been changed permanently into another.Because the ability to cause disease was inherited by the offspring of the transformed bacteria, Griffith concluded that the transforming factor had to be a gene.
A group of scientists at the Rockefeller Institute in New York, led by the Canadian biologist Oswald Avery, wanted to determine which molecule in the heat-killed bacteria was most important for transformation.Avery and his team extracted a mixture of various molecules from the heat-killed bacteria and treated this mixture with enzymes that destroyed proteins, lipids,

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