What are the properties of genetic material? Describe Griffith\'s experiment. In
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Question
What are the properties of genetic material? Describe Griffith's experiment. In genetic terms, what is the likely reason that the rough bacteria do not make the polysaccharide capsule? In 1944, Avery, MacLeod and McCarty determined that DNA is the transforming principle. What does 'transforming principle' mean? What the two major types of biologically important polymers present in a T2 phage particle? Phosphor (P) has an atomic number of 15. How many protons and neutrons are in an atom of the radioactive isotope^32P? Why couldn't Hershey and Chase have used radioactive C, N or O in their experiment? Can the single strand of DNA 5'-GATTCC-3' pair with the molecule 5'-CTAAGG-3'? Explain. A double-stranded DNA molecule has 15%T. What are the proportions of the other three bases? A virus is found that has [A] = 12%, [T] = 28% in its DNA. Why might this DNA not follow Chargaff's rules? Describe the conservative model of DNA replication. How did the Meselson-Stahl experiment prove that DNA replication is a semi-conservative process?Explanation / Answer
Answer:
1.The Basic properties for Genetic Material - the material that determines the inherited characteristics of a functional organism:
It must be stable
It must be capable of being expressed when needed
It must be capable of accurate replication
It must be transmitted from parent to progeny without change
2. Griffith Experiment & Transforming Principle
Griffith experiment was a stepping stone for the discovery of genetic material. Frederick Griffith conducted experiments with Streptococcus pneumoniae.
During the experiment, Griffith cultured Streptococcus pneumoniae bacteria which showed two patterns of growth. One culture plate consisted of smooth shiny colonies (S) while other consisted of rough colonies (R). The difference was due to the presence of mucous coat in S strain bacteria, whereas the R strain bacteria lacked them.
Experiment:Griffith injected both S and R strains to mice. The one which was infected with the S strain developed pneumonia and died while that infected with the R strain stayed alive.
In the second stage, Griffith heat-killed the S strain bacteria and injected into mice, but the mice stayed alive. Then, he mixed the heat-killed S and live R strains. This mixture was injected into mice and they died. In addition, he found living S strain bacteria in dead mice.
Rough strain(nonvirulent)-----> Mouse lives
smooth strain (virulent)-------> Mouse dies
heat killed smooth strain------> Mouse lives
Rough strain and heat killed smooth strain-----> Mouse dies
Conclusion: Based on the observation, Griffith concluded that R strain bacteria had been transformed by S strain bacteria. The R strain inherited some ‘transforming principle’ from the heat-killed S strain bacteria which made them virulent. And he assumed this transforming principle as genetic material.
3. The bacteriologists were interested in the difference between two strains of Streptococci that Frederick Griffith had identified in 1923: one, the S (smooth) strain, has a polysaccharide coat and produces smooth, shiny colonies on a lab plate; the other, the R (rough) strain, lacks the coat and produces colonies that look rough and irregular. The relatively harmless R strain lacks an enzyme needed to make the capsule found in the virulent S strain. Mice injected with S-strain of the pneumococcus bacteria die from pneumonic infection within a few days, while mice injected with the R-strain bacteria continue to live. Injection with heat-killed S-strain bacteria also results in the mice surviving.
He hypothesize that the R-strain bacteria had somehow been transformed by the heat-killed S-strain bacteria. Some "transforming principle", transferred from the heat-killed S-strain, had enabled the R-strain to synthesize a smooth polysaccharide coat and become virulent.
The transformation feature of DNA and exsistence of gene is the main genetic reason behind this.
4. At that time it was thought protein might be the hereditary material. In their paper of 1944, Avery and his colleagues suggest that DNA, rather than protein was the hereditary material of bacteria, and could be analogous to genes and/or viruses in higher organisms.
Oswald Avery, Colin MacLeod, and Maclyn McCarty showed that DNA (not proteins) can transform the properties of cells, clarifying the chemical nature of genes. They identified DNA as the "transforming principle" while studying Streptococcus pneumoniae, bacteria that can cause pneumonia.
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