Theme 3.1 - DNA Structure Flashcards
What is “nuclein”?
Friedrich Mieshcher, while studying the composition of cell nuclei, collected large quantities of an acidic substance with a high phosphorus content. He called the substance nuclein. (now known as DNA)
Why were proteins originally considered the most likely candidates for hereditary molecules?
Proteins appeared to offer greater opportunities for information coding than nucleic acids. Proteins contain 20 types of amino acids, while nucleic acids have 4 different nitrogenous bases.
In Griffith’s experiments with Streptococcus pneumoniae, which strain was virulent and which avirulent? Why?
The smooth strain, S, was virulent and the rough strain, R, avirulent. The S strain possesses a polysaccharide capsule that hinders the ability of the host’s immune system to detect the pathogen, thereby allowing it sufficient time to multiply and cause fatal pneumonia.
What was the transformation and transforming principle that Griffith described in his experiments?
When Griffith injected mice with living R bacteria along with heat-killed S bacteria, the mice died. The R bacteria had acquired the ability to make the polysaccharide capsule and this change was permanent and stably inherited by the next generations. Griffith called this change of R to S “transformation”. He called the agent responsible for causing this change the “transforming principle”.
Why were proteins and nucleic acids candidates for the transforming principle, but not carbohydrates and lipids?
Carbohydrates and lipids have highly repetitive structure and are therefore not likely to be carrying any information. Proteins and nucleic acids, on the other had, are built of various combinations of amino acids/nucleotides, which makes them complex molecules able to to carry the information needed for transformation.
How did Avery, McLeod and McCarty show that DNA was the transforming principle?
They grew smooth strain S. pneumoniae in culture, then used used head to kill the virulent S bacteria. They then extracted the remaining macromolecules and treated 3 groups of R bacteria - each with an enzyme that would destroy one of proteins, DNA and RNA. While the tubes containing no RNA and protein still transformed to S strain bacteria, the one containing DNAse (and therefore no DNA) did not transform.
