14.1 Flashcards
Describe the evidence that DNA is the genetic material (Griffith)
R strain bacteria was changed by S strain bacteria and R strain contained a “transforming principle” from the heat killed S strain which made it virulent. He assumed the transforming principle as genetic material.
Describe the evidence that DNA is the genetic material (Avery, Macleod & McCarty)
Studied S-strain bacteria. found that mixture of protein-digesting enzyme (protease), RNA digesting enzyme (RNAse), and lipid digesting enzyme (lipase) with S strain first then with R stain didn’t affect transformation and mice died after injection of both strains. Digestion of DNAse inhibited transformation and mice lived so DNA was concluded to be the genetic material
Describe the evidence that DNA is the genetic material (Hershey & Chase )
phages attached to the surface of a host bacterial cell and injected a substance in them. They measured radioactivity in the pellet and supernatant and found a large amount of 32P appeared in the pellet and 35S in the supernatant. They concluded that DNA was injected into host cells and made up the gen. Mat. Of the phage.
Describe the evidence that DNA is the genetic material (Watson & Crick)
found structural evidence of it (double helix)
Illustrate Griffith’s experiments discovering that bacteria can be transformed.
the R-strain bacteria must have taken up what he called a “transforming principle” from the heat-killed S bacteria, which allowed them to “transform” into smooth-coated bacteria and become virulent.
Compare and contrasts Avery, MacLeod, and McCarty’s experiment to that of Griffith.
o Griffith discovered it when heat killed smooth strain is mixed with rough strain and injected in mice the mice died. The first result was surprising it means something was getting transferred from heat-killed S strain to the live R strain that made the rough strain virulent showing the presence of a transforming principle
o Mccleod did series of experiments to find transforming principles using lysate of heat S strain and treated with different enzymes. Once enzyme treatment is given the mixtures treated in R strain and incubated. The presence of smooth colonies means that strain got converted smooth strain. It was only DNAs treatment that failed to convert the rough drawing to the smooth strains This means the DNA was transforming principle.
Describe how Avery, MacLeod, and McCarty identified that DNA is the genetic material.
observed that proteases - enzymes that degrade proteins - did not destroy the transforming principle. Neither did lipases - enzymes that digest lipids. They found that the transforming substance was rich in nucleic acids, but Ribonuclease, which digests RNA, did not inactivate the substance. They had isolated DNA. This was the agent that could produce an enduring, heritable change in an organism.
Identify Chargaff’s rules regarding DNA composition and explain how this supports the complimentary base pairing of nucleotides
The rule is that a purine (two rings base) must always pair with a pyrimidine (single ring base) and found that the % of adenine was equal to the % of thymine and the % of guanine was equal to the % of cytosine.
Describe Wilkins and Franklin’s contribution to understanding the structure of DNA.
X-rays through the molecule yielded a shadow picture of the molecule’s structure, by how the X-rays bounced off its component parts. Called x-ray crystallography
Describe Watson and Crick’s DNA model.
o a double helix that contained two long, helical strands wound together. With individual units (bases) along each strand that complimented each other
o Sugar-phosphate backbone with phosphodiester bonds
Identify the nitrogenous bases in DNA and RNA.
o DNA- Adenine, Thymine, Guanine, cytosine
o RNA- Adenine, Uracil, Guanine, cytosine
Identify the bond that holds together the sugar phosphate backbone.
phosphodiester
Illustrate what is meant by antiparallel and complimentary base pairing.
o The DNA strands are complementary to each other, run in opposite directions, and are called antiparallel strands
o One runs 5’ to 3’, the other 3’ to 5’
Differentiate between purine and pyrimidines.
o Purine-two ring base (6-membered ring fused to a 5-membered ring) (adenine and guanine)
o Pyrimidine- single-ring base (single 6 membered ring) (thymine and cytosine)
Identify the sugars of DNA and RNA.
o DNA- 2-deoxy ribose (C5H10O4)
o RNA- ribose (C5H10O5)
