DNA Structure and Function

Question 1

Frederick Griffith

Answer 1

TRANSFORMATION
can a genetically encoded trait be transferred btw different bacterial species?
-treated mice with S (pathogenic) cells, R (non-pathogenic) cells, heat killed S cells, and a mix of heat-killed S cells in R cells
-once dead, the S cells were no longer pathogenic BUT
-the R cells were able to uptake and express the genetic material that kills the mice, becoming S cells themselves

Question 2

Avery, MacLeod and McCarty

Answer 2

what is the transforming principle?
Took samples heat killed S cells and treated each with a different enzyme that would degrade a particular macromolecule
-the tubes that still had DNA resulted in mouse death while the tube with DNAse added did not
-conclude that DNA is the TRANSFORMING PRINCIPLE
BUT many still though DNA wasn’t complex enough, and that humans and bacteria might not share the same genetic material

Question 3

Hershey and Chase

Answer 3

Is it the DNA or the protein in a bacteriophage that infects and reprograms host cells?
-DNA labelled with 32P
-Protein labelled with 35S
infected bacteria with samples that had one or the other labelled, centrifuged to separate the bacteria from the phages, looked to see whether the pellet (bacterial cells) or supernatant (phages) had radioactivity
-when labelled, the DNA turned up in the bacteria while the protein was in the supernatant, meaning DNA must be the hereditary material

Question 4

Purines

Answer 4

nitrogenous bases in DNA (also in RNA)
Adenine (A) and Guanine (G)
-two fused rings
-bond with thymine (T) and cytosine (C) respectively

Question 5

Pyrimidines

Answer 5

nitrogenous bases
thymine (T) and guanine (G)
-single, six membered rings
-bond with adenine and guanine respectively

Question 6

Erwin Chargaff

Answer 6

-all DNA made of same 4 bases
A=T
G=C
purines=pyrimidines

Question 7

Franklin and Wilkins

Answer 7

What is the structure of DNA?

Franklin produced a diffraction image of DNA with X-ray crystallography

Question 8

Watson and Crick

Answer 8

built a structural model to interpret Franklin’s diffraction image of DNA

• DNA is a double helix
• two nucleotide strands
• fixed width of 2nm between backbones (this is why a purine MUST pair with a pyrimidine)
• nucleotides within a strand are joined by covalent, phosphodiester bonds
• sugar and phosphate backbone faces out, bases face in
• strands held together in middle by H-bonds (2 contacts between A-T, 3 contacts between G-C)
• two strands are antiparallel