DNA Structure Flashcards
Who discovered, in 1953, that DNA is a double helix?
Rosalind Franklin and Maurice Wilkins
Who discovered, in 1949, the base-pairing proportions and DNA varies between species?
Erwin Chargaff
In 1953, who discovered the organization of DNA + complimentary base-pairing?
James Watson and Francis Crick
In 1958, who discovered DNA replication?
Matthew Meselson & Franklin Stahl
Erwin Chargaff determined base pair proportions through what?
paper chromatography (he invented the technique)
Ratio of A equals that of ___
T (adenine = thymine)
Ratio of G equals that of ___
C (cytosine = guanine)
In humans, cytosine and guanine are less or more present in the composition than adenine and thymine?
LESS C-G
MORE A-T
DNA is a ___ acid.
nucleic
The building blocks of DNA are____.
nucleotides
What composes nucleotide?
5-carbon sugar (deoxyribose)
Phosphate group
Nitrogenous base
What are purines bases ?
Adenine and Guanine (A & G)
What are pyrimidines bases?
Cytosine, Thymine and Uracil (C & T & U)
What does 2nd position of carbon molecule mean?
If nucleotide is RNA of DNA
What happens in the 3rd position of carbon?
Incoming nucleotide binds during replication
DNA chains are ___
antiparallel (5’to 3’ orientation)
How did Rosalind Franklin and Maurice Wilkins discover that DNA is helical?
X-ray chrystallography (3D structure of DNA)
[X-ray diffraction of DNA double helix]
Franklin had concluded that:
_____ and ____
However, organization of bases was unclear.
- there were two antiparallel sugar-phosphate backbones
2. the nitrogenous bases paired in the molecule’s interior .
Who in 1953 deduced the structure of DNA using evidence from: Chargaff Franklin/Wilkins others?
James Watson and Francis Crick
What did Watson and Crick show?
- DNA composed of 2 chains of nucleotides, each in a helix
- DNA chains run anti-parallel to each other
- Purine-pyrimidine base pairs (keep distance between chain constant)
What happened when they tried to match purine and purine?
too wide
What happened when they tried to match pyrimidines and pyrimidines?
too narrow
What happened when they tried to match purine + pyrimidine?
width consistent with X-ray data
Two strands of DNA are _______.
Complementary
What did Watson and Crick deduce from replication?
Each strand acts as template for building a new strand in replication
Parent molecule unwinds and 2 daughter strands are built based on complemetary base-pairing rules
What are “daughter” DNA molecules?
each consisting of one parental strand and one new strand
What is the dispersive model?
Each strand is a mix of old and new
What is the semiconservative model?
Predicts each daughter molecule will have one old strand
What is the conservative model?
Two parent strands rejoin
Matthew Meselson & Franklin Stahl, 1958
Showed the process of DNA replication uses
semi-conservative replication
Used gradient centrifugation, E.coli, and nitrogen isotopes
Matthew Meselson and Franlinn Stahl
Meselson and Stahl concluded that the mechanism of DNA replication is the _____ model.
Semi-conservative model
OR
Each strand of DNA acts as a template for the synthesis of a new strand.
