DNA History
Who perfected X-ray diffraction in order to get one of the first clear images of DNA, confirming it was a double helix?
Rosalind Franklin in 1953
What are the base pairs of DNA?
Adenine (A) can form two hydrogen bonds with thymine (T) in an A-T base-pair, and guanine (G) can from three hydrogen bonds with cytosine (C) in a G-C base-pair.
What is the phosphodiester backbone?
Two strands of the double helix are made up of long polymers of nucleotides, each strand is made up of repeating sugar and phosphate units joined by phosphodiester bonds.
Where does DNA replication take place?
In the nucleus of eukaryotic cells and the nucleoid region in prokaryotic cells.
Who informally learned of Rosalind Franklin’s results before they were published, and ended up getting the credit for it?
James Watson and Francis Crick
What is a phosphodiester bond?
Phosphodiester bonds are formed when nucleotide monomers are joined together via a dehydration reaction involving the 5’ phosphate of one nucleotide and 3’ hydroxyl of another.
What type of bonds form between bases and how many are there?
Two hydrogen bonds form between adenine and thymine, three hydrogen bonds form between guanine and cytosine.
What three things does DNA replication require?
A template/something to copy (the parental DNA molecules), nucleotides act as the building blocks, and enzymes perform the actions of copying.
Besides the photo from Franklin’s X-ray diffraction, what other piece of information allowed Watson and Crick to quickly construct a model of DNA?
Information on the tautomeric forms of bases, or tautomers.
What are the three components of nucleic acids?
1. A 5-carbon sugar
2. A Phosphate (PO4-) group
3. A nitrogenous base: Either a two ringed purine (Adenine, A, or Guanine, G) or a single-ringed pyrimidine (Thymine, T, or cytosine, C); in RNA the pyrimidine uracil, U, replaces thymine.
What are the two types of polarity for strands?
Strands can either have a 5’ -to- 3’ polarity or a 3’ -to- 5’ polarity.
What is a DNA polymerase?
The enzyme that actually matches the existing DNA bases with complimentary nucleotides and then links the nucleotides together to make the new strand.
Who discovered DNA
Friedrich Miescher in 1869
What does it mean for a base pair to be “complementary“, and why is it important?
Each base-pair combines a two-ringed purine with a single-ringed pyrimidine making the diameter of each base-pair the same. This makes them complimentary, which is important as it keeps the double helix undistorted and allows us to only need to identify one strand of DNA since its complimentarity dictates the above base-pairs.
What are the configurations for two strands and what configuration does DNA have?
Parallel is when the polarities are the same (one strand running 5’ to 3’ and the other also running 5’ to 3’) or antiparallel when the polarities are different (one strand running 5’ to 3’ and the other running 3’ to 5’).
What does a polymerase need to begin synthesis?
All DNA polymerase require a primer to begin synthesis.
What was the white substance Miescher extracted from the nuclei of white blood cells? Hint: It is later called nucleic acid because it was acidic.
Nuclein
Why is the dehydration reaction between two nucleotide monomers called a phosphodiester bond? Hint: it is mostly in the name.
Because the phosphate group is now linked to the two sugars by means of a pair of ester bonds.
What configuration does DNA have in terms of polarity?
Native double-stranded DNA always has an antiparallel configuration (one strand runs 5’ to 3’ while the other runs 3’ to 5’)
Of the three models that were proposed, which model is accepted for DNA replication And what is it?
Hint: the proposed models were the conservative model, the semiconservative model, and the dispersive model.
The semiconservative model is accepted. This model states that one strand of the parental duplex would remain intact in each daughter duplex; a new complimentary strand would be synthesized with each parental strand. Each daughter duplex would consist of one parental strand and one newly synthesized strand.