DNA structure - M2 Flashcards
Components of DNA
Nucleotide :
base
deoxyribose sugar
Phosphate group
Who named the nucleotide?
Phoebus Levene
How are nucleotides linked?
Sugar phosphate backbone
How does the sugar phosphate backbone work?
The phosphate groups bonds to the sugar on another nucleotide
What did Erwin Chargraff find?
There is significant variation in the base numbers between different species
Key findings of Chargraff?
1st rule: A=T and C=G
2nd rule: there is variation in the DNA of different species
Why did Wilkins use x-rays to study structure of DNA
The rays bombarded on the molecule would bounce off based on its structure and the x-rays patterns can be analysed to find the structure
What did photo 51 show?
*DNA was a double stranded helix structure
*The bases pointed inwards at 90º of the backbone
What did Watson and Crick find out from photo 51
*DNA had a constant diameter
*Two purines form a a combined 2 ring structure and Two pyrimidines form a a combined 4 ring structure so to have a constant diameter one purine + 1 pyrimidine
What is the difference in the pentose sugars of DNA and RNA
The OH attatched to the C2 Carbon, in DNA does not have the O just the H
What is the 3’ position?
3’ C with the OH- group attatched
What is the 5’ position?
5’ c with the phosphate group attached to it
Bonds that link nucleotides?
Phosphodiester bonds
What is a phosphodiester bond?
Bond where a 3’C OH reacts with a 5’C phosphate group to form a bond + H2O
How are DNA and RNA synthesised?
In the 5’ to 3’ direction is the direction of DNA
Imagine reading left to right, expands towards 3’ end
How do the two strands run?
Antiparallel to each other so that the bases can face inwards towards each other, bases are complementary
5’ to 3’
3’ to 5’
How many H bonds between G and C
3
How many H bonds between A and T
2
What is semi-conservative replication
Where half the parental DNA is conserved in the newly synthesised DNA strand
Why do we need semi-conservative replication?
To produce more cells with the DNA
What are purines?
2 ring structures: A and G
What are pyrimidines?
