DNA structure Flashcards
What is the difference between purines and pyrimidines?
Purines (A & G): Two-ring structure.
Pyrimidines (C & T): One-ring structure.
Always pair a purine with a pyrimidine for a constant DNA diameter.
How are the two DNA strands held together?
Hydrogen bonds between base pairs:
A-T: 2 hydrogen bonds
G-C: 3 hydrogen bonds (stronger)
How are nucleotides joined together?
Via phosphodiester bonds between:
The 3’ hydroxyl group (OH) of one nucleotide.
The 5’ phosphate group of another nucleotide.
What is the direction of DNA synthesis?
Always in the 5’ to 3’ direction.
New nucleotides can only be added to the 3’ end.
What is the semi-conservative model of DNA replication?
Each parental strand is used as a template to create a new complementary strand.
Each new DNA molecule consists of one parental strand and one newly synthesized strand.
What is DNA composed of?
A sugar-phosphate backbone (on the outside).
Nitrogenous bases (A, T, C, G) inside.
Two strands held together by hydrogen bonds.
Double-stranded helix structure
Why is DNA stable despite hydrogen bonds being weak?
There are many hydrogen bonds, making the overall structure strong.
Stacked base pairs also contribute to stability.
What enzyme is responsible for adding new nucleotides?
DNA polymerase III.
In which direction does DNA polymerase synthesize new DNA?
5’ to 3’ direction only.
What is the role of free nucleotides in replication?
Free nucleotides have three phosphate groups.
When added to the growing DNA strand, energy is released from breaking the bond between phosphate groups.
This energy helps form the new phosphodiester bond.
