Nucleic Acids Flashcards
DNA nucleotide structure
Phosphate < deoxyribose < nitrogen-containing organic base
DNA structure (+ function)
- Double helix (bases protected + compact)
- Sugar phosphate backbone (strength + stability)
- Many hydrogen bonds (strength + stability)
- Weak hydrogen bonds (strands separated easily for DNA replication)
- Long polymer (so a lot of genetic information can fit into a small space in the cell nucleus)
Complementary base pairing
2 hydrogen bonds form between Adenine and Thymine, 3 hydrogen bonds form between Guanine and Cytosine. Purines always pair with pyrimidines
RNA structure
- Sugar in RNA nucleotides is a ribose sugar
- Uracil replaces thymine as a base
- Nucleotides form a single polynucleotide strand
- Strands are shorter
Why does DNA replicate?
DNA copies itself before cell division so that each new cell has the full amount of DNA. Semi-conservative replication means half of the strands in each new DNA molecule are from the original, meaning that there’s genetic continuity between generations of cells
Semi-conservative DNA replication
- DNA helicase breaks hydrogen bonds between complimentary bases, unwinding the helix to form two single strands
- Each original strand acts as a template
- Free DNA nucleotides attach to their complementary exposed bases on each template strand by complimentary base pairing
- DNA polymerase catalyses condensation reactions, joining nucleotides, forming phosphodiester bonds
- Hydrogen bonds reform
How does DNA polymerase work?
Active site of DNA polymerase is only complementary to the 3’ end of the new DNA strand, so DNA polymerase moves down the template strand in a 3’ to 5’ direction and the new strand is made in a 5’ to 3’ direction and that
Who determined the structure of DNA?
Watson and Crick (using Franklins X-ray diffraction patterns)
Meselson and Stahl’s experiment theory
If replication was semi-conservative, the new bacterial DNA molecules would contain one strand of the old DNA containing heavy nitrogen and one strand of new DNA containing light nitrogen, so the DNA would settle in the middle of the centrifuge tube (which it did)
