1.5.2 nucleic acids : DNA replication Flashcards
Process of DNA replication
DNA helicase causes hydrogen bonds to break
Both strands act as templates
Free nucleotides attach to complementary base pairs
DNA polymerase joins nucleotides, hydrogen bonds reform
Replication is semi-conservative - new molecules contain one old and one new strand
DNA polymerase
DNA has antiparallel strands
Enzyme with a specific shaped active site which can only bind to substrate with a complementary shape
Can only bind to and add nucleotides to the phosphate (‘3) end of the developing strand (5’ to 3’ direction)
5’ and 3’
Indicate carbon numbers in DNA’s sugar backbone
5’ carbon has a phosphate group attached
3’ has a hydroxyl group
Evidence for semi-conservative replication
Sample 1: DNA from bacteria grown for several generations in a nutrient solution containing 15N
- DNA molecules contain 2 heavy strands
Sample 2: DNA from bacteria grown originally in a nutrient solution containing 15N, then transferred for one division to a solution containing 14N
- DNA molecules contain 1 original heavy and 1 new light strand
Sample 3: DNA from bacteria grown originally in a nutrient solution 15N then transferred for 2 divisions to a solution containing 14N
- 50% DNA molecules contain 1 original heavy and 1 new light strand, 50% contain both light strands
Describe how, after the parent DNA strands separate, the second strand of DNA in region Y was formed
Through semi-conservative replication
Hydrogen bonds form after DNA polymerase joins nucleotides together
Explain why the arrows point in opposite directions
DNA has antiparallel strands
Nucleotides are aligned differently
Enzymes have active sites with a specific shape
Only substrates with complementary shape can bind with active site of enzyme
DNA helicase is important in DNA replication
Explain why
Breaks hydrogen bonds
So nucleotides can attach
