3.1.5.2 DNA replication Flashcards
Why is DNA replication described as semi-conservative?
New replicated molecule of DNA consists of one original and one newly formed strand
What is the process of DNA replication?
- DNA helicase unwinds the DNA double helix
- This breaks the hydrogen bonds between complementary bases in polynucleotide strands
- Free nucleotides line up with their complementary bases as bases are unattached, hydrogen bonds now form between bases, no sugar phosphate backbone yet
- DNA polymerase attaches to the ‘leading’ strand and synthesise a new DNA strand
- Another DNA polymerase attaches to the ‘lagging’ strand and synthesise a new DNA strand
6.Helicase continues to unwind the DNA double helix and continuous synthesis proceeds on the ‘leading’ strand
- DNA polymerase on ‘lagging’ strand detaches once it reached the end and re-joins further down, synthesis continues
- DNA polymerase is unable to join up fragments on the ‘lagging’ strand - gap from original point
- Enzyme ligase joins ‘lagging’ strand together
9.Two sugar-phosphate backbone are now formed
What is the role of DNA helicase?
It is an enzyme that unwinds the DNA and break its hydrogen bonds
What is the role of DNA polymerase in DNA replication?
It is an enzyme that catalyses the formation of phosphodiester bonds (sugar backbone) by joining complementary nucleotide to the template strand
What is the ‘leading’ and ‘lagging’ strand of DNA?
Leading - 3’ to 5’
Lagging - 5’ to 3’
What type of reaction forms phosodiester bonds?
Condensation reaction
Why does DNA polymerase add nucleotides to new strand at the 3’ end?
Active site of DNA polymerase is only complementary to 3’ end
