DNA replication Flashcards
Explain why the replication of DNA is referred to as ‘Semi-conservative’
Each strand copied acts as a template; each daughter DNA is one new strand and one original strand;
Explain how the features of DNA are important in semi-conservative replication.
Weak, easily broken hydrogen bonds between bases allow two strands to separate; There are two strands, so both can act as templates; Complementary base pairing allows accurate replication;
Describe and explain how the structure of DNA results in accurate replication.
Two strands make semi-conservative replication; base pairing mean hydrogen bonds holds strands together, and hydrogen bonds are weak and easily broken, allowing strands to separate; bases act as a template so they can be copied; A with T, C with G making a complementary copy; DNA one parent and one new strand;
Give the names, and describe the roles of the enzymes involved in semi-conservative replication.
DNA helicase causes breaking of hydrogen/H bonds between DNA strands; DNA polymerase joins the DNA nucleotides into a polynucleotide, forming phosphodiester bonds;
Describe how DNA is replicated.
The DNA double helix strands separate as the DNA helicase breaks the H-bonds. Both strands act as a template. Free nucleotides are attracted and attach to the complementary base pairs, AT and GC. DNA polymerase joining nucleotide together to form a new strand, creating phosphodiester bonds from a condensation reaction. The H-bonds reform. This is Semi-conservative replication as new DNA molecules contain one old strand and one new strand.
Explain why new nucleotides are only joined together in opposite directions (5’ to 3’).
DNA polymerase is an enzyme, which has an active site that is specific and only complementary to bind to 5’ end of the strand.
Bacteria with ‘heavy’ DNA labelled with 15N is mixed with free nucleotides that contain 14N, and left to undergo replication. If the resulting DNA is extracted and centrifuged, there will be a middle ‘hybrid’ band. Explain why this is evidence of semi-conservative replication.
The middle ‘hybrid’ band will have one strand of the original 15N DNA and one new strand using the 14N nucleotides. This shows that each daughter DNA is made of one old strand and one new strand.
