DNA and RNA replication

differences between DNA and RNA

DNA is double-stranded, RNA is single-stranded

DNA has deoxyribose sugars, RNA has ribose sugars

DNA has bases A,T,G,C; RNA has bases A,U,G,C

DNA is a longer chain, RNA is a relatively short chain

how is DNA replicated

enzyme Helicase binds to DNA and breaks hydrogen bonds between complementary base pairings

Helicase unwinds the double helix and separates the strands to create a replication fork

separated strands act as templates during replication

free nucleotides in the nucleus line up against exposed bases on each template strand and attach via complementary base pairings

DNA Polymerase joins nucleotides together and forms phosphodiester bonds between them

semi conservative replication: each DNA molecule contains one original and one newly made strand

which direction does DNA polymerase work in

3’ to 5’ direction

Polymerase synthesises the new daughter strand in a 5’ to 3’ direction (strands are anti-parallel)

how does DNA polymerase work in the leading strand

binds to the 3’ end, newly synthesised strand is formed in opposite direction (5’ to 3’)

the leading strand is made continuously because DNA polymerase works in the 3’ to 5’ direction, the same direction as the replication fork and DNA helicase

how does DNA polymerase work in the lagging strand

other daughter strand (running in 5’ to 3’ direction away from the replication fork) will be lagging strand

this strand cannot be made continuously because DNA polymerase can only read bases in 3’ to 5’ direction

DNA polymerase will need to keep detaching and reattaching to this strand

new strand built in short segments - okazaki fragments