Objectives 1 Summarize the roles of the different enzymes involved in replication of DNA 2 Explain how the leading and lagging strands are replicated differently Semiconservative Replication ID: 585164
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Slide1
Replication of DNA
Objectives:1. Summarize the roles of the different enzymes involved in replication of DNA.2. Explain how the leading and lagging strands are replicated differently Slide2
Semiconservative Replication
When Watson and Crick proposed the model of the structure of DNA they also proposed a method of its replication, Semiconservative.Slide3
Aspects of Semiconservative
ReplicationOriginal strands separate, and serve as template strands
.
These template strands copy themselves forming two molecules of DNA
Each DNA molecule has one strand of parental DNA and one strand of new DNASlide4
3 stages of the process of Semiconservative
replicationUnwindingBase pairingJoining of the strandsSlide5
Unwinding
The Double Helix of DNA must be unwound in order to allow base pairing (copying) of the DNA molecule.An enzyme called Helicase unwinds the DNA molecule.Helicase
does this by breaking the weak hydrogen bonds between the two strand of DNA.Slide6
The Enzyme Helicase
http://www.youtube.com/watch?v=UWNhwceMjfkSlide7
Base Pairing
The enzyme DNA polymerase attaches appropriate nucleotides to the new DNA strandsThe nucleotides are added to the 3’ so we say that the DNA synthesis moves in the 5’ to 3’ direction.Slide8
Okazaki Fragments
and the leading and lagging strand The two strands are made in a different manner.One strand is called the leading strand
. This strand is built continuously from the 5’ to 3’ ends.
But, since the strands are
antiparallel
, the
lagging strand
can not be built continuously.
This strand is built into small segments, called Okazaki fragments.
The fragments are later connected by the enzyme
DNA
ligase
.Slide9
http://www.youtube.com/watch?v=teV62zrm2P0Slide10
Joining the Strands
When the DNA molecule is finished replicating the enzymes release the strands and they reform two double helix’s, Each with a parental template strand, and with a new strand from replication. Slide11
Comparing DNA Replication between
Prokaryotes and EukaryotesIn Prokaryotes the circular DNA strand is opened at one origin of replication. In Eukaryotes, with up to one million bases pairs to copy there are multiple origins of replication.Both replicate in two directions, that is to say they are both semiconservative
(one parent strand and one new strand).