dna replication Flashcards
what is DNA replication?
the process of making an exact copy of all the DNA in the nucleus.
what are the first two main steps of DNA replication?
1) DNA is separated into two strands by DNA helicase (enzyme)
2) single-strand binding proteins attach to each strand of DNA and prevent them from reannealing. the point at which the strands separate is called the replication fork.
this forms a template for new strands to be made
what happens after these main steps?
1) RNA primase (enzyme) adds a short sequence of RNA nucleotides called a primer to the DNA, which initiates the process of replication
2) DNA polymerase (enzyme) adds complementary nucleotides to the template one strand at a time, starting from the 3’ end of the RNA primer. a sliding clamp (protein) helps DNA polymerase slide along the template strand
3) nuclease (enzyme) removes the primers from the template DNA strands and DNA polymerase fills in the gaps with complementary DNA nucleotides
4) DNA ligase joins the sections of replicated DNA into a single long strand
what are leading and lagging strands?
1) they exist due to the fact that new DNA is made from 5’ to 3’, since new nucleotides can only be added to the 3’ end of the strand.
2) replication cannot progress in the same direction on both strands due to their antiparallel nature.
leading strand: towards the replication fork, it is continuous.
lagging strand: away from the replication fork, it is discontinuous which produces short sequences of new fragments called Okazaki fragments.
what is semi-conservative replication?
1) produces 2 identical double helices
2) only one of the strands is newly synthesised
3) helps reduce the number of errors made during replication.
