3.9 DNA Replication and the
Genetic Code
First review @October 17, 2023
Practise Q's Done
cells divide for growth or repair of tissues
two daughter cells produced by mitosis are genetically identical and diploid
before cells begin to divide they prepare, this stage is interphase
this is when DNA is replicated
Semi-conservative replication
for DNA to be replicated, the hydrogen bonds between base pairs must be broken to
expose one strand of DNA that can be copied
DNA replication is described as semi-conservative (half the same) since the two new
DNA helices formed are each made of one old and one new strand of DNA
roles of enzymes in replication
DNA Helicase— travels along the polynucleotide chains and breaks the hydrogen
bonds between base pairs to leave one strand of DNA that can be replicated
DNA polymerase only travels in the 3’ to 5’ direction which results in a ‘lagging’ and
a ‘leading’ strand— only the leading strand can have DNA replicated from it as the
DNA unwinds and the lagging strand has to be replicated backwards in sections
called Okazaki fragments which are later joined together by DNA ligase
DNA polymerase— catalyses the formation of phosphodiester bonds between free
nucleotides to reform the sugar-phosphate backbone
3.9 DNA Replication and the Genetic Code 1
Genetic Code
First review @October 17, 2023
Practise Q's Done
cells divide for growth or repair of tissues
two daughter cells produced by mitosis are genetically identical and diploid
before cells begin to divide they prepare, this stage is interphase
this is when DNA is replicated
Semi-conservative replication
for DNA to be replicated, the hydrogen bonds between base pairs must be broken to
expose one strand of DNA that can be copied
DNA replication is described as semi-conservative (half the same) since the two new
DNA helices formed are each made of one old and one new strand of DNA
roles of enzymes in replication
DNA Helicase— travels along the polynucleotide chains and breaks the hydrogen
bonds between base pairs to leave one strand of DNA that can be replicated
DNA polymerase only travels in the 3’ to 5’ direction which results in a ‘lagging’ and
a ‘leading’ strand— only the leading strand can have DNA replicated from it as the
DNA unwinds and the lagging strand has to be replicated backwards in sections
called Okazaki fragments which are later joined together by DNA ligase
DNA polymerase— catalyses the formation of phosphodiester bonds between free
nucleotides to reform the sugar-phosphate backbone
3.9 DNA Replication and the Genetic Code 1
