MCDB 2150 Lecture 1: Class 2 dna structure and replication

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DNA Structure and Replication
Class Notes:
DNA has a 5’ to 3’ directionality
o Growing chain + precursor (nucleoside triphosphate) 5’ end attaches to a 3’ end with a
3’ to 5’ phosphodiester bond
DNA replication depends on the structure of DNA
o New nucleotides can only be added at the 3’ end of a strand
In replication, the 3’-OH group of the last nucleotide on the strand attacks the 5’-
phosphate group of the incoming dNTP, two phosphates are cleaved off and a
phosphodiester bond forms between two nucleotides
o The two strands are not copied at the same rate
Gaps are present in the DNA sequence when RNA primers are removed
o DNA polymerase can only add to the 3’ end of a strand
o These gabs exist only at the ends of chromosomes and are filled by a special enzyme
called telomerase
Taking advantage of normal DNA replication to generate copies of DNA in the lab
o Polymerase chain reaction (PCR): makes multiple copies of a specific sequence of
DNA
o Uses primers to initiate replication: short segments of DNA that guide DNA
polymerase to the section of DNA to copy
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