BIOL 1030H Lecture Notes - Lecture 7: Eukaryotic Dna Replication, Dna Replication, Isotopes Of Nitrogen
13 May 2018
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DNA Replication
DNA Replication
●Incoming nucleotides are accepted if they correctly base pair with the template.
●The 3' OH of the growing strand attacks the high energy phosphate bond of the incoming
nucleotide to initiate the synthesis reaction
●During replication, the two strands of the parental duplex separate.
●The bases are paired in the parental duplex, either A–T or G–C.
●Each parental strand serves as a template for the synthesis of a new daughter strand, using
the base-pairing rules of A with T and G with C.
Bacterial DNA Replication
●At the beginning of the experiment, both strands are labeled with heavy nitrogen (15N).
The molecules form a band with the density of “heavy” DNA.
●After one round of replication in the absence of heavy nitrogen, the parental strand still
contains the heavy nitrogen (15N), but the daughter strand contains light nitrogen (14N).
The daughter DNA molecules form a band with an intermediate density
●After two rounds of replication, half of the duplex DNA molecules have one strand with
15N and one with 14N, and the other half have both strands with 14N. The daughter
DNA molecules therefore form two bands, one intermediate in density and the other
light.
Eukaryotic DNA Replication
●After two rounds of DNA replication in a labeled medium, one daughter molecule is half
labeled, and the other is fully labeled (compare with Figure 12.2).
Replication Occurs 5’ to 3
●Incoming nucleotides are accepted if they correctly base pair with the template
●The 3' OH of the growing strand attacks the high energy phosphate bond of the incoming
nucleotide to initiate the synthesis reaction.
Continuous/Discontinuous Replication
●Unwinding of the DNA duplex results in a replication fork.
●Replication always occurs in the 5' to 3' direction. The daughter strand on top elongates
from left to right, that on the bottom from right to left.
DNA Synthesis and RNA Primers
●RNA primase lays down an RNA primer.
Document Summary
During replication, the two strands of the parental duplex separate. The bases are paired in the parental duplex, either a t or g c. Each parental strand serves as a template for the synthesis of a new daughter strand, using the base-pairing rules of a with t and g with c. At the beginning of the experiment, both strands are labeled with heavy nitrogen (15n). The molecules form a band with the density of heavy dna. After one round of replication in the absence of heavy nitrogen, the parental strand still contains the heavy nitrogen (15n), but the daughter strand contains light nitrogen (14n). The daughter dna molecules form a band with an intermediate density. After two rounds of replication, half of the duplex dna molecules have one strand with. 15n and one with 14n, and the other half have both strands with 14n. Dna molecules therefore form two bands, one intermediate in density and the other light.
