ZOOHCC - 501: Molecular Biology (Theory)
Unit 2: DNA Replication
Bidirectional replication
Bidirectional replication is the method of DNA replication found in all major kingdoms of life. In bidirectional replication, DNA is replicated in her two directions simultaneously, resulting in a leading strand (where replication occurs faster) and a lagging strand (where replication occurs slower). Each of these strand properties is caused by a DNA polymerase and the ability to replicate only in the 5' to 3' direction. In the main strand, a single DNA polymerase can replicate most of the strand before it dissociates (approximately x 1000-5000 bases before being shed from the DNA due to its high processivity). However, on the lagging strand, the DNA is duplicated into fragments called Okazaki fragments. Each of these fragments is later fused by DNA ligase to create a complete, unfragmented strand.
Explanation:
The DNA also has two replication forks, which are regions where nucleotides are actively added to the growing chain. Prokaryotes have circular chromosomes with a single origin of replication (OriC) and a single termination site. However, similar to eukaryotes, linear chromosomes have multiple origins of replication and two replication forks each, so replication is much faster [1]. At all replication origins, replication occurs in a bidirectional fashion, resulting in the formation of a 'replication bubble'. These bubbles grow larger as replication progresses. Eventually, two replication forks meet (at opposite ends of the bubble), at which point they merge to create a larger bubble. Eventually, all replicative bubbles along the chromosome fuse into one large bubble joint only at telomeres. These are split to give two identical DNA strands. This process continues to generate many DNA strands that are passed on to daughter cells.
Bi-directional replication is the method of DNA replication found in organisms of all major kingdoms. In bidirectional replication, DNA is replicated in two directions simultaneously, resulting in a leading strand (which replicates faster) and a lagging strand (which replicates slower). Each of these strand properties is caused by a DNA polymerase and the ability to replicate only in the 5' to 3' direction. In the main strand, a single DNA polymerase can replicate most of the strand before it dissociates (approximately x 1000-5000 bases before being shed from the DNA due to its high processivity). However, on the lagging strand, the DNA is duplicated into fragments called Okazaki fragments. Each of these fragments is later fused by DNA ligase to create a complete, unfragmented strand. The chromosome also has two replication forks, which are regions where nucleotides are actively added to the growing chain. Prokaryotes have circular chromosomes with a single origin of replication (OriC) and a single termination site. However, similar to eukaryotes, linear chromosomes have multiple origins of replication and two replication forks each, so replication is much faster [1]. At all replication origins, replication occurs in a bidirectional fashion, resulting in the formation of a 'replication bubble'. These bubbles grow as replication continues. Eventually, two replication forks meet (at opposite ends of the bubble), at which point they merge to create a larger bubble. Eventually, all replicative bubbles along the chromosome fuse into one large bubble joint only at telomeres. These are split to give two identical DNA strands. This process continues to generate many strands of DNA that are passed on to daughter cells [
Bidirectional replication is a method of
DNA
replication found in organism from each of
the main kingdoms. Bidirectional replication involves replicating DNA
in two directions at the same time resulting in a leading strand (were
replication occurs more rapidly) and a lagging strand (with slower replication).
The properties of each of these strands is caused by
DNApolymerase
and its ability to only replicate in the 5' to 3' direction. In the
leading strand, a single DNA
polymerase
can replicate large portions of the strand (approximately X1000-5000 bases before it falls off the DNA
due to its high processivity) before dissociating. However, in the lagging strand, the
DNA
is replicate in chunks which are called Okasaki fragments.
Each of these fragments is later fused together by DNA ligase
to
produce the full, unfragmented strand. The
chromosome also has two replication forks which are the regions where
nucleotides are actively added to growing strands.
Prokaryotes have a circular chromosome with a single origin of replication (OriC) and a
single termination site. However the linear chromosomes,ike those in
eukaryotes, have several origins of replication and two
replication forks for each of these, replication therefore occurs much more quickly.
At all replication origins, replication takes place in a bidirectional
format
which results
in the
formation of ‘replication bubbles’. These bubbles grow in size as replication continues. Eventually, two replication forks (at each end of a bubble) meet, at which point they
fuse together producing a larger bubble. Ultimately, all the replication bubbles along the
chromosome merge into one large bubble joint only at the telomeres; these split to give two identical strands of
DNA. This process continues to produce a many strands of DNA which are then passed on to
daughter cells
Why is DNA replication bi-directional?
DNA replication is the process of creating new copies of double-stranded DNA by synthesizing new DNA strands. DNA replication is a bidirectional process because the DNA strands are antiparallel. H. 3'-5' on one strand and 5'-3' on the other. DNA polymerases synthesize DNA in the 5'-3' direction. Synthesis therefore occurs continuously in the 5'-3' direction on the template strand, but discontinuously in the 3'-5' direction on the non-template strand, giving rise to small fragments of DNA known as Okazaki fragments. increase. Bidirectional replication, therefore, involves the simultaneous replication of DNA in two directions, resulting in leading and lagging strands. DNA replication can be unidirectional or bidirectional. If replication is two-way, neither end is stationary, both are moving.
