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DNA Replication

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by

Sabrina Keo

on 7 October 2014

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Transcript of DNA Replication

When the
Okazaki fragment

is formed with a primer and DNA polymerase adding nucleotides, it soon reaches the primer of another.
DNA Polymerase I
replaces the RNA of that primer with DNA by adding to the 3’ of the first fragment.
DNA ligase
then comes in to bond the newly formed DNA with the DNA of that first fragment.


In certain cells , an enzyme called
telomerase
helps restore the original length of the DNA.
It has a built-in RNA chain with nucleotides that match up with part of the DNA strand. The rest of the chain is used to extend the
telomeres
at the end of DNA. Once a section is done,
telomerase
moves down and starts the process again.
This is especially important for germ cells (used in reproduction) because it keeps the offspring from missing parts of their DNA.

Since
DNA polymerase III
can only add from the 3’ of the primer, the new strand is replicated in the 5’ to 3’ direction.
The
leading strand
is the half of the new strand that is continuously replicated because it already has the correct directionality.
The
lagging strand
is the other half of the new strand that is made in bits and pieces. These bits and pieces are called
Okazaki fragments
and are started with several new primers.

Sometimes, errors are made during replication or DNA is damaged. To fix this, an enzyme named
nuclease

cuts out the damaged section.
DNA polymerase
fills in the missing nucleotides through repair synthesis.
DNA ligase
seals the new DNA and old DNA together to make the strand complete.


Primase
is an enzyme that makes a primer, which is a short strand of RNA. This primer starts the new strand of DNA.
Single-strand binding proteins
keep the unwounded strands from rejoining.
Topoisomerase
relieves the strain ahead of the replication that is caused by the unwinding; it breaks, swivels, and rejoins the strands (making it easier to unwind when the time comes).


When DNA is fully copied, the lagging side of the new strand ends up being shorter than the parental strand.
This is because the primer is removed from the end of it and DNA polymerase cannot add to the 5’ end of the strand.
Thus, more and more rounds of replications occur that form shorter DNA molecules.
Telomeres
are nucleotide sequences at the ends of DNA to protect the genes from disappearing over time as the shortening occurs. They are shortened in place of the genes

DNA Replication
An enzyme named
helicase
strips the parental DNA into two parental strands from specific locations called, "the origin of replication".
Bubbles are formed with replication due to the replication forks, moving in both direction until everything is copied and creates two new complementary DNA's


The

sliding clamp
is circular protein complex that connects the polymerase to DNA for replication.
DNA

polymerase III

makes the new strand of DNA by adding nucleotides to the primer. Due to its structure, it can only add to the 3' end.
By: Shakira King, Sabrina Keo, Amanda Dixon, and Diva Sanchez
Overview
As replication begins,
several enzymes are at work...
However, this presents a problem...
Formation of Lagging Strand

DNA Repair
DNA Shortening
To Stop the Shortening of DNA....
Here's How It Works....
Here's How It Works...
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2011). Campbell biology(Ninth edition, global ed.). San Francisco, CA: Pearson.
Citations
Full transcript