The document discusses two scientific articles about DNA replication. The first article describes an enzyme called NEIL1 that acts as a "cowcatcher" by binding to single-stranded DNA damage before replication to stop the process and allow for repair. The second article reveals new details about the mechanism of DNA unwinding during replication through cryo-electron microscopy images of protein complexes involved. Studying these replication processes has implications for understanding and treating cancer.

1. 'Cowcatcher' Enzyme
Fixes Single-Strand DNA
AND Key Step in
Molecular 'Dance' That
Duplicates DNA
Deciphered
CARMEN SOFIA TORRES DAZA
Medical Student
III semester
Medellín/UPB

4. DNA, or deoxyribonucleic acid, is the hereditary
material in humans and almost all other organisms.
An important property of DNA is that it can
replicate, or make copies of itself. Each strand of
DNA in the double helix can serve as a pattern for
duplicating the sequence of bases. This is critical
when cells divide because each new cell needs to
have an exact copy of the DNA present in the old
cell.
Before it can occur, the length of the DNA double
helix about to be copied must be unwound. In
addition, the two strands must be separated, much
like the two sides of a zipper, by breaking the weak
hydrogen bonds that link the paired bases. Once
the DNA strands have been unwound, they must
be held apart to expose the bases so that new
nucleotide partners can hydrogen-bond to them.
If in this important process is found an error , its
necessary stop the replication for correct the
implicated bases and then continue whit this.

5. 'Cowcatcher'
Enzyme Fixes
Single-Strand
DNA
“science daily, July 29 2013”
FIRST NEW

6. When a cell divides, this cell exposes
its genome. Prior to cell division, this
DNA splits into two single strands and
these splits are so vulnerable to many
assaults.
This assaults can generates changes in
the genetic information and if the
assaults don´t correct will be generate
mutations…
this damage can produce cancers and
other illness to the people.
FIRST NEW

7. According with the authors, this
investigation helps us to imagine
the DNA separation during
replication as a zipper.
This zipper opens and expose it
bases, and the problem is that the
new strand is susceptible to
damage and lead to breaking it.
FIRST NEW

8. Was Founded!!! NEIL 1 : “The Cowcatcher” …
In a in vitro experiments, scientists founded a enzyme called NEIL 1 .
This enzyme actually rides in front of the replication process looking a single strand DNA damage.
For this reason was called “ cowcatcher”.
If the cowcatcher detect a damage the NEIL 1 binds to the damage site and "stop" the replication .
literally it works of this way: “There is a regresses and the two strands come back together which
allows repair of the damaged base in duplex DNA, replacing the damaged base with the
appropriate normal base.“
for understanding this, the author of the article, Sankar Mitra, makes an analogy for the
function of NEIL 1: he call it the cowcatcher by comparing it with the structure of a
“locomotive on it front side” that is used to take off the animals or debris out of the road.
“basically the cowcatcher is in front of the train of the replication to see if there is any
damage in front of it” “if there is any damaged found, the train moves back, repairs it and
then start to moving again”
FIRST NEW

9. PERSONAL OPINION:
this investigation is a
good example for
show as molecular
biology is becomes
today in the way to
new goals and
knowledge that help
to improve the life
quality of the
people.
FIRST NEW

10. Key Step in
Molecular 'Dance'
That Duplicates
DNA Deciphered
“science daily, July 14
2013”
SECOND NEW

11. This research, was published in
the journal Nature Structural &
Molecular Biology and give us
information about the some
key step-molecular through
images showing how the
enzyme that unwinds the DNA
double helix gets drawn to and
wrapped around its target. And,
also the details and mechanism
of DNA replication with
important implications in
current cáncer investigations.
SECOND NEW

12. The "origin recognition complex" (ORC), identifies and binds to DNA-
replication "start" sites, and it is a important factor in this is process
because this protein also interacts with the enzyme that eventually
unwinds the DNA double helix into two separate strands. There are a
kind of missing link- what happens to this helicase. This helicase needs
different protein components to generate a helicase loading complex.
SECOND NEW

13. They purified and then remixed together pieces of the protein including the
origin recognition complex, the replication initiator, the core of the helicase,
and other components and embedded them in ice, took pictures with a cryo-
electron microscope and reconstructe the 3-D structure in a computer. "The
3-D reconstruction gave their a snapshot of the elusive intermediate
structure. This intermediate structure is a very important part of the
molecular machinery that exist on fleeting timescales.
This investigations about the helicasa have important implications, possibly
pointing to new ways to fight cancer, because irregularities in DNA
duplication and uncontrolled cell division are hallmarks of the disease.
SECOND NEW

14. PERSONAL OPINION
I think in a way this article keeps
relation with the previous ,
because "stop" the cell replication
when it detects any damage is
very important to save the lives of
many people with many types of
cancers.

15. MEDICAL UTILITY
The DNA is contained all the genetic information of a living being. The study of DNA is
important in many subjects of the science but in medicine specially because we can know
why some people are more predisposed than others to certain diseases or why some
people respond better than others to the treatments used against some diseases. You
can also learn what environmental factors influence people with a particular genetic
heritage that make developing certain diseases and those same people in another
environment does not develop.
MEDICAL UTILITY

16. This whole set of genetic
studies / genome will allow
researchers to develop better
treatments for some diseases
and determine which factors
should be avoided by individuals
to prevent the development of
some diseases.
MEDICAL UTILITY

17. We know some genes are involved in certain hereditary
diseases and today are conducting studies to discover exactly
the site or sites in the genome that are involved in it, knowing
the risk factor in the population and its mode of inheritance.
Also used for human identification, for paternity, forensic
identification which has been very useful in the judicial
branch.
MEDICAL UTILITY

18. And as we know the great utility of
the DNA molecule, it is also clear the
importance of today of repair
damage to the genome level. In this
way, doctors can improve and even
slow the lives of their patients.
MEDICAL UTILITY

19. BIBLIOGRAPHY
¨ Science daily , “ 'Cowcatcher' Enzyme Fixes Single-Strand DNA “ ,
published on July 29 2013, in the National Academy of Sciences,
[ http://www.sciencedaily.com/releases/2013/07/130729161751.htm ] .
¨ Science daily, “Key Step in Molecular 'Dance' That Duplicates
DNA Deciphered ” , published on July 14 2013, in the journal Nature
Structural & Molecular Biology , [
http://www.sciencedaily.com/releases/2013/07/130714160514.htm ] .

20. THANKS!!