BIO 1140 Lecture Notes - Lecture 13: Polymerase Chain Reaction, Sticky And Blunt Ends, Restriction Enzyme

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Telomeres: They protect the DNA from degradation which protects the cell from premature
death.
Why do e hae the 3’ oehag? No where for DNA polymerase I to come in and bring in new
NT, nothing to hook them on to. Everytime the cell divides, it needs to replicate its DNA and
every time that happens you run into the same problem so the efficient double stranded DNA,
its length shortens every cycle, as soon as it is coding material this becomes a problem.
These problems include:
Interacting with other piees of 3’ oehag that ould e opleetay ee
partially would lead ot having different chromosomes associated with each other
Premature degradation of DNA as being recognized as broken or damaged
To prevent the above from happening we have, telomerase which is a reverse transcriptase
(TERT). It is a different enzymes from what we have seen before as it carries its own template
and that template is in the form of a short RNA strand that is complementary to the repeated
sequence that the telomere will e ade of. Our eze reogizes the 3’ oerhag > rig the
teplate to lie up to that portio ad eteds the 3’ oer hag. We are left ith a uh
greater 3’ oerhag. Oe e eteded our 3’ oerhag, e ake a opleettar DNA
strand. Telomerase uses RNA as a template and reverse transcribes a repetitive sequence of
DNA to eted the 3’ ed. No e hae a ouple thousad ase pairs of repetitie TTAGG.
Now we need to make a complementary DNA strand to that extended structure that is in the
process to become a telomere. Now primase will come and add a primer so that then we are
ale to reruit DNA Polerase III ad ake a opleetar strad to that iitial 3’ oerhag
that has been extended. Now we are left with a very long portion of repetitive 6 NT sequence
but is not coding (nothing transcribed from this region). This gives time for cell to go through
many cycles. Where would the telomeres always have the possibility to re-extend so that the
cell is immortal? Stem cells, cancer cells (any cell that should’e orall stopped siiig ut
for a combination of things including reactivated telomerase they start getting telomeres so
the get eteded life). Most soati ells do’t ee hae teloerase epressed. “oeties it
might be expressed (cancer).
“tuk ith 3’ oerhag, hat ould preet this fro eig a issue? Single stranded binding
proteins, not same as ones used in DNA replication but we are gonna use proteins to create a
gap. Gap the little portion so that we can tuck it in and keep it from being a problem. The
teloee oally has to e paked ut e do’t fo uleosoes ith that patiula
aea. We ap the usig poteis alled sheltei hih help to eate a ap to peet the 3’
overhang from being a problem and help tuck the DNA ito a T loop. (ap the 3’ ed ith
shelterin proteins and help form the T loop is good enough). This whole region is non-coding
as there are no promoters in the area.
No telomeres in Prokaryotes as they have circular DNA.
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