telomere question.

[westernmed007]

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I have read various sources and there is discrepancy between if the telomerase acts on just the lagging strand or also on the leading strand, it would make sense to me if it also acted on the leading, does anyone know for sure?

 

[SkylineMD]

according to what I read in HY cell and molecular, the telomerase recognizes the GGGTTA sequence on the leading strand and then adds nucleotides to it. Following this, polymerase alpha fills in the complementary strand

 

[Medikit]

How many amino acids are there in the beta chain of hemoglobin?

 

[UCLAstudent]

How many amino acids are there in the beta chain of hemoglobin?

Lol ... well, more than 6!

 

[westernmed007]

i am reading the same book and i only read lagging strand, so im guessing it does both? skyline could u tell me what page u read that on? I'm not trying to be a DB but I'm just trying to figure out whatever I must have read over too quickly, thanks for any help. PS they are bringing the SKYLINE here soon, u see the pics from arizona or whatever?

 

[Taus]

i am reading the same book and i only read lagging strand, so im guessing it does both? skyline could u tell me what page u read that on? I'm not trying to be a DB but I'm just trying to figure out whatever I must have read over too quickly, thanks for any help. PS they are bringing the SKYLINE here soon, u see the pics from arizona or whatever?

my understanding (and I could easily be wrong) is that after you take out the last primer of the lagging strand you have the problem of not being able to use DNA poly 3 to synth 3'->5' and can't use DNA poly 1 on the end.....so you need a telomere to fill in that last spot on the lagging strand.....correct me if I'm wrong here.....I wasn't a hardcore science major in undergrad so I've really tried to learn this stuff well in the past month or so

 

[G0S2]

With each S phase, the lagging strand end (5') is cut short due to "discontinuous" replication. In order to make more lagging strand the LEADING 3' strand is extended. The 3' extension serves as a template for lagging 5' synthesis.

--------------3' (lead)
---5' (lag)



-------------------------------3' +Telomerase
---5'


Primer and Extension


-------------------------------3'
-------------------------------5' (Extension)

 

[westernmed007]

is it both?

 

[SkylineMD]

page 9 in the 1st edition and page 72 of 2nd edition

 

[blkkd]

nm...GOS2 layed it out

 

[G0S2]

is it both?

The LEADING strand is elongated. Telomerase is a ribonucleoprotein, which , by name, contains an RNA template (human telomerase (hTERT) and its RNA (hTR). That template (hTR) only recognizes the leading strand sequence.

 

[G0S2]

It needs to elongate the LEADING strand so that the LEADING strand can serve as the complement of more LAGGING strand.

 

[guitarguy09]

To help visualize this, here is a low-tech animation that I came across.

http://faculty.plattsburgh.edu/donald.slish/Telomerase.html

Just pay attention that the synthesized T's should be U's (because we're talking about RNA)...

 

[Dotoday]

Telomerase elongates either leading or lagging strand, because telomere is basically an overhang from a 3' end. You do not know which strand is leading or lagging sometimes, because it depends on the transcription factors which can bind to either strand. Any strand can become leading or lagging at any time, depending on where transcription factor recognizes a sequence. Telomerase binds specifically to a certain sequence, no matter weather it is on the leading or the lagging strand. This is the current idea, since literature (pubmed) up to date did not show any specific preference of Telomerase to either leading or lagging strand.
Hope this helps.

 

[G0S2]

When I refer to leading strand it depends on the one end of the chromosome I am looking at.

If the end is


--------------3'
-----5'

The upper is leading since as it open for synthesis, DNA pol can start from there rather than waiting for the sequence to unwind and lay down a primer downstream ( and "lag" behind). At the other end of this chromosome the bottom strand shown here would have the 3' overhang and would be leading from that view. If this happened to be a Q on your exam, which I bet it wouldn't, the figure should be labeled well.

Telomerase will involve a question involving identifying cells or tissues with telomerase activity or asking something like this:


The gene encoding a specific protein was transfected into normal fibroblasts (A) (or insert cell line with limited dividing capacity) and the growth curve for this cell line was plotted versus a cell transfected with control DNA (B). (The B curve for control will grow and then level off and the curve for the experimental gene (A) will continue to rise). Which gene was transfected into the cells represented by curve A?

A) p53
B) Bcl-2
C) Bax
D) Telomerase
E) Actin