Pro And U Questions Asked In Class & Random Thoughts

1) Proto-oncogenes promotes cell growth. Checked.

But did you realise cell growth is related to cell division because the growth of a cell is limited by the cell size due to the surface area:volume ratio. Thus once it has reached a certain size, cell will undergo cell division.

Proto-oncogenes promotes cell growth and cell division.



*2) What happen to the telomeres of the template strand during replication (somatic cells).Do they get shorten or do they remain in length?

Bravo! you are right! Those that get shorter are the daughter strands due to "end replication problem". Thus we have a blunt end and one with a 3' overhang.

But do we have a problem here as some of you had thought about - the template strand will remains just as long regardless of the number of replications - so has the original first-ever cell achieve immortality?

The status of immortality is given if a cell has the capacity to undergo unlimited cell divisions and is, of course, closely associated with the activation of telomeres (telomerase activity is found in ~90% of cancer) . But even those cells can die.

Cell are suscepticle to chemical or physical insults and older cells also tend to accumulates more DNA damages or mutations that will trigger off apoptosis and thus the original cell does not persist in our body but give way to new cells (why cells undergo mitosis?)

Nonetheless, cancer cells are more persistant because they are more resistance to various insults due to possible defects in the apoptotic pathway etc

Thus, after successive cell divisions, we will eventually get to a daughter cell with telomeres of a critical length and will not undergo mitosis (cell senescence/arrested cell growth). That limits the no. of cell divisions a cell can undergo.

http://en.wikipedia.org/wiki/Hayflick_limit

If replication does ever happen beyond the critical length, the cell will undergo apoptosis because the telomeres/chromosomes are damaged.



Consensus Sequences

Are consensus sequences only found in prokaryotes?
Nope. Although we only briefly talked about it under prokaryotes, consensus sequences are also found in TATA box, CAAT and GC boxes of the eukaryotes as well.
In fact gene mutation can alter the correlation with the consensus sequence.


Does plastid contains DNA?

Plastids is a general term that includes chloroplasts. So yes to that question but it is more appropriate at this level to talk simply about chloroplasts than involves plastids.


Are 30nm fiber and solenoid the same?

Yes. They are the same thing. The 30nm fiber is so called because of its size. Solenoid is a model that is attributed to the 30nm fiber. There is also a cross-linker model.
To be sure, we will make reference to 30nm fiber.