Lesson Video 19-8

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Lesson Video 19-8

Postby ArielM » Wed Dec 20, 2017 12:42 am

This question is about lesson video 19-8, on slide #8.

In the video, Dr. Anthony mentions that there are a few phenotypes that, together, can indicate a senescence state of a cell.
The definition is given at the beginning of the slide of what a senescent cell is and it is stated that Senescence refers to a state of essentially irreversible growth arrest that occurs when cells that can divide encounter certain stresses.

He mentions that there is no specific way to identify senescence; however, there are some phenotypes that can indicate senescence. He goes on to describe the phenotypes by stating:
1. The arrested growth is irreversible
2. Senescent cells increase in size, relative to the size of non-senescent cells
3. Senescent cells express a senescence-associated B-galactosidase, with a decrease in NAD+

So for senescent cells, when he says "irreversible growth arrest", does this mean that the cells stop growing? And if they are supposed to stop growing- what does he mean when he says that an increase in size is a phenotypic indicator of senescence?

-Ariel Morrow
Site Admin
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Re: Lesson Video 19-8

Postby NS_Tutor_Andrew » Wed Dec 20, 2017 6:56 pm

Hi Ariel,

Excellent question! Tracking this back, this review article on cellular senescence covers a lot of information on the senescence phenotype and provides further sources. Interestingly, the statement about senescent cells increasing in size is backed up with a reference to a 1965 study. It sounds like what's happening is that growth in the sense of moving through the cell cycle towards division is arrested, but other intracellular mechanisms contributing to an increase in size can take place nonetheless. I'm not sure what those mechanisms are, and the abstract of the 1965 article doesn't really shed much light on it, so it seems to be somewhat of a mystery...however, the details involved absolutely do go beyond the scope of the MCAT. Generally, you should know what senescence means, but it's extremely unlikely that they will go into details about the machinery involved in the increase in cell size -- and if they do, they would give you the needed information in the passage.

Hope this is helpful!!
Andrew D.
Content Manager, Next Step Test Prep.

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