jayel

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In the 7th ed, Examkrackers Biology book, #36's choice A (which is the correct answer) states:

"Normal cells have more time between S phases to repair damaged DNA."

The explanation says that cancer cells replicate faster than normal cells. But when I took Cell Bio, my professor said that cancer cells do not replicate faster than normal cells, they just don't have to ability to regulate replication, so they keep dividing.

Which is actually correct? and how should I answer this on the MCAT?
 
Mar 11, 2010
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Great question.

The bulk of cell mitosis is in the copying of the genetic material in the nuclei. Part of that process involves checking to see that nuclei were copied correctly. If this were to happen for a cancerous cell, then clearly the daughter cells would self-cure. A perfectly normal set of chromosomes would regulate all aspects of cell function properly, including the RNA that operate on the DNA.

That the cancer continues suggests that process skipped out on the checking of the DNA. Since this process is missing, the cancer cell replicates faster.

Just my 2c, which could be very wrong.
 

StIGMA

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Cancer is a multifactorial, extremely diverse disease. Whether the time between S phases is changed depends on the tissue from which the cancer arises. Hematopoietic cells, gastric cells, skin epithelia, and so on divide continually or near-continually. Cells such as muscle cells, kidney cells, brain or other nervous tissue, and so on divide less frequently or potentially not at all (where interphase, mainly G1, is reduced to shorten the cell cycle). Hence, the timing between S phases is drastically shortened in certain types of cancer relative to the underlying tissue and not change or not changed as much in other tissues.

Stick to your cell bio text and ignore docelh. All cells have intrinsic DNA repair systems and cell cycle checkpoints. When DNA is damaged, even perfectly functional DNA repair systems do not work perfectly. Genetic material and nuclei are not interchangeable terms. RNA operating on DNA is not a well documented mechanism of cell cycle repair or checkpoint. What you mean is that if the DNA is not damaged, the protein products should function normally (certain classes of non-coding RNAs - a clear distinction from messenger RNAs - mediate genomic integrity and regulation, but I doubt this is discussed in undergraduate courses).

Re: "my professor said that cancer cells do not replicate faster than normal cells, they just don't have to ability to regulate replication, so they keep dividing."

The maximal rate of cancer cell growth is not faster than normal cells, if they are continually dividing tissue. Cancer cells, as part of their pathogenesis, lose the ability to regulate multiple cell processes (not just regulation of replication) in order to become pathogenic. Both answers are correct, and your professor is being simple with you.
 
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