Ca asked -
1. What caused the decline of "maturation promoting factor" (M-phase) at the end of the mitosis cycle?
Answer - The M-phase promoting factor, the complexing of B-cyclin and Cdk-1, signals the cell to move to metaphase and initiate the anaphase-promoting complex (APC). Once activated the APC will signal the separation of sister chromatids and the destruction of B-cyclins thus "turning off" the M-phase promoting factor.
2. A protein is released by a certain body to stimulate other cells to divide. At which point would cells stop dividing?
Answer - I don't know much about this but what I know is, a cell is signaled to grow and divide when growth factors are released from other cells. When this signal is turned off cells cease growing a dividing. This is an area of active research.
3. What are the differences between density-dependent inhibition and anchorage dependence?
Answer - Both are related to the growth and division of cells but are different in that density-dependent inhibition is about the restraint of cell division and anchorage dependence is about stimulating cell division. As the number of cells increases and thus the density, a point is reached where the cells no longer divide. This is density-dependent inhibition. In anchorage dependence cells do not divide unless they are on some sort of substrate (surface). This was originally discovered when researchers notice that when cultured cells were suspended in a liquid medium they greatly slowed or stopped their division. But when placed on a solid medium the same cells freely divided (until density-dependent inhibition).
Tahira, your questions make me smile. I am not sure how to answer them but I like 'em.
Hong-An asked -
1. In many online science website, mitosis has a prometaphase. Does that mean that the distinction between prophase and metaphase stage is very broad?
Answer - Really, the entire cell cycle is a continuous process not a series of steps. We teach it as steps to aid understanding and the introduction of intermediate steps such a prometaphase introduces emphasis on what is happening. So regarding prophase, prometaphase, and metaphase; prophase is when the chromosomes are condensing and the nuclear membrane disintegrates, prometaphase is when further condensation happens and microtubules begin to attach to the kinetochore, and metaphase is when the chromosomes have lined-up at the equator of the cell.
2. In pictures they always show four chromosomes. Is this to simplify?
Answer - You bet. The mechanics of mitosis is the same no matter the number of chromosomes. It is just easier and hopefully clearer if we sketch 4 chromosomes rather than 46 (humans), 68 (coastal cutthroat trout), or 114 (lilly).
That took two cups of coffee and I am sufficiently caffinated but it is Saturday and I will have more. BTW - did you know that coffee has its origins in Ethiopia? I learned that when the family visited the Lucy exhibit at the Pacific Science Center over winter break.
More Later Ta-Ta,
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