Biological complexity: cell division controls (Introduction)

by David Turell , Sunday, July 30, 2017, 23:44 (2673 days ago) @ David Turell

Our cells are in constant division and reproduction. Chromosomes must be controlled to always keep the same number with the same genes:

https://phys.org/news/2017-07-human-cells-chromosomes.html

"Cell division is an essential process in humans, animals and plants as dying or injured cells are replenished throughout life. Cells divide at least a billion times in the average person, usually without any problem. However, when cell division goes wrong, it can lead to a range of diseases, such as cancer, and problems with fertility and development, including babies born with the wrong number of chromosomes as in Down's syndrome.

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"During cell division, a mother cell divides into two daughter cells, and during this process the DNA in the mother cell, wrapped up in the form of chromosomes, is divided into two equal sets. To achieve this, rope-like structures called microtubules capture the chromosomes at a special site called the kinetochore, and pull the DNA apart," said Dr Viji Draviam.

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"We have identified two proteins - tiny molecular machines - that enable the correct attachment between the chromosomes and microtubules. When these proteins don't function properly, the cells can lose or gain a chromosome. This finding gives us a glimpse of an important step in the process of cell division."

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"Using high resolution microscopes to video the inner workings of live human cells, Dr Draviam and her colleagues at the University of Cambridge (UK) and the European Molecular Biology Laboratory in Heidelberg (Germany), discovered that two proteins - Aurora-B kinase and BubR1-bound PP2A phosphatase - act in opposition to each other, adding or removing phosphate groups respectively, to correctly control the attachment of microtubules to the chromosomes.

"Co-author Duccio Conti, who is Dr Draviam's PhD student, said: "We found that a balance between Aurora-B kinase and BubR1-bound phosphatase is important to maintain correct chromosome numbers in human cells.'"

Comment: A microscopic picture of cell division shows the chromosomes lined up across the median of the cell about to divide. The microtubules stretch in either direction to points at opposite sides like two back to back harps. Then the chromosomes are pulled apart as the cell divides, with DNA equally divided in two. We now know that two enzymes play a major role. How this developed through chance evolution cannot be explained. It has to be put together by design all at once to have any possibility of proper development. Further, old story, enzymes are very exactly designed for their purpose, and are giant molecules made up of exactly sequenced and folded amino acids numbering from the several hundreds to thousands. Life functions only because of thousands of these specialized molecules which have just one function, or occasionally two. Not by chance!