The Science of Existence (103) Mitosis


The fact that mitosis is a universal eukaryotic property suggests that it arose at the base of the eukaryotic tree. ~ English biologists Adam Wilkins & Robin Holliday

Mitosis results in somatic or stem daughter cells, each with a full set of chromosomes. Daughter cells have the same genome as their mother cell. A crucial process within mitosis is chromosomal replication, which is regulated epigenetically.

A chromosome is a genetic package in the nucleus of a eukaryotic cell, comprised of DNA base pairs. A DNA base pair comprises 2 complementary nucleobases on opposite sides of a DNA double helix, linked by hydrogen bonds.

A chromosome is a single macromolecule, the largest in Nature. Human DNA has 46 chromosomes. Chromosome 1 in the human body, the biggest, has 10 billion atoms. The average human chromosome has ~140 billion base pairs.

Mitosis begins with chromosomal DNA base pairs being cleaved in half: the hydrogen bonds holding each ladder rung broken by enzymes. This happens in several sections simultaneously. To keep things tidy, proteins neatly stack the chromosomes in layers, forming multilaminar plates.

Then each half-ladder has its complement rebuilt. The result is 2 DNA ladders: half each of the original nucleotide string. The other side of each ladder is reconstructed.

Then these 2 sets of chromosomes are pulled apart from the center of the cell, in opposite directions, by protein ropes. These microtubules are part of the cytoskeleton, and play numerous roles in cell upkeep, mostly in moving bits about the cell.

Mitosis is an incredibly intricate process: an orchestration of many thousands of proteins moving through space, finding their exact positions at just the right time. While the proteins remember where they are supposed to go, and have an innate affinity to the right location, innumerable decisions must be made for cell division to succeed.

For normal tissue structure and function, cells exert strict control over growth versus differentiation. The distribution of organelles influence the outcome of stem cell division. ~ American cytologist Elaine Fuchs

Epigenetic influences take effect during mitosis. Hence, life experiences are passed on during each cell replication.

Mitosis takes 15–30 minutes per chromosome. Replication of a human cell DNA takes up to 10 hours. Yet human cells may divide as often as every day.

When the whole DNA molecule has been duplicated, the chromosomes move to opposite ends of the cell. Then cytokinesis kicks in: the cytoplasm of a eukaryotic cell divides; whence 2 cells are constituted.