Organelles

The new colour scheme is hideous, and mainly because I can't change and harmonise the khaki border colours. Yet.... In the process, I've learned more than I wished to but less than I needed of CCS formats and templates. Is this what's called 'life-long learning'?

For distraction purposes, 'Microcosmos' by Margulis and Sagan has been top of the bookpile for the last 2 days, sending me off to sleep. I skimmed this in December, but as usual need a second read to let it sink in and synthesise. Microcosmos collates for a popular market some of the hypotheses on the evolution of key organelles in the eukaryotic cell, such as chloroplasts, mitochondria, cilia and cytoplasmic movers in the form of microtubules. Margolis' central theorem is that these organelles are protist remnants of a symbiosis so close that prokaryote symbiotes were incorporated into the cytoplasm, metabolism, motility and reproduction of eukaryotes. Both chloroplasts (convertors of sunlight and CO2 into energy, O2 and H2O) and mitochondria (convertors of O2 into energy, CO2 and H2O) are found in ancient prokaryotes.

Mitochondrion

Chloroplast


Cilia/flagellums/undulipodia and the microtubule apparatus essential to eukaryotic meiosis (gamete production) and mitosis (cell division), Margulis suggests, may be rudimentary incorporated spirochaetes. One of the less testable but interesting hypotheses advanced is that the neural system with multiple dendritic synapses that lets me write this is also dependent on microtubule structures.

Neuron

Motile cilia

Structures of mitosis


Had I not lent this out, I'd be reading Nick Lane's 'Oxygen' alongside Microcosmos to give a sense of deep time and the magnitude of environmental modification on this Third Stone from the Sun over 4 billion years.

Deep time and its attached comprehension of one's insignificance are remarkably therapeutic in making proportional day-to-day problems. Symbiosis with indwelling organelles or dependence on their oxygen pollution also introduce a whole new understanding (or a lack of it) of levels of organisation in biology.

Darwin/Mendel/Dawkins tended to instruct that the fundamental level at which natural selection is operating is at the level of the 'individual' organism. However, this sometimes helpful construct starts to collapse with realisation the existence and survival of every cell in one's body is dependent on the *independent*, autonomous reproductive system of its ATP-producing mitochondria or (in plants) chloroplasts. Natural selection cannot truly operate on 'me' and 'my mitochondria' independently, because we/me/they are so beautifully interbound. And for better or worse, my son inherited by the gift of meiosis half my somatic (nuclear) genes and half his father's courtesy of a motile, undulipodium-equipped spermatozoan. But all his mitochondrial genes and his microtubules are mine/my egg's/my great-grandmother's eggs. That's ma boy.

Fertilisation