Power, sex, suicide: Mitochondria and the meaning of life
In each of the cells of your body there are many small subcellular objects called mitochondria. They act as the powerhouses of the cell, but in this fascinating book by Nick Lane he shows that they do much more than carry out a single function. It is thought that approximately one and a half billion years ago two types of bacteria forged a symbiotic union to create the eukaryotic cell. Those that became mitochondria may seem to have the subservient role, but in this work we hear how recent discoveries in the subject are changing this view.
The origin of the eukaryotic cell
Precisely how two different types of cell joined together in this cooperative venture is a tricky question. Indeed it isn't known whether this evolutionary step might be considered inevitable, or whether its occurrence was just an unlikely chance. Possibly there are many worlds where life has arisen but never got beyond the bacterial stage. But it happened on Earth, even if we're not really sure how. It used to be thought that the mitochondria originated from oxygen-requiring bacteria which joined with anaerobic, yeast like cells. But more recently, many researchers have come to believe in the Hydrogen hypothesis. This is the idea that the host cell was originally a methanogen - a bacterium which produces methane from hydrogen. Since such cells exist in the absence of oxygen, the prospective mitochondria must have been more flexible than originally thought, only later evolving into their present form. It's a subtle argument, but Lane explains it well and shows why it is thought to be more probable than the alternatives. Similarly subtle arguments are dealt with throughout the book, showing how the thinking about mitochondria has changed in recent decades.
The benefits we get from mitochondria
Respiration, that is the conversion of food and oxygen into useful work, requires a membrane in order to take place. In bacteria this is typically at the boundary of the cell, and scaling arguments show that this limits the size which they can reach. In eukaryotic cells the membrane is at the boundary of the mitochondria, and the number of these can increase proportionally to the volume of the cell. Hence such cells can be much bigger. Bigger cells can then support more genetic material, which leads to the possibility of more greater complexity - and in particular to multicellular organisms. But multicellular organisms require more than just more information to build them. They also need some way of asserting their individuality, against that of their cells which might have a tendency to go their own way. Lane explains how mitochondria play a part in apoptosis, that is the programmed destruction of aberrant cells by an organism.
Mitochondria are probably best known for the fact that their genetic information is passed down along the female line, thus enabling researchers to map the relatedness of different people. In this book we are told why this should be the case, and indeed why the presence of mitochondria lead to sex evolving in the way that it did, and why there are two different sexes.
Ageing and what we can do about it
The final part of the book looks at the rôle mitochondria play in ageing, and how we might be able to slow it down. Ageing and eventual death is naturally a subject of great concern to everyone. It may look like our bodies just wear out, but there are many problems with this view. In particular the lifespans of different mammals vary with their sizes in such a way to suggest that bodies don't just wear out, they are programmed to do so. But is this inevitable? It doesn't seem so, as birds seem to live much longer than mammals of the same size. If we could copy how birds did this then maybe we could live for hundreds of years. The final chapter of the book considers such possibilities, and what problems there are likely to be in carrying them out. Some people might find such ideas of prolonging our lives unnerving, but that's why I feel that it is important that as many people as possible find out about this subject in order to have an informed debate about the ethical issues involved.
In this work Lane looks at ideas arising from recent research into mitochondria - ideas which are often still controversial. Although this work is aimed at non-specialists, I think that readers without some background knowledge of cellular biology are likely to struggle. Its a fairly long book, often requiring subtle arguments on why we think differently now from 20 or 30 years ago. It does make some important points, so maybe you should consider doing some preliminary study and then tackling this book. If you do have the required background knowledge then reading it will be very rewarding.
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