Nick Lane. Mitochondria and the meaning of life.Oxforf University Press. New York, NY, USA.

By: Bruno Alejandro Aguilar López

The mitochondrion is an organelle of eukaryotic cells of bacterial origin (perhaps from an a-proteobacteria). An endosymbiotic association between this bacteria and a nucleated cell originated millions years ago. The main function of the mitochondria is the generation of the major part of energy required for cell activity but many other functions have been uncovered more recently.

The first chapters of “Power, sex and suicide. Mitochondria and the meaning life”,authored by Nick Lane, Senior lecturer at University College London, explain the environmental conditions of the earth that gave rise to the endosymbiosis between a bacteria and a nucleated cell, the differences between bacteria and eukaryotic cells, such as size and complexity.

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Bacteria had evolved to survive in an anoxic atmosphere and then had to adapt to survivein new oxygenated surroundings.Primitive eukaryotic cells, possessing everything that characterizes modern eukaryotes, except for mitochondria, interiorized bacteria similar to modern time Rickettsia that could survive within the cell, beginning an endosymbiotic relationship when still increased atmospheric oxygen concentrations followed.

Host bacteria were likely methanogen, since the atmosphere consisted ofhydrogen and carbon dioxide, which these bacteria could transform into methane. Methanogen bacteria could tolerate some oxygen in their surroundings.

In later chapters the book explains how cells produce their energy by metabolizing substrates such as glucose which is oxidizeto water and carbon dioxide through cellular respiration and how cellular respiration is carried out through an electron transport chain composed of different complexes (I, II, III and IV), coenzymes and cytochromes, when the electrons pass through the transmembrane complexes (I, III and IV), protons of the mitochondrial matrix translocate to the intermembrane space, creating a proton gradient that generates a mitochondrial membrane potential that is used by the ATP synthase for ATP synthesis. These chapters not only deal with the biochemistry of ATP synthesis, they also provide a vivid account on the intellectual atmosphere that leaded to the key discoveries.

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The ATP synthase, the book explains, is a marvelous example of nature’s nanotechnology: it works as a molecular motor, and as such is the smallest known machine. The enzime has a rotating head, the pressure of protonsoutside of the membrane forces protons through the drive shaft to rotate the head, and as 3 protons pass, one molecule of ATP is synthetized.

Another issue that the book talks about is the origin of life, in the primitive earth a primordial soup existed composed of various inorganic compounds, they reacted among them with the help of abiotic factors,originating the first organic molecules, which in turn joined together to create LUCA (Last Universal Common Ancestor), from which 3 major kingdoms (Bacteria, Archaea and Eukarya) were derived.

The book also discusses the relationship between the number of mitochondria, the animal size and the metabolic rate. It indicates how these parameters change depending on the species habitat, their habits or if they are hot or cold blood animals.The book tells the story of a constant called the log metabolic rate originally standardized at 3/4 (0.75), and how in fact this “constant” varies among species.

Then it comes cell death, which is caused by some irreparable cell damage, a type of cell death is programmed and it is called apoptosis. Programed cell death is necessary for balance and integrity of multicellular organisms and when this mechanism fails and a damaged cell does not enter the apoptotic process it can become a cancer cell.Cancer is the result of a genetic mutation, when a cell accumulates many genetic mutations in specific genes is transformed into a malignant cell, these mutations can take place in oncogenes and tumor suppressor genes.The malignant cells do not respond normally to the instructions of the body and begin to proliferate uncontrollably, they produce growth factors that induce angiogenesis allowing transformed cells to receive nutrients, and these cells can spread to other organs by a processknown as metastasis. Mitochondria have a central role in programed cell death.

The penultimate chapter discusses the use of mitochondrial DNA for diverse applications, from the use of mitochondrial DNA to reconstruct prehistory, solve forensic cases and establishthe identity of an unknown individual. It explains how all this is possible because in the union of human gametes (sperm and egg) only the mother’s mitochondrial DNA is inherited.

The last chapter deals with aging. This chapter considers free oxygen radicals as the main cause of cell aging. Oxygen free radicals are formed in the process of cell respiration and are very damaging; they attack several cell components including mitochondrial DNA, causing mutations that disrupt mitochondrial function and therefore cell function. Much of this damage can be repaired by some enzymes or prevented by antioxidants intake in the normal diet. Nonetheless, free radicals are not purely detrimental, they also carry out essential cell signaling roles.

In my opinion, “Power, sex and suicide. Mitochondria and the meaning life” is an excellent book worth reading. It covers a wealth of information regarding mitochondria, it is easy to understand for people with some knowledge of Biology and Biochemistry but it can also be read and understood by a more general public. The book provides us with a glossary of terms that facilitates comprehension. It is nicely structured, provides many original references and it is written in such a style that keeps readers attention and you do not want to miss a page.

I personally loved reading this book because it answer many of my questions regarding mitochondria but also gave me a completely new perspective on the topic.

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