Cells

An adult human (page references to "Power, Sex, Suicide: Mitochondria and the meaning of life"):

• has 15.10¹² cells (p67)
• 10% of body weight is mitochondria (p12: 10¹⁶ mitochondria per person; p1: on average 300-400 mitochondria in each cell)
• converts 10,000 times more energy than the sun per second! (p67: sun 0.2uJ/g/sec, human 2mJ/g/sec = 2mW/g = 140W)
• turns-over (produces & consumes) around 65kg of ATP per day (p80: 9.10²⁰ molecules/sec)
• each day 10¹⁰ cells die by apoptosis & are replaced by new ones (p204: 1 in 1500 die per day - 4 years = completely new body)

Mitochondria pump protons across a membrane: reverse proton flow is used (among other things) to make ATP or heat.

A representation of complexes I-IV in mitochondria respiratory membrane chains:

See also: ATP and Oxidative Phosphorylation Reactions (including animations) and OXPHOS (Oxidative Phosphorylation) system in mammalian mitochondria

If the respiratory chain is blocked, redox poise is disturbed & it leaks electrons, forming free-radicals which signal either the production of more respiratory chain sub-units (if ATP levels are low), or uncoupling the respiratory chain & generating heat (if ATP levels are high).

Mutations in mitochondrial DNA (often cause by free-radicals) impair energy generation efficiency and eventually lead to apoptosis (programmed cell death), and ageing as tissue cells become less efficient. Birds live longer because they have more spare energy generating capacity in their mitochondria - if we could reduce free-radical leakage in our cells, we could live healthier and longer!

Sex

• a fertilized egg cell contains 10⁵ mitochondria, 99.99% from the mother
• during first 2 weeks, mitochondria don't divide: they are distrubuted between the cells (1000 at week 2)
• oocytes (egg cells in female embryo) increase from 100 at week 3 to 7.10⁶ after 5 months (x 2¹⁸), each with 10,000 mitochondria per cell (x 2²⁹)
• oocytes fall to 2.10⁶ at birth; at the onset of menstruation 3.10⁵ remain; at 40 there is only 25,000

Darwinian competition occurs between mitochondria within a cell, between cells in a tissue, and between organisms.

Cell volume of a eukaryote (typically 20 - 50 microns in size) is from 10⁴ to 10⁵ times that of a bacteria, which are a few microns (10^-3 mm) in size (p30).

Links

• "Power, Sex, Suicide: Mitochondria and the meaning of life" by Nick Lane
• "Sex as a division of labour between mitochondria" John & Carol Allen
• Biochemistry Online

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