Mitochondria: The Veiled Lady of The Cell

They are so enigmatic they can be easily termed the 'veiled lady'(ladies). You might argue that ladies, in general, are by nature, quintessential enigma themselves. Mitochondria, then ( plural for mitochondrion) are even more elusive.

Cells need power to operate. They have some tiny organelles, lined by a double layer of membranes called mitochondria. These sausage shaped organelles produce power in the form of an energy rich compound, the ATP or adenosine tri phosphate, by a process called oxidative phosphorylation. It then supplies ATP to the rest of the cells. Thus ATP might be thought of as 'portable batteries'. As in power producing factories, mitochondria also produce 'pollution' in the form of highly dangerous free radicals. These free radicals damage the organelles themselves in addition to other parts of the cells. Free radical injury also leads to aging and other disease states. The double layered membranes prevent them from diffusing out to the cytosol. In addition, mitochondria play a vital role in apoptosis (programmed cell death).

The history of the mitochondria is even more interesting. Billions of years ago, eukaryotic cells (cells containing nucleus and cytoskeleton) engulfed aerobic bacteria to survive. Aerobic bacteria, by definition, use oxygen (air) and generate energy. By engulfing and incorporating them, cells could have independent energy producing units in them. Thus mitochondria are actually endosymbionts (chloroplast is another example: endosymbiotic theory of Lynn Margulis). This explains why mitochondria have separate genomes. Apart from the nucleus, DNA can be found only in the mitochondria.

A cell can contain few hundreds to thousands of mitochondria, depending the energy requirements of that particular cell/tissue. For example, the heart, kidney, muscle, nervous tissues are voracious energy spenders, and hence have more mitochondria. As expected, mitochondrial diseases affect them most.

Mitochondria has a double stranded circular DNA (mtDNA). They are capable of transcription (copying of the DNA code in a complementary manner, much like the 'negative' of a photo film), and translation (execution of the software like code into real chemical ingredients-proteins). It is 16,569 bp long (base pairs; adenine, guanine, cytosine and thymine are the four nitrogen containing bases, and since the DNA is double stranded->pairs). This DNA codes for 13 proteins, 2 rRNAs (ribosomal Ribo Nucleic Acid) and 22 t RNAs (transfer RNA). Most (99%) of mitochondrial proteins are produced by the nuclear DNA (nDNA) though.

Evolutionarily, we inherited the mitochondria from bacterias, eons ago. But whom did I inherit them from? My mother! Sperms contribute little mitochondria (if any): mitochondria come exclusively from mother. Thus in contrast to Mendelian genetics, where genes from both parents determine the genotype; mitochondrial genetics is entirely different. My mitochondrial DNA was inherited from my mother, who inherited her own mitochondrial DNA from her mother. Thus if you backtrack up the family tree, you will find the mitochondrial eve, the proverbial first lady ( or a cohort of ladies, to be more precise).
So, in essence, mitochondrial genetics is population genetics. They are widely used in anthropological, demographical and forensic studies. But not all mitochondrial genes are same, mutations occur very frequently and theres no paternal gene to compensate for them. Unmutated mitochondrial genes can coexist with mutated ones, in a state called heteroplasmy (as opposed to homoplasmy where all genes are the same). Mutations cost dear, since mitochondrial DNA lacks the repair mechanism of their nDNA counterpart. In addition they lack the protective histone covering.

As is expected, tissues having high energy demands suffer. Leber's hereditary optic neuropathy(LHON), cardiopathy, myopathy (ragged red fibres: surplus mitochondria give them these distinctive appearance on histology), Luft's syndrome (a very rare condition where the person sweats a lot to dissipate the extra heat generated by mitochondria gone wild, in addition to raised core body temperature and polyphagia and other abnormalities), MELAS (mitochondrial encephalomyopathy, lactic acidosis, stroke) and many others.

Right is Might

You have forgotten your car keys and done hours of thinking; but to no avail. You give up in despair and start sipping your evening cup of coffee. Suddenly, out of nowhere you remember where you kept your keys. What you could not remember thinking, came so abruptly on its own. This is intuition and it is said that its the right brain (right half of the brain, obviously!) that is responsible for this. The famous scientist, Albert Einstein said “The only real valuable thing is intuition.”

When we copy a 'normal' picture, the 'logical' brain breaks down the picture into graphical pixels. These pixels are then plotted in their graphical co-ordinates. This is rather like mathematics. The picture on the left have been intentionally placed upside down. When you try to draw this picture, you just can not take anything for granted, because the orientation is just not right. The mathematical plotting can not be activated. Where reasoning ends, intuition begins. It is much easier to draw (copy a picture) a picture placed upside down, since our logic takes the back seat then; and the intuitive role of the right hemisphere ('intuitive brain') starts to play. We are no longer primed to 'assign' any coordinates preemptively. The right hemisphere of the brain is not only associated with intuition and drawing (art), but also emotion, music and other artistic abilities. The left brain is rather logical and deals with mathematics and other tasks that require calculations. When a subject is told to recall words, the activity in left frontal cortex increases (left parahippocampal area is also stimulated); while activities in the right frontal cortex (along with para hippocampal areas of both sides) are increased when a subject recalls sceneries or pictures. These activation patterns of the brain have been measured by fMRI scans (functional Magnetic Resonance Imaging), PET scans (Positron Emission Tomography), ERP studies (event related potential or evoked potential) and other medical investigations.

Have you noticed that when we hold babies in our arms, we put them on our left? This left cradling is puzzling, because its the right arm that is stronger. So, why do mothers hold their babies on their left laps? It has been suggested that our expressions show better on the left side of the face and left cradling fosters stronger mother-baby relationship. This arises from the fact that the hemispheres of the brain is cross-wired. The (some of the) neural pathways from the brain cross to the opposite sides, as they enter the spinal cord, to supply peripheral circuits. The right brain (the one responsible for emotion etc) is wired to the left side of the body and the left brain is wired to the right. Thus the 'emotion generator' right brain, will have its manifestation on the left side of the face. Mothers possibly don't bother about all this, but evolutionary anthropology has left its indelible footprints on bipeds.

To become a creative genius, you need both intelligence (a faculty usually attributed to the left brain) and intuition (typically a right brain's domain). Albert Einstein, it is said, had strong intuitive powers, which helped him to formulate his famous theory of relativity, ahead of the contemporary knowledge. So, its time we wake up to this fact and start exercising our right brains as well.

The Baffling Hairs

Scanning down the evolutionary tree, one can find semblances with our ancestors (naturally, as a part of the legacy). But there are instances when one can not explain certain things. For example, in humans we find hairs in the axillary areas (armpits), pubic areas which seem to defy logic, from an evolutionary perspective. Goats, lions or chimpanzees don't have them. Why in the first place did we need to have them or what is the purpose they serve, or couldn't have we done without them? We don't find any evolutionary parallel in the vertebrate kingdom (to the best of my knowledge).

One might say that the conversion of testosterone to dihydrotestoterone, in the said areas, by 5 alpha reductase, is the reason why they grow at those places. This DHT ( dihydrotestoterone) then combines with its receptor within the cytoplasm of the cells, and the receptor- ligand- combine translocate to the nucleus to exert their effects. My point is not that. I just want to know why, all of a sudden, humans needed to grow 'beard' at those odd places. I mean, what's so Darwinian about this?

One reason that seems to make sense is that those hairs at the intertriginous areas may help reduce friction while we move. But I am not sure, as it has not yet been documented. There are instances where there are excessive body hairs all over, hypertrichosis (a condition that could even be caused by the antihypertensive agent 'minoxidil') or hirsutism, where females produce excessive body or facial hairs. How heavily a woman is 'furred' could be determined by Ferriman Galway scale. Well these conditions do NOT have a predilection towards those key areas (that is, they are not axilla/pubis specific) and we can safely discard them as not being relevant here.

Body hairs may have some roles in heat regulation (erection of hair [known by various terms as: horripilation, goose-bumps, piloerection, cutis anserina etc. etc]---> increased depth of skin---> more insulation, provided by the subcutaneous tissue occupying this place). Body hairs could also provide superficial protection, or the maintenance of beneficial microbial flora, what purpose these intertriginous hairs serve is a mystery.

Another possible explanation is that, hairs being great thermal insulators (and electrical too), can prevent the heat of the adjacent thigh skin, to reach the testes. The testes are normally cooler than the core body temperature by about 2 degree centigrade. This way they may be doing great evolutionary service, by letting us procreate.
Can you shed some light on this thread?

Women On Top

Today, the 8th of March, is the International Women's Day. Lets celebrate one more time to the health of the fairer sex. Though throughout the animal kingdom(almost), it is the male who looks better than the other of the species (take the case of a lion or a horse or a peacock, you will instantly realize who looks better), in the case of human beings, the situation is starkly the opposite. The females have a melodious voice, a glowing skin, a beautiful figure and what not.

They even have the genes on their side. When one considers the sex chromosomes, there are two X chromosomes in females vs one X and one Y chromosomes in the males. That way, they have less of many diseases including hemophilia. But they pass the bad genes onto the hapless male offspring, courtesy a poor Y chromosome. Their roles as mothers, daughters, girlfriends, or wives (bear in mind that not all wives are bad!), are irreplaceable in the society.

We must also be grateful to them that they don't eat us alive. Look at the sexual cannibalism that goes in the animal kingdom. Though the term is sexual cannibalism, actually it means devouring of the males by the females, always. It is practiced by the spiders, scorpions, mantids, and others. We are lucky, in that we are not bullied to that extent. We are a wee bit safer at the top ( of the pyramid) of the evolutionary tree.

So, next time don't grieve for the black widow spider, shed your tears for the male spider instead. God save the queen, and to hell with the king. Who bothers?

P.S. This article is dedicated to the most beautiful creatures on earth. Though some jokes have been cracked, it is really them who make us smile. Femme fatale, cherchez la femme, etc., are not only misleading but also misogynistic. I would rather say: 'No woman no smile' ( to rhyme like the Boney M).