rain water

Tropical rain recycling

Water must be along with oxygen amongst the most important provision to life. Useable water is essential. Water movements on earth are central to climate and life. The process is a little like the chicken and egg but if one starts with water evaporation from oceans, accumulates in the atmosphere, followed by coalescence and falling as rain or snow. Some directly into the oceans, other on land and enters the terrestrial water cycle. A very complex process.
Tropical ocean waters evaporate, the water is lifted to cloud level by convection and transported towards the poles and lost progressively as rain or snow.
Rain sometimes in hot regions never reaches the ground but evaporates again in the sky. This depends upon the ambient relative humidity
Rahn T in Nature 2007, vol 445, pp495-6.
Worden et al Nature 2007, vol 445, pp 528-531.

The chemistry of food pungent tastes

Despite their highly dissimilar flavours, garlic, horseradish and cinnamon each can have a fiery taste. . This pungency has been attributed to chemicals that activate a specific ion-channel protein, known as transient receptor potential ankyrin 1 (TRPA1). Activated TRPA1 facilitates the flow of ions into the endings of specialized neurons in the mouth and skin. This excites the neurons, resulting in local inflammation and a sensation of burning pain. The activation of many ion channels by chemicals involves a readily reversible binding of the stimulating molecules. New evidence shows that the spicy compounds found in the foods listed above activate TRPA1 in a different, and often more sustained, manner, by covalently attaching themselves to cysteine amino-acid residues on the channel protein. . The TRPAl channel can be activated by an array of chemical and physical signals. There are a number of food constituents that act on TRPA1, as well as acrolein (an environmental irritant) and icilin (a substance that evokes a cooling sensation), each quite different structurally. TRPA1 can also be activated by several other cell-communication pathways, including G-protein-coupled signalling pathways and membrane depolarisation . All of this may be involved in cold-sensing and mechanosensation’.
The question is how can one channel be activated by so many and such varied stimuli? Macpherson and his colleagues in Nature 2007, vol 445, p 541 and discussed by Caterina Nature 2007 vol 445 p 491 note that many TRPAI stimuli are electrophiles capable of reacting with cysteine residues (albeit by different mechanisms). This property, rather than chemical geometry, night account for their shared activation of TPA1. They showed that the cysteine-reactive agonists must enter the cell before activating TRPAl. Covalent modification of these cysteines, individually or, together or in combination with others accounts for the activation of TRPAI by electrophiles.. Only-one cysteine residue was identified as crucial, possibly reflecting subtle differences between species in overall TRPAI structure. Aside from the newly identified sites of electrophile action, the TRPAI N-terminal domain contains 18 ankyrin repeat motifs and an EF-hand domain. These two features have been proposed to contribute to the regulation of the channel by mechanical force and calcium ions, respectively. The duration of covalent TRPA1 activation differs between species. The lifetimes of covalent cysteine modifications can vary, depending on the modifying agent and on environmental factors such as pH or redox state and lead to differences in the duration, magnitude and qualitative features of TRPA1-mediated food pungency, inflammation and pain. Electrophilic agents can be damaging to DNA and proteins, one possible step towards cancer.
Many of the cysteine-reactive compounds that activate TRPA1 induce the expression of the enzymes that detoxify them protecting against such injury.

sleep patterns in teenagers

Sleep is an essential part of life . We spend a third of our life asleep. It is believed that growth takes place during sleep. As a thought do the developing adult obese grown fat during sleep.
Much is known about sleep intensity and levels of sleep eg REM ( Rapid eye movement ) Phase.
According to the Oxford University neuroscientist , Professor Russell Foster, adolescents have different sleep patterns to adults, and may need to lie around in bed all morning. In fact he believes that youngsters would achieve more if they were allowed to get up and start school later in the day. In the US and Germany, some schools have tried switching to later start times and have seen better exam results, as well as lower rates of truancy and depression.
Researchers in Germany, he added, have found that our sleep patterns change with age.We know teens want to go to bed two hours later than 40- to 50-ycar-olds and in 10% of them there's a four-hour delay. It is interesting to know that the sleep patterns alter with age. Certainly the older one becomes, then the sleep pattern changes , for the worse.

The Week January 27th p 17

body size, body mass, obesity, child obesity

Size rules biology to a great.extent. . When things get bigger, their length increases linearly but their surface area increases by the square and their volume by the cube. So when the proportions, properties and performances of organisms, such as body shape, life span or speed of movement, are plotted against size or weight in log-log graphs, they fall on straight lines. The relationship between weight and strength dates back to Galileo, who calculated the effect of increases in animal size on body proportion.
In general life is shorter, hence the time flies faster, the smaller the organism.. And the bacteria zipping around in the water sample under a microscope are not an optical illusion; rather, they are moving at more than a hundred body lengths a second — equivalent to 720 kilometres per hour for a 2-metre-sized organism like humans. The same rate as planes .
What made size matter in the first place? Selection by predators is the most obvious reason, with increasing size. Selection by predators with increasing size a way to escape. Also there is always room at the top, implying that organisms can always get bigger. But the bigger they are, they harder they fall, so it is the small ones that are less vulnerable in the long run.
Victor Smetacek Nature vol 445, February 22 9 821 writing about the book
Why Size matters, from Bacteria to blue whales John Tyler Bonner Princeton University Press.

Height may be of importance, but much more important from the health point of view is obesity and the corollary of this anorexia nervosa. Will people born in the developed world in the 1990s have shorter lives than those born 60 years ago? The upward trend in life expectancy over the past century is set to reverse unless the life style of young people dramatically improves. The steady-rise of childhood obesity in the USA is likely to reduce life expectancy by 2 to 5 years by the middle of the century, with enormous increases in morbidity from type 2 diabetes, heart disease and other vascular disorder. Obesity during pregnancy may well have consequences for the foetus.
The average stature and physique of humans from different parts of the world reflect the local nutritional regime by processes that are established in utero and transmitted to succeeding generations. It seems that obesity and its consequences are likely to emerge when there is freely available food.
In the developing world, those released from the grip of historic poverty are most affected, whereas in the developed world, for reasons that are less well understood, the victims are the least educated and the least affluent.
The Pima Indians of Arizona and the inhabitants of the Pacific island of Nauru. until a few decades ago were lean and fit and free of diabetes. Now the majority of their young adults are obese, develop diabetes and die prematurely of heart disease. There may be a genetic predisposition to diabetes but the abrupt decline in strenuous physical activity along with the loss of the traditional foods by energy-dense food is the real cause. .
We have to return to a different way of life, in our new context. The food styles of our ancestors, clean food, water and decent sanitation, accompanied by exercise appropriate to our age and stage of life.
Michael Sargent reviewing Mismatch: Why Our World No Longer Fits Our Bodies
by Peter Gluckman & Mark Hanson ; Oxford University Press. 2006. 304 pp in Nature vol 445, pp 600
The terrible scourge of obesity in children is reviewed in the BMJ 2006, vol 33 pp1207-10 in a review article ( JJ Reilly and D Wilson )
They define obesity as an excessive body fat content with an increased risk of morbidity. BMI is probably the best measure of obesity., overweight being a BMI > than 91st percentile using the UK BMI charts and obesity > 98th centile. The epidemic of childhood obesity began in the UK in the 1980s.In 2004 14% of 2-11 year old children are obese and 25 % of 11-15 year olds obese.
The health consequences of this is wide. Psychological health health , cardiovascular overload, asthma, diabetes, orthopaedic problems,
And these persist into adult life with worsening seriousness and added the risk of diabetic problems.
Guide lines to prevention are complex and must be introduced with compassion and care.
The family as an entity must be treated and overall dietary changes are needed. A restriction in high energy foods to eating only at meals especially low energy containing foods is important.

The brain, genes, fish oils and folic acid

The mammalian central nervous system is a very complicated system, with an array of different cell types each with its singular morphology , connections and function. The phenotypic properties of each cell are the product of combinations of expressed gene products peculiar to that cell type. The Allen brain atlas project ( http://www.brain-map.org is studying the genetic structural and cellular architecture of the mouse brain. A mammoth undertaking using complex techniques. There are approximately 20,000 expressed genes in the adult mouse brain. The project looks at genes with regional expression patterns allowing descriptions for functional similarities across the 12 major brain regions.
Classical definitions of brain regions is based upon a combination of overall morphology, cellular cytoarchitecture, ontological development and functional connections. Such studies offer insights into brain structure and function, and may also challenge our definitions of brain structure which are anatomical and to an extent functional.
Lein et al 2007, Nature Jan 11, vol 445 pp 168-176

However these genes can only effectively express themselves if they have substrates to work with. The foetal brain grows rapidly during gestation ,weighs 350g (of which 50% is lipid ) at birth and triples in weight during the first two years of life. The lipids are predominantly polyunsaturated long chain fatty acids , some of which are essential fatty acids. .These are derived from preformed fatty acids or precursors. Of the fatty acids docosahexaenoic and arachidonic acids are the most important. Much of which is obtained from the diet.
It would appear that eating fish results in better neurological development than when the mother has a poor or absent fish intake.
This raises two questions. Fish contain small amounts of unwanted contaminants e.g. methylmercury, and possible toxicity problems for the foetus. .
And raises the irreverent thought, should Eskimos be the cleverest people on earth.
Lancet vol 369, February 17th, pp537-8 ; and Hibbeln et al Lancet , vol 369. pp 578-85
Flippancy apart this is very important observation

At the other end of life the brain begins to loose cognitive function, largely expressed as failing memory. The elderly with low serum folate and raised homocysteine concentrations are at risk of reduced cognitive function. In a large double blind randomised placebo controlled clinical trial in the Netherlands it was shown that taking 800 ųg of folic acid a day significantly improved cognitive memory. Again nutrition affecting a complex system.
Durga et al Lancet 2007, vol 369, pp 208-16

We Nutritionists live in a world which generates a fantastic array of scientific advances especially in molecular biology which appear to make nutrition less relevant. Perhaps we should see this as a great opportunity to clarify many of the mysteries of nutrition and health.

Global Warming

For many of us in the Western, more privileged world
It is possible that we have had the best of everything.
We are now to pay the cost of this life style.
We are the reason for that best of worlds to disappear or be severely modified.

Marine life, Marine nitrogen fixation cycle

Marine life and nitrogen cycle fix
I live by an estuary and this stretch of water is inhabited by lots of fish who have seals as predators. The local fishermen dislike the seals and would rather they left.
In the last month their wishes have come true and a pod of killer whales has appeared on the scene and they are feasting on the baby seals. The baby seals are very vulnerable as they begin to swim out of their mothers care.
The natural balance of he shore life will no doubt change as a result of these new visitors. Killer whales are the third most common mammal on the planet after man and the rat.
The cycle of life is ultimately dependent upon the massive food cycles. One such is the nitrogen fixation that takes place in the oceans.
The flow of nitrogen compounds between the oceans and the atmosphere is central to life, as nitrogen is a fundamental component of bio-mass and is essential for many biological processes. Much is known about the nitrogen cycle of the oceans, but there unanswered question.
Evidence is developing which shows that the primary process which puts nitrogen compounds into the sea i.e. biological nitrogen fixation is intimately associated, with marine nitrogen removal. The ratio of nitrogen to phosphorus in sea water may be the central factor that regulates nitrogen fixation.
Biological nitrogen fixation, the enzyme-catalysed reduction of nitrogen gas (N:) continually adds nitrogen to the sea in the form of compounds that can be used as nutrients. Nitrogen fixation is commonly associated with certain cyanobacteria that live in the warm, sunlit surface waters of low-latitude oceans'. These photosynthetic bacteria tap the immense reservoir of dissolved N: gas in sea water, but their growth is often limited by the scarcity of other nutrients such as phosphorus and iron . A ratio of iron to phosphorous of 16:1 is the norm.
Fixed nitrogen is eventually converted to nitrate by nitrifying bacteria. Ultimately, the loss of nitrogen from the ocean occurs by denitrification, a process that converts nitrogen compounds such as nitrate back to N-. Denitrification occurs mostly at depths of 200-700 metres in the 'oxygen minimum zones' (OMZs) of the ocean — that is, in the eastern tropical north Pacific, the eastern tropical south Pacific Ocean , the Arabian Sea and in marine sediments.
The unusually high growth rates of nitrogen fixers in the north Atlantic result from the high rate of growth of nitrogen fixers stimulated by the high flux of iron containing dust blown in the wind from North Africa
Capone and Knapp Nature 2007, January 11, vol 445, pp 159-160
Deutsch et al Nature, 2007, , vol 445, 163-167.

Geophagia

Earth eating or geophagia has been practised for thousands of years. There are recordings of this practice from ancient Sumeria, Egypt and China.
Some nutritionists sympathise with the value of this supplement to the diet , usually a clay as there is a rich provision of silicon, aluminium and traces of iron, calcium and zinc. However the clay may bid trace elements and prevent their absorption, worsening a precarious nutritional status. Geophagia in communities with marginal nutrition geophagia may cause anaemia. Especially in women who can in some cultures be the last to eat at meals.
Other studies suggest that geophagia is desired by and provides trace elements to individuals deficient .in a trace element.
It has also been suggested that clays act as a detoxicant, whatever that means.
Perhaps in some states e.g. pregnancy the earths just taste nice , filling and not harmful. Or causing sickness.
The studies on geophagia are very welcome. On the one hand there is ingrained folk tradition and ascribed virtues of say eating clay. The reasons for such a practice should be examined and tested scientifically. This is so necessary and welcome.
Such a course of action is in contrast to some vocal media pundits who make ill founded claims which are totally untested scientifically
Trevor Stokes Nature 2006, 444, 30th November 543-4

genes, disease liability, genome wide association, diabetes

In 1913, RA Fisher, an evolutionary biologist and pioneer of modern statistics, published a paper on the genetic causes of dis­ease that brought together two rival factions.
1. Geneticists who proposed a theory that diseases worked like Mendel’s pea plants, with just one or two genes responsible for each condition.
2. Biometricians, however, advocated a continuous distribution of phenotypes.
Fisher suggested that many mendelian traits could result in the continuous distribution of a disease.
But Fisher’s theories had been difficult to substantiate. Even the much-heralded Human Genome Project in the 1980s didn’t help as much as expected.
The two methods traditionally used to hunt down disease genes are linkage analysis, which uses large family trees to work out which genes are shared by affected individuals, and the candidate-gene approach, which uses physiological clues to narrow down potential culprits. But when it comes to complex conditions such as heart disease or diabetes, in which multiple environmental and genetic factors combine, neither method is very powerful- Scientists have identified just a handful of disease genes, along with lots of weak, unconfirmed hits.
Modern gene-chip technology combined with recently published maps of human genetic variants that groups together related variants single nucleotide polymorphisms enables the entire genomes of thousands of people to be scanned The GWA approach ( genome wide association )
Yet new results, including a stud)- en type 2 diabetes published this week (R. Sladek et al. .(Nature doi :10.1038/nature05616;2007 ) suggest that the GW’A approach will bear fruit, and lots of it This study on large numbers of type 2 diabetics and normals show . four genomic regions that confer a significant risk to developing the disease. Along with the pre­viously identified TCF7L2 gene, these regions together account for 70% of the genetic risk for the disease.
Of the four new genes, the best hit is SLC30A8, a zinc transporter, which is important because zinc assists with insulin secretion
Other diseases in the pipeline include coronary heart disease and rheumatoid arthritis.
Gene Russo Nature vol 445, 15 February 2007 pp 688-9

Seed preservation

Seeds and the preservation of seed lines is an important silent part of nutrition. We assume as constancy in our vegetables and fruit. Changes in this forms part of our unease over GM crops. Are they as good as we have preciously experienced and enjoyed.
There are some 1.5 million different crop strains. These are always at risk from war, climate change and economic and cultural change.
The Norwegian Government has developed the Svalbard International Seed Vault where examples of most seeds in the world will be stored deep in an Arctic mountain. The first seeds will be stored in 2008. A global insurance policy. Or shuffling the deckchairs on the Titanic. .
The caveat to this wonderful and imaginative idea is that seeds loose their ability to germinate in about 20 years. This will mean a massive programme in addition to the $125,000 costs for maintaining the bank.

Michael Hopkin Nature vol 445—February 2007 p 693

Dirty food

Food safety supervision in the USA is split across a number of Agencies.
According to the Centers for Disease Control and prevention in Georgia 76 million Americans contract food-borne illnesses each year and 5000 die.
Culprits include spinach and lettuce contaminated with E coli and salmonella bearing tomatoes.
These infections must relate in part to farm practices eg managing manure, irrigation and farm worker hygiene.
Nature vol 445, 15/2/2007 pages 683-4

However recent problems with turkeyys,humous in the UK show how omnipresent the problem can be. It goes to underline the worth of proper home cooking in a clean environs and washing raw fruit and vegetables before eating.

Isoflavones, oestrogen like activity

Isoflavones and their similarity to oestrogens., structurally and functionally

Isoflavones are plant chemicals which belong to the family of phyto-oestrogens. There are of interest to nutrition and health due to their potential oestrogenic properties in the body. There is close structural relationship of genistein and daidzein compared with 17ß-oestrodiol. Although oestrogenicity assays have reported low oestrogenic potency for dietary isoflavones (100-1000 times less than I7p-oestradiol;. However when dietary intakes of isoflavones are high their circulating concentrations could exceed endogenous oestradiol concentrations by up to 10000-fold which suggests potential physiological effects.
Isoflavones predominantly occur in plants as the water-soluble ß-glucosides, genistin. daidzin, glycitin which are hydrolysed by intestinal and bacterial ß-glucosidases. Genistein, daidzein and glycitein may be absorbed or further metabolised by gut microflora enzymes to isoflavone metabolites such as equol, dihydrogenistein. dihydrodaidzein, 6'-hydroxy-O-desmethylangolensin and -O-des-methylangolensin before absorption.
There is substantial evidence that oestrogen has beneficial effects on the cardiovascular system by enhancing NO production and thereby maintaining normal endothelial vasodilatory response and integrity of the vascular system. Oestrogen-like compounds such as isoflavones are also suggested to protect the endothelium and therefore be protective against the development of CVD.
Oestrogen-induced NO release occurs by more than one pathway. . Oestrogen can act through the classical oestrogen receptor (ER)-transcriptional pathway, whereby eNOS gene expression is increased and NO production increases over hours or days. The 'genomic' effects of oestrogen. However, the acute effects, which are rapid in response and short in duration, may involve ERa-mediated activation of none-transcriptional pathways (non-genomic), or by a direct activation of cell-signalling pathways.
Oestrogen also appears to increase NO availability by modulating reactive oxygen species (ROS) and antioxidant status within the endothelial cell. Oestrogen has been shown to inhibit the production of NADPH oxidase and superoxide, attenuating the potential for superoxide-mediated degradation of NO and formation of peroxynitrites . In addition to its positive effects on NO. oestrogen has been shown to promote the release of other vasodilator agents from endothelium.
There are two known classical oestrogen receptors ERα and ERß both widely distributed throughout the body. Oestrogen, or other oestrogcnic ligands. bind to these nuclear receptors in the cytosol. which allows the receptor to enter the nucleus and bind to response elements on DNA, and modulate gene transcription. ERα and ERß bind to the same oestrogen response elements (therefore affecting transcription of the same genes. However, they are functionally distinct and will not necessarily affect these genes in the same direction or with the same potency Although ERα and ERß are both expressed throughout the vasculature ERB is the receptor that predominates in this tissue, particularly in women. In addition, there are specific functional domains on the two receptor proteins that have a degree of divergence in their homology, which may affect binding of oestrogenic ligands . This is illustrated by the greater binding affinity of isoflavones for ERß compared with ERa .
Since ERa and ERß have different tissue distributions and binding affinities, it seems probable that the protective effects of oestrogen, or indeed oestrogen-like compounds, on the endothelium would vary with receptor type.
ERa appears to be the most important receptor for the protective effects of oestrogen in the endothelium.
Since isoflavones have a greater binding affinity for ERp compared with ERa then it might be expected that any protective effect of isoflavones against vascular injury would be weak compared with that of oestrogen, unless the isoflavone- ERß conformation induced a greater affinity for the oestrogen response element than the oestrogen- ERß conformation. Isoflavones bind more effectively to ERß compared with ERa, but they are also 1000 times more potent at generating transcriptional activity via ERß compared with ERa, due to selective recruitment of co-regulators to ERp. In addition, isoflavones are more effective at triggering transcriptional repression rather than activation, suggesting that isoflavones may repress transcription of some genes that are normally activated by ERa.

Hall WL et al 2005, Nutrition Research Reviews, 18, 130-144

Tell us the truth about Nutritionists

In the BMJ of 10th February 2007 p 334 Ben Goldacre makes a real point in decrying the veracity of media nutritionists.
His case is, that in their presentations the level of proof is never discussed and strong nutritional recommendations made without real evidence.
The statement "I am a nutritonist" appears to be all that is required as the basis for the claims. Papers are misquoted to suit the case that is being made. A regular claim is for some plant extract or chemical derived from plants to have anti tumour activity based on animal experiments and unproven in man. Or epidemiological studies quoted again without proof in intervention human trials. It is difficult to get water tight evidence because of the time scale but such proof is needed.
The disappointing results from the large experiments in China on protection from cancer by vitamins underlines this point even though epiemiological studies show that fruit and vegetables are protective.
Always there is a grain of science, but this is not enough. In contrast, Medical claims have to be strongly based on probability clearly supported by vigorous statistical evidence. This does not always apply to Nutrition.
Ben Goldacre places much of the media nutrition advise in the catergory of the entertainment industry,. Harsh but true.
The UK has an excellent record in registering Nutritionists who have to prove their credentials. However when any Nutritionist brings the discipline into indiscipline or ridicule then that registration should be looked at or even removed.
It is sad that Nutrition looses credibility by such activities.

Water disputes

As global warming becomes more of a day to day reality the most conspicuous effect is on the availability of water. In parallel with the drying of the terrestrial surface there is increasing requirements for water by growing populations as well as industry.
There are many instances of this but a recent example is recorded in the London Times of February 6th 200. India is enjoying increasing prosperity and with this an increasing requirement for water. After a 17 year long tribunal the southern state of Karnataka in Southern India is obliged to allow more water to flow down the River Cauvery to States downstream. The disputes over this originate in the 19th century from the time of the Raj.
The amounts of water in discussion are massive and are in excess of 500 billion cubic feet. The States downstream are desperate for water and their needs are, they feel, unmet. Lack of water makes population panic and there have been riots in response to the most recent decisions of the Tribunal. This decision is to insist that half of the 500 billion cubic feet of water is allowed to flow down stream to fed the other States.
Such arguments abut the distribution of water are happening all over the world for example the Jordan in the Middle .East.
Elsewhere there are problems attendant upon excess rain .

Nutrition, telomere length and aging

Nutrition now and in the future is about understanding biological proceses and how the constituents of food may affect these processes. An obvious statement.
A very interesting article in the Lancet ( Spyridopoulos and Dimmeler 2007 , 369, 81-2
Can telomere length predict cardiovascular risk ? )

Telomeres—TTAGGG DNA are the repeats at the ends of chromosomes—and are widely regarded to be the internal biological clock of a living organism as they shorten with every cell division.1 Telomeres in human blood cells contain about 10000-20000 nucleotides at birth. This length decreases by about 50 bp a year, thereby being reduced to a few thousand bp in elderly individuals.' Critically short telomeres are assumed to have functional implications, such as the induction of cellular senescence, which is characterised by the expression of specific markers of ageing and the inability of the cell to divide further.1 Although age is an important independent predictor for the development of cardiovascular disease, shortening of age-corrected telomere length in leucocytes exposes individuals to an additional substantial risk of mortality from cardiovascular and infectious complications.'1
In the Lancet, Scott Brouilette and colleagues ( Lancer 2007, 369, 107-114 ) report the correlation between telomere length and risk of developing coronary heart disease/ Telomere length was measured in white blood cell DNA from a subgroup of more than 1500 patients in the West of Scotland Primary Prevention Study (WOSCOPSJ, in which the use of pravastatin was tested in men with raised concentrations of LDL cholesterol to prevent cardiovascular events. This substudy shows that individuals with shorter telomere length have about a two-fold increased risk of developing coronary artery disease in the 5 years from the start of treatment. Interestingly, pravastatin completely attenuated this telomere-attributed risk. The randomised case-control design of the study is better than to all previous studies on the association of telomere length and cardiovascular risk.
Several aspects of Brouilette and colleagues' study merit special attention. The first is the potential mechanism behind the correlation between mean telomere length and coronary heart disease. One might speculate that shorter telomeres could indicate functional changes within cell populations—eg, senescent lymphocytes that produce higher amounts of inflammatory cytokines. Furthermore, telomere shortening in stem or progenitor cells could limit the repair capacity of the vessel wall. Telomere shortening associated with a dysfunction of circulating endothelial progenitor cells, which contribute to endothelial repair and seem to be atheroprotective, could aggravate atherosclerotic disease progression.
Interestingly also smoking and obesity accelerate this shortening process.
What a rich field for nutritional studies. -

Metabolic paths relevant to nutrition

A good knowledge of metabolism is essential fot a career in Nutrition. This article in Nature is a wonderful essay in metabolic controls.
Metabolic pathways Reinhart Heinrich Nature 2006 447, p700
Pioneer in systems biology.
In biology, mathematical systems analysis was until recently nearly invisible in the dazzling light of twentieth-century discoveries. But it has emerged from the shadows in the field of systems biology, a subject buoyed by immense data sets, conveyed by heavy' computing power, and addressing seemingly incomprehensible forms of complexity. If systems biology has heroes, one of them is Reinhart Heinrich, a former professor at the Humbotdt University in Berlin, who died on 23 October, aged 60. His most famous accomplishment was metabolic control theory, published in 1974 with Tom Rapoport and formulated independently by Henrik Kacser and James A. Burns in Edinburgh, UK.
From the 1930s to the 1960s, biochemists were busy describing metabolic pathways, just as molecular biologists today are feverishly trying to inventory the cell's gene-transcription and signalling circuits. The basic kinetic features of the enzymes in the major pathways were studied in great detail and with exceeding care. It seemed self-evident that, knowing the properties of each element, the behaviour of a pathway at vivo could simply be understood as the sum of its enzymes.
One assertion, drilled into the head of every biochemist, was the concept of the rate-limiting step. In this view, the flux through a pathway was determined by the slowest reaction, in the way a bucket brigade fighting a fire would be limited by the speed of the slowest member. Yet this concept, as shown by the metabolic control theory, was theoretically flawed, practically incomplete and often wrong, as many efforts to genetically engineer enzymes by changing 'rate-limiting steps' would ultimately show.
Metabolic control theory introduced the concept of control coefficients dimensionless quantities indicating how the flux of a pathway depended on a given step. Only a pathway where every control coefficient except one was zero would have a rate-limiting step, since the flux of that pathway would depend only on that step. Several pathways in fact had rate-limiting steps, but that often reflected the structure of the pathway, and could not simply be deduced from the maximum rates of the individual enzymes, their Michaelis constants or their displacement from equilibrium. Many pathways were instead networks, with the fluxes distributed in a self-governing way among its various branches.
Heinrich went on to apply this theory to the real case of glycolysis in red blood cells, where he showed that the flux of the reaction was shared by several enzymes. Much later, he extended his ideas to signal-transduction pathways, introducing control coefficients to dynamic processes. Sticking to real examples, such as the Wnt signalling and MAP kinase pathways, he again demonstrated that new properties and constraints emerge when the individual steps are combined into a complete pathway.
Heinrich also pointed the way to considerations of optimality theory and evolution that will confront systems biology for the next century. The question of evolution lies just beneath any effort to understand biology. Yet in most cases, physiological function and evolutionary change are considered distinct and are investigated by different people. Heinrich's work illustrated how systems biology might develop, where the central question will be not only how a system.