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By utilizing these comprehensive organic chemistry notes, you'll have a valuable tool at your disposal to enhance your understanding, improve your grades, and succeed in your organic chemistry journey. Invest in these notes today and empower yourself with the knowledge needed to excel in this fascinating field!
Typology: Lecture notes
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Though they can be harmful at very high levels. All the well known toxic elements, are extremely rare in the earth’s crust: As (~ 2 х 10-4^ %), Pb (~ 1.3 х 10-3^ %), Cd (~ 2 х 10-5^ %) and Hg (~ 5 х 10-5^ %).
Essential elements are absolutely essential or necessary for life processes. Trace elements are also necessary for life processes. Non-essential elements are not essential. If they are absent other elements may serve the same function. Toxic elements disturb the natural functions of the biological system.
Concentration of metal ions in our system is controlled within very fine limits. This control is generally exercised by certain biological complexing agents. The deficiency or excess of metal ions causes disorders, which leads to various diseases. This can be seen in Figure 1.
Figure 1 : Effect of concentration of elements in our body
Calcium is a critical element in all animals and human beings. A healthy human adult has about 1.05 kg Ca, of which 99% exists as phosphates resembling the mineral hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 , in bones and teeth.
The small remainder is in cellular fluids, existing in partly ionized, or protein bound forms. The primary dietary source of Ca is milk (65-76%), with smaller amounts derived from meat, fish and eggs (5-10%), and still less from non-dairy foods such as nuts, fruits, beans etc (Figure 3).
Figure 3: Dietary source of Calcium
An adult human has approximately 140 g of potassium of which more than 90% is both intracellular and exchangeable (K+^ is the predominant cation in intracellular space) since muscles contain most of the body’s intracellular fluid, they also contain most of the potassium. Since K+^ is found in most animal and vegetable foods, dietary deficiency is exceedingly rare except under unusual conditions (such as diets containing high quantity of refined sugars, alcoholic individuals deriving most of their calories from low-potassium alcoholic beverages in a state of starvation etc.).
Sodium is the predominant extracellular cation in all animals, including human beings. An adult human body contains about 105g sodium, of which approximately 24% is located in bones and about 65% is contained in extracellular fluid. Sodium ion equilibrium is maintained primarily by the kidney, the key organ in water and electrolyte balance. Sodium chloride (salt) is the predominant dietary source. Although excessive dietary Cl-^ appears to have no significant ill effect on health, there is much evidence dictating that excessive Na+^ intake results in elevated blood pressure (hypertension)
Cobalt is an essential element for humans, although it is present only in trace amounts. Only a little over 1 mg Co is present in an adult human body. It is the main component of vitamin B 12 (Cobalamin) (Figure 7).
Figure 7: Cobalt in Vitamin B 12
Vitamin B 12 is synthesized only by bacteria. It enters the human food chain from animal sources such as meat. The dietary deficiency of Cobalt is likely only among strict vegetarians or when the intrinsic factor from the stomach that facilitates B 12 absorption is absent or severely decreased as is the case in pernicious anaemia.
An adult has about 1.5-3.0 g of Zn and the largest amounts are present in liver and bone. There is evidence that Zinc concentrations in blood and several tissues vary considerably in response to many stimuli. Zinc appears to be critical in many functions. Human zinc deficiency is inherited in infants and is termed as acrodermatitis enteropathica and is characterized by behavioral disturbances, diarrhea, hair loss and severe peri-orificial skin rash, all of which respond with remarkable promptness to zinc administration.
Similar syndromes have now been reported many times with penicillamine treatment of other disorders, presumably due to chelation of Zn, as well as during total parenteral nutrition when Zn was not added to the nutritional solutions for even as short a time as two weeks. A more chronic dietary deficiency of Zn (combined with other deficiencies) include dwarfism, hypogonadism and sexual immaturity, the latter devised with Zn therapy. There is much evidence for marginal dietary deficiencies in humans. The effects include decreased acuity of taste (hypogeusia), importance, delayed wound healing, hypogonadism and oligospermia, poor development and possible foetal wasting and teratogenesis. Dietary source range in Zn concentrations from1400 μg g-1^ to 2 μg g-1^ or less in fresh fruit and vegetables. Bioavailability of Zn is especially high from animal tissues and is low from milk and from grains. The latter effect is apparently due to binding to phytic acid and fibre. Figure 8 shows the country-wide prevalence of zinc deficiency all over the world. As you can see, India has one of the highest prevalence rates of zinc deficiency.
Figure 8: Global prevalence of zinc deficiency
The essentiality of Mo in animals and human beings is assumed from its presence in the metalloemzymes -xanthine oxidase and aldehyde oxidase. Mo is also part of the enzyme sulphite oxidase, an inherited deficiency of which causes severe neurologic disorders and early death in humans. However, no naturally occurring Mo deficiency has ever been documented in animals or human beings, even though several animal deficiencies have been produced experimentally, particularly by using the Mo antagonist. Molybdenum is present in very small quantities. Molybdenum appears to be readily absorbed from the gastro-intestinal tracts and excreted
infidelity (mis-reading) during synthesis of DNA copies. Thus the story of Cr once again illustrates the principle of essentiality in small amounts and potential toxicity in large amounts.
Normal adult human has about 100-110 mg Cu, highest concentrations are found liver, kidney, heart and brain. The prototype functional deficiency of Cu in humans is an X-linked inherited disorder called Menke’s syndrome (Kinky or steely hair syndrome) (Figure 10).
Figure 10: Menke’s syndrome (Kinky or steely hair syndrome)
Cu insufficiency was first suspected by analogy with abnormal wool in Cu-deficient sheep. The defect appears to be decreased gastrointestinal absorption and /or cellular utilization of Cu. The essentiality of Cu is the consequence of its role in metalloenzymes involving several critical biochemical pathways. Several of these enzymes are noted here. For example, Superoxide dismutase metabolizes the potentially damaging superoxide anion. Lysyl oxidase is a monoamine oxidase required for cross-linking collagen and elastin, the structural macromolecules of connective tissue. Dopamine β-hydroxylase, amine oxidase and tyrosinase are all Cu containing enzymes that interconvert the major neurotransmitters dopamine, noradrenaline and adrenaline, probable accounting for the high concentration of Cu in the brain. The latter enzyme, tyrosinase, is also a key step in pigment production. Cytochrome C oxidase is the key and terminal enzyme of the respiratory chain, accounting for more than 90% of the energy of muscular contraction. Ferroxidase (better known as ceruloplasmin before its role in mobilizing and oxidizing Fe from storage sites was recognized) is believed to account for 95% of serum Cu, and appears to be a multi-functional protein serving as a major transport system for Cu as well. Copper is widely distributed in the food chain, a notable exception being cow’s milk. Copper concentration ranges from 20-60 μg g-1^ in animal tissues to less than 2 μg g-1^ in leafy green vegetables and fruits to less than 0.2 μg g-1^ in cow’s milk, which is much less than in human milk. Infants, especially if premature and not breast-fed, are therefore most susceptible to dietary deficiencies; excessive loss of Cu from gastro-intestinal tract due to diarrhoea is the most common precipitating factor. In Wilson’s disease, copper concentration increases up to one hundred times greater than normal. Copper is accumulated in a number of tissues but in particular is found in the liver, brain and kidney which leads to liver and kidney failure and various neurological abnormalities. Death results if the condition is not recognized and treated.
The average human adult has about 4-5 g Fe. Of this amount, about 60-70% is present in haemoglobin in red blood cell, 3-5% is in muscle myoglobin, 15% is bound to the Fe storage cellular protein, ferritin, 0.2% occurs as a component of critical respiratory enzymes and 0.004% is bound to the serum transport protein transferin. Iron deficiency causes anemia because red cells of blood containing less hemoglobin than in normal condition. Acute iron poisoning leads to vomiting, pallor, shock, circulatory collapse and coma. Chronic conditions are also known in which iron is deposited in tissues and organs of the body. This condition is known as siderosis.
In this module you have learnt that: Elements are classified into four categories: Essential, Trace, Non-essential and Toxic. No common element is toxic at levels normally encountered though almost anything can be harmful at too high levels. Concentration of metal ions in human being’s system is controlled within very fine limits.
