Minerial , 2ed Class , Biochemistry

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Minerals and trace elements

University of Missan

College of Medicine

Department of Biochemistry

BY

ALI J. AL-MALIKI


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Minerals

The elements essential for life , can be divided

into macro elements (daily requirement > 100 mg)

and microelements (daily requirement < 100 mg).

The macroelements include the electrolytes sodium

(Na), potassium (K), calcium (Ca), and magnesium

(Mg), and the nonmetals chlorine (Cl), phosphorus

(P), sulfur (S), and iodine (I)..


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The essential microelements are only required

in trace amounts . This group includes iron (Fe),

zinc (Zn),manganese (Mn), copper (Cu), cobalt

(Co), chromium(Cr), selenium (Se), and

molybdenum (Mo). Fluorine (F) is not essential for

life, but does promote healthy bones and teeth. It is

still a matter of controversy whether vanadium,

nickel, tin, boron, and silicon also belong to the

essential trace elements .


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Minerals stored in the body include water, which is

distributed throughout the whole body; calcium, stored in

the form of apatite in the bones ; iodine, stored as

thyroglobulin in the thyroid; and iron, stored in the form

of ferritin and hemosiderin in the bone marrow, spleen,

and liver . The storage site for many trace elements is the

liver. In many cases, the metabolism of minerals is

regulated by hormonesfor example, the uptake and

excretion of H2O, Na+,Ca2+, and phosphate , and storage

of Fe2+ and I.


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Mineral deficiencies

An unbalanced diet, resorption disturbances,

and diseases.

Calcium deficiency can lead to rickets,

osteoporosis, and other disturbances.

Chloride def iciency is observed as a result of

severe Cl

losses due to vomiting. Due to the lowcontent of iodine in food in many regions of central

Europe, iodine def iciency is widespread there and


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Magnesium deficiency can be

caused by digestive disorders or an

unbalanced diete. g., in alcoholism.

Trace element deficiencies often

result in a disturbed blood picture

i. e., forms of anemia.


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Iodine (as a result of its incorporation

into iodothyronines) and calcium act assignaling substances. Most trace elements are

cofactors for proteins, especially for enzymes.Particularly important in quantitative terms

are the i ron proteins hemoglobin, myoglobin,and the cytochromes , as well as more than

300 different zinc proteins.


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Biologically important elements

More than 99% of the atoms in animals bodies are

accounted for by just four elements hydrogen (H),

oxygen (O), carbon (C) and nitrogen (N). Hydrogen and

oxygen are the constituents of water, which alone makes up

6070% of cell mass . Together with carbon and nitrogen,

hydrogen and oxygen are also the major constituents of the

organic compounds on which most living processes

depend. Many biomolecules also contain sulfur (S) or

phosphorus (P). The above macroelements are essential for

all or anisms.


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inorganic ions includes the alkali metals sodium

(Na) and potassium (K), and the alkaline earth metal

smagnesium (Mg) and calcium(Ca). The halogen chlorine

(Cl) is also always ionized in the cell. All other elements

important for life are present in such small quantities that

they are referred to as trace elements. These include

transition metals such as iron (Fe), zinc (Zn), copper (Cu),

cobalt (Co) and manganese (Mn). A few nonmetals, such as

iodine (I) and selenium (Se), can also be classed as essential

trace elements.

I t b l


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Iron metabol sm

Distribution of iron (Fe) is quantitatively the most

important trace element . The human body contains 45g

iron, whichis almost exclusively present in protein-bound

form. Approximately three-quarters of the total amount is

found in heme proteins , mainly hemoglobin and

myoglobin. About 1% of the iron is bound in ironsulfur

clusters , which function as cofactors in the respiratory

chain, in photosynthesis, and in other redox chains. The

remainder consists of iron in transport and storage

roteins transferrin ferritin .


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Iron can only be resorbed by the bowel in

bivalent form (i. e., as Fe2+). reducing agents in

food such as ascorbate (vitamin C) promote iron

uptake. Via transporters on the luminal and basal

side of the enterocytes, Fe2+ enters the blood,

where it is bound by transferrinHeme groups can

also be resorbed by the small intestine. Most of the

resorbed iron serves for the formation of red blood

cells in the bone marrow (erythropoiesis).


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Electrolyte and water recyclingCalcium and phosphate ions. Calcium (Ca2+) and phosphate

ions are almost completely resorbed from the primary urine by active

transport (i.e., in an ATP-dependent fashion). The proportion of Ca2+

resorbed is over 99%, while for phosphate is 8090%. The extent to

which these two electrolytes are resorbed is regulated by the three

hormones parathyrin, calcitonin, and calcitriol.The peptide hormone parathyrin (PTH), stimulates Ca2+ resorption in

the kidneys and at the same time inhibits the resorption of phosphate. In

conjunction with the effects of this hormone in the bones and intestines ,

this leads to an increase in the plasma level of Ca2+ and a reduction in

the level of phosphate ions.


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Sodium ions. Controlled resorption of Na+ from

the primary urine is one of the most important

functions of the kidney. Na+ resorption is highly

effective, with more than 97% being resorbed. Several

mechanisms are involved:some of the Na+ is taken up passively in the

proximal tubule through the junctions between the

cells (paracellularly). There is secondary active

transport together with glucose and amino acids


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Bone and teethThe family of connective-tissue cells includes

fibroblasts, chondrocytes (cartilage cells), and

osteoblasts (bone-forming cells). They are

specialized to secrete extracellular proteins,

particularly collagens, and mineral substances,

which they use to build up the extracel lular matrix .

By contrast, osteoclasts dissolve bone matter again

by secreting H+ and collagenases


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Calcium metabolismA.Functions of calcium

The human body contains 11.5 kg Ca2+,

most of which (about 98%) is located in the

mineral substance of bone . In addition to its

role as a bone component, calcium functions as

a signaling substance .


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Ca2+ ions act as second messengers in signal

transduction pathways , they trigger exocytosis and muscle

contraction , and they are indispensable as cofactors in

blood coagulation . Many enzymes also require Ca2+ for

their activity. The intracellular and extracellular

concentrations of Ca2+ are strictly regulated in order to

make these functions possible . Proteins bind Ca2+ via

oxygen ligands, particularly carboxylate groups and

carbonyl groups of peptide bonds

Calcitriol increases blood Ca2+


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Calcitriol increases blood Ca2+

levels through increased Ca2+

mobilization from bone. An overdose of

vitamin D (cholecalciferol), theprecursor of calcitriol, can therefore

have unfavorable effects on the skeleton

similar to those of vitamin deficiency

h ervitaminosis.


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Calcium homeostasis


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Calcium homeostasisCa2+metabolismis balanced in healthy adults. Approximately

1g Ca2+ is taken up per day, about 300 mg of which is resorbed. The

same amount is also excreted again. The amounts of Ca2+ released

from bone and deposited in it per day are much smaller. Milk and

milk products, especially cheese, are particularly rich in calcium.Calcitriol and parathyroid hormone, on the one hand, and

calcitonin on the other, ensure a more or less constant level of Ca2+

in the blood plasma and in the extracellular space . The peptideparathyroid hormone and the steroid calcitriol promote direct or

indirect processes that raise the Ca2+ level in blood. Calcitriol

increases Ca2+ resorption in the intestines and kidneys .


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Minerial , 2ed Class , Biochemistry

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