CALCIUM

Total calcium in the human body is 1 to 1.5kg, out of which 99% is seen in bone and 1% in extracellular fluid. The main source of calcium is milk.

The daily requirement of calcium for child is 1200mg/day and for adult it is 500mg/day. During pregnancy /lactation the calcium requirement is 1500mg/day.

The absorption of calcium takes place in 1st and 2nd part of deuodenum. Calcium absorption requires carrier protein, helped by Ca²⁺ - dependent ATpase.

Factors responsible for increase in calcium absorption include Vitamin D, Parathyroid hormone, acidity and amino acids. Factors such as phytic acid,oxalates, malabsorption  syndromes and Phosphates decreases calcium absorption. The normal calcium level in blood is 9-11mg/dl.

Weak Acids and pKa

• The strength of an acid can be determined by its dissociation constant, Ka.

• Acids that do not dissociate significantly in water are weak acids.

• The dissociation of an acid is expressed by the following reaction: HA = H⁺ + A^- and the dissociation constant Ka = [H⁺ ][A^- ] / [HA]  

• When Ka < 1, [HA] > [H⁺ ][A^- ] and HA is not significantly dissociated. Thus, HA is a weak acid when ka < 1.

• The lesser the value of Ka, the weaker the acid.

• Similar to pH, the value of Ka can also be represented as pKa.

• pKa = -log Ka.

• The larger the pKa, the weaker the acid.

• pKa is a constant for each conjugate acid and its conjugate base pair.

• Most biological compounds are weak acids or weak bases.

MAGNESIUM

The normal serum level of Magnesium is 1.8 to 2.2. mg/dl.

Functions of Magnesium

(a) Irritability of neuromuscular tissues is lowered by Magnesium

(b) Magnesium deficiency leads to decrease in Insulin dependent uptake of glucose

(c) Magnesium supplementation improves glucose tolerance

Causes such as liver cirrhosis, protein calorie malnutrition and hypo para thyroidism leads to hypomagnesemia

The main causes of hypermagnesemia includes renal failure, hyper para thyroidism, rickets, oxalate poisoning and multiple myeloma.

Step 1.  Acyl-CoA Dehydrogenase catalyzes oxidation of the fatty acid moiety of acyl-CoA, to produce a double bond between carbon atoms 2 and 3.

There are different Acyl-CoA Dehydrogenases for short (4-6 C), medium (6-10 C), long and very long (12-18 C) chain fatty acids. Very Long Chain Acyl-CoA Dehydrogenase is bound to the inner mitochondrial membrane. The others are soluble enzymes located in the mitochondrial matrix.

FAD is the prosthetic group that functions as electron acceptor for Acyl-CoA Dehydrogenase. 

A glutamate side-chain carboxyl extracts a proton from the a-carbon of the substrate, facilitating transfer of 2 e^- with H⁺ (a hydride) from the b position to FAD. The reduced FAD accepts a second H⁺, yielding FADH₂

The carbonyl oxygen of the thioester substrate is hydrogen bonded to the 2'-OH of the ribityl moiety of FAD, giving this part of FAD a role in positioning the substrate and increasing acidity of the substrate a-proton

The reactive glutamate and FAD are on opposite sides of the substrate at the active site. Thus the reaction is stereospecific, yielding a trans double bond in enoyl-CoA.

FADH₂ of Acyl CoA Dehydrogenase is reoxidized by transfer of 2 electrons to an Electron Transfer Flavoprotein (ETF), which in turn passes the electrons to coenzyme Q of the respiratory chain.

Step 2. Enoyl-CoA Hydratase catalyzes stereospecific hydration of the trans double bond produced in the 1st step of the pathway, yielding L-hydroxyacyl-Coenzyme A

Step 3. Hydroxyacyl-CoA Dehydrogenase catalyzes oxidation of the  hydroxyl in the b position (C3) to a ketone. NAD⁺ is the electron acceptor.

Step 4. b-Ketothiolase (b-Ketoacyl-CoA Thiolase) catalyzes thiolytic cleavage.

A cysteine S attacks the b-keto C. Acetyl-CoA is released, leaving the fatty acyl moiety in thioester linkage to the cysteine thiol. The thiol of HSCoA displaces the cysteine thiol, yielding fatty acyl-CoA (2 C shorter).

A membrane-bound trifunctional protein complex with two subunit types expresses the enzyme activities for steps 2-4 of the b-oxidation pathway for long chain fatty acids. Equivalent enzymes for shorter chain fatty acids are soluble proteins of the mitochondrial matrix.

Summary of one round of the b-oxidation pathway:

fatty acyl-CoA + FAD + NAD⁺ + HS-CoA → 
            fatty acyl-CoA (2 C shorter) + FADH₂ + NADH + H⁺ + acetyl-CoA

The b-oxidation pathway is cyclic. The product, 2 carbons shorter, is the input to another round of the pathway. If, as is usually the case, the fatty acid contains an even number of C atoms, in the final reaction cycle butyryl-CoA is converted to 2 copies of acetyl-CoA

ATP production:

• FADH₂ of Acyl CoA Dehydrogenase is reoxidized by transfer of 2 e^- via ETF to coenzyme Q of the respiratory chain. H⁺ ejection from the mitochondrial matrix that accompanies transfer of 2 e^- from CoQ to oxygen, leads via chemiosmotic coupling to production of approximately 1.5 ATP. (Approx. 4 H⁺ enter the mitochondrial matrix per ATP synthesized.)
• NADH is reoxidized by transfer of 2 e^- to the respiratory chain complex I. Transfer of 2 e^- from complex I to oxygen yields approximately 2.5 ATP.
• Acetyl-CoA can enter Krebs cycle, where the acetate is oxidized to CO₂, yielding additional NADH, FADH₂, and ATP. 
• Fatty acid oxidation is a major source of cellular ATP

b-Oxidation of very long chain fatty acids also occurs within peroxisomes

FAD is electron acceptor for peroxisomal Acyl-CoA Oxidase, which catalyzes the first oxidative step of the pathway. The resulting FADH₂ is reoxidized in the peroxisome producing hydrogen peroxide FADH₂ + O₂ à FAD + H₂O₂

The peroxisomal enzyme Catalase degrades H₂O₂ by the reaction:
2 H₂O₂ → 2 H₂O + O₂
These reactions produce no ATP

Once fatty acids are reduced in length within the peroxisomes they may shift to the mitochondria to be catabolized all the way to CO₂. Carnitine is also involved in transfer of fatty acids into and out of peroxisomes

Monosaccharides: Aldoses (e.g., glucose) have an aldehyde at one end

They are classified acc to the number of carbon atoms present

Trioses, tetroses, pentose ( ribose, deoxyribose), hexoses  (glucose, galactose, fructose) Heptoses (sedoheptulose)

Glyceraldehyde simplest aldose

Ketoses (e.g., fructose) have a keto group, usually at C 2.

Dihydroxyacetone simplest Ketoses

The higher sugar exists in ring form rather than chain form

Furan  : 4 carbons and 1 oxygen

Pyrans : 5 carban and 1 oxygen

 These result from formation of hemiacital linkage b/w carbonyl and an alcohol group

LIPOPROTIENS

Lipoproteins Consist of a Nonpolar Core & a Single Surface Layer of Amphipathic Lipids

The nonpolar lipid core consists of mainly triacylglycerol and cholesteryl ester and is surrounded by a single surface layer of amphipathic phospholipid and cholesterol molecules .These are oriented so that their polar groups face outward to the aqueous medium. The protein moiety of a lipoprotein is known as an apolipoprotein or apoprotein,constituting nearly 70% of some HDL and as little as 1% of Chylomicons. Some apolipoproteins are integral and cannot be removed, whereas others can be freely transferred to other lipoproteins.

There  re five types of lipoproteins, namely chylomicrons, very low density lipoproteins(VLDL)  low density lipoproteins (LDL), high density Lipoproteins (HDL) and free fatty acid-albumin complexes.