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.

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.

The input to fatty acid synthesis is acetyl-CoA, which is carboxylated to malonyl-CoA.

The ATP-dependent carboxylation provides energy input. The CO₂ is lost later during condensation with the growing fatty acid. The spontaneous decarboxylation drives the condensation. 

 fatty acid synthesis
acetyl-CoA + 7 malonyl-CoA + 14 NADPH → palmitate + 7 CO₂ + 14 NADP⁺ + 8 CoA

ATP-dependent synthesis of malonate:
8 acetyl-CoA + 14 NADPH + 7 ATP → palmitate + 14 NADP⁺ + 8 CoA + 7 ADP + 7 P_i

Fatty acid synthesis occurs in the cytosol. Acetyl-CoA generated in the mitochondria is transported to the cytosol via a shuttle mechanism involving citrate

FLUORIDE

The safe limit of fluorine is about 1PPM in water. But excess of fluoride causes Flourosis

Flourosis is more dangerous than caries. When Fluoride content is more than 2 PPM, it will cause chronic intestinal upset, gastroenteritis, loss of weight, osteosclerosis, stratification and discoloration of teeth

Enzymes are protein catalyst produced by a cell and responsible ‘for the high rate’ and specificity of one or more intracellular or extracellular biochemical reactions.

Enzymes are biological catalysts responsible for supporting almost all of the chemical reactions that maintain animal homeostasis. Enzyme reactions are always reversible.

The substance, upon which an enzyme acts, is called as substrate. Enzymes are involved in conversion of substrate into product.

Almost all enzymes are globular proteins consisting either of a single polypeptide or of two or more polypeptides held together (in quaternary structure) by non-covalent bonds. Enzymes do nothing but speed up the rates at which the equilibrium positions of reversible reactions are attained.

 In terms of thermodynamics, enzymes reduce the activation energies of reactions, enabling them to occur much more readily at low temperatures - essential for biological systems.

Glucagon

Glucagon, a peptide hormone synthesized and secreted from the α-cells of the islets of Langerhans of pancreas, raises blood glucose levels. The pancreas releases glucagon when blood sugar (glucose) levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream. Glucagon and insulin are part of a feedback system that keeps blood glucose levels at a stable level.

Regulation and function

Secretion of glucagon is stimulated by hypoglycemia, epinephrine, arginine, alanine, acetylcholine, and cholecystokinin.

Secretion of glucagon is inhibited by somatostatin, insulin, increased free fatty acids and keto acids into the blood, and increased urea production.