IONIZATION OF WATER, WEAK ACIDS AND WEAK BASES

The ionization of water can be described by an equilibrium constant. When weak acids or weak bases are dissolved in water, they can contribute H+ by ionizing (if acids) or consume H+ by being protonated (if bases). These processes are also governed by equilibrium constants

Water molecules have a slight tendency to undergo reversible ionization to yield a hydrogen ion and a hydroxide ion :

H₂O = H⁺ + OH⁻

The position of equilibrium of any chemical reaction is given by its equilibrium constant. For the general reaction,

A+B = C + D

PHOSPHOLIPIDS

These are complex or compound lipids containing phosphoric acid, in addition to fatty acids, nitrogenous base and alcohol 

There are two  classes of phospholipids

1. Glycerophospholipids (or phosphoglycerides) that contain glycerol as the alcohol.

2. Sphingophospholipids (or sphingomyelins) that contain sphingosine as the alcohol

Glycerophospholipids

Glycerophospholipids are the major lipids that occur in biological membranes. They consist of glycerol 3-phosphate esterified at its C1 and C2 with fatty acids. Usually, C1 contains a saturated fatty acid while C2 contains an unsaturated fatty acid.

In glycerophospholipids, we refer to the glycerol residue (highlighted red above) as the "glycerol backbone."

Glycerophospholipids are Amphipathic

Glycerophospholipids are sub classified as

1. Phosphatidylethanolamine or cephalin also abbreviated as PE is found in biological membranes and composed of ethanolamine bonded to phosphate group on diglyceride.

2. Phosphatidylcholine or lecithin or PC which has chloline bonded with phosphate group and glycerophosphoric acid with different fatty acids like palmitic or hexadecanoic acid, margaric acid, oleic acid. It is a major component of cell membrane and mainly present in egg yolk and soy beans.

3. Phosphatidic acid (phosphatidate) (PA)

It consists of a glycerol with one saturated fatty acid bonded to carbon-1 of glycerol and an unsaturated fatty acid bonded to carbon-2 with a phosphate group bonded to carbon-3.

4.Phosphatidylserine (PS)

This phospholipid contains serine as an organic compound with other main components of phospholipids. Generally it found on the cytosolic side of cell membranes.

5. Phosphoinositides

It is a group of phospholipids which are negatively charged and act as a a minor component in the cytosolic side of eukaryotic cell membranes. On the basis of different number of phosphate groups they can be different types like phosphatidylinositol phosphate (PIP), phosphatidylinositol bisphosphate(PIP2) and phosphatidylinositol trisphosphate (PIP3). PIP, PIP2 and PIP3 and collectively termed as phosphoinositide.

6. Cardiolipin :

lt is so named as it was first isolated from heart muscle. Structurally, a cardiolipin consists of two molecules of phosphatidic acid held by an additional glycerol through phosphate groups. lt is an important component of inner mitochondrial membrane. Cardiolipin is the only phosphoglyceride that possesses antigenic properties.

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.

PHOSPHORUS

Serum level of phosphate is 3-4 mg/dl for adults and 5-6 mg/dl in children. Consumption of calcitriol increases phosphate absorption.

Functions of phosphorus
(a) Plays key role in formation of tooth and bone

(b) Production of high energy phosphate compounds such as ATP, CTP, GTP etc.,

(c) Synthesis of nucleotide co-enzymes such as NAD and NADP

(d) Formation of phosphodiester backbone structure for DNA and RNA synthesis

Hypophosphatemia is the condition which leads to decrease in absorption of phosphorus. it leads to hypercalcamia

Hyperphosphatemia, increase in absorption of phosphate was noticed. Hyperphosphatemia leads to cell lysis, hypocalcemia and thyrotoxicosis.

The amino acids buffer system

Amino acids contain in their molecule both an acidic (− COOH) and a basic (− NH₂) group. They can be visualized as existing in the form of a neutral zwitterion in which a hydrogen atom can pass between the carboxyl and amino groups. 

By the addition or subtraction of a hydrogen ion to or from the zwitterion, either the cation or anion form will be produced 

Thus, when OH⁻ ions are added to the solution of amino acid, they take up H⁺ from it to form water, and the anion is produced. If H⁺ ions are added, they are taken up by the zwitterion to produce the cation form. In practice, if NaOH is added, the salt H₂N - CH₂ - COONa would be formed. and the addition of HCl would result in the formation of amino acid hydrochloride.

Erythrocytes and the Pentose Phosphate Pathway

The predominant pathways of carbohydrate metabolism in the red blood cell (RBC) are glycolysis, the PPP and 2,3-bisphosphoglycerate (2,3-BPG) metabolism (refer to discussion of hemoglobin for review of the synthesis and role role of 2,3-BPG).

Glycolysis provides ATP for membrane ion pumps and NADH for re-oxidation of methemoglobin. The PPP supplies the RBC with NADPH to maintain the reduced state of glutathione.

The inability to maintain reduced glutathione in RBCs leads to increased accumulation of peroxides, predominantly H₂O₂, that in turn results in a weakening of the cell wall and concomitant hemolysis.

Accumulation of H₂O₂ also leads to increased rates of oxidation of hemoglobin to methemoglobin that also weakens the cell wall.

Glutathione removes peroxides via the action of glutathione peroxidase.

The PPP in erythrocytes is essentially the only pathway for these cells to produce NADPH.

Any defect in the production of NADPH could, therefore, have profound effects on erythrocyte survival.