NEET MDS Lessons
Biochemistry
Classification of Fatty Acids and Triglycerides
Short-chain: 2-4 carbon atoms
Medium-chain: 6-12 carbon atoms
Long-chain: 14-20 carbon atoms
Very long-chain: >20 carbon atoms
• are usually in esterified form as major components of other lipids
A16-carbon fatty acid, with one cis double bond between carbon atoms 9 and 10 may be represented as 16:1 cisD9.
Double bonds in fatty acids usually have the cis configuration. Most naturally occurring fatty acids have an even number of carbon atoms
Examples of fatty acids
|
18:0 |
stearic acid |
|
18:1 cisD9 |
oleic acid |
|
18:2 cisD9,12 |
linoleic acid |
|
18:3 cisD9,12,15 |
linonenic acid |
|
20:4 cisD5,8,11,14 |
arachidonic acid |
There is free rotation about C-C bonds in the fatty acid hydrocarbon, except where there is a double bond. Each cis double bond causes a kink in the chain,
Applications of the Henderson-Hasselbalch equation
• Calculate the ratio of CB to WA, if pH is given
• Calculate the pH, if ratio of CB to WA is known
• Calculate the pH of a weak acid solution of known concentration
• Determine the pKa of a WA-CB pair
• Calculate change in pH when strong base is added to a solution of weak acid. This is represented in a titration curve
• Calculate the pI
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.
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
Clinical significance
Primary hyperparathyroidism is due to autonomous, abnormal hypersecretion of PTH in the parathyroid gland
Secondary hyperparathyroidism is an appropriately high PTH level seen as a physiological response to hypocalcemia.
A low level of PTH in the blood is known as hypoparathyroidism and is most commonly due to damage to or removal of parathyroid glands during thyroid surgery.
SELENIUM
normal serum level is 50-100 mg/day
Selenium dependent enzymes include glutathione Peroxidase and 5-de-iodinase. Selenium concentration in testis is the highest in adult. It is very necessary for normal development and maturation of sperm.
Niacin: Vitamin B3, Nicotinamide, Nicotinic Acid Niacin, or vitamin B3,
is involved in energy production, normal enzyme function, digestion, promoting normal appetite, healthy skin, and nerves.
RDA Males: 16 mg/day; Females: 14 mg/day
Niacin Deficiency : Pellagra is the disease state that occurs as a result of severe niacin deficiency. Symptoms include cramps, nausea, mental confusion, and skin problems.