NEET MDS Lessons
Biochemistry
LIPIDS
The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, which are related more by their physical than by their chemical properties.
Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents.
Most membrane lipids are amphipathic, having a non-polar end and a polar end
Lipids are important in biological systems because they form the cell membrane, a mechanical barrier that divides a cell from the external environment.
Lipids also provide energy for life and several essential vitamins are lipids.
Lipids can be divided in two major classes, nonsaponifiable lipids and saponifiable lipids.
A nonsaponifiable lipid cannot be broken up into smaller molecules by hydrolysis, which includes triglycerides, waxes, phospholipids, and sphingolipids.
A saponifiable lipid contains one or more ester groups allowing it to undergo hydrolysis in the presence of an acid, base, or enzyme.
Nonsaponifiable lipids include steroids, prostaglandins, and terpenes
Nonpolar lipids, such as triglycerides, are used for energy storage and fuel.
Polar lipids, which can form a barrier with an external water environment, are used in membranes.
Polar lipids include glycerophospholipids and sphingolipids.
Fatty acids are important components of all of these lipids.
FAT-SOLUBLE VITAMINS
The fat-soluble vitamins, A, D, E, and K, are stored in the body for long periods of time and generally pose a greater risk for toxicity when consumed in excess than water-soluble vitamins.
VITAMIN A: RETINOL
Vitamin A, also called retinol, has many functions in the body. In addition to helping the eyes adjust to light changes, vitamin A plays an important role in bone growth, tooth development, reproduction, cell division, gene expression, and regulation of the immune system.
The skin, eyes, and mucous membranes of the mouth, nose, throat and lungs depend on vitamin A to remain moist. Vitamin A is also an important antioxidant that may play a role in the prevention of certain cancers.
One RAE equals 1 mcg of retinol or 12 mcg of beta-carotene. The Recommended Dietary Allowance (RDA) for vitamin A is 900 mcg/ day for adult males and 700 mcg/ day for adult females.
Vitamin A Deficiency
Vitamin A deficiency is rare, but the disease that results is known as xerophthalmia.
Other signs of possible vitamin A deficiency include decreased resistance to infections, faulty tooth development, and slower bone growth.
Vitamin A toxicity The Tolerable Upper Intake Level (UL) for adults is 3,000 mcg RAE.
VITAMIN D
Vitamin D plays a critical role in the body’s use of calcium and phosphorous. It works by increasing the amount of calcium absorbed from the small intestine, helping to form and maintain bones.
Vitamin D benefits the body by playing a role in immunity and controlling cell growth. Children especially need adequate amounts of vitamin D to develop strong bones and healthy teeth.
RDA From 12 months to age fifty, the RDA is set at 15 mcg.
20 mcg of cholecalciferol equals 800 International Units (IU), which is the recommendation for maintenance of healthy bone for adults over fifty.
Vitamin D Deficiency
Symptoms of vitamin D deficiency in growing children include rickets (long, soft bowed legs) and flattening of the back of the skull. Vitamin D deficiency in adults may result in osteomalacia (muscle and bone weakness), and osteoporosis (loss of bone mass).
Vitamin D toxicity
The Tolerable Upper Intake Level (UL) for vitamin D is set at 100 mcg for people 9 years of age and older. High doses of vitamin D supplements coupled with large amounts of fortified foods may cause accumulations in the liver and produce signs of poisoning.
VITAMIN E: TOCOPHEROL
Vitamin E benefits the body by acting as an antioxidant, and protecting vitamins A and C, red blood cells, and essential fatty acids from destruction.
RDA One milligram of alpha-tocopherol equals to 1.5 International Units (IU). RDA guidelines state that males and females over the age of 14 should receive 15 mcg of alpha-tocopherol per day.
Vitamin E Deficiency Vitamin E deficiency is rare. Cases of vitamin E deficiency usually only occur in premature infants and in those unable to absorb fats.
VITAMIN K
Vitamin K is naturally produced by the bacteria in the intestines, and plays an essential role in normal blood clotting, promoting bone health, and helping to produce proteins for blood, bones, and kidneys.
RDA
Males and females age 14 - 18: 75 mcg/day; Males and females age 19 and older: 90 mcg/day
Vitamin K Deficiency
Hemorrhage can occur due to sufficient amounts of vitamin K.
Vitamin K deficiency may appear in infants or in people who take anticoagulants, such as Coumadin (warfarin), or antibiotic drugs.
Newborn babies lack the intestinal bacteria to produce vitamin K and need a supplement for the first week.
These amino acids have aromatic side chains, which contribute to protein structure, UV absorbance, and biochemical signaling.
1. Phenylalanine (Phe, F)
-
Structure: Contains a benzyl side chain (a phenyl group attached to a CH₂).
-
Properties: Non-polar, hydrophobic.
-
Function: Precursor to tyrosine, dopamine, norepinephrine, and epinephrine.
2. Tyrosine (Tyr, Y)
-
Structure: Similar to phenylalanine but with a hydroxyl group (-OH) on the aromatic ring.
-
Properties: Polar, can participate in hydrogen bonding.
-
Function: Precursor to catecholamines and thyroid hormones; involved in signal transduction via phosphorylation.
3. Tryptophan (Trp, W)
-
Structure: Contains an indole ring (a fused double ring with nitrogen).
-
Properties: Slightly polar, bulky.
-
Function: Precursor to serotonin, melatonin, and niacin; absorbs UV light strongly at 280 nm.
4. Histidine (His, H) (sometimes included due to its aromatic-like imidazole ring)
-
Structure: Has an imidazole ring (five-membered ring with two nitrogen atoms).
-
Properties: Polar, positively charged at physiological pH.
-
Function: Key role in enzyme active sites; acts as a proton donor/acceptor.
Bonus Insight: UV Absorbance
-
Tryptophan and Tyrosine absorb UV light at ~280 nm, which is useful for measuring protein concentration.
-
Phenylalanine absorbs weakly at ~260 nm.
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.
Vitamin B12: Cobalamin
Vitamin B12, also known as cobalamin, aids in the building of genetic material, production of normal red blood cells, and maintenance of the nervous system.
RDA The Recommended Dietary Allowance (RDA) for vitamin B12 is 2.4 mcg/day for adult males and females
Vitamin B12 Deficiency
Vitamin B12 deficiency most commonly affects strict vegetarians (those who eat no animal products), infants of vegan mothers, and the elderly. Symptoms of deficiency include anemia, fatigue, neurological disorders, and degeneration of nerves resulting in numbness and tingling.
The Bicarbonate Buffer System
This is the main extracellular buffer system which (also) provides a means for the necessary removal of the CO2 produced by tissue metabolism. The bicarbonate buffer system is the main buffer in blood plasma and consists of carbonic acid as proton donor and bicarbonate as proton acceptor :
H2CO3 = H+ + HCO3–
If there is a change in the ratio in favour of H2CO3, acidosis results.
This change can result from a decrease in [HCO3 − ] or from an increase in [H2CO3 ]
Most common forms of acidosis are metabolic or respiratory
Metabolic acidosis is caused by a decrease in [HCO3 − ] and occurs, for example, in uncontrolled diabetes with ketosis or as a result of starvation.
Respiratory acidosis is brought about when there is an obstruction to respiration (emphysema, asthma or pneumonia) or depression of respiration (toxic doses of morphine or other respiratory depressants)
Alkalosis results when [HCO3 − ] becomes favoured in the bicarbonate/carbonic acid ratio
Metabolic alkalosis occurs when the HCO3 − fraction increases with little or no concomitant change in H2CO3
Severe vomiting (loss of H+ as HCl) or ingestion of excessive amounts of sodium bicarbonate (bicarbonate of soda) can produce this condition
Respiratory alkalosis is induced by hyperventilation because an excessive removal of CO2 from the blood results in a decrease in [H2CO3 ]
Alkalosis can produce convulsive seizures in children and tetany, hysteria, prolonged hot baths or lack of O2 as high altitudes.
The pH of blood is maintained at 7.4 when the buffer ratio [HCO3 − ] / [ H2CO3] becomes 20
Regulation of PTH secretion
Secretion of parathyroid hormone is controlled chiefly by serum [Ca2+] through negative feedback. Calcium-sensing receptors located on parathyroid cells are activated when [Ca2+] is low.
Hypomagnesemia inhibits PTH secretion and also causes resistance to PTH, leading to a form of hypoparathyroidism that is reversible.
Hypermagnesemia also results in inhibition of PTH secretion.
Stimulators of PTH includes decreased serum [Ca2+], mild decreases in serum [Mg2+], and an increase in serum phosphate.
Inhibitors include increased serum [Ca2+], severe decreases in serum [Mg2+], which also produces symptoms of hypoparathyroidism (such as hypocalcemia), and calcitriol.