NEET MDS Lessons
Biochemistry
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.
Thiamin: Vitamin B1
Thiamin, or vitamin B1, helps to release energy from foods, promotes normal appetite, and is important in maintaining proper nervous system function.
RDA (Required Daily allowance) Males: 1.2 mg/day; Females: 1.1 mg/day
Thiamin Deficiency
Symptoms of thiamin deficiency include: mental confusion, muscle weakness, wasting, water retention (edema), impaired growth, and the disease known as beriberi.
Carbohydrates (glycans) have the basic composition
- Monosaccharides - simple sugars, with multiple hydroxyl groups. Based on the number of carbons (e.g., 3, 4, 5, or 6) a monosaccharide is a triose, tetrose, pentose, or hexose, etc.
- Disaccharides - two monosaccharides covalently linked
- Oligosaccharides - a few monosaccharides covalently linked.
- Polysaccharides - polymers consisting of chains of monosaccharide or disaccharide units
Biotin
Biotin helps release energy from carbohydrates and aids in the metabolism of fats, proteins and carbohydrates from food.
RDA The Adequate Intake (AI) for Biotin is 30 mcg/day for adult males and females
Biotin Deficiency Biotin deficiency is uncommon under normal circumstances, but symptoms include fatigue, loss of appetite, nausea, vomiting, depression, muscle pains, heart abnormalities and anemia.
Ampholytes, Polyampholytes, pI and Zwitterion
Many substances in nature contain both acidic and basic groups as well as many different types of these groups in the same molecule. (e.g. proteins). These are called ampholytes (one acidic and one basic group) or polyampholytes (many acidic and basic groups). Proteins contains many different amino acids some of which contain ionizable side groups, both acidic and basic. Therefore, a useful term for dealing with the titration of ampholytes and polyampholytes (e.g. proteins) is the isoelectric point, pI. This is described as the pH at which the effective net charge on a molecule is zero.
For the case of a simple ampholyte like the amino acid glycine the pI, when calculated from the Henderson-Hasselbalch equation, is shown to be the average of the pK for the a-COOH group and the pK for the a-NH2 group:
pI = [pKa-(COOH) + pKa-(NH3+)]/2
For more complex molecules such as polyampholytes the pI is the average of the pKa values that represent the boundaries of the zwitterionic form of the molecule. The pI value, like that of pK, is very informative as to the nature of different molecules. A molecule with a low pI would contain a predominance of acidic groups, whereas a high pI indicates predominance of basic groups.
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.
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 Pi
Fatty acid synthesis occurs in the cytosol. Acetyl-CoA generated in the mitochondria is transported to the cytosol via a shuttle mechanism involving citrate