NEET MDS Lessons
Biochemistry
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.
Monosaccharides: Aldoses (e.g., glucose) have an aldehyde at one end
They are classified acc to the number of carbon atoms present
Trioses, tetroses, pentose ( ribose, deoxyribose), hexoses (glucose, galactose, fructose) Heptoses (sedoheptulose)
Glyceraldehyde simplest aldose
Ketoses (e.g., fructose) have a keto group, usually at C 2.
Dihydroxyacetone simplest Ketoses
The higher sugar exists in ring form rather than chain form
Furan : 4 carbons and 1 oxygen
Pyrans : 5 carban and 1 oxygen
These result from formation of hemiacital linkage b/w carbonyl and an alcohol group
STEROIDS
Steroids are the compounds containing a cyclic steroid nucleus (or ring) namely cyclopentanoperhydrophenanthrene (CPPP).It consists of a phenanthrene nucleus (rings A, B and C) to which a cyclopentane ring (D) is attached.
Steroids are the compounds containing a cyclic steroid nucleus (or ring) namely cyclopentanoperhydrophenanthrene (CPPP).It consists of a phenanthrene nucleus (rings A, B and C) to which a cyclopentane ring (D) is attached.
There are several steroids in the biological system. These include cholesterol, bile acids, vitamin D, sex hormones, adrenocortical hormones,sitosterols, cardiac glycosides and alkaloids
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.
COENZYMES
Enzymes may be simple proteins, or complex enzymes.
A complex enzyme contains a non-protein part, called as prosthetic group (co-enzymes).
Coenzymes are heat stable low molecular weight organic compound. The combined form of protein and the co-enzyme are called as holo-enzyme. The heat labile or unstable part of the holo-enzyme is called as apo-enzyme. The apo-enzyme gives necessary three dimensional structures required for the enzymatic chemical reaction.
Co-enzymes are very essential for the biological activities of the enzyme.
Co-enzymes combine loosely with apo-enzyme and are released easily by dialysis. Most of the co-enzymes are derivatives of vitamin B complex
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.
Riboflavin: Vitamin B2
Riboflavin, or vitamin B2, helps to release energy from foods, promotes good vision, and healthy skin. It also helps to convert the amino acid tryptophan (which makes up protein) into niacin.
RDA Males: 1.3 mg/day; Females: 1.1 mg/day
Deficiency : Symptoms of deficiency include cracks at the corners of the mouth, dermatitis on nose and lips, light sensitivity, cataracts, and a sore, red tongue.