AB Biochemistry

  Glycolysis Glycolysis is a fundamental metabolic pathway that breaks down glucose (a 6-carbon hexose sugar) into two molecules of pyruvate (a 3-carbon compound), releasing energy in the form of ATP and NADH. It occurs in the cytoplasm and functions under both aerobic and anaerobic conditions. It is also known as the Embden–Meyerhof–Parnas (EMP) pathway , named after its discoverers. This pathway consists of 10 enzyme-catalyzed steps , divided into two phases: I Preparatory Phase (Investment Phase / Glucose Activation Phase) - •         ATP is consumed, hence also known as the investment phase. •         Also called the  glucose activation phase . •         In this phase, two molecules of ATP are invested, and the hexose chain is cleaved into two triose phosphates. •         During this, phosphorylation of glucose and its co...

  Chemical reactions of Carbohydrates Tautomerization / Enolization The process of shifting a hydrogen atom from one carbon atom to another to produce enediols is known as tautomerization. Sugars possessing an anomeric carbon atom undergo tautomerization in alkaline solutions. When glucose is kept in an alkaline solution for several hours, it undergoes isomerization to form D-fructose and D-mannose. This reaction is known as the Lobry de Bruyn-von Ekenstein transformation, which forms a common intermediate, namely enediol, for all three sugars. The enediols are highly reactive, hence, sugars in alkaline solution are powerful reducing agents. Important example: Glucose, Fructose, and Mannose can convert into each other through a common enediol form. Reducing properties Sugars are classified as reducing or non-reducing. The reducing property is attributed to the free aldehyde or keto group of the anomeric carbon. Many laboratory tests are employed to identify sugars' reducing...

  Carbohydrate Structural Aspects  Stereoisomerism is a key feature of monosaccharides. Stereoisomers are molecules that have the same molecular formula and order of atoms (structural formula), but differ in the 3D arrangement of atoms in space. Asymmetric (Chiral) Carbon: A carbon is asymmetric or chiral when it is bonded to four different atoms or groups . This asymmetry leads to different spatial forms, or stereoisomers . The number of possible stereoisomers of a molecule = 2ⁿ , where n = number of asymmetric carbon atoms . Example: Glucose Glucose has 4 asymmetric carbons . So, it has 2⁴ = 16 stereoisomers . Glyceraldehyde – The Reference Carbohydrate Glyceraldehyde is the simplest monosaccharide (triose) . It has one asymmetric carbon , so 2ⁱ = 2 stereoisomers . These two forms are: D-glyceraldehyde L-glyceraldehyde Glyceraldehyde is used as a reference molecule to define the D- and L configuratio...