Biochemistry of Carbohydrates PDF - 2024/2025

Biochemistry of dietary, functional and structural carbohydrates-I, II year 1 dent-students 2024/2025 Ass.Prof. Marwa Abdel Naeem Medical Biochemistry Department Faculty of Medicine Assiut University Ob...

Biochemistry of dietary, functional and structural carbohydrates-I, II year 1 dent-students 2024/2025 Ass.Prof. Marwa Abdel Naeem Medical Biochemistry Department Faculty of Medicine Assiut University Objectives Identify different classes of carbohydrates, and list their biological importance. Define Chemistry and functions of monosaccharides, and oligosaccharides and their derivatives Define and classify polysaccharides. Discuss structure and function medically important homo and hetero-polysaccharides.  Definition of Carbohydrates: Definition: Carbohydrates are aldehyde (- CHO) or ketone (-C=O) derivatives of polyhydric alcohols (have more than one -OH group) or compounds which yield these derivatives on hydrolysis.  Classification of carbohydrates according to the number of sugar units in the molecule Monosaccharides (simple sugars): They contain one sugar unit, the simplest form of sugars and cannot be further hydrolyzed. They are the end products of CHO digestion in the human body. For example, glucose and fructose. Oligosaccharides: They contain 2 – 10 sugar units per molecule and give monosaccharides on hydrolysis. e.g., lactose and maltose. Polysaccharides: They contain ˃10 sugar units per molecule and give monosaccharides on acid hydrolysis. e.g., starch and glycogen Classification of Monosaccharides: According to the number of carbon atoms in each molecule into six groups, Bioses (2Cs), Trioses (3Cs), Tetroses (4Cs), Pentoses (5Cs) and Hexoses (6Cs) Each of these groups is subdivided according to the type of functional chemical group into: Aldoses: the molecule begins with a formyl group H(C=O) Ketoses the molecule has a keto group, a carbonyl - (C=O)- between two carbons. Medical significance of some Monosaccharides: Ribose: is structural component in nucleic acids (DNA, RNA) & free nucleotides (ATP). Glucose (grape sugar, blood sugar or dextrose). It is produced by hydrolysis of starch, glycogen, sucrose, maltose and lactose. It is a fermentable and reducing sugar. Other hexoses are converted into glucose to be utilized in the body. It appears in urine (glucosuria) in diabetes mellitus.  Mannose: It is a subunit in glycoproteins and glycolipids. It is obtained by hydrolysis of plant gums. Galactose: It is a subunit of the milk sugar (lactose) It is a component of glycolipids, glycoprotein and mucopolysaccharides.  Fructose: It is the main sugar in bee's honey and fruits and is the sweetest sugar known. It is converted into glucose in the body and failure of its metabolism leads to accumulation in cells and blood (hereditary fructose intolerance). It is a reducing and fermentable sugar. It is called the semen sugar  Optical activity It is the ability of the sugar to rotate the plane polarized light. The sugars that rotate the light to the right are called dextrorotatory (d or +) such as Glucose, galactose and starch those rotating light to the left are called levorotatory (l or -) such as fructose and invert sugar.  Optical activity is due to the presence of asymmetric carbon atom. Asymmetric carbon atom is the carbon atom attached to which 4 different groups or atoms. A racemic mixture is a mixture of equal amounts of dextrorotatory and levorotatory isomers of a compound (dl mixture). This mixture is optically inactive because they equalize the effect of one another. THANK YOU