Biochemistry Lecture Notes PDF

Biochemistry I Chemistry of Biomolecules Lecture II Dr. Mohamed Hemdan 1 Definition Biochemistry is the study of the structure and function of biomolecules and their chemical reactions that occur in our body. Thes...

Biochemistry I Chemistry of Biomolecules Lecture II Dr. Mohamed Hemdan 1 Definition Biochemistry is the study of the structure and function of biomolecules and their chemical reactions that occur in our body. These biomolecules include: - Carbohydrates - Lipids - Proteins - Nucleic acids Biochemistry is sometimes called biological chemistry. 2 1  Biochemistry I 1. Carbohydrates 2. Lipids & Fatty Acids 3. Proteins & Amino Acids 4. Enzymes & Coenzymes 5. Vitamins 3 Carbohydrates: Definition Carbohydrates are molecules composed of C, H & O with H & O exist in the ratio of 2:1 (as present in water). The general formula is (CH2O)n (or Hydrate of carbon), hence the name Carbohydrates. Carbohydrates consist of sugars, which are: - polyhydroxy aldehydes (e.g. glucose, galactose, mannose) or - polyhydroxy ketones (e.g. fructose). 4 2 5 Classification of Carbohydrates Carbohydrates Mono - Oligo - Homo-Poly - Hetero-Poly - Saccharides Saccharides Saccharides Saccharides (1 Unit) (2-10 Units) - Glucose - Disaccharides - Cellulose - Glycoproteins - Fructose -Tri-saccharides - Chitin - Glycolipids - Galactose -Tetra (4 units) -Starch - GAGs - Mannose - Penta (5 units) -Dextrins Hyaluronic acid, - Hexa (6 units) - Glycogen Dermatan - Ribose - Hepta (7 units) sulphate, - Ribulose Heparin, - Octa (8 units) - Xylose Chondroitin – Nona (9 units) - Xylulose - Deca (10 units) sulfate Keratan sulfate. 6 3  Monosaccharides [Greek monos = single; sacchar = sugar] or simple sugars They consist of a single polyhydroxy aldehyde (Glucose, Galactose) or ketone units (Fructose). They cannot be hydrolyzed into simpler units. 7 8 4  Monosaccharides Functional Groups Number of C Atoms Aldoses: Ketoses: 3C 4C 5C 6C 7C Glucose Fructose Triose Tetrose Pentose Hexose Heptose Galactose Ribulose Mannose Xylulose Ribose Xylose 9 10 5  Monosaccharides according to No. of carbon atoms No. of Carbon atoms Aldose Ketose 3C Glyceraldehyde Dihydroxy acetone 4C Erythrose Erythrulose 5C Ribose, Xylose Ribulose, Xylulose 6C Glucose, Galactose, Mannose Fructose 7C L-glycero-D-manno-heptose sedoheptulose 11 Triose Tetrose Hexose Pentose 12 6  Monosaccharides can join together to form complex carbohydrates, for example: 2 monosaccharides form disaccharides 3-10 monosaccharides form oligo-saccharides 11 or more of monosaccharides form polysaccharides 13 Structure of Monosaccharides Glucose is the most important physiological and medicinal mono-saccharide. Glucose molecule can be represented in: - Straight chain structure. - Ring / Cyclic Structure (Cyclic Fischer /Haworth Projection) 14 7  Straight Chain Structure vs Fischer Cyclic Structure Glucose 15 Cyclic Fischer Projection vs Haworth Projection Structures 1 6 2 5 3 4 1 4 3 2 5 6 16 8  Isomerism of Monosaccharides Isomers are compounds that possess the same molecular formula but different structure or configuration. The existence of isomers is called Isomerism. There are 2 main types: A. Structural Isomerism, e.g. Aldose – Ketose isomerism. B. Stereoisomerism, e.g. - Enantiomerism (D- and L- enantiomers) - Optical isomerism - Epimerism - Anomerism (α- vs β- Anomers). 17 A. Structural Isomerism Having the same molecular formulae, but with different structures (functional groups). Aldose-Ketose isomerism Glucose (Aldose) and Fructose (Ketose) are structural isomers of each other. They have the same molecular formula (C6H12O6), but differ in their structural formula. 18 9  Aldose Ketose Isomerism Anomeric Carbon C-1 in Glucose C6H12O6 Anomeric Carbon C-2 in Fructose 1 1 2 2 3 3 4 4 5 5 6 6 D- D- 19 B. Stereoisomerism Stereoisomers have the same molecular and structural formulae but differ in configuration Stereoisomerism depends on the presence of an asymmetric carbon atom (chiral). Types of Stereoisomers are: 1) Optical isomerism (Enantiomerism) (D- and L- isomerism). 2) Epimerism 3) Anomerism 20 10  1) Enantiomerism (D- and L- Enantiomers) D- and L- Isomers are mirror image of each other. These 2 forms are called Enantiomers 21 Is the capacity of a substance to rotate the plane polarized light passing through it. These substances contain Asymmetric (chiral) carbon atom. When light rotates to right (clockwise) direction; the substance is called dextrorotatory (d) or (+). When light rotates to left (anticlockwise) direction. The substance is said to be levorotatory (l) or (-). When equal amounts of (d) and (l) isomers are present; the mixture is called racemic/dl mixture. 22 11 23 Polarimeter Measurement of Specific Rotation The plane of polarization of plane polarized light (4) rotates (6) as it passes through an optically active sample(5). This angle is determined with a rotatable polarizing Filter (7). 24 12  3. Epimerism Epimers are sugars which differ from each other with respect to one carbon, other than anomeric carbon. Galactose and mannose are the epimers of glucose. They differ from glucose with respect to C-4 and C-2, respectively. 25 Epimers of Glucose: Mannose & Galactose 26 13  4. Anomerism In Solution, glucose exists as closed chain structure. Because of cyclization of the sugar, an additional Asymmetric Center is created at C-1 (the anomeric carbon). This leads to the formation of two isomers (called Anomers) namely: α- Glucopyranose and β- Glucopyranose. 27 α- and β- anomers of Glucose α- anomer β - anomer 28 14 29 30 15 31 32 16 33 α - Fructofuranose β - Fructofuranose 34 17  Physiologically important monosaccharides 2-Deoxy D- D-Ribose D-Glucose Ribose D- D-Fructose Galactose 35 v Pentoses D-Ribose is an important structural component of ribonucleic acid (RNA) and other important biomolecules such as NAD, ATP and others. While, 2-deoxy ribose participates in the structure of DNA. vHexoses 1. D-Glucose ( grape sugar, dextrose) The most important and abundant monosaccharide. Normal blood glucose level is 70-100 mg/dl. It is the primary source of energy for living organisms. It is mainly made by plants and most algae during photosynthesis. It is present in fruit juices and can be also obtained by hydrolysis of starch, sucrose and maltose. 36 18  2. D-Fructose ( fruit sugar, honey sugar, levulose) It is absorbed directly into blood during digestion. It is found in honey, fruits and berries. It can be obtained by hydrolysis of sucrose and inulin. Commercially, it is derived from sugar cane and sugar beets. It can be found in semen in the pyranose form. 3. D-Galactose It is C-4 epimer of glucose. It is found in dairy products, avocados and sugar beets. It is also synthesized by the body, where it forms part of glycolipids and glycoproteins in several tissues. It is component of antigens present on blood cells. It can be obtained by hydrolysis of lactose. 37 THANKYOU 38 19