Lec -1 CHO Biochemistry 1 PDF

BIOCHEMISTRY 1  ‫)‪Carbohydrates (CHO‬‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ ‫‪❑Definition‬‬ ‫‪❑Classification.‬‬ ‫‪❑Properties.‬‬ ‫‪❑Functions.‬‬  Definition of CHO _______________...

BIOCHEMISTRY 1  ‫)‪Carbohydrates (CHO‬‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ ‫‪❑Definition‬‬ ‫‪❑Classification.‬‬ ‫‪❑Properties.‬‬ ‫‪❑Functions.‬‬  Definition of CHO ____________________________________________ Polyhydroxyaldehydes or polyhydroketones or substances that can be converted to such aldehydes or ketones on hydrolysis. Widely distributed in plants and animals for structural and metabolic roles. In plants: & stored as starch or converted into cellulose. In animals: the bulk of carbohydrates are derived from plant origin & stored as glycogen in the liver and muscles. Classification of CHO ____________________________________________ three to ten More than ten  1- Monosaccharides ____________________________________________ These are the simplest of all carbohydrates, having the general formula Cn H2n On. A- Classification: ❖ According to the Presence of Aldehyde or Ketone Group: 1) Aldoses (aldehyde ) and 2) Ketoses (ketone) ❖ According to the Number Of Carbon Atoms: (1) Trioses (3 C) (2) Tetroses (4 C) (3) Pentoses (5 C) (4) Hexoses (6 C) (5) Heptoses (7 C) 1- Monosaccharides ____________________________________________ ❖ According to both presence of aldehyde or ketone groups and number of carbon atoms: (1) Aldotrioses and Ketotrioses (2) Aldotetroses and Ketotetroses (3) Aldopentoses and Ketopentoses (4) Aldohexoses and ketohexose 1- Monosaccharides ____________________________________________ Trioses Tetroses Pentoses Hexoses  Heptoses Note: The suffix ulose means keto sugar.  General Properties of Monosaccharides ____________________________________________ (A) Physical Properties 1- Optical Activity: Ability of certain substances to rotate a plane polarized light through a certain angle. The Direction of rotation might be To the right, called Dextrorotation or positive rotation (+). To the left, called Levorotation or negative rotation (-). The direction and angle of rotation are measured by polarimeter.  General Properties of Monosaccharides ____________________________________________ Cause of Optical Activity Due to presence of one or more asymmetric carbon atom or the carbon atom which is attached to 4 different groups or atoms. Example: glyceraldehyde, the simplest monosaccharide, has one asymmetric carbon atom.  General Properties of Monosaccharides ____________________________________________ Cause of Optical Activity There are two form of glyceraldehyde depending upon the orientation of OH around the asymmetric carbon: D-glyceraldehyde and L- glyceraldehyde Both are mirror or images to each others, and called "Isomers" or “optical.  General Properties of Monosaccharides ____________________________________________ Note that: ❖Expect dihydroxyacetone (Ketotriose) which has no asymmetric carbon, all monosaccharides are optically active. ❖Glyceraldehyde is called “Reference sugar”, because all monosaccharides derived from D-glyceraldehyde are D- sugars; those derived from Lglyceraldehyde are L-sugars.  General Properties of Monosaccharides ____________________________________________ By increasing the number of asymmetric carbon atoms, the number of isomers increases. If (n) is the number of asymmetric carbon atoms the number of Isomers will be 2n. Glucose has 4 asymmetric carbons, hence it has 24 or 16 isomers.  General Properties of Monosaccharides ____________________________________________ Note that: The D and L are used to denote the configuration of OH around the carbon atom which is adjacent to the terminal alcoholic group (original in reference sugars). Most monosaccharides occurring in mammal are D-form. D and L forms have no relation to the direction of rotation of plane- polarized light. D or L denotes orientation of OH around the asymmetric carbon while (+) and (-) denote direction of rotation. You might have D (-) or L (+) compound e.g. the naturally occurring fructose is D (-) and glucose is D (+).  General Properties of Monosaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ 2- Racemic mixture It is a mixture containing equal number of molecules of 2 optically active sugars, one is dextrorotatory (+), and the other is levorotatory (-). Thus it shows no optical activity. The separation of these two compounds from each others is called «resolution».  General Properties of Monosaccharides _________________________________________ 3- Cyclic structure of monosacchardies (anomeric forms) ❖In solution, monosacchardies are found in cyclic or ring form, called pyranose or furanose ring structure. ❖This is described by Haworth  General Properties of Monosaccharides _________________________________________ -CHO in aldoses or –C=O in ketoses, takes H2O and form aldehyde hydrate, which is unstable, soon water is lost and a ring is formed either between: C1 and C5 → pyranose C2 and C5 → furanose e.g. glucose.  General Properties of Monosaccharides _________________________________________ In this cyclic form, the down OH means right, and up OH means left. Generally, aldohexoses tend to form pyranose structure while keto hexoses tend to form furanose (between C2 and C5) structure. Only 1% of glucose forms furanose structure (glucofuranose).  General Properties of Monosaccharides _________________________________________ ❖Anomers Owing to the formation of ring structutre, in aldoses carbon atom number 1, becomes asymmetric, and called now «Anomeric carbon». The anomeric carbon in ketoses is number 2. Now, we have 2 isomers, obtained from the change of position of – OH gp attached to the anomeric carbon, (α =OH to the right) and (β =OH to the left). These are called Anomers  General Properties of Monosaccharides _________________________________________ 4- Mutarotation It is the change in specific rotation of a chiral compound due to epimerization. eg: D-glucose exists in two cyclic forms, α-D-glucose = +112.5 and β-D-glucose = +19.  General Properties of Monosaccharides _________________________________________ 5- Mutarotation When one of the cyclic forms of D-glucose is added to water, it undergoes reversible epimerization to the other via the open-chain form, during which the specific rotation of the solution changes gradually until it reaches the equilibrium value +52.5º  Notes There is more than one type of Isomerism in monosaccharides: (1) Optical isomerism This type refers to D and L isomers called optical isomers e.g. D and L glucose.  Notes (2) Aldose – ketose isomerism This isomerism refers to two monosaccharides, which have the same chemical formula, same orientation of OH groups around the asymmetric carbons, but one has aldehyde group while the other has keto group e.g. glucose and fructose, glyceraldehydes and dihydroxy acetone.  Notes (3) Epimers These are two monosaccharides, which differ in the orientation of OH group around carbon, called «Epimeric» carbon e.g.: Galactose is an epimer of glucose in carbon 4. Mannose is an epimer of glucose in carbon 2.  (B) Chemical Properties (1) Properties due to carbonyl group i) Ester formation: e.g. glucose is esterified with phosphopric acid to form glucose-1-phosphate. ii) Oxidation Mild oxidizing agent e.g. bromine water, oxidizes the aldehyde group of glucose gluconic acid (an aldonic acid). Further oxidation by nitric, oxidizes the last alcohol Saccharic acid (an aldaric acid).  (B) Chemical Properties (1) Properties due to carbonyl group iii) Reduction of the carbonyl group, produces the corresponding polyhydric alcohol Glycealdehyde glycerol Glucose sorbitol Mannose mannitol Galactose dulcitol Fructose mixture of sorbitol & mannitol (B) Chemical Properties (1) Properties due to carbonyl group iv) Monosaccharides act-through the carbonyl group-as reducing agents. reduces Fehling and Benedict solution (Alkaline solution of cupric ion, blue in color) forming red precipitate (cuprous oxide). Barfoed reagent is copper salt in acid medium. Fehling and Benedict were of the earliest tests for the presence of glucosuria. They are non-specific, because they can be reduced by all monosacchairdes and other reducing substance e.g. vitamin C, Aspirin…etc (v) Condensation, Ozazone formation Monosaccharides react with phenyl hydrazine (NH2NHC6H5) to form crystalline products, known as «Ozazone». Glucose Phenyl hydrazin Ozazone (B) Chemical Properties (2) Properties due to alcoholic group i) Ester formation The formation of hexoses-phosphate e.g. glucose-6- phosphate is the primary step in all metabolic processes in which glucose is utilized. G-6-phosphate ii) Oxidation of the last alcoholic group: produces uronic acid e.g. glucuronic acid from glucose. iii) Fermentation It is the action of micro-organisms on monosaccharides. Fermentation by yeast produces CO2 and ethyl alcohol.  Physiological significance of some monosaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (1) Trioses Glyceraldehyde and dihydroxy acetone (DHA) in the form of their phosphorlyated esters, i.e. glyceraldehydes-3- phosphate and DHAP are intermediates in glycolysis (anaerobic oxidation of glucose) in every cell. (2) Tetroses Their physiologic significance is uncertain. They might appear as intermediates in some oxidative pathways of glucose metabolism e.g. erythrose. (3) Pentoses D-Ribose is the sugar of RNA. It is also the sugar of many nucleotides e.g. ATP, CTP, UTP, GTP, coenzymes as NAD, NADP, FAD and CoA-SH. 2-deoxyribose is the pentose of DNA. Ribulose is intermediates in HMP shunt  Physiological significance of some monosaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ D-Arabinose Found in gum arabic, and constituent of glycoproteins in plants and animals. Used in bacteriological studies (fermentation test) for identification of bacteria. D-Xylose Found in wood gums, proteoglycans and glycosaminoglycans. D-Xylulose Is intermediate in uronic acid pathway.  Physiological significance of some monosaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (4) Hexoses ❖ Glucose Grape sugar or dextrose, because it is dextro-rotatory. The naturally occurring is the D-form. It is found freely in fruit juice, and honey. Also it is derived from hydrolysis of sucrose, lactose, maltose and starch. It is the principal sugar of the body, carried by blood to various tissues, to be oxidized or stored as glycogen or fat. Diabetes mellitus is the syndrome, characterized by elevated blood glucose (hyperglycemia) and presence of glucose in urine (glucosuria) due to deficiency of insulin, the hormone which regulates glucose oxidation.  Physiological significance of some monosaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (4) Hexoses ❖ Glucose The structural formula can be represented in one of 3 ways: 1) Open (straight) chain. 2) Cyclic structure (Pyranose 99% and furanose 1%). 3) The chair from, that was detected by x-ray diffraction.  Physiological significance of some monosaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ ❖ Fructose Called levulose (it is levorotatory). Found freely in fruit juice and honey. Produced from hydrolysis of sucrose. It can be changed into glucose in the liver. It is the main sugar present in semen, as it is the source of energy to spermatozoa. The natural fructose is D-form and it can form cyclic structure (fructofuranose). ❖ D-Galactose Derived from hydrolysis of lactose (milk sugar). It is converted into glucose is the liver. It is synthesized in the mammary glands, to make the lactose of milk.  Physiological significance of some monosaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ ❖ D-Mannose D-Mannose is a constituent of many glycoproteins. It is obtained from hydrolysis of plant manans and gums.  Monosaccharides derivatives ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (1) Amino sugars (Hexosamines) The OH group of C2 of glucose and galactose is replaced by NH2 group: 2- glucosamine and 2-galactosamine. Amino sugars are constitutents of glycoproteins, gangliosides and glycosaminoglycans. Several antibiotics e.g. erythromycine and carbomycine contain amino sugars in their structure.  Monosaccharides derivatives ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (2) Sugars acids These are produced by oxidation of carbonyl group aldonic acid, terminal alcoholic group uronic acid or both Aldaric or saccharic acid. a) Aldonic acids: D-Glyceric acid from glyceraldehydes. D-gluconic acid from glucose. L-Ascorbic acid (vitamin C) is the aldonic acid of L-glucose. b) Uronic acids: e.g. D-glucuronic acid. (c) Aldaric acid: e.g. glucaric (Saccharic) from glucose.  Monosaccharides derivatives ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (3) Amino sugar acids: These are formed by the addition of acids to the amino sugars e.g. (1) Neuraminic acid: Pyruvic acid and mannosamine. (2) Sialic acid: It is N-acetyl neuraminic acid (NANA). These acids are important constituents of mucopolysaccharides and gangliosides.  Monosaccharides derivatives ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (4) Sugar alcohols: Which are produced by reduction of the carbonyl group. Inositol : is the sugar alcohol of cyclohexane. It is considered as member of vitamin B-complex, and enters in the structure of lipositol (phospholipids present in all tissue).  Monosaccharides derivatives ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (5) Deoxy sugar The OH of carbon 2 is replaced by hydrogen. e.g. 2-deoxyribose of DNA. (6) Glycosides Glycosidic link or bond is the bond formed between a monosaccharide and another compound to form complex carbohydrates. This bond forms between the OH group of the anomeric carbon (1 in aldoses, or carbon 2 in ketoses) and another compound, which might be: a) Another monosaccharide to form disaccharide e.g. maltose, lactose, sucrose. b) Non carbohydrate residue, called «Aglycon».  Disaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ These are formed by condensation between two monosaccharides through glycosidic bond. General formula: Cn(H2O)n-1 The important disaccharides are: 1. Maltose: α- glucose + α- glucose: (α 1- 4glycosidic bond) 2. Lactose: β- glucose + β- galacoste: (β 1- 4 glycosidic bond) 3. Sucrose: α- glucose + β- fructose: (α 1- 2 glycosidic bond) 4. Isomaltose: α- glucose + α- glucose: (α 1- 6 glycosidic bond) 5. Cellobiose: β- glucose+ β- glucose: (β 1- 4 glycosidic bond)  Disaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ 1) Maltose (malt sugar) It is present in the germinating barely and results from digestion or hydrolysis of starch by α-amylase enzyme. It is composed of 2 molecules of α-D-glucose, attached by α 1-4 glycosidic bond. It contains free aldehyde group, so it can reduce Fehling and Benedict. It is fermentable by yeast, gives Ozazone and shows mutarotation.  Disaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (2) Isomaltose It is like maltose, but the 2 glucose are linked by α 1-6 glycosidic link. It results during the hydrolysis of starch and glycogen. (3) Lactose (milk suger) It is composed of β-glucose and β -galactose, linked by β 1-4 glycosidic bond (galactosidic bond). It contains free aldehyde group, hence it can reduce Fehling and Benedict. Forms Ozazone and shows mutarotation. It is not fermented by yeast.  Disaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ (4) Sucrose : cane sugar Used as table sugar. It is composed of α-D-glucose and β-D fructose attached by α 1-2 glycosidic link. It contains no free carbonyl group, hence it is not a reducing sugar. It does not show mutarotation or forms Ozazone.  Disaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ ❖ Invert sugar Sucrose upon hydrolysis yield a crude mixture, called invert sugar which is a mixture of equal amount of both glucose and fructose molecules. It is called «invert sugar» because sucrose is originally dextrorotatory. On hydrolysis, the strong levorotatory fructose is liberated. Fructose «inverts» the rotation from dextro to levorotation. Note Glucose has specific rotation of + 52.5, (dextrorotatory) while fructose has a value of -93 (levororotation). So levorotatory fructose over-powers dextrorotatory glucose.  Disaccharides ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ Sources of invert sugars: 1) Hydrolysis of sucrose. 2) Honey is an invert sugar. Invert sugar thus, can reduce Fehling, forms Ozazone and shows mutarotation (has free carbonyl groups of both glucose and fructose). (5) Cellobiose it is derived from plant cellulose by hydrolysis. It is composed of 2 β-D-glucose molecules attached together by β 1-4 glycosidic bond. THANK YOU