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Monosaccharides(2)

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Monosaccharides(2)

  1. 1. Monosaccharides (Simple sugars) • They may exist in a linear molecule or in ring forms. • They are classified according to the number of carbon atoms in their molecule. 5 carbons are called pentoses ex. Ribose 6 carbons are called hexoses ex. Glucose • Many forms exists as isomers. Isomers are molecules which have the same empirical formula (recipe) but have different structures (shapes) due to arrangement of the atoms in the molecule. This also gives them different properties. Glucose and fructose both have the empirical formula C6H12O6, but they have different structural formulas or shapes. • MONOSACCHARIDES ARE THE BUILDING BLOCKS FOR ALL OTHER CARBOHYDRATES!
  2. 2. MonosaccharidesAldoses (e.g., glucose) Ketoses (e.g., fructose)have an aldehyde group at have a keto group, usuallyone end. at C2. H O C CH2OH H C OH C O HO C H HO C H H C OH H C OH H C OH H C OH CH2OH CH2OH D-glucose D-fructose
  3. 3. Triosesa three-carbon simple sugar.formed during the metabolic breakdown of hexoses inmuscle metabolism.Tetrosesare four-carbon sugars.One tetrose, erythrose, is a intermediate in the hexosemonophosphate shunt for the oxidation of glucose.Pentosesare five-carbon sugar molecules.Ribose and deoxyriboseRibose forms part of ribonucleic acid (RNA), anddeoxyribose forms part of deoxyribonucleic acid (DNA).
  4. 4. D-ribulose an intermediary in the pentose phosphate shunt D-lyxose which is found in heart muscle D-xylose and D-arabinose  which are components of glycoproteins.The Fisher projection representations for the pentoses, are called open-chainstructures. However, the predominant form for pentoses is a ring structures.Recall that aldehydes react with alcohols to form hemiacetals. In the case ofribose, the aldehyde can react with the alcohol at carbon number 4 to form twodifferent compounds..
  5. 5. The Fischer and Haworth projection are related as follows:1) The groups on the right side of the Fisher projection are written below the plane in the Haworth projection. Those on the left side are written above the plane.2) One exception to rule 1 occurs at carbon 4 in pentoses and at carbon 5 in hexoses because of the nature of the creation occurring there. At these carbons, rule 1 is reversed.3.) At carbon 1 form is indicated by the –OH being written below the plane; the form has the –OH above the plane.4.) In both projections the CH2OH group, which has no chiral carbon, is written as a unit.
  6. 6. Haworth Projections◦ aldopentoses also form cyclic hemiacetals◦ the most prevalent forms of D-ribose and other pentoses in the biological world are furanoses HOCH2 H HOCH2 OH () O O H H H H H OH () H H OH OH OH H -D -Ribofuranose -2-D eoxy-D -ribofuranose (-D -Rib os e) (-2-D eoxy-D -rib os e)
  7. 7. Hemiacetal & hemiketal formation H HAn aldehydecan react with C O + R OH R O C OHan alcohol to R Rform a aldehyde alcohol hemiacetalhemiacetal. R RA ketone can C O + "R OH "R O C OHreact with an R Ralcohol to form ketone alcohol hemiketala hemiketal.
  8. 8. HEXOSESThe six-carbon sugars.The most common of all the carbohyrates. The most important as far as the human body is concerned are glucose, galactose and fructose.The have the same molecular formula but havediff. structural formulas; they are isomers.
  9. 9. 1 CHO H C OH 2 HO C HGlucose 3 D-glucose OH (linear form)Is an H 4 C H C OHaldohexose 5 CH2OHand can be 6represented 6 CH2OH 6 CH2OH 5 O 5 Ostructurally H H H H H OH 4 1 4 1as OH H OH H OH OH OH H 3 2 3 2 H OH H OH -D-glucose -D-glucose
  10. 10. is known commonly as dextrose, orgrape sugar.It is a white crystalline solid that is soluble in water and insoluble in most organic liquids.It is found, along with fructose, in many fruit juices.It can be prepared by the hydrolysis of sucrose, a disaccharide, or by the hydrolysis of starch, polysaccharides.
  11. 11. It is normally found in the bloodstream and in the tissue fluids.“Metabolism of Carbohydrates,” glucose requires no digestion and can be given intravenously to patients who are unable to take food by mouth.is found in the urine of patients suffering from diabetes mellitus and is an indication of this disease
  12. 12. GALACTOSE An isomer of glucose, is also an aldohexose.Glucose and galactose differ from each otheronly in the configuration of the H and OHabout a single carbon atom.Two sugars that differ only in theconfiguration about a single carbon atom arecalled epimers.D-Galactose is converted to D-glucose in theliver by a specific enzyme called an epimerse.is present in some glycoproteins andglycolipids.
  13. 13. Galactosemiasevere inherited disease, results in theinability of infants to metabolize galactosebecause of a difiency of either the enzymegalactose 1-phosphate uridyl transferase orthe enzyme galactokinase. The galactose concentration increases inthe blood the urine (galactosuria).
  14. 14. a-D-galactoseD-galactose
  15. 15. FRUCTOSEcan be represented as a straight-chain or as a ringcompound.The ring structure is predominant. Note that thering structure represents a hemiketal.often called levulose, or fruit sugar and it occursnaturally in fruit juices and honey. It can be prepared by the hydrolysis of sucrose, adisaccharide, and also by the hydrolysis of insulin,polysaccharides found in Jerusalem artichokes.the most soluble and also the sweetest of all sugars,being 75 percent sweeter than glucose.
  16. 16. Fructosemia,fructose intolerance, is an inheriteddisease due to a deficiency of adeficiency of the enzyme fructose 1-phosphate aldolase. An infant sufferingfrom this disease experienceshypoglycemia, vomiting, and severemalnutrition. Such a condition is treatedby placing the infant on a low-fructosediet.
  17. 17. a-D-fructose
  18. 18. Reactions of the HexosesHexoses, which are either aldoses or ketoses, show reducing properties.This reducing property is the basis of the test sugar in the urine and inthe blood.When a reducing agent is treated with an oxidizing agent such as Cu2+complex, a red-orange precipitate of copper(I) oxide(Cu2O) is formed heataldehyde + Cu2+ acid + Cu2O +water NaOH deep blue red-orange solution precipitateIn this reaction the aldehyde is oxidized to the corresponding acid.
  19. 19. When glucose is treated with Cu2+ complex ion and themixture is heated, the reaction is as follows: heat Cu2+ + Cu2O + NaOH Copper(II) Copper(I) Complex ion oxide (deep-blue color) (red-orange D-glucose precipitate) D-gluconic acid
  20. 20. Benedicts Reagent O ORCH + 2Cu2+ + 5HO– RCO– + Cu2O + 3H2O • Benedicts reagent is a solution of the citrate complex of CuSO4 in water. It is used as a test for "reducing sugars." Cu2+ is a weak oxidizing agent. • A reducing sugar is one which has an aldehyde function, or is in equilibrium with one that does. • A positive test is the formation of a red precipitate of Cu2O.
  21. 21. Examples of Reducing Sugars• Aldoses: because they have an aldehyde function in their open-chain form.• Ketoses: because enolization establishes an equilibrium with an CH OH 2 CHOH CH O aldose. C O C OH CHOH R R R oxidized by Cu2+
  22. 22. OxidationIf the aldehyde end of the molecule is oxidized,the product is named and –onic acid. When thealdehyde end of glucose is oxidized, the product iscalled gluconic acid.If the alcohol at the end opposite the aldehyde isoxidized, the product is called a –uronic acid. Theooxidation of the alcohol end of glucose yieldsglucuronic acid.If both ends of the glucose molecule are oxidizedat the same time, the product is called saccaharicacid.
  23. 23. Gluconic acid Glucuronic acidSaccharic acid
  24. 24. REDUCTIONWhen glucose is reduced, sorbitol isformed. Sorbitol accumulation in the eyesis a major factor in the formation ofcataracts due to diabetes.Reduction of galactose yields dulcitol.Reduction of fructose yields a mixture ofmannitol and sorbitol.MannitolUsed in the treatment of malignant braintumors.a
  25. 25. FERMENTATIONGlucose ferments in the presence of yeast, forming ethylalcohol and carbon dioxide. This reaction will not readilyoccur in the absence of yeast. Yeast contains certainenzymes that catalyze this particular reaction. enzymes +Glucose ethyl alcoholFructose will also ferment; galactose will not readily ferment.Pentoses do not ferement in the presence of yeast
  26. 26. Fermentation of Phosphate Esters Phosphate esters such as D-glyceraldehyde 3-phosphate and dihydroxyacetone phosphate estersinvolved in glycolysis.
  27. 27. Amino sugars D-glucosamineAn amino group in place of an –OH group.These amino sugars have been found innature.

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