L4) Structure and Function of Carbohydrates.pdf

Structure and Function of Carbohydrates Color Index: Main text (black) Female slides (pink) Male slides (blue) Important (red) Dr’s Notes (green) Editing file Extra Info (grey) ...

Structure and Function of Carbohydrates Color Index: Main text (black) Female slides (pink) Male slides (blue) Important (red) Dr’s Notes (green) Editing file Extra Info (grey)  Objectives To understand: The structure of carbohydrate of physiological significance. The main role of carbohydrates in providing and storing of energy. The structure and function of glycosaminoglycans.  OVERVIEW Most abundant The empirical formula It is called organic molecule in for carbohydrates “hydrates of nature is (CH2O)n carbon” FUNCTIONS Provide important Act as the storage Are structural part of energy in form of energy in component of cell diet “glucose” the body membranes “galactose”  OVERVIEW Many Diabetes Glycogen diseases associated 1 Mellitus 3 Storage Diseases with disorders of carbohydrate metabolism 2 Galactosemia 3 Lactose intolerance including:  CLASSIFICATION Monosaccharides Disaccharides Simple sugar 2 monosaccharide units oligosaccharides Polysaccharides More than 10 sugar units: 3-10 monosaccharide units Homopolysaccharides Heteropolysaccharides  Monosaccharide Functional sugar Number of group: carbons Aldehyde (aldose) Ketone (ketose) *names are important aldose ketose Triose (3 C) Glyceraldehyde Dihydroxyacetone Pentose (5 C) Ribose Ribulose Hexose (6 C) Glucose Fructose  ISOMERISM Isomers: compounds having same chemical formula but different structural formula Aldo-Keto Isomers Example: Glucose (aldose) and Fructose (ketose) 441Note: Fructose and Glucose both share the same chemical formula (C6H12O6) but different structural formula.  Epimers CHO dimers that differ in configuration around only one specific carbon atom, and the rest of the Carbons are the same. Example: Glucose and galactose → C4 Glucose and mannose → C2 Galactose and mannose ARE NOT epimers  Enantiomers Enantiomers are structures that are mirror images of each other and are designated as D- and L- sugars, based on the position of -OH group on the farthest asymmetric carbon from the carbonyl carbon. - Majority of sugars in humans are D-sugars.  α & β forms Cyclization of Cyclization monosaccharides with 5 creates an or more carbons are anomeric predominantly found in carbon (former the ring form. carbonyl The Aldehyde or Ketone carbon) group reacts with the generating the -OH group on the same α and β sugar. configurations. The location of -OH group in the anomeric carbon determines the form: below→ α above→ β  MUTAROTATION In a solution, the cyclic α and β anomers of a sugar are in equilibrium with each other, and can be interconverted spontaneously. 439Note: Sugar in its normal condition is always in a ring form 441Note: In Fischer (Haworth projection) Projection: We add but the α configuration when the sugar is put in when the OH group is water, the ring is near the O atom, and separated and becomes the β group when the a OH group is far from linear form (Fischer the O atom. (Look at projection) so the -OH the arrows). location changes and isn’t stable. are 2 monosaccharides joined by a O-glycosidic bond by O-glycosidic bond Note: Disaccharides O-glycosidic bond: an oxygen is shared between the monosaccharides Maltose Sucrose Lactose (α-1, 4) = (α-1,2) = (β-1,4) = glucose + glucose glucose + fructose galactose + glucose head to tail head to head head to tail Note: Carbon next to the oxygen is anomeric oxygen taken from galactose free anomeric C= reducing sugar.  Polysaccharides Homopolysaccharides Heteropolysaccharides Branched: Unbranched: glycosaminoglycans Glycogen and Starch Cellulose (GAGs) (α-glycosidic bond) (β-glycosidic bond) Reducing Sugars If the O on the anomeric C of a sugar is not attached to any other structure (Free), that sugar can act as a reducing agent Reducing sugars reduce Examples: chromogenic agents like Benedict’s reagent — Monosaccharides or Fehling’s solution to give a colored — Maltose and Lactose precipitate But! Sucrose is non-reducing, Why?? Urine is tested for the presence of reducing because both anomeric carbons sugars using these are busy (due to the linkage they colorimetric tests have '(α-1, 2) glucose + fructose')  Complex Carbohydrates Carbohydrates attached to non-carbohydrate structures by glycosidic bonds (O- or N-type) Glycosidic Bonds: Examples: —————————— Purine and N-Glycosidic: attachment happens Pyrimidine bases in at N atom (e.g., Asparagine). nucleic acid. O-Glycosidic: attachment happens at O atom (e.g., Serine). Bilirubin Proteins in glycoproteins and proteoglycans. Lipids in glycolipids.  Glycosaminoglycans (GAGs) Glycosaminoglycans (GAGs) are large complexes of negatively charged heteropolysaccharide chains - Associated with a small amount GAGs are linear polymers of repeating of protein to form proteoglycans disaccharide units: which are 95% carbohydrates. [acidic sugar-amino sugar]n. - Bind with large amounts of water; forming the gel-like matrix that Amino sugars (usually sulfated) either: forms body's ground substance. D-glucosamine or D-galactosamine. - GAGs also gives mucous secretions its viscous and Acidic sugars either: lubricating properties. They were D-glucuronic acid or L-iduronic acid. originally named mucopolysaccharides. GAGs are strongly negatively charged because of the carboxyl and sulfate groups.  Relationship between GAGs structure and functions Glycosaminoglycans (GAGs) - Because of its negative charge, GAG chains tend to be extended in solutions and repel each other. When brought together they 'slip' past each other. - This produces the slippery consistency of mucous secretions and synovial fluid. - When a solution of GAGs is compressed; the water is 'squeezed out' and the GAGs are forced to occupy smaller volume. When the compression is released the GAGs spring back to their original volume and gain water back (like a sponge). - This contributes to the resilience of synovial fluids and vitreous humor of the eye. Examples of: Glycosaminoglycans (GAGs) Chondroitin sulfates Keratan sulfates Most abundant GAG Most heterogeneous GAGs Hyaluronic acid Heparin Compared to other GAGs, is intracellular and it is unsulfated and not serves as an covalently attached to anticoagulant protein  Take Home Message Structure and function of carbohydrates Mono-, Di-, and Poly- saccharides Sugar Isomers: Aldo-keto, epimers, D- and L-, α- and β-anomers Complex carbohydrates: e.g., Glycosaminoglycans and proteoglycans Structure and function of GAGs Examples of GAGs: chondroitin sulfate, keratan sulfate, hyaluronic acid and heparin  MCQs Which one of these is classified as branched 1 homopolysaccharides? A Glycogen B Glycosaminoglycan C Cellulose D Maltose Carbohydrates that have similar structure but differ in 2 configuration at one carbon are: A Isomers B Enantiomers C Epimers D Anomeric 3 Fructose structure is classified as: A Aldopentose B Aldohexose C Ketopentose D Ketohexose 1-A 2-C 3-D  MCQs Cyclization of monosaccharides generates which kind of 4 isomers? α and β Aldo-keto A Epimers B D and L forms C D anomers isomers 5 Glycosaminoglycans (GAGs) are large complexs of Homo- Hetero- Branched Unbranched A polysaccharide B C D polysaccharide polysaccharides polysaccharides 6 Majority of sugars in humans are L configuration T True F False 4-C 5-B 6- F  Biochemistry Team Saad AlDosari Leaders Nada AlMuhawwis Abdulrahman Turki Members Kadi Jood Alnasser Alanazi Alluhayyan Alqosi Faisal Salman Norah Horia Alnemri Almutairy Alrashid Alotaibi Abdulaziz Rahaf Latifah Mohammed Alotaibi Alshalawi Aldossary Alqahtani Basma Renad Fahad Albahkly Alsanad Almosa Ruba Team MED445 Aldibas