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BIOC12H3 (56)
Lecture 11


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Biological Sciences
Shelley A.Brunt

lec11 carbohydrates and glycoproteins 1. level to which things are covered is the level to which you need to know it 2. pay attention to the last half of the lecture saccharides 1. monosaccharides a. monomeric unit of carbohydrate structure (CH O)n 2 b. greater than 3 repeats, max of 9 c. usually 5 or 6 repeats d. one is the carbonyl carbon and each remaining carbon bears a hydroxyl group 2. oligosaccharides a. 2 to 20 monosaccharides in a polymer 3. polysaccharides a. more than 20 monosaccharide residues 4. remember water is eliminated during polymerization of glycan structures 5. glycoconjugate a. carbohydrates linked covalently to a peptide or protein or lipid b. results in i. proteoglycans ii. peptidoglycan iii. glycoproteins iv. glycolipids 6. prof notes a. DNA and RNA are building blocks b. so are carbohydrates built from polysaccharides c. generally have 5-6 repeats on monosaccharides d. theres generally a hydroxyl group present e. difference between oligosaccharides and polysaccharides is their length of repeats f. important to remember is the elimination reaction i. water is eliminated in polymerization of sugars g. carbohydrates can be linked covalently to peptide protein or lipid h. different glycoconjugates i. proteoglycan 1. large amount of carbohydrate to small amount of protein ii. peptidoglycan 1. short peptide + repeating polysachharide chain iii. glycoprotein 1. iv. glycolipid 1. sugars + fatty acid monosaccharides 1. most monosaccharides are a. chiral compounds b. water soluble c. white crystalline d. aldoses i. polyhydroxyl aldehydes 1. with the most oxidized carbon designated C1 2. drawn at the top of a fischer projection e. ketoses i. polyhydrxyl ketones ii. most oxidized carbon is C2 1. usually near the center (for monosaccharides) sugars 1. have the D configuration when the chiral carbon with the highest number (i.e. the chiral carbon most distant from the carbonyl carbon) is the same as that of C2 of D-glyceraldehyde (i.e. the OH group attached to this carbon atom is on the right side of the fischer projection) a. simpler -- the farthest chiral carbon from the CHO group has the OH group on the right side of the fischer projection 2. it is mostly D enantiomers that are synthesized in living cells 3. sugar molecules that differ in configuration at only one of the several chiral centers are called epimers a. e.g. D-mannose / D-galactose are epimers of D-glucose but not each other 4. prof notes a. D configuration is when chiral charbon has OH group attached to right side b. L forms most common in proteins c. D forms most common in living cells i. i.e. carbohydrates and sugars d. sugar molecules normally differ in configuration at only one of several chiral centers i. called epimers fischer projections of the three to six carbon D-aldose 1. most common aldoses a. D-ribose b. D-glucose c. D-mannose d. D-galactose 2. identical number of L forms, but not as important in carbohydrates a. 4 chiral centers leads to 16 possible stereoisomers i. 8 of which are D form fischer projection of L and D-glucose 1. differentiating between D or L a. position farthest from the most oxidized carbon has OH on right or left of that carbon fischer projections of the three to six carbon D-ketoses 2. ketoses have one fewer chiral carbon than the aldose with the same empirical formula 3. most important ketoses a. dihydroxyacetone b. D-ribulose c. D-fructose 4. prof notes a. cascades with two forms expanding into more forms cyclic monosaccharide structures and anomeric forms 1. glucose (an aldose) can cyclize to form a cyclic hemiacetal a. cyclic form is pyranose 2. fructose (a ketose) can cyclize to form a cyclic hemiketal a. cyclic form is furanose 3. cyclic forms possess anomeric carbons (most oxidized carbon) a. the most oxidized carbon is attached to two oxygens 4. in ring structures a. the anomeric carbon is chiral 5. for D sugars a. alpha configuration has OH down b. beta configuration has OH up 6. for L sugars a. alpha configuration has OH up b. beta configuration has OH down c. i.e. the reverse is true 7. the anomeric forms (alpha/beta) are in rapid equilibrium 8. prof notes a. what makes a cyclic saccharide D, what makes it L? i. look at the alpha / beta configurations to determine between D or L 1. D - alpha:down / beta:up 2. L - alpha:up / beta:down pyran vs furan 1. difference between pyran and furan is having either a 6 member or 5 member ring a. two double bonds b. oxygen linking both ends of the chain cyclization of D-glucose 2. cyclization of D-glucose to form glucopyranose a. the fischer projection rotation of the bond between C4 and C5 brings the C5 hydroxyl group close to the C1 aldehyde group b. reaction of the C5 hydroxyl group with one side of C1 gives alpha-D-glucopyranose c. reaction of the hydroxyl group with the other side gives beta-D-glucopyranose 3. prof notes a. bringing C5 close to C1 to form a ring structure b. how the C5 binds to C1 determines whether it is an alpha conformation or beta conformation i. i.e. attacking from top or from bottom 1. OH group up or down linear form of D-fructose undergoes an intramolecular reaction to form cyclic hemiketal 1. prof notes a. alcohol and ketone  hemiketal b. process of linking C6 and C1 is different from linking C5 and C1 i. how? c. key point i. if OH group has OH down or up? D-glucose can cyclize in two ways forming either furanose or pyranose 2. in most monosaccharides there are two or more hydroxyl groups a. that can react with an aldehyde or ketone i. at the other end of the molecule to form a 1. hemiacetal or hemiketal 3. if the C5 OH reacts, a 6 member ring is formed 4. if the C4 OH reacts with the aldehyde of glucose, a 5 member ring is formed 5. prof notes a. glucose tends to form a pyranose i. but can also form furanose b. difference is between C5 linking C1 and C6 linking C1 D-ribose (5C) readily forms five or six member rings 1. depends on which OH groups are carrying out the attack cyclization of D-ribose to form both alpha and beta D-ribopyranose or alpha/beta D-ribofuranose 2. pyranose vs furanose formation depends on cyclization 3. for D sugars, a. OH down is alpha b. OH up is beta chair and boat configurations of a pyranose sugar 1. two possible chair configurations of glucose a. chair and boats are the favored structures of pyranose rings 2. for each pyranose there are two distinct chair conformations and six distinct boats 3. the chair conformations minimize steric repulsion of ring substituents and are generally more stable than boats a. chairs are more stable than boats b. because they minimize steric repulsion 4. equatorial a. coplanar with the ring 5. axial a. parallel to an axis drawn through the ring 6. prof notes a. carbohydrates can take on different structures (conformations) b. chair and boat conformations are favored conformations c. pyranose i. has two distinctive chair conformations ii. has six distinctive boat conformations d. chair conformations minimize steric hindrance the best i. that way ring substituents are more stable ii. depending on how you put the structures (axis straight down) 1. if substituents are equatorial to ring  they are more stable 2. if axial  less stable the two chair conformations of beta-D-glucopyranose 1. equatorial OH groups are more stable since the bulky ring substituents are away from each other 2. prof notes a. bulky side chains being equatorial to axis will result in more stabilized conformation b. bulky side chains being axial to axis will result in more unstable conformation axial substituents sterically hinder each other if they emerge on the same side monosaccharide derivatives 1. sugar phosphates a. monosaccharides in metabolic pathways are often converted into phosphate esters i. sugar esters 1. phosphate esters like ATP are important 2. deoxy sugars a. constituents of DNA etc 3. amino sugars a. contain an amino group in place of a hydroxyl group in the parent monosaccharide b. occasionally acetylated 4. sugar alcohols a. mild reduction of sugars 5. sugar acids a. reducing sugars b. carboxylic acids derived from aldoses c. sugars with free anomeric carbons i. they will reduce oxidizing agents such as 1. peroxide 2. ferricyanide 3. some metals (Cu/Ag) d. these redox reactions convert the sugar to a sugar acid e. glucose is a reducing sugar i. so these reactions are the basis for diagnostic tests for blood sugar metabolically important sugar phosphates 1. sugar phosphates a. dihydrxyacetone phosphate b. D-glyceraldehyde-3-phosphate i. D-G3P c. alpha-D-ribose-5-phosphate d. alpha-D-glucose-6-phosphate e. alpha-D-glucose-1-phosphate 2. prof notes a. missed this slide sugar esters 1. alpha-D-Glucose-1-phosphate 2. alpha-D-fructose-1,6-bisphosphate 3. adenosine-5-triphosphate deoxysugars 1. beta-2-deoxy-D-ribose 2. alpha-L-fucose a. AKA 6-deoxy-L-galactose sugar alcohols 1. glycerol 2. myo-inositol 3. D-ribitol amino sugars 1. alpha-D-glucosamine 2. N-acetyl-alpha-D-galactosamine 3. N-acetyl-alpha-D-neuraminic acid a. N-acetyl-D-neuraminic acid (open chain form - noncyclic) 4. prof notes a. amino groups added to sugars for final exam 1. important to recognize between different sugars  the extent to which need to know these sugars a. sugar phosphates i. sugar esters b. deoxy sugars c. amino sugars d. sugar alcohols e. sugar acids disaccharides a. glycosidic bond is the primary structural linkage for joining monosaccharides b. the glycosidic bond is an acetal linkage a. in which the anomeric carbon of the sugar is condensed with an alcohol, amine, or thiol c. the end containing the free anomeric carbon atom is called the reducing sugar a. the other end is the nonreducing end d. prof notes a. glycosidic bond is an important acetyl linkage between anomeric carbon i. acetyl linkage condensed with alcohol / amine / thiol important disaccharides a. HOH means that the configuration can be either alpha or beta b. note sucrose is distinguished as a sugar made by plants a. with its glycosidic bond linking two anomeric carbons b. therefore neither residue is free to equilibrate between alpha and beta anomers c. prof notes a. linkage drawn with oxygen above ring structures indicate beta linkage b. drawn with oxygen below ring structures indicate alpha linkage c. note sucrose has no reducing sugar (anomeric end) i. need HOH at the end for it to be a reducing sugar ii. sucrose is sugar made by plants 1. reason it has no anomeric end is because beta anomer of maltose a. prof notes a. understand difference between i. pyran and furan ii. L and D forms iii. alpha and beta form polysaccharides a. nomenclature a. homopolysaccharide vs heteropolysaccharide i. homo for same sugars ii. hetero for different sugars b. starch and glycogen are storage molecules c. chitin and cellulose are structural molecules d. cell surface polysaccharides are recognition molecules structures of some common polysaccharides a. table on slide 29 b. hyaluronic acid is a very important structural polysaccharide in extracellular matrices starch and glycogen a. glucose is stored until needed for energy b. D-glucose is made by all species c. storage in plants vs animals a. most common storage in plants and fungi is a homoglycan of glucose called starch i. plant storage is starch 1. starch is a mixture of amylose and amylopectin 2. most starch is 10-30% amylose and 70-90% amylopectin 3. amylose is a. unbranched D-glucose residues (~1000 residues) b. connected with alpha (1-4) glycosidic links c. with one reducing end (seen in maltose) 4. amylopectin is a. branched every 12-30 residues b. via an alpha (1-6) glycosidic linkages b. most common storage in animals is glycogen i. animal storage is glycogen d. storage in bacteria a. contains both starch and glycogen structure of amylose vs amylopectin a. difference between amylose and amylopectin a. amylose has alpha 1-4 b. amylopectin has alpha 1-4 and alpha 1-6 the starch phosphorylase reaction cleaves glucose residues from amylose a. producing an alpha-D-glucose-1-phosphate b. prof notes a. missed slide - talked too fast cellulose and chitin a. cellulose a. is a structural polysaccharide of the cell wall b. is a linear polymer of glucose joined by beta (1-4) linkages i. also true of cellobiose c. vary in size i. up to 15000 glucose residues b. chitin a. is a structural homoglycan found in the exoskeletons of insects and the cell walls of fungi and algae b. is a linear polymer of N-acetylglucosamine joined by beta (1-4) linkages c. adjacent strands of chitin form h bonds resulting in a linear fibril of great strength d. can be associated with protein and inorganic material action of enzymes on amylopectin a. beta-amylase cleaves at nonreducing ends b. alpha-amylase cleaves at internal alpha (1-4) glycosidic linkages c. prof notes a. two enzymes important in breaking down amylopectin i. alpha-amylase 1. internal cleavage ii. beta-amylase 1. cleavage at nonreducing ends the structure of cellulose a. shows h bonds a. intrachain h bonds b. interchain h bonds c. intersheet h bonds b. prof notes a. h bonds is what provides structure to plants and allow them to stand straight up b. chains of sugar i. intrachain h bonds 1. confirm c. between chains of sugar i. interchain h bonds glycoconjugates a. consist of polysaccharide linked to proteins or peptides b. usually composed on many different monosaccharides a. i.e. they are heteroglycans c. proteoglycans are complexes of proteins a. with a specific group of polysaccharide called glycosaminoglycans i. glycosamineglycans are unbranched heteroglycans of repeating disaccharides 1. amino sugar D-glactosamine or glucosamine a. which can be acetylated combined with an alduronic acid b. predominantly found in the extracellular matrix (connective tissue) of multicellular animals d. prof notes a. proteoglycans i. are proteins attached to large amounts of polysaccharides b. difference between glycoprotein and proteoglycans i. in general they are the same 1. proteoglycans have much more carbohydrates 2. missed some other point proteoglycans a. include a variety of structures a. include soluble proteins and integrated membrane proteins i. composed of 1. carbohydrate 2. o linked glycosylation 3. proteins 4. n linked glycosylation b. prof notes a. attaching hydroxyl group to proline i. allows it to be glycosylated b. hydroxylating amino acids allow those hydroxyl groups to be glycosylated i. normally only serine and threonine can be glycosylated 1. natural occurrence of OH group c. N linked glycosylation i. missed what she said d. missed some points e. anything that sticks on the outside of the cell (or is secreted) is almost always glycosylated i. significantly glycosylated 1. adds protection for the proteins that are on the extracellular areas of the cell 2. structural protection 3. ensures function within these molecules proteoglycans a. serve in the cytoplasm and extracellular space / surface b. prof notes a. within extracellular matrix many only structure that are highly modified with
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