Biochemistry

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Monosaccharides

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-building blocks of polysaccharides
-aldehyde or ketone derivatives of straight chain polyhydroxyalcohols (aldose or ketose)
-differ in number of carbon atoms and in arrangement of H and O atoms attached to carbons

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Simplest monosaccharides:

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contain 3 carbons and are called trioses; the aldehyde triose is called glyceraldehyde and the ketone triose is called dihydroxyacetone

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Monosaccharides form polysaccharides by which bonds?

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glycosidic bonds

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Carbohydrate functions

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-source of energy; glucose is the primary fuel (starch in plants and glycogen in animals)
-structural components (cellulose, chitin, peptidoglycan)
-mediate recognition events (oligosaccharides on cell surfaces)
-protective functions (biofilms on bacteria; hylauronic acid --> glycosaminoglycan)

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The most abundant sugars in nature are composed of how many carbons?

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five and six membered rings

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Aldoses are ______ sugars because:

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aldoses are reducing sugars because they have a free aldehydic group; some ketoses can also be reducing sugars because they can isomerize to aldoses

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Oxidation of the Carbonyl Group in Monosaccharides:

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one of the OH groups can be oxidized to a carbonyl group via Tollens Reagent, Ag(NH3)2, which is an oxidizing agent

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Oxidation of an aldose produces a:

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lactone

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Sugar Alcohols:

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produced by the reduction of the carbonyl group; also called alditols; not full sugars b/c they are missing C=O; two examples are the sweeteners, xylitol and sorbitol

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Reduction of a hydroxyl group on a sugar results in:

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a deoxy sugar; one example is fucose, where the CH2OH was reduced to a CH3

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Esterification of Monosaccharides produces:

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sugar esters; many of these reactions take place between sugar and ATP, where one of the H off the OH is replaced with a phosphate group, forming a negatively charged sugar

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T/F: glycosidic bonds can be hydrolyzed back to the alcohols

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true

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What happens to anomeric carbon in during formation of polysaccharides?

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a new chiral carbon is created

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How do linear monosaccharides form cyclic structures?

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the OH on the second to last carbon (next to the terminal CH2OH)attacks the carbonyl carbon; 5 or 6 membered rings will form preferentially; either the alpha or beta anomer will form

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Difference b/w alpha and beta anomers?

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alpha: OH on anomeric carbon is pointing down
beta: OH on anomeric carbon is pointing up

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Uronic Acids:

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have a COOH instead of a CH2OH, which can ionize to become negative

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Amino Sugars:

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an amino group is substituted for one of the OH on the sugars

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Two components of bacterial cell walls:

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N Acetyl-B-D-glucosamine
N Acetylmuramic acid

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Oligosaccharides are made up of between ___ to ___ sugars.
A polysaccharides is made up of at least ___ sugars.

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Oligosaccharides are made of 2-20 sugars; polysaccharides are made up of at least 20 sugars

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Homopolysaccharide:
Heteropolysaccharide:

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-polysacc made of one sugar
-polysacc made of of 2+ sugar

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Cellulose:

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-structural polysaccharide
-plant cell walls
-homopolysaccharide (glucose)
-Beta (1--4) linkages

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Chitin:

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-structural polysaccharide
-insect exoskeleton
-homopolysaccharide (GlcNAc)
-Beta (1--4) linkages
-similar to cellulose

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Chitosan:

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chemically deacelyated chitin that is more soluable and used for drug delivery

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Starch:

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-storage polysaccharide
-heteropolysaccharide (alpha-amylose & amylopectin)

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*alpha-Amylose
*amylopectin

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*linear chain; alpha(1--4) linkages
*branched polysaccharide (24-30 residues); alpha(1--4) and alpha(1--6)

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alpha-Amylase:
beta-Amylase:
Debranching Enzymes:

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endoglycosidase
exoglycosidase
cut branch points

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Glycogen:

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-storage polysaccharide
-similar to amylopectin except is more highly branched
-found in liver, skeletal muscle; NOT found in heart/brain
-contains glycogenin protein at heart of every molecule
-linear chains; alpha (1--4)
-branches; alpha(1--6)

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Glycosaminoglycans:

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linear unbranched chains of repeating disaccharide units; one sugar is N-acetylhexosamine and other is uronic acid; one or both sugars can be sulfated
-adopt highly extended helical conformations
-high density of negative charges attract cations/water

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Proteoglycans:

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-85-95% carb by weight
-glycosaminoglycan usually found covalently attached to protein
-glycosidic linkage w/ Ser OH
-found in extracellular matrix organization
-"Aggrecan" = cartilage proteoglycan
-"Heparin/HS" bind antithrombin III
Hyaluronic acid = viscous

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Peptidoglycan:

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-bacterial cell walls
-polysacc of alternating NAM and NAG residues
-tetrapeptide linked to NAM via lactate moiety
-peptidoglycan chains are parallel and covalently cross linked through peptide side chains

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Penicillin:

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-affects peptidoglycan synthesis
-inhibitor of transpeptidase that cross links peptidoglycan strands
-results in cell lysis
-contains thiazolidine ring fused to B-lactam ring

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Penicillinase:

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cleaves amide bond of B-lactam ring

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Glycoproteins:

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-protein with little bit of carbohydrate
-synthesized via glycosyltransferases

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N-linked Glycoproteins:

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-glycosylation occurs cotranslationally, during protein synthesis in ER
-oligosaccharide is linked to asparagine side chain via amide linkage
-diff types depending on ER/Golgi processing
-High mannose and GlcNAc

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O-linked Glycoproteins:

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-glycosylation occurs post translationally
-oligosaccharide linked to OH of Ser/Thr via glycosidic bond

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N v O linked:

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-amide v glycosidic
-co v post translationally
-asp v ser/thr

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Oligosaccharide Effect on Protein 3D Conformation:

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-stiffens peptide backbone
-limits conformational freedom of polypeptide chain
-stabilize folded conformation

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Oligosaccharide Effect on Protein Solubility and Stability:

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shields protein from proteases

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Oligosaccharide Effect on Protein Localization:

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-recognition process aid in taking protein to designated location
examples: M6Phosphate-M6 Phosphate Receptor; Asialoglycoprotein receptor

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Oligosaccharide Effect on Protein Function:

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glycoprotein hormones: FH, LSH, TSH, hCG; tissue plasminogen activator

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Lectins:

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proteins that recognize carbohydrates

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Examples of Protein/Carb Interactions:

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viral infection
fertilization
cell adhesion, differentiation and growth

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Selectins:

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-glycoproteins that recognize specific carb structures
-mediate binding b/w leukocytes and endothelial cells
-3 types: P, E, L
-sialyl Lewis epitope recognized by selectins

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Biomosiamose

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-inhibits selectin by mimicking the structure of the sialyl Lewis; contains a mannose instead of fucose ring