Ch. 9 Carbohydrates
Carbohydrates
-"Hydrate of Carbon" -Have empirical formula of (CH2O)n, where n> or = to 3 -Aldehyde or ketone derivatives of straight chain poly-hydroxy alcohols
Cell Wall Biosynthesis in Bacteria
-Alternate N-acetylglucosamine and N-acetylmuramic acid -Site of cleavage by lysozyme (beta 1-->4) -reducing edn -pentaglycine cross-link
Amino Sugars
-Amino group replaces OH -Amino group sometimes acetylated -Amino sugars of glucose and galactose occur commonly in glycoconjugates
O-linked oligosaccharides
-Attach to serine or Threonine residues in proteins -Most common disaccharide linkage to an aa residue shown in diagram (R= H or CH3)
Sugar Alcohols (Polyhydroxy alcohols)
-Carboxylic acid group can be reduced to an alcohol 1) Ribitol: component of flavin structure 2) Xylitol: non-metabolized artificial sweetener 3) Glycerol: & myo-Inositol: both are important components of modified lipids in membranes
Starch & Glycogen
-D-Glucose store intracellularly in polymeric form -Plants and fungi = starch -Animals = glycose -Starch is mixture of different types of linear and branched glucose polymers: amylose (linear) and amylopectin (branched)
D-sugars (Numbering & chirality)
-Have same configuration as D-glyceraldehyde in chiral carbon most distant from carbonyl carbon -Numbering starts with MOST oxidized carbon and the aldehyde C-1 is drawn at top of Fischer projection -The -OH at C5 of D-glucose is on the right in Fischer model -Glyceraldehyde (aldotriose) is chiral - C2 carbon has 4 different groups attached to it
Dihydroxyacetone (ketotriose)
Does not have an asymmetric or chiral carbon and is not a chiral compound -Ketose >3 C are chiral -Ketoses = CH2OH
Softwood Lignin fragment
Aromatic ring polymer (cellulose based?)
Amylose (starch)
Glucose alpha-(1-->4) linkages, unbranched but forms
Amylopectin (starch)
Glucose alpha-(1-->6) linkages, branched
Aldose Monosaccharides Lactose --> galactose beta connection to Glucose
-Hemiacetals: form a ring that is in equilibrium with open chain form -Open chain form contains reactive carbonyl group (ie aldehyde) -Called Reducing sugars: because aldehyde carbonyl group can reduce metal ions; any sugar with free anomeric carbon is considered "reducing" Ex: glucose, maltose, cellobiose, lactose **O-Beta-D-galactopyranosyl-(1->4)-D-glucopyranose
N-Acetylneuraminic Acid
-Important part of glycoproteins and glycolipids -Top: pyruvic acid residue -Bottom: N-Acetyl-mannosamine (amino sugar derivative of mannose) -Pyranose form = sialic acid
Aminoglycosides
-Kanamycin A -Neomycin -Streptomycin
Natural sweeteners
-Monellin (serendipity berry - x800-2000) -Thaumatin (katemfe fruit - x2000)
Anomeric Carbon
-Most oxidized carbon (originally carbonyl carbon of linear form) of a cyclized monosaccharide -Chiral carbon in ring structures and thus can adopt alpha or beta configuration
Protein glycosylation
-N-linked oligosaccharides attach to Asn residues in proteins -Typically Asn is in Asn-X-Ser or Asn-X-Thr motif in protein sequence **GlcNAc (N-acetyl-D-glucosamine) directly attached to aa residue but further oligosaccharides branch off from it -Secreted and membrane proteins are glycosylated
Cyclic Monosaccharide Conformation
-Not actually planar, but exist in chair conformations -Due to tetrahedral coordination around all ring atoms -Bulky groups occupy equatorial positions (less steric clash) or bulky groups occupy axial positions (more steric clash; less stable)
Glycocalyx on surface of erythrocyte cell
-Oligosaccharide cell surface determinants -Different individuals can have A, B, A/B, or H only (Type O) determinants -An indidividual will have antibodies against determinant they don't possess -Can't transfuse Type A erythrocytes into Type B individual (triggers an immune response against erythrocytes)
Cellulose
-Plays an important structural role in plant cell walls; accounts for over half of total carbon in biosphere -Cellulose strands associate together and form stacked sheets -Beta-(1->4) linkages {flips each glucose 180 deg with respect to each other) **Glucose-glucose chains
Proteoglycan aggregate of cartilage
-Proteoglycan: core proteins with glycosaminoglycan chains attached {Keratan sulfate, chondroitin sulfate} -Central strand of hyaluronic acid -Link proteins
Artificial Sweeteners
-Saccharin -Acesulfame -Alitame (x2000 - relative to sucrose) -Aspartame -Sucralose
Cellulose Make-up
-Strong H-bonding networks provide strength to cellulose strands/sheets -Within strands, C3 -OH group of one glucose residue H bonds with ring O5 of next glucose residue -Multiple strands held together by interchain H-bonds btwn O of one -OH group and H of another -OH group -Multiple sheets held together by H-bonds above and below as well as van der waals forces
Sucrose --> Glucose alpha connection to fructose
-Sucrose is unusual in that BOTH anomeric carbons are involved in glycosidic bond -NO free anomeric carbon that can open up to provide its aldehyde group -Sucrose is considered NON-reducing sugar **O-alpha-D-glucopyranosyl-(1->)-beta-D-fructofuranoside
Epimers
-Sugars that differ at only ONE of several chiral centers -EX: D-glucose is an epimer of D-mannose -Aldoses (CHO): aldotriose, -tetroses, -pentoses, -hexoses
Glycogen
-Very similar to starch amylopectin but found in animals and even more highly branched -Glycogen is a storage form for glucose that's highly abundant in liver
N-glycosylation occurs co-translationally
1) 14-residue oligosaccharide is attached to Asn of polypeptide 2) Removal of monosaccharide units produces a (mannose)3(GlcNAc)2 oligosaccharide --> It's core is found in all N-linked oligosaccharides 3) Further trimming and addition of other sugars yields variety of N-linked oligosaccharides with same core pentasaccharide
Reaction of alcohol with carbohydrates to cyclize as Hemiacetals/Hemiketals
1) An aldehyde (aldoses >4 C can cyclize when forming a hemiacetal) 2) A ketone (ketoses >5C can cyclize when forming a hemiketal -Most carbs are actually in cyclic forms in vivo; cyclized sugars are generally PURANOSES (6 ring) or FURANOSES (5 ring)
Congenital disorders of glycosylation
1) CDG Type I 2) CDG Type II (inefficient golgi remodeling)
Disaccharides and Glycosides
1) Glycosidic Bond: primary structural linkage involving monosaccharides --> It's an acetal linkage - the sugar anomeric carbon is condensed with an alcohol (most commonly another monosaccharide), amine, or thiol -Cmpds containing glycosidic bonds are called glycosides
Polysaccharides
1) Homoglycans: polysaccharides containing only one type of monosaccharide 2) Heteroglycans: polysaccharides containing more than one type of monosaccharide -Lengths & compositions of polysaccharide can vary within population of these molecules -Polysaccharides usually perform structural roles or carbohydrates storage functions
Types of carbohydrates
1) Monosaccharides: one monomeric unit 2) Oligosaccharides: ~2-20 monosaccharides 3) Polysaccharides: >20 monosaccharides 4) Glycoconjugates: linked to proteins or lipids 5) Aldoses: polyhydroxy aldehydes 6) Ketoses: polyhydroxy ketones **Most oxides carbon: aldoses C-1, ketoses C-2
Derivatives of Monosaccharides
1) Oxidation of aldehyde group converts it to aldonic acid (C1) 2) Oxidation of primary alcohol group creates an uronic acid (C6)
Deoxy Sugars
H replaces an OH
Core Pentasaccharide
Man alpha(1->6) & Man alpha(1->3) -------> Man beta(1->4)GlcNAc Beta(1->4) GlcNAc-
Mucopolysaccharidoses (MPS)
Many different diseases (enzyme deficiency diseases)
Energy Cycle
Sun > Photosynthesis > C6H12O6 + 6O2 > ADP to ATP Respiration > 6CO2 + 6H20
Alpha configuration (anomeric C)
The -OH on the anomeric carbon (C1) is on opposite side of ring from -CH2OH group on chiral carbon that designated D or L (C5 in hexoses)
Beta configuration (anomeric C)
The -OH on the anomeric carbon (C1) is on same side of ring from -CH2OH group
Glycosaminoglycans
Unbranched heteroglycans of repeating disaccharides (many sulfated hydroxyl and amino groups) --> Major component of connective tissues and bone and cartilage
Chitin
[N-acetylgocosamine bonded by O to N-acetylglucosamine]n
