14 - Carbohydrates Flashcards
Isomer =
2 molecules same MOLECULAR formula
What is constitutional isomer?
change order of atoms (connectivity of atoms)
- macromolecular constitutional isomers = TAUTOMERS
- carbohydrate tautomers = aldose + ketose
- relocation H+ –> bond order rearrangement (movement pi bond/carbonyl) NO break/form bonds!
Aldose + Ketose
Tautomers
– relocation H+ changes which C forms pi bond w/ O
where C # begin in carbohydrate structure?
starts terminal carbonyl C of aldose
What are stereoisomers?
change spatial orientation of atoms; fixed bond order (connectivity)
2 main stereoisomers + major differences:
Configurational isomers – chiral C’s and changes spatial orientation around chiral C
Conformational isomers – reversible rotation around single bond (nucleotide glycosidic bond)
How many chiral C are possible in 3 C sugar structure?
1
– Both terminal C always Achiral
Enantiomers
Mirror images @ ALL chiral centers
Distereomers
- contain multiple chiral centers
- NOT mirror images at ALL chiral centers
4-C sugar:
- 2 chiral centers
- 4 distereomers (2 pairs of enantiomers)
Fisher projection
– linear model of carbohydrate structure
structure
Haworth Projection
– cyclical 2D representation carb structure
Pyran ring
- 6 member ring
- most 6-C carbs
Furan
- 5 member ring
- - most 5-C carbs, except fructose (6-C)
What is anomeric C?
– Carbonyl C in linear structure and is the 1st C to right O in cyclic structure carbs
After cyclicization (carbonyl –> hydroxyl), how do you determine orientation (alpha vs beta) of hydroxy at anomeric C?
CANNOT determine alpha/beta orientation of OH from Fisher projection
alpha vs beta carbohydrate:
alpha carbohydrate – OH oriented DOWN
beta carbohydrate – OH = UP
2 types of Distereomers:
Anomers – differ ONLY orientation of OH @ anomeric C (1 alpha, 1 beta)
Epimers – SAME anomeric orientation but differ in OH orientation at any other C in ring (both alpha or both beta)
Configurational isomers
differ order (spatial orientation) around chiral C
conformational isomers
REVERSIBLE free rotation around single bond
– think syn/anti nucleotides, endo/exo, sugar-pucker, boat/chair conformations
FURANose vs PYRANose conformational isomers
Furanose = 5-member rings; endo/exo conformations Pyranose = 6-member rings; boat/chair conformations
C3H6O3 =
Trioses common structure
C5H10O5 =
Pentose common structure
C6H12O6 =
Hexoses common structure
Fucose =
- Galactose derivative
- only L-monosaccharide synth/used mammals
- part A/B/O blood antigens
- excess free blood fucose = liver damage, cancers, diabetes, heart disease
***L-enantiomer galactose + OH replaced CH3 (mod forms C-C bond, rare)
Phosphorylation modifications
- Ester linkages
- part nucleic acids
- -**important reactive intermediates of carb metabolism
- negative charge to sugar
- name molecule tell you where phosphate located in molecule
Oxidation modifications
REDUCING SUGARS
- oxidized @ carbonyl-C (anomeric)
- 2 step process creating acid + lactones
- old diabetes urine tests looked reducing sugars as indicator high blood glucose concentrations
Why reducing sugars primarily monosaccharides?
– oxidation rxn requires a FREE anomeric C for enzyme locate & interact carbonyl
Reduction Modifications
- reduction @ carbonyl C = ALDITOLS
- Sorbitol reduced form glucose
**Reduced sugars can cause CATARACTS
Amino Sugars
- common branched polysaccharides (cell walls)
- common addition to proteins (N-linked glycosylation)
- N-linked glycosides
**OH replaced N of amino that’s attached to acetyl
Methylation modifications
O-linked methylation
– same rxn mechanism monosaccharide polymerization but + non-sugar
– fucose = methylation is C-C linkage
N-linked vs. O-linked glycosides:
- N-linked glycosides = common branched carb structures, protein glycosylation, nucleosides (ribose + N-base bond)
- O-linked glycosides = methylation, important TOXINS
O-linked Glycosides
= some important toxins
– mech of methylation
Essential Monosaccharides:
D-glucose D-galactose D-Mannose D-Xylose L-Fucose N-Acetylgalactosamine (GalNAc) N-Acetylglucosamine (GlcNAc) N-Acetylneuraminic acid (Sialic acid) (NeuNAc)
Maltose:
- what 2 monosaccharides
- C #’s from each participating
- position of O-linked glycosidic bond
- position anomeric OH monosaccharide
Maltose =
- 2 alpha-D-glucose
- 1 –> 4
- alpha-glycosidic bond
Sucrose
- alpha-D-glucose –> beta-D-fructose
- 1 –> 2
- alpha-glycosidic bond
Lactose
- Beta D-galactose + D-glucose
- 1 –> 4
- beta-glycosidic bond
Polysaccharide fxns:
- glucose storage
- structure
- protein diversity
List structural differences of blood type antigens
Type O (non-antigenic)
Type A + GalNAc
Type B + Gal
difference between A and B = N-linked acetyl
Glucose storage structures
- -Glycogen: 1–>6 linkages (branched); 1–>4 linear linkages
- Amylose (unbranched) = Helical structure
Structural polysaccharides
- -Cellulose & chitin
- - commonly Beta-glycosidic bonds
List protein residues with sides chains capable forming N- or O-glycosidic bonds (glycosylation)
Asn = N-linked
Ser and Thr = O-linked
Glycoproteins
- -Protein > Sugar (weight)
- -membrane proteins (cell adhesion)
- -soluble (cell signaling)
- erythropoietin hormone + GlcNAc (E stores cel)
Glycosaminoglycans
- protein < sugar
- repeating disaccharide structure
- part of proteoglycans (huge ECM proteins-chondrotin sulfate, hyaluronic acid etc)
- Heparin
Mucins
- protein < sugar
- more complex structure pattern than glycosaminoglycans
- Lubrication fxn: protection & hydration
