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BIOC 2580 Study Guide - Fischer Projection, Reducing Sugar, Glycosidic Bond


Department
Biochemistry
Course Code
BIOC 2580
Professor
E P Wijekoon

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BIOC 2580 Final Exam Notes
2. Carbohydrates
Functions
Energy metabolism
Essential components of nucleic acids (DNA and RNA)
Structure
Glycoproteins: sugars attached to proteins
Monosaccharides
Structure
Combine 2 organic chemical functional groups:
Carbonyl (C=O):
Ketone: Bonded to 2 other carbons
Aldehyde: bonded to 1 other Carbon and 1 Hydrogen
Hydroxyl groups (OH): alcohol groups
Have at least 2 C-OH
Therefore sugars are polyhydroxy aldehydes or polyhydroxy ketones
Ketoses: ketone sugars
Aldoses: aldose sugars
aldehyde ketone
Properties
Hydrophilic, polar
Poorly soluble in organic solvents (ether, hexane)
Colourless
Sweet to taste
Standard formula: (CH2O)n
Trioses
Simplest monosaccharides
3 C atoms: 1 carbonyl group, 2 Cs bearing hydroxyl groups

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Hexoses are the most common monosaccharides in nature
Chirality
Asymmetry or handedness
Needs to have 4 different constituents (cannot superimpose)
*dihydroxyacetone in not chiral
Enantiomers
Mirror images (left handed or right handed)
Have identical chemical properties
Have different optical activity
Plane of polarization when polarized light is passed through each is bent in different
directions
Right handed Left handed
Diastereomers
Stereoisomers that differ in handedness at some C atoms but not others
Do not have identical chemical properties
Spatial arrangements among atoms are different
*red C = chiral
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Number of Possible Stereoisomers
2n – n = number of chiral centres
E.g. 5 carbons, 3 Chiral centres = 23=8
Half will be D sugars, half will be L
Most sugars are D
Everytime C atom is added, # of isomers doubles
D and L Sugars
D: chiral atom furthest away from carbonyl group has same configuration as D-glyceraldehyde
OH to the right
L: chiral atom furthest from carbonyl group has OH to the left
Epimers
Pair of sugars identical except at 1 C atom
Just special case of diastereomers
Fischer Projection Formula
Emil Fischer (1852-1911)
Studied analysis, synthesis, and stereochemistry of simple sugars
Introduced much of the terminology/notation we use
Use projection formula to represent 3D sugar structures on paper
C atoms in vertical row numbered from top to bottom
Vertical bonds project behind the plane, horizontal bonds project out
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