Question

MCAT Biochemistry Tutorial: Monosaccharides

Answer 1

\({\bf{Basic~Terminology:}}\)
- monosaccharides: carbohydrate with one saccharide unit
> classified by carbon # (triose, tetrose, etc.) and the carbonyl functional group in the backbone (aldehyde --> aldose; ketone --> ketose)

ex: glyceraldehyde

Answer 2

\({\bf{Properties~of~Monosaccharides:}}\)
- can form hydrogen bonds
- water soluble
- high melting point
- at least one chirality center

\({\bf{Fischer~Projections:}}\) align the carbon backbone vertically; each intersection represents a chirality center



Notice the D designations. Monosaccharides are given either a D or L designation depending on the last chirality center and the location of the hydroxyl group. If on the right, give D designation, if on the left, give L designation.

Answer 3

epimer: D or L stereoisomers that only differ by one chirality center

\({\bf{Chain~to~Ring~Form:}}\)
in solution, chain and ring forms are in equilibrium
- conversion to ring produces new chirality center + hemiacetal
- furanose: 5C chain becomes 5C ring with oxygen atom
- pyranose: like furanose except with 6C
- anomer: cyclic sugar epimers (differ by the position of the hydroxyl group)



Notice the alpha designation. Alpha = the hydroxyl groups on either side of the oxygen are on opposite sides of the ring. If on the same side, designate beta. Alpha is favored due to lower steric hindrance.
- mutarotation: reaction that produces a mix of alpha and beta monosaccharides

\({\bf{Haworth~Projections:}}\) take the fischer projection, groups on the right side become the bottom of the haworth ring, groups on the left become the top.

Answer 4

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT