Carbohydrates

Question 1

What are carbohydrates and what do they do?

Answer 1

they have the formula Cn(H20)n and are produced via photosynthesis in plants. Range from very small (90 g/mol) to large (200,000,000 g/mol).
functions include energy source/storage, structural component in cell walls/exoskeletons, and informational molecules in cell-cell signaling

Question 2

which location determines D and L and what does D and L mean?

Answer 2

the most distant chiral center from the carbonyl carbon. D is right and L is left, they are enantiomers. Most carbohydrates (sugars) are in the D configuration in nature.

Question 3

what are epimers?

Answer 3

two sugars that differ only in the configuration around ONE carbon atom. For example glucose, mannose, and galactose.

Question 4

what forms Hemiacetals and hemiketals?

Answer 4

aldehydes attacked by alcohols= hemiacetal (only 1 R group, other attachment is H)
ketone attacked by alcohols = hemiketal (2 R groups)

Question 5

what is an anomeric carbon?

Answer 5

the carbonyl carbon that becomes a new chiral center during cyclization. position of alcohol on anomeric determines alpha or beta. Opposite of CH2OH is alpha, same as CH2OH is beta

Question 6

name of 5 and 6 membered rings?

Answer 6

pyranose for 6 membered ring
furanose for 5 membered ring
ex: glucopyranose, fructofuranose

Question 7

what does it mean to be reducing and what are the tests for it?

Answer 7

reducing sugars have a hemiacetal, so aldehydes are reducing and ketones are not. Closed rings are also not reducing, but ring form exists in equilibrium with open chain form so can still be considered reducing if it is a hemiacetal.
Fehlings test reduces Cu2+ to Cu+ (only aldehydes)
Tollens test reduces Ag+ to Ag (only aldehydes)

Question 8

How are nonreducing disaccharides formed?

Answer 8

two sugar molecules are joined via a glycosidic bond between two anomeric carbons, the product has no acetal groups and no Hemiacetals.