Carbohydrates Flashcards
Aldoses & Ketoses
sugars with aldehydes and ketones as their most oxidized group, respectively
what is nomenclature of all sugars based on?
D- and L- forms of glyceraldehyde
D- and L- sugars
D-sugars have highest-numbered numbered chiral carbon with -OH group on the right (in Fischer projection)
L-sugars have highest-numbered chiral carbon with -OH group on the left
D- and L-forms of the same sugar are:
enantiomers
Diastereomers
nonsuperimposable configurations of molecules with similar connectivity that differ at at least 1 (but not all) chiral carbons
Epimers
diastereomers that differ at exactly one chiral carbon
Anomers
subtype of epimers that differ at one chiral carbon
anomeric carbon
the new chiral center formed in a sugar which has undergone a ring sugar to become a cyclic sugar; it was the carbon containing the carbonyl in the straight chain form
alpha-anomers
-OH on the anomeric carbon is trans to the free -CH2OH group
beta-anomers
-OH on the anomeric carbon is cis to the free -CH2OH group
what are the three main reactions that monosaccharides can undergo?
- redox
- esterification
- glycoside formation
aldoses can be oxidized to (a)___ and reduced to (b) ___
(a) aldonic acids
(b) alditols
reducing sugar
any sugar containing a free aldehyde or ketone group that is capable of acting as a reducing agent (thus all monosaccharides are reducing sugars)
two standard reagents used to test reducing sugars
oxidizing agents: Tollen’s reagent & Benedict’s reagent
Tollen’s reagent positive test
Ag(NH3)2+ used as oxidizing agent
aldehydes reduce Ag+ to metallic silver in positive test
Benedict’s reagent positive test
aldose that is oxidized yields a red precipitate of Cu2O
Enol
a compound with a double bond and alcohol group
alditol
an aldehyde group of an aldose that has been reduced to an alcohol
deoxy sugar
sugar in which a hydroxyl group is replaced with a hydrogen
esterification reaction
reaction between sugar and -CO2H to form an ester
mutarotation
interconversion between alpha and beta anomer with the straight chain form as an intermediate
sugar must be a reducing sugar to undergo mutarotation
glycosidic bond
covalent bond that links a sugar or cabohydrate to another molecule via the anomeric carbon
glucose-alpha-1,2-fructose
sucrose
galactose-beta-1,4-glucose
lactose
glucose-alpha-1,4-glucose
maltose
cellulose
main structural component for plant cell walls
main source of fiber in the human diet
beta-D-glucose molecules linked via beta-1,4-glycosidic bonds
starch
main energy storage form in plants
- amylose: alpha-1,4 glycosidic bonds
- amylopectin: alpha-1,4 bond and alpha-1,6 branches every ~25 glucose residues
beta-amylase
cleaves amylose at the nonreducing end of the polymer (end with the acetal) to yield maltose
alpha-amylase
cleaves randomly along amylose chain to yield shorter polysaccharide chains, maltose, and glucose
debranching enzyme
used to cleave amylopectin due to its highly branched nature
glycogen
main energy storage for animals
- alpha-1,4 chain
- alpha-1,6 branches every ~10 glucose residues
glycogen phosphorylase
cleaves glucose at the nonreducing end of a glycogen branch and phosphorylates it to produce glucose-1-phosphate which plays an important role in metabolism
which form of starch is more soluble in solution and why?
amylopectin is more soluble in solution than amylose because of its branched structure which decreases intermolecular bonding between polysaccharide polymers and increases interaction with the surrounding solution
what characteristic of glycogen optimizes its energy efficiency in the body and how?
the highly branched structure increases glycogen’s energy efficiency because it makes glycogen more soluble in solution, thereby allowing more glucose to be stored in the body. Additionally its branching pattern allows enzymes to cleave glucose from glycogen
