Chapter 4- Carbohydrate Structure and Function Flashcards
monosaccharides
trioses- 3 carbons
tetroses- 4 carbons
pentoses- 5 carbons
hexoses- 6 carbons
aldoses
carbohydrates that contain an aldehyde group as their most oxidized functional group
ketoses
carbohydrates that contain a ketone group as their most oxidized functional group
simplest aldose sugar
glyceraldehyde (aka. aldotriose)
which carbon is typically the most oxidized
the carbonyl carbon (attached to the doublebonded O)
glycosidic linkages
sugars acting as substituents (typically aldehyde carbon)
dihydroxyacetone
simplest ketone sugar (ketose). carbonyl carbon is most oxidized (carbonyl carbon is usually C2)
stereoisomers
optical isomers. compounds that have the same chemical formula (only differ from one another in terms of spatial arrangement)
enantiomers
same molecular formula
nonsuperimposable
mirror images of each other.
any molecule that contains chiral carbons and no internal planes of symmetry.
number of stereoisomers with common backbone
2^n (n = number of chiral carbons in the molecule)
fisher projection
horizontal lines (wedges)-- out of page (right side pointing down) vertical lines (dashed)-- into page
diastereomers
same molecular formula
nonsuperimposable
not mirror images
epimers
subtype of diastereomers that differ in configuration at exactly one chiral center (ex: D-ribose and D-arabinose)
most common electrophile
carbonyl group (C doublebonded to O)
pyranose and furanose rings
pyranose- 6C rings
furanose- 5C rings
rings are typically hemiacetals or hemiketals
what happens when you expose a hemiacetal ring to water?
they will spontaneously cycle b/w open and closed form
mutarotation
interconversion between anomers of a compound (ex: a and B conformations)
spontaneous change of configuration about C-1 and occurs more rapidly when the reaction is catalyzed with an acid or base.
reactions that monosaccharides can undergo and why
b/c they contain alcohols and either aldehydes or ketones they can undergo….
- oxidation/reduction
- esterfication
- nucleophilic attack (creating glycosides- sugar bound to another functional group)
aldonic acid
the aldehyde group of a monosaccharide is oxidized to a carboxylic acid. this oxidized aldose (reducing agent) is called an aldonic acid.
reducing sugars
any monosaccharide with a hemiacetal ring
lactone
cyclic ester. when aldose being oxidized is in ring formation then the oxidation yields a lactone. (ex: vitamin C)
how to detect the presence of reducing sugars?
Tollen’s reagent: uses Ag(NH3)2+ as oxidizing agent. so aldehydes reduce Ag+ to metallic silver
Benedict’s reagent: aldehyde group of an aldose is readily oxidized by Cu(OH)2, indicated by a red precipitate of Cu2O
*note: ketose sugars are also reducing sugars and give positive test results for these.
Tautomerization
rearrangement of bonds in a compound, usually by moving a hydrogen and forming a double bond.
enol
compound with a double bond and an alcohol group
alditol
formed when the aldehyde group of an aldose is reduced to an alcohol
deoxy sugar
contains a hydrogen that replaces a hydroxyl group on the sugar (most well known is the deoxyribose which is the carbohydrate found in DNA)
esterfication
carbohydrates have hydroxyl groups which can react with carboxylic acids and their derivatives to form esters. (most important reaction in body is the phosphorylation of glucose to form a phosphate ester, this uses hexokinase or glucokinase as an enzyme)
acetals/ ketals
formed when hemiacetals (hemiketals) react with alcohols under acidic conditions, resulting C-O bonds are called glycosidic bonds and the acetals (ketals) formed are glycosides –dehydration reaction
furanosides and pyranosides
glycosides derived from furanose and pyranose rings, respectively – dehydration reaction
esterfication vs. glycoside formation
esterfication- reaction by which a hydroxyl group reacts with either a carboxylic acid or a derivative to form an ester
glycoside formation- reaction b/w alcohol and hemiacetal (or hemiketal) group on a sugar to yield an alkoxy group.
how are carbohydrates usually metabolized
oxidized, so they can reduce electron carriers for oxidative phosphorylation
what is a complex carbohydrate
all carbohydrates with at least 2 sugar molecules linked together.
3 important polysaccharides
All made of D-glucose monosaccharide
- Cellulose (main structural component of plants, we cant digest it so it works as fiber for us- drawing water into the gut)
- Starches (linked a-D-glucose monomers, digestible by humans)
- Glycogen (carbohydrate storage unit in animals, highly branched-making it more soluble)
amylose and amylopectin
amylose: plants store starch as this, broken down by B-amylase to yield maltose
amylopectin: starts the same as amylose, but also has a branch of a-1,6 glycosidic bonds.
a-amylase– cleaves randomly along the chain to yield shorter polysaccharide chains
glycogen phosphorylase
functions by cleaving glucose from the nonreducing end of a glycogen branch and phosphorylating it
enantiomerization
aka racemization. the formation of a mirror-image or optically inverted form of a compound.
anomerization
ring closure of a monosaccharide, creating an anomeric carbon
