Biochemistry Midterm 2.4 - Carbohydrates Flashcards
glycome and glycode
genome of sugars
sugar code designated by monosaccharides, oligosaccharides, polysaccharides and complex glycoconjugates
glycan
polysaccharides made up of monosaccharides linked by glycosidic bonds
aldose vs ketose
aldose - aldehyde containing sugar (=O on the end)
ketose - ketone containing sugar (=O anywhere but the end)
oligosaccharides
3-10 monomers long
linked onto lipids and proteins
smallest carbohydrate and its constitutional isomer
reference compound for naming D and L sugars
3 carbons: glyceraldehyde (aldiose) and dihydroxyacetone (ketiose)
reference compound is glyceraldehyde
basic monosaccharide nomenclature
n = 3-7 –> tri, tetr, pent, hex, hept
sugar = ose, aldo or keto
aldotriose, ketotetrose
D vs L enantiomers
Dextro: OH of the chiral carbon farthest from the carbonyl group is on the right
Levo: OH of the chiral carbon farthest from the carbonyl group is on the left
number of stereoisomers formula
2^n
n = # of chiral centers
epimer definition
equation for # of epimers
stereoisomers that differ in only one chiral carbon orientation
type of diastereomer
# of chiral carbons - 1
diastereomers
differ in chiral centers but are not enantiomers
non-mirror image
have different physical properties
requires 2+ chiral centers
constitutional isomer’
stereoisomer
same formula different connectivity
same formula, same connectivity, different spatial arrangement
4 carbons D-aldoses diastereomers
D-erythrose
D-threose
5 carbon D-aldoses stereoisomers
D-ribose (standard 5 carbon sugar)
D-arabinose
D-xylose
D-lyxose
six carbon D-aldoses stereoisomers
D-glucose and D-manose are epimers of each other on C-2
structure D-glucose (C-2 OH is on right)
D-glucose and D-galactose are epimers of each other on C-4
Glucose is standard 6 carbon sugar
3 carbon D-ketose
dihydroxyacetone
no chiral center
4 carbon D-ketose
D-Erythrulose
5-carbon D-ketoses
D-Ribulose
D-Xylulose
epimers
6 carbon D-ketoses
D-fructose (C3 OH is on left)
ketose form of glucose
how hemiacetals and hemiketals are formed and what happens
hemiacetal is formed from an aldose (pyranose)
hemiketal is formed from a ketose (furanose or pyranose)
in both cases the carbonyl carbon is reduced to an alcohol and creates new C1 chiral center
pyranose
furanose
pyranose: sugar with 6 membered ring
more stable than furanose
furanose: sugar with 5 membered ring
alpha vs beta
Alpha is C1 carbon OH group faces down (trans)
Beta is C1 carbon OH group facing up (cis)
both in relation to OH group attached to C on otherside side of O atom in the ring
anomeric carbon
The anomeric carbon is the carbonyl carbon atom of a sugar which is involved in ring formation
becomesC1 chiral center
attached OH group is determiner of alpha or beta
aka differ in configuration around hemiacetal/hemiketal carbon
mutarotation
conversion between alpha and beta anomers
chair conformations
preferred by pyranoses
requires energy to change conformation
change of conformation vs configuration
change of conformation requires no break of bonds
change of configuration requires breaking bonds
how to recognize fructose vs. ribose?
it is a ketose, it has CH2OH on 1’ and 5’ carbons
ribose is an aldose, it has CH2OH on only 5’ C, and an OH on 1’
glycoside definition
A glycoside is an acetal formed between a sugar anomeric carbon hemi-acetal and an alcohol, which may be part of a second sugar.
Glucose fischer structure
definition of a free anomeric carbon
carbon attached to an OH, but no bonds to other molecules
once it makes a glycosidic bond, it is no longer reducing
types of tests to check for reducing ends
Fehling test: Cu2+ reduced to Cu+ (color change from blue to brown)
Tollen’s Test: Ag+ reduced to Ag
Enzymatic test: uses glucose oxidase which produces ROOR which oxidizes organic molecules into highly colored compounds which can be measured colormetrically
acetal/ketal are
glycosidic bonded monosaccharide at the anomeric carbon that is more stable and less reactive (non reducing)
hemiacetal –> acetal
hemiketal –> ketal
naming disaccharides
First sugar: 1) alpha/beta 2) D/L 3) monosaccharide prefix (fructo/galacto/gluco/ribo) 4) furano/pyrano 5) “syl” suffix
(carbon # –> carbon #)
Second Sugar: 1) alpha/beta 2) D/L 3) prefix 4) furano/pyrano 5) suffix “side”
common names for disaccharides
maltose - glucose x2
sucrose - glucose + fructose
lactose - galactose + glucose
ether bond vs ester bond vs phosphoester vs phosphodiester
examples of each
ether - R-O-R (ex. glycosidic)
ester - R-C(=O)-OR (ex. triacylglycerides)
phosphoester - R-O-P (ex. phosphatidate)
phosphodiester - R-O-P-O-R (ex. nucleic acids)
chemical modifications of monosaccharides
add groups OTHER THAN H, C, O
phosphorylation - adding phosphate
amidation - adding NH2 to replace OH
acetylation - adding OCH3 double bonded
oxidation - increase C-heteroatom bonds and decrease in C-H bonds
methylation - adding CH3
functions of homopolysaccharides and heteropolysaccharides
homo: energy storage and structure
hetero: structure and cellular functions
starch description and types
storage in plants
amylose - unbranched glucose alpha1–>4 glycosidic bonds
amylopectin - branched glucose, alpha1–>4 glycosidic bonds and branches alpha1–>6 every 24-30 residues
amylopectin can be up to 200 million Da
glycogen description
branched glucose homopolysaccharide storage in animals
alpha1–>4 linear and alpha1–>6 branches every 8-12 residues
7% of the liver by weight
solubility of glycogen and starch
insoluble due to high molecular weight and form granules
granules contain enzymes for quick breakdown and formation at non reducing ends
cellulose
insoluble unbranched glucose homopolysaccharide
beta1–>4 linkages
H bonds form between chains excluding water from H bonding
who can hydrolyze cellulose bonds?
fungi, bacteria and protozoa can hydrolyze beta1–>4 linkages so they can use wood as source of energy
symbiotic organisms in the gut of ruminants and termites
what is chitin
N-acetyl modified glucose unbranched homopolysaccharides that form skeleton in insects, spiders and crustaceans
example of unbranched heteropolysaccharides
bacterial sugar coat - they can change sugar coat to hide from the immune system
only 2 monomers used
branched heteropolysaccharides
contain 3 or more monomers
glycosylation of proteins - monosaccharides and oligosaccharides are added shortly after synthesis
roles: cell-cell interactions (ex. lectins), stabilize against degradation and role in folding of proteins
heteropolysaccharides are mostly associated with
proteins and lipids
N linked oligosaccharides
when sugars are added to protein with consensus sequence it is a N-glycosidic bond
added to proteins with Asn-AA-Serine/Threonine as reassembled oligosaccharide units
added to proteins destined for extracellular side of membrane
O linked oligosaccharides
added directly onto Serine or Threonine side chain (no consensus sequence)
can be destined for intra or extracellular
