Carbohydrates Flashcards
are polyhydroxy aldehydes or ketones with an empirical formula Cn (H2O)n. except for deoxy sugars.
carbohydrates
Functions of carbohydrates
source of energy: 65% of calorie requirement
structural components: component of connective tissue and nucleic acids
role in cellular interaction and immune recognition
Classifications of carbohydrates
monosaccharides
disaccharides
polysaccharides
the simplest sugars and do not undergo hydrolysis
monosaccharides
can be classified according to the functional group (carbonyl) present (aldose or ketose) and number of carbons
monosaccharides
ketose
naa sa sud
aldose
naas gawas
common aldoses
allose
altrose
glucose
mannose
gulose
idose
galactose
talose
simplest sugar aldose and ketose
glyceraldehyde and dihydroxyacetone
cyclic hemiacetals (for aldoses) and hemiketals (for aldoses) formed due to the intramolecular interactions between the hydroxyl and carbonyl groups of the monosaccharides
Haworth projections
sugars with six-membered rings
pyranose
sugars with five-membered rings
furanose
two sugars which are mirror images of each other
enantiomers
two sugars that differ only in the configuration around one carbon atom
epimers
two sugars that differ only in the orientation of the OH around the anomeric carbon in the Haworth Projection.
anomers
consist of two simple sugar units linked by glycosidic bonds
disaccharides
Maltose
alpha(1,4)
a-D-glucose
B-D-glucose
Lactose
B(1,4)
B-D-glucose
B-D-galactose
Sucrose
a(1)-B(2)
a-D-glucose
B-D-fructose
Cellobiose
B(1,4)
2 B-D-glucose
Gentobiose
B(1,6)
a-D- glucose
B-D- glucose
made up of 3–10 monosaccharide units joined by glycosidic bonds
oligosaccharides
raffinose
glucose+galactose+fructose
stachyose
2galactose+glucose+ fructose
verbascose
3galactose+glucose+fructose
made up of more than 10 monosaccharide units joined by glycosidic bonds
polysaccharides
cellulose
B-D-glucose
B(1,4)
starch (Amylose & Amylopectin)
a-D-glucose
Amylose: a(1,4)
Amylopectin: a(1,4) and a branching at a(1,6) in every 15-30 glucose units
glycogen
a-D-glucose
a(1,4) and a brancing at (1,6) in every 8-12 glucose units
chitin
N-acetylglucosamine
B(1,4)
a glucose polysaccharide that provides strength to plant cell walls and consists of the repeating disaccharide cellobiose.
Cellulose
a storage polysaccharide in plant cell
starch
a storage polysaccharide in animals
glycogen
a linear hexosamine polysaccharide that forms the structural component of invertebrate exoskeletons in insects and crustaceans
chitin
is also a component of the cell walls in many types of fungi, including mushrooms
chitin
composed of glucosamine and glucuronic acid or iduronic acid that is present in liver, lung, spleen; anticoagulant
heparin
compose of N-acetylgalactosamine + glucuronic acid; present in cartilage, tendons, ligaments
chondroitin sulfate
is a heteropolysaccharide which is used as plasma volume expander
dextran
made are proteins or lipids with covalently attached glycans, which play a critical role in cellular communication
glycoconjugates
contain combinations of modified and unmodified monosaccharides, which are covalently attached to proteins and lipids as branched and unbranched structures
glycoconjugates
Glycan modification of proteins takes place within the
lumen of the endoplasmic reticulum compartment of the cell
glycolipids are primarily generated in
Golgi apparatus
protein glycoconjugates in which the bulk of the macromolecule consists of protein
glycoprotein
protein glycoconjugates that consist mostly of carbohydrates (of greater portion by mass) with only a small protein component; provide points of adhesion, recognition, and information transfer between cells, or between the cell and the extracellular matrix.
proteoglycans
are proteoglycans that are found in bacterial cell walls consisting of multiple strands of hexosamine polysaccharide chains
peptidoglycans
have a thick peptidoglycan cell wall and no outer membrane
gram-positive bacteria
have a thin peptidoglycan cell wall surrounded by an outer membrane
gram-negative bacteria
are lipids with a carbohydrate attached by a glycosidic bond
glycolipids
maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the connections that allow cells to connect to one another to form tissues
glycolipids
converts the aldehyde group into a carboxylic acid, yielding aldonic acids
oxidation of an aldose
sugar + Cu2+ complexed with tartrate ion –> gluconic acid
red precipitate
Fehling’s reagent
sugar + Ag+ in aqueous ammonia –> gluconic acid
silver precipitate
Tollen’s reagent
is also a method of shortening sugar chains which begin with (1) the conversion of an aldose to aldoxime by reaction with hydroxylamine and sodium methoxide (2) the conversion of oxime into nitrile with simultaneous conversion of all alcohol groups to acetate groups by reacting with acetic anhydride and sodium acetate and (3) removal of acetate groups and ejection of nitrile group by adding sodium methoxide in methanol resulting in the formation of an aldehyde group at C2, hence giving an aldose with one less carbon
Wohl degradation
a two-step method of shortening sugar chains that begins with the oxidation of the aldose to its aldonic acid. The aldonic acid is treated with hydrogen peroxide and ferric sulphate which oxidizes the carboxyl group to CO2, hence giving an aldose with one less carbon.
Ruff degradation
a substitution reaction of a glycosyl halide with an alcohol to give a simple glycoside.
Koenigs-Knorr Reaction
detects reducing sugars and differentiates a monosaccharide from a disaccharide
Barfoed’s test
can be used to detect the presence of starch, showing blue-black coloration (starch-iodo complex. Glycogen gives red coloration with the iodine.
iodine test
method of extending an aldose carbon chain by adding one carbon atom at a time. This process involves the conversion of aldose to two diastereomeric cyanohydrins of the next higher carbon number by addition of HCN. The resulting cyanohydrins will be partially reduced
to imines and then hydrolyzed to diastereomeric sugars
Kiliani-Fischer Synthesis
