14. glycoconjugates Flashcards
what are glycoconjugates
polysaccharides linked to proteins, small peptides, or lipids
are glycoconjugates homoglycans or heteroglycans? why
heteroglycans since the polysaccharides are composed of more than one type of monomer
list the three types of glycoconjugates important at the cell surface
proteoglycans, glycoproteins, glycosphingolipids
what is the sugar bound to in a glycoprotein
protein
what is the sugar bound to in a proteoglycan
protein
what is the sugar bound to in a glycosphingolipid
lipid
where are proteoglycans located
on the cell surface or in the ECM
what are proteoglycans
proteins complexed with large polysaccharides called glycosaminoglycans
what are glycosaminoglycans
unbranched heteroglycans of repeating disaccharide units
what are the disaccharide components of a glycosaminoglycan
one disaccharide in an amino sugar, the other in an uronic acid
list the types of amino sugars present in glycosaminoglycans
D-galactosamine or D-glucosamine (or their acetylated formed)
what are uronic acids
acidic sugars (a monosaccharide derivative)
how are uronic acids formed
when the C6 glucose/mannose/galactose is oxidized to a carb acid
describe the basic structure of a proteoglycan
a core protein with glycosaminoglycans attached at Ser residues. The glycosaminoglycans are joined at tetrasaccharide bridges/linkers
T or F: lots of glycosaminoglycans have esterified sulfate groups on their GlcN or GalN
true
what is the charge on GAGs and why
negative, because there are carb acids in the uronic acid (+ all the sulfate groups)
how do GAGs minimize repulsion of all those negative charges
they extend into a rodlike helix, which the carboxylate groups on alternating ends for maximum separation
what is the longest GAG called
hyaluronic acid
what type of sugar is hyaluronic acid
disaccharide
what are the two monomers of hyaluronic acid
glucuronic acid and N-acetylglucosamine
what is the role of hyaluronic acid
it forms a viscous non compressible solution to reduce friction in joints
T or F: proteoglycans are highly hydrated
true
why are proteoglycans highly hydrated
they have a bunch of polar groups
how do proteoglycans help skin
they confer elasticity to skin (as well as other parts)
where are proteoglycans located
some are in the ECM, some are integral membrane proteins
T or F: some proteoglycans can form aggregates to produce enormous assemblies
true
describe proteoglycan aggregation
an aggrecan core protein has multiple glycosaminoglycans joined to Ser residues. This serves as the monomer. monomers join to the central strand of hyaluronic acid
describe how defects in glycosaminoglycan synthesis/degradation can lead to disease
a defective enzyme leads to a truncated glycosaminoglycan, which produces multiple large bone spurs covered in cartilage
what are peptidoglycans
heteroglycans attached to very short peptides
describe the structure of peptidoglycans
composed of alternating residues of N-acetylglucosamine and N-acetylmuramic acid joined by β-(1→4) glycosidic linkages
what organism and what part of that organism uses peptidoglycans
cell walls of bacterial contain extensive peptidoglycan
describe peptidoglycan within bacterial cell walls
peptidoglycan polymers are highly cross linked by a transpeptidase enzyme to create huge rigid molecules that define the shape of bacterial cell walls and protect against fluctuation in osmotic pressure
what is the role of transpeptidase enzyme in peptidoglycans
it’s used to cross link peptidoglycan polymers to create huge rigid molecules within bacterial cell walls
what are gram negative bacterial
small amounts of peptidoglycan in between inner and outer cell membranes
what are gram positive bacteria
up to 40 layers of peptidoglycan and no external cell membrane
describe the relationship between penicillin and peptidoglycan
the antibiotic penicillin binds irreversibly to the transpeptidase active site and blocks peptidoglycan cross-linking
how do glycoproteins differ from proteoglycans
they’re branched, smaller, and more structurally diverse
describe the structure of glycoproteins
the carbohydrate is attached at its anomeric carbon through a glycosidic linkage to either the OH of Ser or Thr, or the amine nitrogen of Asn
what are glycosphingolipids
membrane lipids with a sphingosine backbone and at least one monosaccharide as ahead group
which carbon of sphingosine has the hydrocarbon chain attached to
C3
describe what each carbon in sphingosine is bonded to
C1: head group
C2: fatty acid
C3: hydrocarbon chain
where are glycosphingolipids commonly located
in the outer layer of the plasma membrane
what is a cerebroside
single sugar head group with no net charge
what is a globoside
a multisugar head group with no net charge
what is a ganglioside
a multisugar head group with at least one sialic acid = net negative charge
describe how blood type is determined by gangliosides
the ganglioside will have the same base, but can have one of three different head groups
in regards to ganglioside structure, what is O type blood
just the base
in regards to ganglioside structure, what is A type blood
an extra acetylgalactosamine
in regards to ganglioside structure, what is B type blood
an extra galactose
what happens when you receive blood with a different sugar head group than your own
it will be recognized as foreign and attacked by your immune system
what is the role of lysosomal enzymes in gangliosides
they remove specific sugars one by one from gangliosides until only a ceramide molecule is left with a single H as a head group
what happens when lysosomal proteins malfunction
they cannot break down glycosphingolipids, leading to many diseases (lipids accumulate in tissues)
describe how tay-sachs disease is caused
caused by a malfunctioning enzyme that can no longer cleave a ganglioside called GM2. GM2 deposits accumulate in lysosomes causing blindness, paralysis, and death by 3 or 4 years old
