Unit 5 Glycosides and Glycolipids
What is a glycoside?
a glycoside is a molecule in which at least one monosaccharide is attached to another molecule through the anomeric hydroxyl of the monosaccharide
Is a polysaccharide a glycoside? Why?
a polysaccharide is not a glycoside because the binding partner of a glycoside is not another sugar, although it does have glycosidic bonds as in polysaccharides
Where are monosaccharides attached to molecules?
monosaccharides are mainly attached to hydroxyl groups, except the amide group of asparagine in proteoglycans and glycoproteins, and the carboxyl group of bilirubin
The nucleotide-activated form is specific for a given monosaccharide. It is usually UDP, but there are three exceptions, what are they?
most sugars are UDP activated to be attached to another molecule; the three exceptions to this include GDP-mannose, GDP-L-fucose, CMP-N-acetylneuraminic (sialic) acid
What provides energy for the formation of a glycosidic bond?
the hydrolysis of the nucleotide-linkage provides energy for the formation of the glycosidic bond
What is UDP-glucose used to synthesize?
UDP-glucose is used to synthesize glycogen, proteoglycans, glycoproteins, glycolipids, UDP-glucuronate, UDP-glactose > lactose
What is UDP-glucuronate used to synthesize?
UDP-glucuronate is used to synthesize bilirubin (+ bilirubin= bilirubin diglucuronide), glucuronides (steroids, drugs, xenobiotics, bilirubin) -OH, UDP-xylose (GAGs), iduronate (GAGs), proteoglycans, glycoproteins
How is UDP-glucuronate synthesized?
UDP-glucose is oxidized by UDP-glucose dehydrogenase + NAD+ to form UDP-glucuronate
Bilirubin is the degradation product of what? How is it excreted from the body?
the heme group of hemoglobin is degraded to bilirubin; (2) glucuronate residues are added to bilirubin in the liver to increase solubility; bilirubin diglucuronide is exreted into the bile
What enzyme adds glucuronate to bilirubin?
bilirubin glucuronyltransferase adds glucuronate to bilirubin
What is the function of glucuronyltransferases?
the function of glucuronyltransferases is to add glucuronate to hormones and drugs in the liver, and excrete them in the urine or bile; eg estrogens, progesterone, triiodothyronine, morphine
Glycolipids are a subgroup of what kind of lipids?
glycolipids are a subgroup of sphingolipids and they include cerebrosides, sulfatides, globosides, gangliosides
What is the carbohydrate on a cerebroside, sulfatide, globoside, and ganglioside?
carbohydrate on- cerebroside: single glucose or galactose, sulfatide: sulfated galactose, globoside: neutral oligosaccharide, ganglioside: acidic oligosaccharide (contains sialic acid)
What are four glycolipid functions?
glycolipid functions: outer layer of plasma membrane, brain and peripheral nervous system, myelin sheets, blood group antigens (w/ glycoproteins)
Genes that code of glycosyltransferases determine what about a person's blood?
genes that code for glycosyltransferases determine a person's blood type
Ceramide is synthesized by what? and where does this occur?
ceramide is synthesized by serine, palmitoyl CoA, and fatty acy CoA; this takes place in the liver; glycolipid synthesis starts in the ER and ends in the golgi
What is the defective process in Pompe disease?
the defective process in pompe disease is glycogen degradation
What is the defective process in Mucopolysaccaridoses?
the defective process in mucopolysaccaridoses is GAG degradation
What is the defective process in Sphingolipidoses?
the defective process in sphingolipidoses is sphingolipid degradation
What is the defective process in Mucolipidoses (I-cell)?
the defective process in mucolipidoses is the targeting of lysosomal enzymes (lack of Man-6-P)
Deficient enzymes and accumulated metabolites in GM1 gangliosidosis
GM1 gangliosidosis: deficient enzyme- beta galactosidase, accumulated metabolites- GM1 gangliosides and KS
Deficient enzymes and accumulated metabolites in Tay-Sachs
Tay-Sachs: deficient enzyme- beta-hexosaminidase A, accumulated metabolites- GM2 gangliosides
Deficient enzymes and accumulated metabolites in Sandhoff
Sandhoff: deficient enzyme- beta-hexosaminidase A and B, accumulated metabolites- GM2 gangliosides, globosides
Deficient enzymes and accumulated metabolites in Fabry
Fabry: deficient enzyme- alpha-galactosidase, accumulated metabolites- globosides
Deficient enzymes and accumulated metabolites in Gaucher
Gaucher: deficient enzymes- glucocerebrosidase, accumulated metabolites- glucocerebroside
Deficient enzymes and accumulated metabolites in Metachromatic Leukodystrophy
Metachromatic Leukodystrophy: deficient enzyme- arylsulfatase A, accumulated metabolites- sulfatides
Deficient enzymes and accumulated metabolites in Krabbe
Krabbe: deficient enzymes- galactocerebrosidase, accumulated metabolites- galactocerebroside
Deficient enzymes and accumulated metabolites in Niemann-Pick
Niemann-Pick: deficient enzymes- spingomyelinase, accumulated metabolites- sphingomyelin
Deficient enzymes and accumulated metabolites in Farber
Farber: deficient enzymes- ceraminidase, accumulated metabolites- ceramide
Many sphingolipid storage diseases have what kind of common symptoms?
many sphingolipid storage diseases have neurological symptoms