73 terms

Synthesis of Glycosides, Lactose, Glycoproteins, and Glycolipids

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Describe the role of UDP-glucose in synthesis of other molecules
transfer sugars from nucleotide sugars (ex: UDP-Glucose) to an alcohol or other nucleophilic group
Define the general role of glycotransferases
Negatively charged carboxyl group of the glucuronate increases water solubility and allows otherwise nonpolar compounds to be excreted in the urine or bile
Explain how the formation of glucuronides can increase excretion
Glucuronides
Glucuronate is an intermediate in the formation of
nonpolar compound
Glucuronides are produced when the glucuronate is attached to the hydroxyl group of a
degradation of inositol
Glucuronate is present in the diet and can be formed from the
Bilirubin
What is the degradation product of heme?
reticuloendothelial
Bilirubin is formed in what system
Diglucuronide
What is actively transported into the bile for excretion
plasma
Bilirubin is only slightly soluble in
monoglucuronide, diglucuronide
Once Glucuronate is transported to the liver bound to albumin, what two residues are transferred to two carboxyl groups on bilirubin
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Describe/outline the two steps of lactose synthesis (reactions)
No. It changes the alpha beta position
Does UDP-glucose 4-epimerase transfer the hydroxyl group from UDP-glucose to UDP-Galactose? What does it do?
epimerase
Identify the enzyme responsible for the epimerization of UDP-glucose to UDP-galactose
Glucosamine 6-P
List the precursor to actylglucosamine
Rare fatal childhood disease (1-5 years life expectancy). Due to lack of mannose phosphate, lysosomal enzymes are secreted from the cells
Briefly describe I-cell disease
lysosomal enzymes lacking the mannose phosphate marker that targets them to lysosomes.
What is missing in I-cell disease?
golgi apparatus
The deficient enzyme in I-cell is a phosphotransferase located in the
lysosomal proteins based on their 3D structure and tags them for transport to the lysosome
The phosphotransferase that is defective in I-cell disease recognizes
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What is the 2 step process to tagging (found in normal humans who don't have I-cell disease)
Progressive fatal genetic condition that affects nerve cells in the brain. Ability to degrade glycolipid results in the accumulation of that lipid in residual bodies within nerve cells
Briefly describe Tay-Sachs disease
Hexosamindase A α-unit.
What enzyme activity is lost in Tay-Sachs disease?
Hydrolyzes a specific bond between N-acetyl-D-galactosamine and D-galactose residue in the polar side of the ganglioside (affects nerve cells in the brain)
What does Hexoamindase A do
ganglioside Gm₂, but not the globoside
What is accumulated in Tay-Sachs disease?
Globoside
What accumulates in Sandhoff disease
Sandhoff disease. Loss of β-subunit. Accelerated time table
What is a similar disease to Tay-Sachs?
4-base insertion occurs. Reading frame is altered, premature stop codon is introduced further down so that no functional α-subunit can be produced
How is the HexA gene mutated in Tay-Sachs disease
lipid with carbohydrate attached
Glycolipid
contain oligosaccharide chains (glycans) that are covalently attached to *polypeptide* side-chains
Glycoproteins contain __________ that are covalently attached to _____________
disaccharide sugar derived from galactose and glucose that is found in milk
Lactose
A molecule in which a sugar is bound to another functional group via a glycosidic bond
Glycosides
Activated Sugar Nucleotides
______________ are the precursor to Glycosides, Glycoproteins and Glycolipids
Glycogen, Lactose, UDP-glucuronate, Glucuronides, Carbohydrate chain in prteoglycans, glycoproteins, and glycolipids
UDP-Glucose is a precursor of
glycotransferase reactions
UDP-glucose is a substrate for many
covalent bond that joins a carbohydrate (sugar) molecule to another group
Glycosidic bond
the use of UDP
What provides energy for the formation of a new bond in a Glycotransferase reaction
UDP-glucose
UDP-Glucuronate is synthesized from
other sugars and of glucuronides
UDP-Glucuronate serves as a precursor to
compounds of glycosides
"-ide" indicates
glucuronides
UDP-Glucurronate is transferred to carboxyl groups of bilirubin or the alcohol groups of steroid, drugs and xenobiotics to form
D-xylulose 5-phosphate (intermediate of PPP)
Glucuronate can reenter the pathways of glucose metabolism through reactions that eventually convert it to
mammary gland of the adult female for short periods of time during lactation
Lactose is synthesized only in the
lactose synthase
Lactate synthesis is catalyzed by
lowers the Km of galactosyltransferase, thus increasing the rate of lactose synthesis
α-lactalbumin is a part of Lactose synthase. What does it do
transfers galactose to glucose
Galactosyltransferase, part of Lactose synthase, does what
Provides for relatively specific and different functions such as targeting a protein towards a membrane and providing cell surface recognition sites
Why is there a large variety of sugars attached to proteins and lipids?
glucose
All the different sugars found in glycosaminoglycans, gangliosides, and other compounds can be synthesized from
fructose 6-phosphate
Mannose and glucose are interconverted at the level of
GDP- fructose
GDP-mannose is the precursor of
glucosamine 6-phosphate
Animo sugars are derived from
N-acetylneuraminic acid
N-acetylmannosamine is the precursor of
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Formation of N-Acetylglucosamine-6-phosphate
serine/threonine or asparagine residues in the protein
Glycoproteins contain short carbohydrate chains covalently linked to either
hormones, antibodies, enzymes, and as structural components of extracellular matrix (Collagen)
Glycoproteins serve as
mucus-producing cells
Glycoproteins are secreted as
salivary gland (ex: mucin)
What is an example of a gland that produces glycoproteins
enzymes that degrade various types of cellular and extracellular material
Lysosomal glycoproteins serve as
receptor
Mannose-P targets lysosomal glycoproteins to lysosomes via its
Its hydrophobic regions remain attached to the cell membrane, and the carbohydrate portion extends into the extracellular space
How does a lysosomal glycoprotein work
carbohydrate portion. You need it to extend into the extracellular space
Failure to add what portion of the lysosomal glycoproteins leads to lysosomal storage diseases?
ER
The protein portion of glycoprotein is synthesized on the
lumen of the ER and Golgi complex
Carbohydrate chains are attached to glycoproteins at the
transferring branched sugar chains to the amide nitrogen of asparagine residues. Involved in synthesizing the High-Mannose form of Oligosaccharides
Dolichol phosphate is involved in
ER through the Golgi complex
Sugars are removed and added as a glycoprotein moves from the __ through the __________________
GDP-sugars
What are the precursors for the addition of mannose and L-fucose
Dolichol
What serves as an anchor during the synthesis of the high-mannose form of oligosaccharides
sphingosine
Glycolipids are derivatives of the lipid
cerebrosides and gangliosides
Sphinoglipids include the
ceramide
Glycolipids contain _____ with carbohydrate moieties attached
ceramide and UDP-glucose or UDP-galactose
Cerabrosides are synthesized from
oligosaccharide products from UDP-sugars and CMP-NANA
Gangliosides contain
sphinolipidoses
Defects in the degradation of sphingolipds leads to
Glutamine
What donates the amide Nitrogen to fructose 6-phosphate to form glucosamine 6-phosphate
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