L13- Carbohydrate Conjugation Flashcards
Which carbon of monosaccharides is chemically reactive?
The anomeric carbon.
What is a glycoside?
The product of the condensation of a sugar with a hydroxyl-containing molecule.
What is the difference between a glucoside and a galactoside?
Glucosides are glycosides that have a glucose, whereas galactosides have a galactose.
What is a glycosidic bond?
A covalent bond that joins a sugar to the hydroxyl group of another molecule.
Maltose is composed of which sugars bound in what linkage?
Two molecules of glucose in an alpha(1->4)-linkage.
Lactose is composed of which sugars bound in what linkage?
Galactose and glucose in a beta(1->4)-linkage.
Sucrose is composed of which sugars bound in what linkage?
Glucose and fructose in an alpha(1->2)-linkage.
What is the composition and structure of amylose?
Amylose is a starch composed of glucose molecules in alpha(1->4)-linkages. Its structure is that of an unbranched polymer that typically forms a helical coil within cells.
What is the composition and structure of amylopectin?
Amylopectin is a starch composed of glucose polymers arranged in alpha(1->4)-linkages. It has branches in alpha(1->6)-linkages every 10-12 residues.
What is the composition and structure of glycogen?
Glycogen is a carbohydrate composed of glucose polymers arranged in alpha(1->4)-linkages. It has branches in alpha(1->6)-linkages every 8-10 residues and it exists as spherical particles in cells.
What is the composition and structure of cellulose?
Cellulose is composed of glucose polymers arranged in beta(1->4)-linkages. It is typically unbranched.
What is the composition and structure of dextrans?
Dextrans are composed of glucose polymers arranged in alpha(1->6)-linkages. They have some branches in alpha(1->3)-linkages.
What are glycosaminoglycans (GAGs)?
They are long unbranched polysaccharides of repeating anionic disaccharides. They may be sulfated and are an important component of connective tissues.
What is a proteoglycan?
Glycosaminoglycans that are covalently linked to a protein.
Which glycosaminoglycan (GAG) is not linked to a core protein?
Hyaluronic acid.
Alpha(1->4)- vs. beta(1->4)-linkages. Which can we NOT digest?
Beta(1->4)-linkages.
What is the composition and location of hyaluronic acid?
Hyaluronic acid is composed of repeating disaccharides of D-glucuronic acid and N-acetylglucosamine. It is typically found in connective tissue like synovial fluid in joint spaces and in the vitreous fluid of the eye.
Which chemical reaction involves the formation of a Schiff base between the aldehyde of a sugar and the amino group of a protein to generate a ketoamine?
Glycation.
True or False. Glycation is a form of tissue damage.
True.
What is the clinical significance of hemoglobin A1c (HbA1c)?
HbA1c provides a 3-month ‘history’ of blood glucose levels.
What is aggrecan?
It is a proteoglycan (composed of chondrotoin sulfate attached to collagen type II) that acts as a shock absorber by cycling water in and out of cartilage.
Which nucleotide is NOT involved in the activation of sugars?
Adenine.
Which amino acids are involved in N-linked glycosylation?
Asparagine (almost always).
Which amino acids are involved in O-linked glycosylation?
Serine and threonine.
What is glycosylation?
An enzymatic reaction for secreted or extracellular protein (including proteins that are meant to be stored in the ER lumen).
Which glycoprotein is typically NOT secreted from cells?
O-linked N-acetylglucosamine (O-GlcNac).
In which cellular compartment are O-linked glycoproteins usually glycosylated?
The Golgi apparatus.
Which class of enzymes adds sugars to a growing O-linked glycoprotein?
Glycosyltransferases.
True or False. O-links of glycoproteins have carbohydrate molecules first added as a pre-assembled 14 sugar block.
False. The statement is true for N-linked glycoproteins.
What lipid carrier molecule is used for the synthesis of the branched oligosaccharide of N-linked glycoproteins?
Dolichol phosphate.
Which sugars are used for the synthesis of the initial branched chain oligosaccharide of N-linked glycoproteins?
N-acetylglucosamine, mannose and glucose.
Where in the cell are sugars added to proteins to form N-linked glycoproteins?
The ER membrane.
Which antibiotic inhibits the addition of N-acetylglucosamine-phosphate to dolichol phosphate?
Tunicamycin.
What class of enzymes is responsible for degradation of glycoproteins?
Glycosidases.
Deficiency of acid glucosidase results in what storage disease?
Pompe’s syndrome.
What is the enzymatic defect in Hunter syndrome?
Iduronate sulfatase.
What are proteoglycans?
Macromolecules consisting of polysaccharide glycosaminoglycan chains that are attached to core proteins.
What is the most abundant glycosaminoglycan in the human body?
Condrotoin sulfate.
Where is keratan sulfate type I typically found in the human body?
The cornea.
Where is keratan sulfate type II typically found in the human body?
Cartilage.
Which class of proteins bind carbohydrates?
Lectins.
What is the difference between the terminal sites of Type A, B and O blood groups?
Type A blood has UDP-N-acetylgalactosamine as a terminal residue, Type B has UDP-galactose and Type O has neither.
H-pylori preferentially binds to gastric epithelial cells of individuals with which blood type?
O-type.
