Lecture 13: Carbohydrate Conjugation Flashcards
What is a hexose?
Name a common example.
A six-carbon sugar. Glucose is an example of a hexose.
What is a pentose?
Name a common example.
A five-carbon sugar. Ribose is an example of a pentose.
Name a carbohydrate that is an aldehyde.
Glucose.
Name a carbohydrate that is a ketone.
Fructose.
True or false?
Glucose, galactose, and mannose are all stereoisomers of the same chemical structure.
True.
What is a glycosidic bond and where are they found?
The charecteristic bond through an anomeric carbon of a sugar. It may be an alpha (hydroxyl down) or beta conformation (hydroxyl up).
What kind of polysaccharide makes up dental plaque?
Dextrans.
Why are mammalian enzymes unable to digest polysaccharides such as dextrans or cellulose?
Cellulose is linked via beta 1-6, while dextrans is linked via alpha 1-6.
Mammalian enzymes are not capable of cleaving these bonds.
How can one differentiate the starches amylose and amylopectin?
Although amylose and amylopectin are both homopolymers of glucose linked primarily through alpha 1-4 linkages, only amylopectin branches via alpha 1-6 linkages.
What is glycogen?
A homopolymer of glucose linked via alpha 1-4 linkages with alpha 1-6 branching approximately every 8-10 residues.
What is dextrans?
A homopolymer of glucose linked via alpha 1-6. Synthesized by bacteria and is partially responsible for dental plaque.
What are the five major glocosaminoglycans?
- Hyaluronate
- Chondroitin sulfate
- Keratan sulfate
- Dermatan sulfate
- Heparin
What is the general structure of a glycosaminoglycan?
Long linear polysaccharides with repeating disaccharide units with considerable negative charge (including sulfate).
What are glycolipids (e.g. gangliosides) composed of?
They are lipids modified with sugars.
What is glycation?
The non-enzymatic glycosylation of proteins that occurs by a simple reaction of a protein side chain and a carbohydrate.
What is the clinical relevance of glycation?
Since we know the rough half life of an erythrocyte, one can calculate the % of hemoglobin that has been glycated to form hemoglobin A1c…a 3 month “average” of blood sugar levels.
How is enzymatic conjugation of carbohydrates achieved?
Activation of the sugar by formation of sugar-nucleotides, such as UDP-glucose.
How is the enzymatic formation of polysaccharides performed?
By enzymatic addition of one sugar at a time, using an enzyme of the correct specificity and the appropriate substrate.
Where is the only location of glycoproteins (with the exception of O-GlcNac)?
“Outside” of the cell, such as in the lumern of the ER, ectoplasmic face of the plasmolemma, or secreted from the cell.
How are O-linked structures constructed?
O-linked structures are built one sugar at a time on serine or threonine residues.
How are N-linked structures constructed?
N-linked structures are initially added in a 14-sugar block to asparagine constructed on a dolichol phosphate lipid.
True or false?
The initial transfer to N (in N-linked structure construction) is cotranslational (occuring while translation is underway) in the endoplasmic reticulum.
True.
What happens to both N and O linked carbohydrate structures once they are constructed in the ER?
They are processed as they are trafficked through the Golgi apparatus.
What is the relationship between lysosomes and glycoprotein/polysaccharide sugars?
The lysosome contains many enzymes that can degrade glycoprotein/polysaccharide sugars.
What is an LSD that occurs from a single defective enzyme?
Pompe disease.
What kind of diseases result from the lysosomes inability to degrade its contents?
Lysosomal storage diseases, or LSDs.
What LSD results from the complete lack of enzymes in the lysosome due to a trafficking/targeting defect?
I-Cell disease. It results from a failure of the mannose-6-phosphate trafficking system.
How are LSDs characterized?
By their cellular inclusions.
What are proteoglycans and why are they named as such?
The suffix is what the majority is.
Therefore, these molecules are mostly sugar (>90%) and a small amount protein.
Where can one find proteoglycans?
In the matrix that makes up tissue structure, such as cartilage, dentin, and predentin.
How do proteoglycans provide cushioning?
They are hydrated.
Other than mechanical purposes, what roles do proteoglycans have?
Because of their negative charge, they can also bind growth factors as well as chemokines/cytokines.
In a general sense, what is one of the main purposes of glycosylation?
Biological recognition.
How does protein recognition of carbohydrate structures occur?
Via lectin domains.
What contributes to the difference in ABO blood groups?
Carbohydrate structures.
How do viruses (such as influenza) or bacteria (such as H. pylori) infect cells?
They hijack the carbohydrate recognition system.
What is the role of carbohydrates in leukocyte migration/rolling?
They mediate the cell-cell contact between them and the endothelial cells. These interactions can initiate the process of invading into the tissue.
What is the role of carbohydrate binding inside the cell’s ER?
Carbohydrate binding mediates chaperone-mediated protein folding in the ER
What is the role of carbohydrate binding in the golgi apparatus?
It helps to mediate trafficking of enzymes to the lysosomal compartment, as in the mannose-6-phosphate trafficking system.
