Biochemistry Lecture 13 - Carbohydrates Flashcards
Does an alpha sugar have it’s anomeric hydroxyl group above or below the plane?
Below the plane.
Are stereoisomeric sugars metabolized differently?
Yes, they are recognized by different enzymes.
What is one specific carbon atom that can form glycosidic linkages?
The anomeric carbon.
What is the storage polysaccharide in humans?
Glycogen.
What type of linkages are found in glycogen?
1,4 linkages with occasional 1,6 branches.
What linkages form amylose and amylopectin and what is the difference between those two?
They both have alpha (1 -> 4) linkages but amylopectin has alpha (1 -> 6) branches every ~12 residues.
What sugar is glycogen made of and what are the linkages?
Glucose linkages via alpha (1 -> 4) linkages.
What are glycosaminoglycans?
They are repeating disaccharides in a linear chain (up to 500 residues) that are negatively charged with sulfate.
What makes up maltose?
Two glucose
What makes up lactose?
Glucose + galactose.
What makes up sucrose?
Glucose + fructose.
What is the polysaccharide that cannot be digested? What sugar is it made of? What are the links?
Cellulose = glucose with beta (1,4) linkages.
Is heparin a GAG?
Yup
What is the difference between glycosylation and glycation?
Glycosylation is enzyme-catalzyed and requires activation of the anomeric oxygen with a UDP group (nucleotide). It is done for polysaccharide bond formation (glycosidic linkage) and also for addition to proteins. Glycation is not enzyme catalyzed and is damaging.
What is HbA1C and what is its clinical significance?
If glucose is high in blood for extended periods, it will glycate with Hb, generating HbA1C. Clinically the ratio of Hb to HbA1C can give a history of glucose levels in the past 2-3 months.
Where do enzymatically-glycosylated O-linked glycoproteins usually end up? What is the exception?
Secreted, on the ectoplasmic side of a cell, or in the ER lumen. Except O-GlcNac
What AA residue can participate in N-linked glycosylation?
Asparagine.
What AA residues can participate in O-linked glycosylation?
Serine or threonine
Can protein glycosylation lead to complex structures?
For sho.
In polysaccharide chain synthesis, what does the enzyme need to recognize and bind?
- The given sugar-UDP
2. A given acceptor for the sugar
What are the enzymes called involved in each step of glycosylation?
Transferases.
How many transferases are required per step in O-linkages formation.
One is required for each step in O-linkage formation.
Described how and where N-linked sugars are synthesized.
They are also done one at a time on a LIPID called dolichol phosphate. The lipid is associated with the ER membrane. The 14-residue polysaccharide is then transferred to the protein as a unit.
Can further glycoprotein/proteoglycan processing occur throughout the secretory pathway?
Yes, it does!