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!
Many LSD/CDGs are a result of a deficiency of what enzymes?
Endo and exoglycosidases.
What two things make up a proteoglycan? How big can they be? What major component do they make up?
A core protein O-linked to a GAG. Can get as big as bacteria. Major component of basement membrane.
What types of proteoglycans make up the basement membrane?
Type IV collagen, heparan sulfate, laminin.
What proteoglycan acts as a shock absorber? How?
Aggrecan is polar so it attracts water, acting like a sponge in the knee.
Are glycoproteins crucial for biological recognition?
Yes.
What does the filtering in Bowman’s capsule?
Proteoglycans - the GAG parts do the filtering.
What determines the blood groups?
Sugar residues on the ends of glycoproteins and glycolipids on cell surface.
Name five functions of glycosylation of proteins.
- Assist in protein folding in ER
- Intracellular protein folding and transport
- First line of defense in innate immunity.
- Determines half-life of serum proteins
- Direct cellular trafficking in vascular system.
What is defective in I Cell disease?
The M6P receptor that tells the golgi where to send proteins.
Name the structures responsible for leukocyte trafficking/binding.
Both leukocytes and endothelial cells have proteins on the cell surface called selectins. Both have sugars on cell surface. The sugars on the cells bind to the other cells’ lectin domains on the protein (called a selectin). Damage from infection or tissue damage expose these elements, so the leukocytes get bogged down and aggregate where they are needed.
What do people who are deficient in leukocyte adhesion suffer from?
Leukocyte adhesion deficiency II, a defect in fucosylation (glycosylation of fructoses). These folks get repeated infections.
Is O-Glc-Nac (O-linked N-acetylglucosamine) a glycoprotein that is secreted, faces extracellularly, or remains in the ER lumen?
No, it is the only o-linked glycoprotein that is not found in these hydrophilic environments.
