Ch. 9: Glyconjugates/proteins/lipids Flashcards
What is a glycoprotein?
Proteins w/covalently attached polysaccharide chain
Glycoprotein fxn: structure
Example?
Collagen
Glycoprotein fxn: lubrication and protection
Examples?
Epithelial mucins
Synovial fluid
Glycoprotein fxn: transport
Ceruloplasmin (copper carrier)
Transferrin (iron carrier)
Glycoprotein fxn: Endocrine regulation
Thyrotropin
Chorionic gonadotropin
Erythropoietin
Glycoprotein fxn: catalysis
Examples?
Proteases
Nucleases
Glycosidases
Hydrolases
Glycoprotein fxn: Membrane receptors
Examples?
hormones (insulin)
Ach
Cholera toxin
Electromagnetic radiation (rhodopsin)
Glycoprotein fxn: antigens
Examples?
Blood group substances
Glycoprotein fxn: defense against infection
Examples?
Ig's Complement proteins Interferon Selectins Integrins
Glycoprotein fxn: cell-cell recognition and adhesion
Examples?
Fibronectin
Laminin
Chondronectin
Glycoprotein fxn: miscellaneous
Examples?
Glycophorin (intrinsic red blood cell membrane constituent)
Intrinsic factor (absorb dietary vit B12)
Clotting factors (fibrinogen)
a.a. in O-linked glycosidic linkages?
Type of attachment?
Serine
Threonine
Hydroxylated lysine
Hydroxylated proline
Simple attachment
a.a. in N-linked glycosidic linkages?
Type of attachment?
Asparagine
Complicated attachment
Beta-N-glycosidic link: N-acetylglucosamine and Asn
Found where?
Wide occurrence
Alpha-O-glycosidic link: N-acetylgalactosamine and ser/thr
Found where?
Mucus secretions
Blood group substances
Beta-O-glycosidic linkage: galactose & OH-lys
Found where?
Collagen
Beta-O-glycosidic link: xylopyranose & Ser
Found where?
Thyroglobulin
Proteoglycans
Where are glycoproteins synthesized? (Glycosylation)
ER and Golgi
How are glycoproteins made via glycosylation?
Sequential addition of monosaccharide units to non-reducing end ➡️ CHO chain
Which activated sugars act as precursors for glycosylation?
UDP-sugars
GDP-mannose
GDP-L-fructose
CMP-NANA
Membrane phospholipid involved in N-glycosylation?
Dolichol phosphate
sugars added to dolichol (ER membrane) ➡️ CHO chain transferred to Asn
What is non-enzymatic glycation?
Addition of CHO residues w/out complex enzymatic pathways
Hemoglobin A1c: linkage?
Short or long term glucose control indicator?
N-glycosidic link to N-terminal amino group of valine (each beta chain)
Long term (2-3 month lifespan)
Human serum albumin (HSA): produces what condensation product?
Short or long term glucose control indicator?
Fructosamine
Short term (1-3 week lifespan)
Human lens proteins (alpha, beta, gamma-crystallins): age-dependent, non-enzymatic glycation at?
Epsilon-amino groups of lys
Fxn of fibronectin?
Promotes attachment & subsequent spreading of many cell types
3 types of fibronectin?
Cell-surface: adhesion of cell w/ECM
Plasma: wound repair
Fetal: marker for risk for preterm delivery
Binding sites of fibronectin? (NH2 ➡️ S-S)
Fibrin, collagen, (3X), cells, heparin, fibrin
What are blood group antigens?
Oligosaccharides on surface of human RBCs
What determines antigenic variation of blood groups?
Specific glycotransferases which synthesize the specific oligosaccharides (enzymes inherited)
A antigen: what sugar is added?
N-acetylgalactosamine
B antigen: what sugar is added?
Galactose
O (H antigen): what sugar added?
None (no enzyme)
Blood type O: antigens present?
Antibodies in serum?
Serum type causing agglutination when mixed with RBCs?
H
Anti-A, Anti-B
None
Blood type A: antigens present?
Antibodies in serum?
Serum type causing agglutination when mixed with RBCs?
A
Anti-B
O, B
Blood type B: antigens present?
Antibodies in serum?
Serum type causing agglutination when mixed with RBCs?
B
Anti-A
O, A
Blood type AB: antigens present?
Antibodies in serum?
Serum type causing agglutination when mixed with RBCs?
A, B
None
O, A, B
All serum proteins are glycoproteins EXCEPT: ?
serum albumin (but can be glycated)
How does liver recycle glycoproteins? (steps)
Neuraminidase (sialidase) removes terminal sialic acid ➡️ exposes galactose (asialoglycoprotein) ➡️ binding to hepatocyte receptors ➡️ taken up ➡️ receptor-mediated endocytosis ➡️ lysosomal degradation
What is elevated in liver disease?
Plasma asialoglycoproteins
What is Guillain-Barré syndrome (GBS)?
Autoimmune disease (acute neuropathy)
Caused by antecedent, acute bacterial or viral infection
Also seen in children after vaccination
Describe molecular mimicry of C. jejuni
Lipopolysaccharides have terminal tetrasaccharides similar to human gangliosides GM1 ➡️ immune system confused ➡️ immune-mediated destruction of nerve fibers
