Lecture 13 Flashcards
(23 cards)
What is a glycoprotein?
A protein with one or more covalently attached carbohydrate chains (glycans).
What is glycosylation?
The enzyme-catalyzed attachment of glycans to proteins or lipids.
What are the two main types of glycosylation in proteins?
O-linked glycosylation (attached to Ser or Thr residues).
N-linked glycosylation (attached to Asn residues).
What is a glycosidic bond?
A covalent bond formed between the anomeric carbon of a sugar and another molecule (often another sugar or a protein/lipid).
Which amino acids are involved in O-linked glycosylation?
Serine (Ser) and Threonine (Thr).
Which sugar is commonly linked in O-linked glycosylation?
N-acetyl galactosamine (GalNAc).
Which amino acid is involved in N-linked glycosylation?
Asparagine (Asn).
Which sugar is commonly linked in N-linked glycosylation?
N-acetyl glucosamine (GlcNAc).
What is the consensus sequence for N-linked glycosylation?
Asn-X-Ser/Thr (where X can be any amino acid except Proline).
What are the structural differences between O-linked and N-linked glycoproteins?
O-linked glycans are often shorter and less branched.
N-linked glycans have a conserved core structure and are more complex.
What are the key functions of protein glycosylation?
Protection from proteolysis (enzymatic degradation).
Increased hydrophilicity, improving solubility and lubrication.
Mediating cell-cell interactions (e.g., immune response, tissue formation).
Recognition by immune cells (e.g., macrophages recognize glycosylated antibodies).
How does glycosylation affect antibody function?
Glycosylation of IgG antibodies aids in macrophage recognition and phagocytosis of antigen-antibody complexes.
What is the role of glycoproteins in blood circulation?
Surface glycoproteins (e.g., glycophorin) make erythrocytes (RBCs) more hydrophilic, preventing clumping and easing capillary flow.
What is the role of glycoproteins in blood type determination?
Blood types (A, B, AB, O) are defined by differences in glycosylation patterns on erythrocyte membrane proteins.
Type A: Extra N-acetyl galactosamine.
Type B: Extra galactose.
Type O: No additional sugar.
What is an example of a secreted O-linked glycoprotein?
Mucins (found in mucus and snail slime) trap and flush out irritants.
How do antifreeze glycoproteins work in Antarctic fish?
They bind to ice crystals to prevent further crystallization, helping the fish survive in subzero temperatures.
What are the key glycoproteins in the influenza virus?
Hemagglutinin (H): Binds to host cell glycoproteins rich in sialic acid, allowing viral entry.
Neuraminidase (N): Hydrolyzes sialic acid to release new virions.
Why do influenza vaccines need to be updated yearly?
Hemagglutinin and neuraminidase rapidly evolve, altering viral glycoprotein recognition.
What is a glycan?
A general term for carbohydrate chains, including both oligosaccharides and polysaccharides.
What is the mechanism of Oseltamivir (Tamiflu)?
It mimics sialic acid and inhibits neuraminidase, blocking virus release from infected cells.
What is the difference between a homopolymer and a heteropolymer glycan?
Homopolymer glycan: Composed of only one type of monosaccharide.
Heteropolymer glycan: Composed of different types of monosaccharides.
What are the core sugars found in N-linked glycoproteins?
Mannose (Man) and N-acetyl glucosamine (GlcNAc).
What is the role of fucose and sialic acid in glycosylation?
Fucose (Fuc): Important for cell signaling and immune recognition.
Sialic acid (Sia): Often found at the ends of glycan chains, influencing interactions with other molecules.
