chapter 7 section 5

Question 1

What are glycoproteins?

Answer 1

Proteins with covalently attached carbohydrate (saccharide) groups; they play key roles in cell-cell recognition, signaling, and protein stability.

Question 2

What are the two main types of glycoprotein linkages?

Answer 2

N-linked and O-linked.

Question 3

How are N-linked saccharides attached in glycoproteins?

Answer 3

Via the amide nitrogen of asparagine residues.

Question 4

How are O-linked saccharides attached in glycoproteins?

Answer 4

To the hydroxyl groups of serine, threonine, or hydroxylysine residues.

Question 5

Which amino acids are most commonly involved in O-linked glycosylation?

Answer 5

Serine and threonine.

Question 6

What is the functional significance of glycoprotein carbohydrates?

Answer 6

They contribute to protein folding, stability, and mediate cell-cell interactions and recognition.

Question 7

What amino acid is the attachment point for N-linked saccharides in glycoproteins?

Answer 7

Asparagine.

Question 8

What are the three types of N-linked glycoproteins?

Answer 8

High mannose, complex, and hybrid (which combines features of high mannose and complex types).

Question 9

What is the structural role of O-linked saccharides in glycoproteins?

Answer 9

They often adopt an extended conformation resembling “bristle brushes,” which project functional domains above the glycocalyx.

Question 10

How do the extended O-linked structures affect glycoprotein function?

Answer 10

They enhance accessibility and interaction of the protein’s functional domains with the environment, aiding in cell recognition and signaling.

Question 11

What are some functions of N-linked oligosaccharides in glycoproteins?

Answer 11

They can alter chemical and physical properties of proteins, stabilize protein conformations, protect against proteolysis, and mark proteins for degradation when monosaccharides are cleaved

Question 12

How do antifreeze glycoproteins help polar fish survive subfreezing seawater?

Answer 12

They surround nascent ice crystals, inhibiting crystal growth, preventing tissue damage.

Question 13

What is the structure of the repeating disaccharide unit in antifreeze glycoproteins?

Answer 13

It consists of galactose and N-acetyl-galactosamine linked to threonine residues.

Question 14

How can oligosaccharide cleavage serve as a timing device for protein degradation?

Answer 14

Progressive cleavage of sialic acid residues exposes galactose residues, which are then recognized by liver receptors, targeting the protein for degradation.

Question 15

Which amino acid residues in antifreeze glycoproteins are glycosylated?

Answer 15

Threonine residues.