Q: Which repeating disaccharide unit is found in heparin, a glycosaminoglycan?

$$\text{GlcA2S} or$$ $$\text{IdoA2S}$$ - $$\alpha(1 \rightarrow 4)$$ - $$\text{GlcNS3S6S}$$

Question 1

Which of the following best describes the structural role of peptidoglycan in bacterial cell walls?

Accepted Answer

It is a heteropolysaccharide of alternating N-acetylglucosamine and N-acetylmuramic acid units, cross-linked by peptides.

Question 2

Penicillin inhibits bacterial cell wall synthesis by interfering with which specific enzymatic process?

Accepted Answer

Blocking the action of transpeptidases that form pentaglycine crosslinks in peptidoglycan.

Question 3

Which glycosidic linkage connects N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (Mur2Ac) in peptidoglycan?

Accepted Answer

$$\beta(1 \rightarrow 4)$$

Question 4

Lysozyme, found in tears and bacterial viruses, acts on peptidoglycan by:

Accepted Answer

Cleaving the $$\beta(1 \rightarrow 4)$$ glycosidic bond between N-acetylglucosamine and N-acetylmuramic acid.

Question 5

Which of the following is TRUE regarding proteoglycans in the extracellular matrix?

Accepted Answer

Proteoglycans consist of proteins covalently linked to one or more glycosaminoglycan chains, with the polysaccharide making up the greater part of the weight.

Question 6

Which repeating disaccharide unit is found in heparin, a glycosaminoglycan?

Accepted Answer

$$	ext{GlcA2S} or$$ $$	ext{IdoA2S}$$ - $$\alpha(1 ightarrow 4)$$ - $$	ext{GlcNS3S6S}$$

Question 7

Which amino acid side chain is involved in N-linked glycosylation of glycoproteins?

Accepted Answer

Asparagine

Question 8

Glycoproteins are considered 'information-rich' molecules because:

Accepted Answer

They have diverse sugar units, branching patterns, and stereochemistry of glycosidic linkages, allowing for complex recognition.

Question 9

Which of the following is a function of the carbohydrate portion of glycoproteins?

Accepted Answer

Facilitating protein targeting and localization within a cell.

Question 10

Lectins are important in cell-cell recognition because they:

Accepted Answer

Bind with high affinity and specificity to carbohydrates in glycoconjugates.

Question 11

A defect in hexosaminidase A, which removes GalNAc from gangliosides, leads to which disease?

Accepted Answer

Tay Sachs disease

Question 12

Differences in human blood group antigens (A, B, O) are due to:

Accepted Answer

Differences in oligosaccharide structures on cell surface sphingoglycolipids.

Question 13

Which property of glycans allows them to act as specific recognition molecules?

Accepted Answer

Multiple points for linkage, branching, and stereochemistry, resulting in high structural diversity.

Question 14

Which of the following best explains why glycan shields on viral proteins, such as the SARS-CoV-2 spike, contribute to immune evasion?

Accepted Answer

Glycans mask viral protein epitopes, reducing recognition by host antibodies.

Question 15

Which of the following is a correct example of a glycosaminoglycan and its function?

Accepted Answer

Hyaluronate; provides a porous gel in the extracellular matrix for cell migration.

Question 16

Which of the following interactions is most likely to contribute to lectin binding to carbohydrates?

Accepted Answer

Hydrophobic interactions between the indolyl moiety of tryptophan and the carbohydrate.

Question 17

Which statement about glycoprotein recognition by viruses is correct?

Accepted Answer

Avian influenza virus binds only to cell receptors with avian-type glycans, not human-type.

Question 18

Which of the following best describes the composition of the extracellular matrix?

Accepted Answer

A meshwork of glycosaminoglycans and proteoglycans embedded with fibrous proteins.

Question 19

Which of the following is a plausible mechanism by which bacteria develop resistance to penicillin?

Accepted Answer

Producing enzymes (e.g., $$\beta-$$lactamases) that hydrolyze the $$\beta-$$lactam ring of penicillin.

Carbohydrates and Glycobiology: Glycoconjugates, Cell Walls, and Recognition

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