Chapter 46

Question 1

Which of the following statements is true about glycoproteins?
A) Glycoproteins contain only N-linked oligosaccharides.
B) Glycoproteins consist of proteins covalently bonded to carbohydrates.
C) Glycoproteins are found only in the extracellular matrix.
D) Glycoproteins are the same as proteoglycans.

Answer 1

B) Glycoproteins consist of proteins covalently bonded to carbohydrates.
Rationale: Glycoproteins are proteins that have carbohydrate groups attached to the polypeptide chain. These carbohydrates can be either N-linked or O-linked, and glycoproteins serve various functions in and outside of cells.

Question 2

What is the main role of glycoproteins in the cell membrane?
A) Energy storage
B) Structural support
C) Cell-cell recognition and signaling
D) DNA replication

Answer 2

C) Cell-cell recognition and signaling
Rationale: Glycoproteins play an essential role in cell-cell interactions, signaling, and recognition, particularly at the cell surface, where they interact with other cells and molecules.

Question 3

N-linked glycosylation occurs in which part of the cell?
A) Cytoplasm
B) Golgi apparatus
C) Nucleus
D) Endoplasmic reticulum

Answer 3

D) Endoplasmic reticulum
Rationale: N-linked glycosylation, the attachment of carbohydrates to the nitrogen atom of asparagine residues, begins in the endoplasmic reticulum and is further processed in the Golgi apparatus.

Question 4

Which sugar is typically the initial sugar attached during N-linked glycosylation?
A) Glucose
B) Mannose
C) N-acetylglucosamine
D) Galactose

Answer 4

C) N-acetylglucosamine
Rationale: In N-linked glycosylation, the initial sugar that attaches to the asparagine residue of the protein is N-acetylglucosamine, which is part of the precursor oligosaccharide.

Question 5

O-linked glycosylation typically occurs at which amino acid residues?
A) Asparagine
B) Lysine
C) Serine and threonine
D) Glutamate

Answer 5

C) Serine and threonine
Rationale: O-linked glycosylation involves the attachment of sugar molecules to the hydroxyl group of serine or threonine residues in proteins, typically in the Golgi apparatus.

Question 6

What is the primary difference between glycoproteins and proteoglycans?
A) Glycoproteins contain more protein than carbohydrate, while proteoglycans have more carbohydrate than protein.
B) Proteoglycans are only found in prokaryotes.
C) Proteoglycans contain O-linked sugars, while glycoproteins contain N-linked sugars.
D) Glycoproteins contain only one sugar molecule, while proteoglycans contain multiple sugar molecules.

Answer 6

A) Glycoproteins contain more protein than carbohydrate, while proteoglycans have more carbohydrate than protein.
Rationale: Glycoproteins have a higher proportion of protein to carbohydrate, while proteoglycans are heavily glycosylated, with more carbohydrate than protein, often in the form of glycosaminoglycans.

Question 7

Which of the following is an example of a glycoprotein?
A) Collagen
B) Immunoglobulin G (IgG)
C) Chondroitin sulfate
D) Hyaluronic acid

Answer 7

B) Immunoglobulin G (IgG)
Rationale: Immunoglobulins (such as IgG) are glycoproteins that play a critical role in immune responses, with carbohydrate chains attached to their peptide backbone.

Question 8

What role do glycoproteins play in the immune system?
A) They transport oxygen.
B) They act as antigens and help in immune recognition.
C) They degrade pathogens.
D) They are responsible for antibody production.

Answer 8

B) They act as antigens and help in immune recognition.
Rationale: Glycoproteins serve as antigens on the surface of cells, contributing to immune recognition and the ability to distinguish between self and non-self.

Question 9

Which enzyme is responsible for the degradation of glycoproteins?
A) Glycosylase
B) Phosphatase
C) Glycosidase
D) Protease

Answer 9

C) Glycosidase
Rationale: Glycosidases are enzymes that catalyze the hydrolysis of glycosidic bonds in glycoproteins, leading to the breakdown of the carbohydrate component

Question 10

The clinical significance of glycoproteins is seen in which of the following conditions?
A) Diabetes
B) Inherited disorders of glycosylation
C) Hyperthyroidism
D) Osteoporosis

Answer 10

B) Inherited disorders of glycosylation
Rationale: Disorders of glycosylation are a group of genetic conditions that affect the glycosylation process, leading to a range of developmental and physiological abnormalities

Question 11

Which of the following is NOT a function of glycoproteins?
A) Cell-cell adhesion
B) Hormone receptor activity
C) Oxygen transport
D) Enzyme regulation

Answer 11

C) Oxygen transport
Rationale: Glycoproteins are involved in cell-cell adhesion, receptor activity, and enzyme regulation, but oxygen transport is primarily the function of hemoglobin, which is not a glycoprotein.

Question 12

In N-linked glycosylation, the carbohydrate moiety is linked to which amino acid residue?
A) Threonine
B) Asparagine
C) Serine
D) Lysine

Answer 12

B) Asparagine
Rationale: N-linked glycosylation occurs when a carbohydrate group is attached to the nitrogen atom of the amide group of asparagine residues in the protein.

Question 13

O-linked glycosylation typically begins in which cellular organelle?
A) Endoplasmic reticulum
B) Cytoplasm
C) Golgi apparatus
D) Nucleus

Answer 13

C) Golgi apparatus
Rationale: O-linked glycosylation primarily occurs in the Golgi apparatus, where sugars are attached to the hydroxyl groups of serine or threonine residues.

Question 14

Which glycoprotein is important for viral attachment to host cells?
A) Hemoglobin
B) Fibrinogen
C) Hemagglutinin
D) Elastin

Answer 14

C) Hemagglutinin
Rationale: Hemagglutinin is a glycoprotein found on the surface of viruses like influenza, which facilitates viral attachment to host cells by binding to sialic acid-containing receptors

Question 15

Which sugar is a common terminal residue found on glycoproteins involved in cell recognition?
A) Glucose
B) Mannose
C) Sialic acid
D) Ribose

Answer 15

C) Sialic acid
Rationale: Sialic acid is commonly found as a terminal residue on glycoproteins and plays a key role in cell recognition and signaling.

Question 16

Which congenital disorder is caused by defects in glycoprotein processing?
A) Congenital disorder of glycosylation (CDG)
B) Marfan syndrome
C) Cystic fibrosis
D) Duchenne muscular dystrophy

Answer 16

A) Congenital disorder of glycosylation (CDG)
Rationale: CDG is a group of inherited conditions caused by defects in glycoprotein processing, leading to multisystem involvement, including developmental delays and metabolic issues.

Question 17

Dolichol phosphate is involved in which process of glycoprotein biosynthesis?
A) N-linked glycosylation
B) O-linked glycosylation
C) Phosphorylation
D) Proteolysis

Answer 17

A) N-linked glycosylation
Rationale: Dolichol phosphate acts as a carrier for the oligosaccharide chain during the early stages of N-linked glycosylation in the endoplasmic reticulum.

Question 18

How are glycoproteins degraded in the lysosome?
A) By proteases
B) By lipases
C) By glycosidases
D) By hydrolases

Answer 18

C) By glycosidases
Rationale: Glycosidases in the lysosome break down the carbohydrate components of glycoproteins, facilitating their degradation.

Question 19

What is the clinical importance of glycoprotein hormones?
A) They regulate blood sugar levels.
B) They are involved in reproductive functions.
C) They maintain bone density.
D) They carry oxygen in the blood.

Answer 19

B) They are involved in reproductive functions.
Rationale: Glycoprotein hormones such as luteinizing hormone (LH), follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG) play key roles in regulating reproductive processes.

Question 20

Which of the following is a glycoprotein that plays a critical role in the blood coagulation cascade?
A) Prothrombin
B) Hemoglobin
C) Albumin
D) Fibrinogen

Answer 20

D) Fibrinogen
Rationale: Fibrinogen is a glycoprotein involved in the blood coagulation process, where it is converted to fibrin to form blood clots.

Question 21

The carbohydrate component of glycoproteins is important for which cellular process?
A) Transcription
B) Protein folding and quality control
C) DNA replication
D) Mitochondrial respiration

Answer 21

B) Protein folding and quality control
Rationale: The carbohydrate moieties of glycoproteins help in proper protein folding and quality control within the endoplasmic reticulum, ensuring that proteins are correctly folded before they are transported out of the cell.

Question 22

The basic structure of a proteoglycan consists of a core protein and a:

A) glycolipid.
B) glycosaminoglycan.
C) lectin.
D) lipopolysaccharide.
E) peptidoglycan.

Answer 22

B) glycosaminoglycan.

Question 23

In glycoproteins, the carbohydrate moiety is always attached through the amino acid residues:

A) asparagine, serine, or threonine.
B) aspartate or glutamate.
C) glutamine or arginine.
D) glycine, alanine, or aspartate.
E) tryptophan, aspartate, or cysteine.

Answer 23

A) asparagine, serine, or threonine.

Question 24

The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to:

A) amphipathic molecules.
B) hydrophobic molecules.
C) specific lipids.
D) specific oligosaccharides.
E) specific peptides.

Answer 24

D) specific oligosaccharides.

Question 25

The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to:

A) amphipathic molecules.
B) hydrophobic molecules.
C) specific lipids.
D) specific oligosaccharides.
E) specific peptides.

Answer 25

D) specific oligosaccharides.

Question 26

Why is it surprising that the side chains of tryptophan residues in proteins can interact with lectins?

Answer 26

D) because the side chain of tryptophan is hydrophobic and lectins are generally hydrophilic.

Question 27

Which of the following statements concerning sialic acid residues on glycoproteins is true?

A) Sialic residues on erythrocytes are recognized by lectins, leading to removal of the erythrocytes.
B) Sialic residues on ceruloplasmin are recognized by lectins, leading to removal of ceruloplasmin.
C) Sialic residues are removed by neuraminidases.
D) The anti-viral drug oseltamavir accelerates the removal of sialic acid residues.
E) Both A and B above

Answer 27

C) Sialic residues are removed by neuraminidases

Question 28

Which of the following is a serious pathologic consequence of uncontrolled Diabetes Mellitus where there is nonenzymic attachments of sugars to proteins?
● a. Glycosylation
● b. Glycoconjugation
● c. Glycation
● d. Glycans

Answer 28

C

Question 29

Which of the following glycoproteins regulate folding of proteins that are exported from a cell?
● a. Ceruloplasmin
● b. Calnexin
● c. Selectins
● d. Transferrin

Answer 29

A