Complex Carbohydrates

Question 1

Glycoconjugates have a core of ___ or ___

Answer 1

Protein or lipid

Question 2

What 3 groups make up glycoconjugates?

Answer 2

Glycoproteins

Proteoglycans

Glycolipids

Question 3

Glycosaminoglycans are heteropolysaccharides that are consituents of the ______ ______.

Answer 3

Extracellular matrix

Question 4

What are some of the general functions of protein glycosylation?

Answer 4

• Assist in folding
• Aid in solubility
• Stabilize against denaturation and degradation
• Target proteins to subcellular locations
• Recognition signals for lectins

Question 5

What are lectins?

Answer 5

Proteins that have high selectivity and high affinity for specific carbohydrates, bind carbs

Question 6

Protein glycosylation that is N-linked occurs on which amino acid residue?

Answer 6

Asparagine (Asn, N)

Question 7

Protein glycosylation that is O-linked occurs on which amino acid residue?

Answer 7

Serine

Question 8

Describe how a sugar moiety is added to a protein via N-linked glycosylation.

Answer 8

The sugar moiety (may be branched) is built onto a molecule of dilochol phosphate, which is a lipid carrier imbedded in the ER membrane. This process begins on the cytoplasmic side of the ER membrane by using UDP activated sugars to build the oligosaccharide on dilochol phospate. The sugar precursor is then flipped to the inside of the ER where oligosaccharide synthesis is completed. The entire moiety is then transferred to the protein as a whole sugar in the ER after the protein has been translated.

Question 9

N-linked glycosylation only occurs in the _______ (organelle).

Answer 9

ER

Question 10

In N-linked glycosylation, the sugar moiety is transferred to a molecule of ____ ____ (2wds) which is located in the ____ _____ (2wds).

Answer 10

Dilochol Phosphate

Er Membrane

Question 11

The presence of ____ in a sugar moiety on a protein indiates the protein will be retained in the ER.

Answer 11

Glucose

Question 12

Explain how glucosylation regulates protein exit from the ER.

Answer 12

In a normally folded protein, hydrophobic residues should not be accessible inside the ER b/c they will reside inside the protein core. Improperly folded proteins may have hydrophobic sites exposed and Glucosyl-transferase can recognize these hydrophobic sites and add glucose to any sugar moieties in this site. Chaperones then bind to the protein and prevent the proteins transport from the ER.

Question 13

Presence of _____ directs proteins to lysosomes.

Answer 13

Mannose-6-Phosphate

Question 14

What is I-cell disease?

Answer 14

This is a lysosomal storage disease that results from an inability to generate mannose 6 phosphate that results in inability to target proteins for lysosome. Result is insufficient enzymes in lysosomes and thus accumulation of undigested products in lysosomes. Lack of mannose 6 phosphate results in secretion of lysosome enzymes (fusion of endosome w/ membrane, release of contents).

Question 15

Where does O-linked glycosylation occur?

Answer 15

In ER, Golgi and cytoplasm

Question 16

Complete the table.

Answer 16

Question 17

Complete the table.

Answer 17

Question 18

Complete the table.

Answer 18

Question 19

Complete the table.

Answer 19

Question 20

Bombay phenotype occurs in individuals that lack the _____ enzyme.

Answer 20

Fucosyltransferase

Question 21

What is the Bombay phenotype?

Answer 21

When an individual does not have functional fucosyltransferase enzyme, their genotype is hh so they lack the ability to load H antigen onto the surface of their blood cells. As such, they will produce any A or B gene products in accordance with their genotype but they will not be able to express those antigens because the H antigen is the substrate for making A and B antigens. As such, they present as O phenotypically when they may be genotypically different. They will only be able to receive blood from O donors (or other Bombay individuals) because they need blood that is hh.

Question 23

Mucus is greater than ___% weight in carbohydrates.

Answer 23

50

Question 24

Proteoglycan

Answer 24

Sub-category of glycoprotein that contains mucopolysaccharides or glycosaminoglycans where majority of mass is carbohydrate based

Question 25

Where does formation of proteoglycans occur?

Answer 25

Glogi

Question 26

Glycosaminoglycans are carbohydrates that contain ____ groups and ____.

Answer 26

Amino acid groups

Sulfates

Question 27

What are the 4 classes of glycosaminoglycans.

Answer 27

Hyaluronate

Chondroitin 4-Sulfate

Keratan Sulfate

Heparin

Question 28

Of the 4 classes of glycosaminoglycans, what is special about hyaluronate?

Answer 28

Only glycosaminoglycan that is not found attached to protein core and lacks sulfonation