Ch. 13

Question 1

What are glycans?

Answer 1

Synonym for carbohydrate
- Class of molecules with the formula (CH₂O)n where n is greater than 2

Question 2

What is glycobiology?

Answer 2

Study of the biological functions of glycans

Question 3

What are the 3 major groups of carbohydrates?

Answer 3

1. Simple sugars
2. Polysaccharides
3. Glycoconjugates

Question 4

What are simple sugars?

Answer 4

Monosaccharides, disaccharides, and oligosaccharides

Question 5

What do simple sugars often function as?

Answer 5

Metabolic intermediates in energy conversion pathways

Question 6

What are polysaccharides?

Answer 6

Glucose homopolymers or disaccharide heteropolymers
- 1 of the 2 sugars is a hexosamine

Question 7

What are glycoconjugates?

Answer 7

Protein or lipid with covalently linked glycans
- Role in cellular communication

Question 8

What do glycoconjugates have a role in?

Answer 8

Cellular communication

Question 9

What are glycotransferases?

Answer 9

Enzymes that catalyze the ADDITION of glycan units to proteins and lipids to form glycoconjugates

Question 10

What are glycosidases?

Answer 10

Enzymes that catalyze that REMOVAL of glycan units from glycoconjugates

Question 11

What are 4 the glycobiology principles?

Answer 11

Glycan…
1. Biochemistry
2. Biosynthesis
3. Diversity
4. Recognition

Question 12

What is a glycosidic bond?

Answer 12

Bond that joins a carbohydrate to another molecule

Question 13

What is an anomeric carbon?

Answer 13

The carbonyl carbon in the acyclic form of a carbohydrate

Question 14

What are oligosaccharides?

Answer 14

Simple sugars that range from 3 to 20 branched and unbranched sugar residues

Question 15

What examples of oligosaccharides?

Answer 15

• Lacto-N-tetraose
• Stachyose
• Raffinose

Question 16

How do we know that related oligosaccharides are derived from the same disaccharide?

Answer 16

Because of the biochemical characterization of oligosaccharides in human breast milk and the raffinose series of plant oligosaccharides

Question 17

What is the common disaccharide of human breast milk oligosaccharides?

Answer 17

Lactose

Question 18

What is the common disaccharide of raffinose-related oligosaccharides?

Answer 18

Sucrose

Question 19

What happens when some people eat foods high in raffinose-type oligosaccharides?

Answer 19

Can lead to GI discomfort because humans don’t have the enzyme (α-galactosidase) that breaks it down

Question 20

How do polysaccharides differ from each other?

Answer 20

• ID of recurring monosaccharide units
• Length of chain
• Degree of branching
• Type of bonds linking the units

Question 21

What are homopolysaccharides?

Answer 21

Made of 1 type of monosaccharide

Question 22

What are heteropolysaccharides?

Answer 22

Made of more than 1 type of monosaccharide

Question 23

What are the storage forms of glucose?

Answer 23

Starch and glycogen

Question 24

What does starch contain?

Answer 24

Amylose, amylopectin, and other polysaccharides

Question 25

What is amylose?

Answer 25

An α(1⟶4) linear form of starch (unbranched)

Question 26

What is amylopectin?

Answer 26

An α(1⟶6)–branched form of starch - it also has α(1-->4) linkages in the straight part

Question 27

Compare and contrast glycogen and amylopectin.

Answer 27

Similar structure but glycogen is more branched

Question 28

What is glycogen?

Answer 28

Storage polysaccharide in animal cells

Question 29

Where is glycogen abundant?

Answer 29

In the liver

Question 30

What are glycoproteins?

Answer 30

Major class of glycoconjugates characterized by glycans covalently linked to protein molecules

Question 31

What are glycolipids?

Answer 31

Major class of glycoconjugates characterized by glycans covalently linked to lipid molecules

Question 32

What are proteoglycans?

Answer 32

Type of protein glycoconjugate where most of the macromolecule consists of carbohydrates TL;DR - More carb than protein

Question 33

What is peptidoglycan?

Answer 33

Bacterial proteoglycan made of peptide-linked chains of repeating hexosamines; the major component of bacterial cell walls

Question 34

What are the functions of proteoglycans?

Answer 34

- Protein binding activites - Regulate signal transduction - Facilitate cell migration

Question 35

What are the two classes of proteoglycans?

Answer 35

1. Cell surface 2. Extracellular matrix

Question 36

What are N-linked oligosaccharides?

Answer 36

Linkage of short chains of glycans to the amide nitrogen atom in the side chain of asparagine in a glycoprotein

Question 37

What are O-linked oligosaccharides?

Answer 37

Linkage of short chains of glycans to the oxygen atom in the side chain of serine or threonine in a glycoprotein

Question 38

What are mucins?

Answer 38

O-linked glycoproteins that are secreted and bound to the cell surface - Aid in maintenance of mucosal barriers around epithelial cells

Question 39

What amino acids do carbohydrates link to in glycoproteins?

Answer 39

- Asparagine (N-linked) - Serine or threonine (O-linked)

Question 40

Where are oligosaccharides added to proteins in cells?

Answer 40

Added to newly synthesized proteins in the ER and are elaborated in the Golgi complex

Question 41

Why are oligosaccharides added to proteins in cells?

Answer 41

- Destination labels - Increase solubility of proteins - Quality control - Negative charge cluster protects proteins from proteolytic degradation

Question 42

List biomedical examples of glycoconjugates.

Answer 42

- Macular corneal dystrophy - Bacterial cell walls - Blood groups and glycotransferases

Question 43

What determines ABO blood types?

Answer 43

Variant glycosyltransferases

Question 44

What are ABO blood groups?

Answer 44

System for typing blood based on presence of GalNAc and/or galactose bound to O antigen of glycoproteins and glycolipids on surface of RBCs

Question 45

What is type O blood?

Answer 45

Neither GTA nor GTB enzymes present

Question 46

What is type A blood?

Answer 46

Only GTA enzyme

Question 47

What is type B blood?

Answer 47

Only GTB enzyme

Question 48

What is type AB blood?

Answer 48

Both GTA and GTB enzymes present

Question 49

What do β-lactam antibiotics target?

Answer 49

Peptidoglycan synthesis

Question 50

What is Gram-positive bacteria?

Answer 50

Have a thick peptidoglycan layer that retains the Gram stain

Question 51

What is Gram-negative bacteria?

Answer 51

Have a thin peptidoglycan layer that does not retain the Gram stain

Question 52

What color are gram-positive vs gram-negative bacteria after staining?

Answer 52

Gram-positive: dark purple Gram-negative: pink-red

Question 53

What does the thick layer of peptidoglycan contain?

Answer 53

Lipotechoic acid (negatively charged polymer of ribitol phosphate or glycerol phosphate) - Structural support

Question 54

Which type of bacteria has LPS?

Answer 54

Gram-negative (outer membrane)

Question 55

What is an endotoxin?

Answer 55

LPS in outer membrane of Gram-negative bacteria that becomes toxic to the host after the bacteria have lysed

Question 56

How does penicillin work?

Answer 56

Blocks bacterial cell wall biosynthesis by inhibiting the enzyme transpeptidase

Question 57

What makes some bacteria resistant to penicillin?

Answer 57

They produce an enzyme called β-lactamase, which inactivates penicllin by hydrolyzing the β-lactam ring in penicillin

Question 58

What causes macular corneal dystrophy?

Answer 58

Defect in the enzyme that sulfates keratan - Cornea become opaque due to decreased sulfation of keratan

Question 59

What is the role of keratan sulfate?

Answer 59

- Help maintain a hydrated environment - Functional role in promoting structural organization

Question 60

What is the structure of glucose?

Answer 60

Question 61

What is the structure of GlcNac?

Answer 61