Chapter 7 Carbohydrates & Glycobiology

Question 1

What defines a carbohydrate in biochemistry?

Answer 1

Organic molecules with aldehydes or ketones and multiple hydroxyl groups.

Question 2

How are monosaccharides classified?

Answer 2

As simple sugars with one polyhydroxy aldehyde or ketone unit.

Question 3

What is the main difference between monosaccharides and disaccharides?

Answer 3

Monosaccharides have a single unit, while disaccharides consist of two linked monosaccharide units.

Question 4

What are glycosidic bonds?

Answer 4

Covalent bonds between monosaccharides in oligosaccharides and polysaccharides.

Question 5

What characterizes a reducing sugar?

Answer 5

A sugar that can donate electrons in a redox reaction, often due to a free aldehyde group.

Question 6

How do aldoses differ from ketoses?

Answer 6

Aldoses have a carbonyl group at the end of the chain; ketoses have it elsewhere.

Question 7

What is an example of a common aldose?

Answer 7

Glucose.

Question 8

What is a common example of a ketose?

Answer 8

Fructose.

Question 9

Describe pyranoses and furanoses.

Answer 9

Pyranoses are six-membered rings; furanoses are five-membered rings in monosaccharides.

Question 10

What process leads to the formation of hemiacetals and hemiketals?

Answer 10

Reaction of alcohol with aldehydes (hemiacetals) or ketones (hemiketals).

Question 11

What is mutarotation in carbohydrates?

Answer 11

The interconversion between α and β anomers in solution.

Question 12

What distinguishes D- and L-forms in monosaccharides?

Answer 12

The orientation of the hydroxyl group on the reference carbon farthest from the carbonyl group.

Question 13

What are epimers?

Answer 13

Sugars that differ only in the configuration around one carbon atom.

Question 14

What are anomers?

Answer 14

Isomers of a monosaccharide that differ at the hemiacetal or hemiketal carbon.

Question 15

How do polysaccharides like starch and glycogen serve in biological systems?

Answer 15

As energy storage molecules; starch in plants, glycogen in animals.

Question 16

What is the primary structural polysaccharide in plants?

Answer 16

Cellulose.

Question 17

What is chitin, and where is it found?

Answer 17

A structural polysaccharide in fungal cell walls and arthropod exoskeletons.

Question 18

What function do glycosaminoglycans serve?

Answer 18

They provide structural support and hydration in the extracellular matrix.

Question 19

What is a proteoglycan?

Answer 19

A protein core with covalently attached glycosaminoglycan chains, important in the ECM.

Question 20

How are glycolipids significant in cell membranes?

Answer 20

They help with cell recognition and communication.

Question 21

What is an example of a hexose derivative?

Answer 21

Glucose-6-phosphate, used in cellular metabolism.

Question 22

How does the Benedict’s test identify reducing sugars?

Answer 22

By forming a red precipitate when reducing sugars react with Cu²⁺.

Question 23

What is the structure of starch?

Answer 23

Composed of amylose (linear) and amylopectin (branched) glucose polymers.

Question 24

Describe the branching in glycogen.

Answer 24

Extensively branched with α(1→6) linkages every 8-12 residues.

Question 25

How does cellulose differ structurally from starch?

Answer 25

It consists of β(1→4) linked glucose, forming straight, rigid chains.

Question 26

What role do lectins play in glycobiology?

Answer 26

They bind specific carbohydrate moieties, facilitating cell recognition.

Question 27

How does mass spectrometry help in carbohydrate analysis?

Answer 27

It determines the mass and structure of carbohydrate molecules.

Question 28

What information does NMR spectroscopy provide in glycomics?

Answer 28

Details on the structure, conformation, and dynamics of carbohydrates.

Question 29

What are glycoproteins and their function?

Answer 29

Proteins with attached carbohydrate chains, involved in immune response and cell signaling.

Question 30

How do glycolipids participate in cell signaling?

Answer 30

Through oligosaccharide chains that interact with receptors in the cell membrane.

Question 31

What is the glycocalyx?

Answer 31

A carbohydrate-rich layer on cell surfaces involved in cell recognition.

Question 32

Describe the structure of amylose.

Answer 32

Amylose is a linear polymer of D-glucose with α(1→4) linkages.

Question 33

What structural role does cellulose play in plants?

Answer 33

It provides rigidity and strength to plant cell walls.

Question 34

What is a lactone, and how is it formed in carbohydrates?

Answer 34

A lactone is a cyclic ester formed from aldonic or uronic acids.

Question 35

How do phosphorylated sugars function in cells?

Answer 35

They trap sugars inside cells due to lack of transporters for phosphorylated forms.

Question 36

What is chondroitin sulfate?

Answer 36

A glycosaminoglycan in cartilage providing structure and resistance to compression.

Question 37

How does keratan sulfate function in the extracellular matrix?

Answer 37

It contributes to tissue hydration and resilience.

Question 38

What is the main difference between heparan sulfate and heparin?

Answer 38

Heparin is more highly sulfated and used primarily for anticoagulation.

Question 39

What are the roles of selectins in cell interactions?

Answer 39

They mediate cell adhesion, especially in immune responses.

Question 40

What is the role of integrins in glycobiology?

Answer 40

Integrins help cells anchor to the extracellular matrix and facilitate signaling.

Question 41

How does glycosylation affect protein function?

Answer 41

It can impact protein folding, stability, and recognition by other molecules.

Question 42

What is the difference between O-linked and N-linked glycosylation?

Answer 42

O-linked attaches to serine/threonine residues; N-linked attaches to asparagine residues.

Question 43

How does the structure of hyaluronic acid benefit the extracellular matrix?

Answer 43

Its large size and negative charge enable it to retain water and provide cushioning.

Question 44

What is the “sugar code” in glycobiology?

Answer 44

The information encoded by specific oligosaccharide structures on cell surfaces.

Question 45

How do enzymes recognize stereoisomers of sugars?

Answer 45

Enzymes are stereospecific, often recognizing only one isomer, such as D-glucose.

Question 46

What structural feature differentiates α and β anomers?

Answer 46

The orientation of the hydroxyl group on the anomeric carbon.

Question 47

How does tautomerization affect ketoses?

Answer 47

It allows ketoses to rearrange and act as reducing sugars under certain conditions.

Question 48

What is a glycosphingolipid?

Answer 48

A glycolipid with a sphingosine backbone, important in neural tissue.

Question 49

What are the primary bonds in peptidoglycan structure?

Answer 49

β(1→4) linkages between N-acetylglucosamine and N-acetylmuramic acid.

Question 50

What is an aggrecan, and where is it found?

Answer 50

A large proteoglycan in cartilage that binds to hyaluronan, providing compressive strength.

Question 51

How do hydrogen bonds influence polysaccharide structures?

Answer 51

They stabilize folding and contribute to rigidity in structural polysaccharides like cellulose.

Question 52

How are oligosaccharides typically analyzed?

Answer 52

Using methods like mass spectrometry and NMR to determine sequence and structure.

Question 53

What is the role of the conserved RGD sequence in integrins?

Answer 53

It facilitates binding with ECM components, like fibronectin and collagen.

Question 54

What happens during the formation of an acetal or ketal in carbohydrates?

Answer 54

A second alcohol group adds to a hemiacetal or hemiketal, forming a stable linkage.

Question 55

What structural role do glycosaminoglycans play in the ECM?

Answer 55

They form a gel-like matrix that supports cells and allows nutrient diffusion.