Carbohydrates (Module 2 Lecture 1)

Question 1

How many carbons are in monosaccharides?

Answer 1

3-9

Question 2

Define oligosaccharide.

Answer 2

Many monosaccharides linked together.

Question 3

In what form to animals store glucose?

Answer 3

Glycogen

Question 4

Complex carbohydrates are used in what three structures?

Answer 4

1. Extracellular matrix (eukaryotes)
2. Bacteria cell walls
3. Plant cell walls

Question 5

What are two functions of carbohydrates linked to proteins and lipids on the cell membrane?

Answer 5

1. Cell-to-cell communication

2. Interactions between cells and extracellular environment.

Question 6

Define triose.

Answer 6

A monosaccharide made of only three carbons.

Question 7

What is the smallest aldose (aldehyde sugar)?

Answer 7

Glyceraldehide (a triose).

Question 8

What is the smallest ketose (ketone sugar)?

Answer 8

Dihydroxyacetone (a triose).

Question 9

What are the two most common sugars?

Answer 9

Hexoses and pentoses.

Question 10

What is the most common hexose in nature?

Answer 10

Glucose (a D-aldose).

Question 11

Describe the structure and stereochemistry of glucose and related hexoses.

Answer 11

1. The four internal carbons are asymmetric.

2. It has multiple isomeric hexoses.

Question 12

Define epimer.

Answer 12

An epimer is a sugar that differs from another in only the stereoconfiguration around ONE carbon.

Question 13

Name two common epimers of D-glucose.

Answer 13

1. D-mannose (epimeric at C-2)

2. D-galactose (epimeric at C-4).

Question 14

What happens to glucose straight chains in aqueous solution?

Answer 14

1. It forms a pyranose ring by C-1 aldehyde reacting with the C-5 hydroxyl to form a hemiacetal.
2. Open-chain and ring forms are in equilibrium.

Question 15

Explain the two anomers of glucose in solution.

Answer 15

1. After cyclizing, D-glucose turns into two interconvertible anomers around the C-1 carbon.
2. The two configurations are denoted alpha and beta.

Question 16

Describe the structure and formation of fructose.

Answer 16

1. It is a ketose.

2. It cyclizes by forming a hemiketal linkage between C-2 and C-5, forming furanose, a 5-membered ring.

Question 17

Describe the formation of ribose and deoxyribose.

Answer 17

1. Ribose is a pentose sugar formed by the cyclization of C-1 aldehyde and C-4 hydroxyl. 2. Deoxyribose is missing the OH on the C-2 carbon.

Question 18

What is a modified monosaccharide and how is it commonly used by the body?

Answer 18

1. It is a monosaccharide with at least one additional substituent (like methyl, etc.) on its basic structure.
2. It is commonly used on cell surfaces.

Question 19

What is a reducing sugar and why?

Answer 19

1. A sugar that is in equilibrium with its cyclic and open chain forms.
2. Such sugars reduce copper II to copper I by oxidizing the aldehyde into an acid.

Question 20

How are glycosidic bonds formed?

Answer 20

By the reaction of monosaccharides with alcohols and amines.

Question 21

What happens when O-CH3 is added to glucose?

Answer 21

1. An O-glycosidic bond is formed in one of two possible stereoisomers.
2. The products are no longer reducing sugars because they can no longer open up into open chain form.

Question 22

How are oligosaccharides formed?

Answer 22

By linking two or more monosaccharides together with O-glycosidic bonds.

Question 23

Explain the structure of maltose.

Answer 23

A disaccharide formed by linkage of two glucose residues (C-1 -> C-4) forming an alpha-1,4-glycosidic bond.

Question 24

How are disaccharides synthesized and broken?

Answer 24

Via condensation (removal of two water molecules) and the reverse process, which splits the glycosidic bond, is called hydrolysis and requires two water molecules per broken glycosidic linkage.

Question 25

How is lactose formed?

Answer 25

By linking glucose and galactose (C-1 -> C-4)

Question 26

Where in the body are glucose and lactose hydrolyzed and why are they broken down here?

Answer 26

In the gut for the monosaccharide components to be used by individual cells.

Question 27

What is glycogen made out of?

Answer 27

Many glucose units linked together with alpha-1,4-glycosidic linkages and then branches between these polymers made by alpha-1,6-glycosidic linkages.

Question 28

Describe the function and structure of two main glucose homopolymers used in plants.

Answer 28

1. Starch (similar to glycogen only less branched) is for mobile storage in plants.
2. Cellulose is the major structural polymer in plants and is made with beta-1,4-glycosidic linkages.
3. In cellulose, the beta linkages lead to fibril formation which is very strong (tensile).
4. Humans cannot digest the beta-1,4-glycosidic linkages, which is why eating plants helps you go to the bathroom without gaining weight (it just washes through along with everything else in your stomach).