Chapter 4

Question 1

What is mutarotation?

Answer 1

The spontaneous cycling of the alpha and beta anomer forms of a sugar molecule. This results in a mixture of both snorers at equilibrium, with beta configuration being dominant as it is more stable in the chair conformation.

Question 2

In a monosaccharide which group serves as the nucleophile?

Answer 2

Hydroxyl group

Question 3

In a monosaccharide which group serves as the electrophile?

Answer 3

Carbonyl group

Question 4

In a Fischer projection, the horizontal lines are considered (out of the page/ into the page).

Answer 4

Out of the page

Question 5

In a Fischer projection, the vertical lines are considered (out of the page/ into the page).

Answer 5

Into the page

Question 6

Shortcut to figure out # of stereoisomers for a monosaccharide.

Answer 6

2^n; n = number of chiral carbons in molecule

Question 7

Enantiomers are ______?

Answer 7

Stereoisomers which are nonsuperimposable mirror images of each other.

Question 8

Diastereoisomers are _____?

Answer 8

Stereoisomers which are not mirror images, but have the same chemical formula and same connectivity.

Question 9

What are epimers?

Answer 9

A type of diastereomer where the connectivity in space only differs for 1 chiral carbon.

Question 10

How can you tell if a monosaccharide is D or L by looking at a Fischer projection?

Answer 10

If it is D, the OH on last chiral C points to the right.
If it is L, the OH on last chiral C points to the left.

Question 11

A glycosidic linkage occurs between

Answer 11

The anomeric carbon on the first sugar and any carbon on the second sugar (2,3,4,6 etc)

Question 12

Are D-glucose and D-fructose considered diastereomers (stereoisomers)?

Answer 12

No, they are not diastereoisomers/stereoisomers because they have different connectivity in space, that is the carbonyl group (double bond) is located at different C’s. Fructose is a ketose, while glucose is an aldose.

Question 13

What is the difference between stereoisomers and constitutional isomers?

Answer 13

Stereoisomers have the same chemical formula and same connectivity in space.
Constitutional isomers have the same chemical formula, but different connectivity.

Question 14

Name some examples of hexose sugars.

Answer 14

Fructose, glucose, galactose, and mannose

Question 15

An aldose usually forms what kind of cyclic ring?

Answer 15

6 membered pyranose ring.

Question 16

A ketose usually forms what kind of cyclic ring?

Answer 16

5 membered furanose ring

Question 17

When converting a Fischer projection into a Haworth, how do you determine if the last C (CH2OH) group is pointing up or down?

Answer 17

You take the opposite of the direction of OH group on the previous carbon. For example, if the OH is on the right, OH would be down. Meaning the CH2OH would be left and up.

Question 18

Name the three important polysaccharides.

Answer 18

Cellulose, starch, and glycogen

Question 19

What monosaccharide are the three polysaccharides (cellulose, starch, glycogen) composed of?

Answer 19

D-glucose

Question 20

What is the more stable form of glucose, alpha or beta?

Answer 20

Beta glucose because the OH on the anomeric 1st C that is pointing up is in the equatorial position which produces less steric hinderance.

Question 21

Describe characteristics of cellulose

Answer 21

-Composed of beta-D-glucose molecules linked by beta 1,4 glycosidic bonds
-indigestible by humans
-Used by humans as fiber to draw water into the gut

Question 22

Describe characteristics of starch.

Answer 22

-Composed of alpha-D-glucose monosaccharides
-Is digestible by humans
-Further subdivided into amylose and amylopectin
-Used as a source of energy by humans

Question 23

Difference in structure between amylose and amylopectin

Answer 23

Amylose is made of a linear chain of D-glucose monomers linked by alpha-1,4 glycosidic bonds
Amylopectin is not linear; contains both linear chain of glucose monomers linked by alpha-1,4 glycosidic bonds and branches via alpha-1,6 glycosidic bonds.

Question 24

What are some stereoisomers of D-glucose?

Answer 24

D-galactose and D-mannose

Question 25

What is the difference between alpha and beta forms in the Haworth projection and chair conformation?

Answer 25

Alpha means the OH group on the 1st anomeric carbon is pointing down.
Beta means the OH group on the 1st anomeric carbon is pointing up.

Question 26

What makes cellulose indigestible to humans?

Answer 26

Cellulose is composed of BETA-GLYCOSIDIC linkages which humans don’t have the enzymes for to digest those linkages.

Question 27

What kinds of sugar molecules are able to participate in redox reactions?

Answer 27

Aldoses (aldehydes) the carbonyl C should have a H coming off it

Question 28

Ribose and deoxyribose are what kinds of sugars?

Answer 28

They are aldose pentose sugars.

Question 29

D and L sugars are enantiomers. While _____ sugars are the most common form in our body.

Answer 29

D

Question 30

What is meant by non-template synthesis?
Give examples. (This question was on the recent AAMC exam you took)

Answer 30

The synthesis of lipids and polysaccharides which don’t require use of a template.
Ex: Synthesis of fatty acids and glucose (gluconeogenesis)