(Dr. McLachlin) (Unit B) Topic Note 7

Question 1

Monosaccharides

Answer 1

Simplest sugars, have molecular formula (CH2O)n, where n = 3-7

Question 2

Terminology:

Monosaccharide with:
1. 3 carbons
2. 4 carbons
3. 5 carbons
4. 6 carbons
5. 7 carbons

Answer 2

1. Triose
2. Tetrose
3. Pentose
4. Hexose
5. Heptose

Question 3

How are monosaccharides often depicted?

Answer 3

Fischer projections

Question 4

Aldose

Answer 4

Carbonyl group is at the end of the molecule
* Aldehyde group, hence “aldose”

Question 5

Ketose

Answer 5

Carbonyl group is not at the end of the molecule
* Ketone group, hence “ketose”

Question 6

Do all monosaccharides have a carbonyl group?

Answer 6

Yes
* Carbonyl: An oxygen atom double-bonded to carbon

Question 7

How are carbons in the monosaccharide numbered?

Answer 7

Starting from the end closest to the carbonyl group

Question 8

Monosaccharides are called D/L based on what?

Answer 8

Orientation of hydroxyl group on the chiral carbon farthest from the carbonyl group

Question 9

True or False:

Biological sugars are usually L isomers with the hydroxyl group on the right side in a Fischer projection

Answer 9

False, they are usually D isomers
* D isomers have the hydroxyl group on the right side in a Fischer projection

Question 10

Epimers

Answer 10

Monosaccharides that differ in stereochemistry at only one chiral carbon as Fischer projections

Question 11

How are cyclic structures (pentoses and hexoses) depicted?

Answer 11

Haworth projections

Question 12

Anomeric carbon

Answer 12

The carbon of the carbonyl group with reacts with a hydroxyl group to form a ring

Question 13

What are monosaccharide rings called in stereochemistry?

Answer 13

Alpha or Beta

Question 14

How is alpha/beta configuration determined?

Answer 14

Comparing the position of hydroxyl formed at the anomeric carbon with the position of the highest-numbered carbon in the molecule
* Beta: Same side
* Alpha: Opposite sides

Question 15

What type of bond joines two monosaccharides together in a condensation reaction?

Answer 15

O-glycosidic bond

Question 16

What happens to the anomeric carbon if it is involved in a o-glycosidic bond?

Answer 16

It can no longer switch back and forth between the alpha and beta forms

Question 17

Oligosaccharides

Answer 17

A few monosaccharides joined together

Question 18

Polysaccharide

Answer 18

Many monosaccharides joined together

Question 19

Can polysaccharides be branched?

Answer 19

Yes
* E.x. Glycogen, amylopectin

Question 20

Describe:

Glycogen

Answer 20

• Linear chains of 12-14 glucose monomers in alpha(1,4) linkage
• Linear chains are joined at branch points through alpha(1,6) linkage

Main reservoir of carbohydrate energy in animal cells

Question 21

Describe:

Starch

Answer 21

Composed of:
1. Amylose (polyglucose in alpha(1,4) linkages with very few branch points)
2. Amylopectin (polyglucose in alpha(1,4) linkages with an alpha(1,6) branch point every 24-30 glucose units)

Plants store glucose as starch

Question 22

Dietary fibre

Answer 22

Consists of carbohydrates and related polymers that are not digested in the small intestine, either because of the chemical composition of the monosaccharide units or because of the nature of the linkages between them

Question 23

Can dietary fibre be broken down?

Answer 23

Some can by bacteria in the large intestine

Question 24

Cellulose

Answer 24

Dietary fibre
* Unbranched beta(1,4) polyglucose

Question 25

What are some health benefits associated with fibre ingestion?

Answer 25

• Lower LDL-cholesterol levels in the blood
• Reduced risk of obesity, heart disease, diabetes, and colon cancer