Lecture 19 - Carbohydrate Structure and Function

Question 1

What is the difference aldoses and ketoses?

L19 S3

Answer 1

Aldoses:
-carbonyl group is located on carbon 1 of the carbohydrate

Ketoses:
-carbonyl group is located on carbo 2 of the carbohydrate

Question 2

What is the naming convention of disastereromers of carbohydrates?

L19 S8

Answer 2

The D- or S- version of sugar is based off the highest numbered chiral center.

D-:
-furthest chiral center has the hydroxyl on the right

L-:
-furthest chiral center has the hydroxyl on the left

Question 3

What are furan and pyran structures?

L19 S9

Answer 3

Furan:
-5 membered sugar ring

Pyran:
-6 membered sugar ring

Question 4

What is the difference between Fischer and Haworth projections?

L19 S9-10

Answer 4

Fischer:
-linear

Haworth:
-ring

Question 6

What is an anomeric carbon?

L19 S12-13

Answer 6

It is the carbon in a carbohydrate ring that is connected to two oxygens (the carbon with the carbonyl group.

In aldoses it is carbon 1 and in ketoses it is carbon 2.

Question 7

What determines α/β structure of a Haworth projection for a carbohydrate?

L19 S15;9

Answer 7

If the hydroxyl group derived from the carbonyl is oriented down it is α and if it is oriented up it is β.

Question 8

In Haworth projections, __________ hydroxyls are oriented down and __________hydroxyls are oriented up.

L19 S18

Answer 8

Hydroxyls on the RIGHT of the Fischer projection are oriented DOWN.

Hydroxyls on the LEFT of the Fischer projection are oriented UP.

Question 9

What are the different conformational isomers of furanose and pyranose rings?
Which is more favored stature?

L19 S21-22

Answer 9

Furanose:

• C-3’-endo
• C-2’-endo (favored)

Pyranose:

• chair (favored)
• boat

Question 10

Differentiate between anomers and epimers.

L19 S16-17

Answer 10

Anomers:
-only difference is at the anomeric carbon

Epimers:
-different is not located at anomeric carbon

Question 11

What is the diasteromer orientation of most all carbohydrates used by mammals?
What carbohydrate is the exception to this and what is special about it?

L19 S25

Answer 11

D-monosaccharides are used by mammals.

Fucose is the only L-monosaccharide used by mammals.

• galactose derivative
• used in ABO antigens
• can indicate liver damage, cancer, diabetes, and heart disease

Question 12

What are common modifications of monosaccharides (6)?

L19 S25-30

Answer 12

Phosphorylation:

• in DNA and metabolic intermediates
• adds negative charge

Oxidation:
-occurs at carbonyl and results in acids or lactones

Reduction:
-occurs at carbonyl (addition of two hydrogens, one on carbon and other on hydroxyl)

Amino

Methylation

Glycosides:
-O-linked glycosides are mostly toxins

Question 13

What are the essential monosaccharides?

L19 S32

Answer 13

• D-glucose
• D-galactose
• D-mannose
• D-xylose

-L-fucose

• GlcNAc
• GalNAc
• Sialic acid

Question 14

What are the main disaccharides and what monosaccharides are they composed of?

L19 S33

Answer 14

Maltose:

• α-glucose
• α-glucose
• 1-4 bond

Sucrose:

• α-glucose
• β-fructose
• 1-2 bond

Lactose:

• β-galactose
• β-glucose
• 1-4 bond

Question 15

What are the main roles of polysaccharides?

L19 S34;37;39

Answer 15

Glucose storage:

• starch
• glycogen

Structure:

• cellulose
• chitin

Protein diversity:
-cell signaling
—ABO
-cell adhesion

Question 16

What is the difference between amylose and cellulose?

L19 S36-37

Answer 16

Amylose:
-α-glucose

Cellulose:
-β-glucose