Lecture 9: sugars and carbohydrates

Question 1

Why are carbohydrates important for living beings?

Answer 1

1. Principal source of metabolic energy
2. Structural support
3. Biological recognition

Question 2

How do carbohydrates differ from lipids?

Answer 2

1. Carbohydrates are a short term energy source while lipids are a long term energy source
2. Carbohydrates are more digestible than lipids
3. Carbohydrates have a lower energy per gram than lipids
4. Carbohydrates are more soluble in water

Question 3

What is the blood glucose level when there is hypoglycemia?

Answer 3

Below 70mg/dL

Question 4

What is ketoacidosis?

Answer 4

1. Happens when the body is deprived of carbohydrates
2. The body starts to utilise fats to generate energy, which produces keto acids that decrease plasma pH
3. These keto acids are further broken down to produce acetone to give a characteristic smell

Question 5

In a Fischer projection of carbohydrates, which group goes at the top of the structure?

Answer 5

The most oxidised group

Question 6

How do you differentiate between L and D isomers?

Answer 6

1. D-isomer: -OH group on the penultimate carbon is on the right
2. L-isomer: -OH group on the penultimate carbon is on the left

Question 7

Stereoisomers that differ in only 1 chiral centre are called ____________

Answer 7

epimers

Question 8

5- and 6- membered monosaccharides mostly exist as _________ structures.

Answer 8

cyclic

Question 9

The carbon 1 is also called the __________

Answer 9

anomeric carbon

Question 10

How do you draw the Haworth’s projection from a Fischer projection?

Answer 10

1. Groups on the right side of a Fischer projection appear below the plane of the ring on a Haworth’s projection.
2. Groups on the left side of a Fischer projection appear above the plane of the ring on a Haworth’s projection.

Question 11

How do you distinguish glucose anomers?

Answer 11

1. alpha: trans between the -OH group of C1 and the terminal CH2OH
2. beta: cis between the -OH group of C1 and the terminal CH2OH

Question 12

What is the most stable form of pyranose?

Answer 12

beta-D-glucose

Question 13

How do you name acids formed from the oxidation of sugars?

Answer 13

1. If oxidation occurs at the aldehyde –> -onic acid
2. If oxidation occurs at the terminal primary carbon –> -uronic acid

Question 14

What are common disaccharides and how are the monomers joined?

Answer 14

1. Sucrose: glucose and fructose joined by alpha 1,2 glycosidic bond
2. Lactose: glucose and galactose joined by a beta 1,4 glycosidic bond
3. Lactulose: fructose and galactose joined by a beta 1,4 glycosidic bond
4. Maltose: 2 glucose joined by alpha 1,4 glycosidic bond
5. Cellobiose: 2 glucose joined by a beta 1,4 glycosidic bond

Question 15

How are carbohydrates exploited as targets for drugs?

Answer 15

1. Anti diabetic
2. Anti viral agents, eg: neuraminidase
3. Antibiotics, eg: peptidoglycan

Question 16

How are carbohydrates used as therapeutic agents?

Answer 16

1. As supplements, eg: glucosamine for arthritis
2. As prophylactics, eg: heparin to stop coagulation
3. As treatment, eg: aminoglycosides