Lab 3: Carbohydrate Characterization

Question 1

What is a carbohydrate?

Answer 1

Organic compound composed of carbon, hydrogen and oxygen

Question 2

What are the two main functions of carbohydrates?

Answer 2

1) Source of energy for the cells

2) Intermediate-term energy source (starch for plants and glycogen for animals)

Question 3

What are simple sugars called?

Answer 3

Monosaccharides

Question 4

Are monosaccharides and disaccharides soluble in water?

Answer 4

Yes, both of them are

Question 5

What is the function of cellulose?

Answer 5

Adds strength and stiffness to a plant’s cell wall

Question 6

What is the most common carbohydrate in the human diet? Where is it contained?

Answer 6

• Starch

- Potatoes, wheat, corn, rice

Question 7

What are the bonds in glycogen?

Answer 7

• a(1-4) glycosidic bonds

- a(1-6) branches

Question 8

Where is glycogen primarily stored?

Answer 8

Muscle and liver

Question 9

After food is ingested and starches are broken into monosaccharides, where are they transported to?

Answer 9

To the liver, among other tissues

Question 10

Where does glycogen synthesis primarily happen?

Answer 10

In the liver

Question 11

What is the energy source in glycogen synthesis? What does it convert? To what?

Answer 11

• Energy source: UTP

- Converts glucose-1-phosphate to UDP-glucose

Question 12

What is the enzyme that catalyzes the a(1-4) glycosidic bonds in glycogen synthesis?

Answer 12

Glycogen synthase

Question 13

What is needed to form glycogen branches? (2)

Answer 13

• Glycogenin (protein)

- Amylotransglycosylase (enzyme)

Question 14

What do glycogenin and amylotransglycosylase catalyze?

Answer 14

Transfer residues from the non-reducing end of the chain to the C6 hydroxyl group of a glucose molecule in the middle

Question 15

What limits branching?

Answer 15

If a chain does not contain a sufficient number of residues

Question 16

What enzyme is used in glycogenolysis?

Answer 16

• Glycogen phosphorylase

- Glycogen debranching enzyme

Question 17

What is the role of glycogen phosphorylase?

Answer 17

Attacks the Pi on the a(1-4) linkages between glucose units at one end

Question 18

What is glucose?

Answer 18

• Aldose
• Hexose
• Reducing
• Monosaccharide

Question 19

What is fructose?

Answer 19

• Ketose
• Hexose
• Reducing
• Monosaccharide

Question 20

What is xylose?

Answer 20

• Aldose
• Pentose
• Reducing
• Monosaccharide

Question 21

What is sucrose?

Answer 21

• Non-reducing disaccharide

- Made of glucose and fructose monosaccharides

Question 22

What is Benedict’s test used for?

Answer 22

Tests for the presence of reducing sugars

Question 23

What is Bial’s test used for?

Answer 23

Tests for pentoses

Question 24

What is Seilwanoff’s test used for?

Answer 24

Tests for ketoses

Question 25

What is Molisch's test used for?

Answer 25

Tests for all carbohydrates

Question 26

Why do heifers have high blood glucose?

Answer 26

Due to their young age, they require high quantities of glucose to serve as nutrients, which assures proper growth and cognitive development

Question 27

Why do pregnant cows have low blood glucose?

Answer 27

Because glucose is constantly withdrawn from the blood to provide nutrients for the fetus to grow

Question 28

Why do peak lactation cows have the lowest blood glucose?

Answer 28

Because glucose is withdrawn from the blood to make the disaccharide lactose, composed of glucose and galactose

Question 29

What is Benedict's reagent made of?

Answer 29

- Anhydrous sodium carbonate (alkali) - Sodium citrate - Copper sulfate

Question 30

What happens when a reducing sugar is heated with an alkali?

Answer 30

- Transformed into a reactive enediol | - Reduces Cu2+ from the copper sulfate to Cu+

Question 31

What happens to the Cu+ in Benedict's test?

Answer 31

Converted to insoluble red copper oxide

Question 32

What is the role of sodium citrate in Benedict's test?

Answer 32

Preserves Cu2+ ions, avoiding their deterioration to Cu+ in storage

Question 33

What is a positive reaction to Benedict's test?

Answer 33

When a clear blue solution becomes a brick-red precipitate

Question 34

Why does sucrose react negatively to Benedict's test?

Answer 34

The glycosidic bond prevents it from isomerizing to its free ketone and aldehyde form, which prevents it from reacting with Benedict's reagent

Question 35

What is Bial's reagent made of?

Answer 35

- Orcinol - HCl - FeCl3

Question 36

What is the role of HCl in Bial's test?

Answer 36

- Dehydrates pentose sugars | - Forms furfural

Question 37

What does furfural react with in Bial's test?

Answer 37

- In a condensation reaction, furfural reacts with orcinol and ferric ions from FeCl3 - Forms a bluish product

Question 38

What is a positive reaction to Bial's test? What is a negative reaction?

Answer 38

- Positive (pentoses): bluish product | - Negative (hexoses): green, red, or brown products

Question 39

What is Seilwanoff's reagent made of?

Answer 39

- HCl | - Resorcinol

Question 40

What is the role of HCl in Seilwanoff's test?

Answer 40

- Dehydrates the ketone groups of ketoses | - Forms furfural

Question 41

What does furfural react with in Seilwanoff's test?

Answer 41

- In a condensation reaction, furfural reacts with resorcinol - Forms a clear red wine complex in under 5 minutes without a precipitate

Question 42

What is a positive reaction to Seilwanoff's test? What is a negative reaction?

Answer 42

- Positive: clear red wine complex under 5 minutes | - Negative: light colours, and slowly

Question 43

Why does sucrose react positively to Seilwanoff's test?

Answer 43

Hydrolyzed by HCl into its monosaccharides to form a red product, indicating the presence of a ketose (fructose)

Question 44

What is Molish's reagent made of?

Answer 44

- H2SO4 | - a-naphthol

Question 45

What is the role of H2SO4 in Molisch's test?

Answer 45

- Dehydrates pentoses to furfural | - Dehydrates hexoses to 5-hydroxymethyl furfural

Question 46

What is the role of a-naphthol in Molisch's test?

Answer 46

Furfural derivatives react with a-naphthol to produce a purple band between H2SO4 and the sugar olution

Question 47

What is a positive reaction to Molisch's test?

Answer 47

- Positive (monosaccharides): fast | - Negative (disaccharides): slow