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2) Biochemistry II > Lab 3: Carbohydrate Characterization > Flashcards

Lab 3: Carbohydrate Characterization Flashcards

1
Q

What is a carbohydrate?

A

Organic compound composed of carbon, hydrogen and oxygen

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2
Q

What are the two main functions of carbohydrates?

A

1) Source of energy for the cells

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

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3
Q

What are simple sugars called?

A

Monosaccharides

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4
Q

Are monosaccharides and disaccharides soluble in water?

A

Yes, both of them are

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5
Q

What is the function of cellulose?

A

Adds strength and stiffness to a plant’s cell wall

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6
Q

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

A
  • Starch

- Potatoes, wheat, corn, rice

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7
Q

What are the bonds in glycogen?

A
  • a(1-4) glycosidic bonds

- a(1-6) branches

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8
Q

Where is glycogen primarily stored?

A

Muscle and liver

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9
Q

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

A

To the liver, among other tissues

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10
Q

Where does glycogen synthesis primarily happen?

A

In the liver

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11
Q

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

A
  • Energy source: UTP

- Converts glucose-1-phosphate to UDP-glucose

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12
Q

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

A

Glycogen synthase

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13
Q

What is needed to form glycogen branches? (2)

A
  • Glycogenin (protein)

- Amylotransglycosylase (enzyme)

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14
Q

What do glycogenin and amylotransglycosylase catalyze?

A

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

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15
Q

What limits branching?

A

If a chain does not contain a sufficient number of residues

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16
Q

What enzyme is used in glycogenolysis?

A
  • Glycogen phosphorylase

- Glycogen debranching enzyme

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17
Q

What is the role of glycogen phosphorylase?

A

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

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18
Q

What is glucose?

A
  • Aldose
  • Hexose
  • Reducing
  • Monosaccharide
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19
Q

What is fructose?

A
  • Ketose
  • Hexose
  • Reducing
  • Monosaccharide
20
Q

What is xylose?

A
  • Aldose
  • Pentose
  • Reducing
  • Monosaccharide
21
Q

What is sucrose?

A
  • Non-reducing disaccharide

- Made of glucose and fructose monosaccharides

22
Q

What is Benedict’s test used for?

A

Tests for the presence of reducing sugars

23
Q

What is Bial’s test used for?

A

Tests for pentoses

24
Q

What is Seilwanoff’s test used for?

A

Tests for ketoses

25
Q

What is Molisch’s test used for?

A

Tests for all carbohydrates

26
Q

Why do heifers have high blood glucose?

A

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

27
Q

Why do pregnant cows have low blood glucose?

A

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

28
Q

Why do peak lactation cows have the lowest blood glucose?

A

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

29
Q

What is Benedict’s reagent made of?

A
  • Anhydrous sodium carbonate (alkali)
  • Sodium citrate
  • Copper sulfate
30
Q

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

A
  • Transformed into a reactive enediol

- Reduces Cu2+ from the copper sulfate to Cu+

31
Q

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

A

Converted to insoluble red copper oxide

32
Q

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

A

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

33
Q

What is a positive reaction to Benedict’s test?

A

When a clear blue solution becomes a brick-red precipitate

34
Q

Why does sucrose react negatively to Benedict’s test?

A

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

35
Q

What is Bial’s reagent made of?

A
  • Orcinol
  • HCl
  • FeCl3
36
Q

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

A
  • Dehydrates pentose sugars

- Forms furfural

37
Q

What does furfural react with in Bial’s test?

A
  • In a condensation reaction, furfural reacts with orcinol and ferric ions from FeCl3
  • Forms a bluish product
38
Q

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

A
  • Positive (pentoses): bluish product

- Negative (hexoses): green, red, or brown products

39
Q

What is Seilwanoff’s reagent made of?

A
  • HCl

- Resorcinol

40
Q

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

A
  • Dehydrates the ketone groups of ketoses

- Forms furfural

41
Q

What does furfural react with in Seilwanoff’s test?

A
  • In a condensation reaction, furfural reacts with resorcinol
  • Forms a clear red wine complex in under 5 minutes without a precipitate
42
Q

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

A
  • Positive: clear red wine complex under 5 minutes

- Negative: light colours, and slowly

43
Q

Why does sucrose react positively to Seilwanoff’s test?

A

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

44
Q

What is Molish’s reagent made of?

A
  • H2SO4

- a-naphthol

45
Q

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

A
  • Dehydrates pentoses to furfural

- Dehydrates hexoses to 5-hydroxymethyl furfural

46
Q

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

A

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

47
Q

What is a positive reaction to Molisch’s test?

A
  • Positive (monosaccharides): fast

- Negative (disaccharides): slow

2) Biochemistry II (23 decks)

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