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OrgBio Chem > Experiment 7: Carbohydrates > Flashcards

Experiment 7: Carbohydrates Flashcards

1
Q

What are Carbohydrates?

A

Carbohydrates are biological sugar molecules. They are composed of carbon, hydrogen & oxygen. They are also known as polyhydroxy aldehydes or polyhydroxy ketones.

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2
Q

The four classifications of carbohydrates are:

A
  1. Monosaccharide
  2. Disaccharide
  3. Oligosaccharides
  4. Polysaccharides
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3
Q
  • They are simple sugars; basic constituents of all carbohydrates
  • Contain only 1 saccharide group
  • Can’t be hydrolyzed into simpler forms
A

Monosaccharides or C6H12O6

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4
Q

Most important monosaccharides:

A
  • Glucose or dextrose or corn sugar
  • Fructose or levulose or fruit sugar
  • Galactose
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5
Q

What are disaccharides made of?

A

Two monosaccharide molecules minus a molecule of water

C6H12O6 + C6H12O6 = C12H24O12 - H2O = C12H22O11

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6
Q

What happens to disaccharides when they are hydrolyzed?

A

When hydrolyzed, disaccharides yield 2 molecules of monosaccharides, either they are the same or different

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7
Q

The most common disaccharides, and what they are built from:

A
  • Sucrose or cane or beet sugar: Glucose + Fructose
  • Lactose or milk sugar: Glucose + Galactose
  • Maltose or malt sugar: Glucose + Glucose
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8
Q

Classification of carbohydrate that when hydrolyzed, yields 3-6 monosaccharide units

A

Oligosaccharides

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9
Q
  • Made up of several monosaccharide groups; most complex classification of all the carbohydrates
  • They are white, crystalline, tasteless
  • Have high molecular weight
  • Mostly insoluble and non-fermentable
A

Polysaccharides or C6H10O5

  • Starch
  • Cellulose
  • Dextrin
  • Glyocogen
  • Inulin
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10
Q

What do polysaccharides yield when hydrolyzed?

A

They yield more than 6 monosaccharides units

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11
Q

A.1. It is the general test for carbohydrates

A

Molisch Test

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12
Q

A.2. Molisch Test process:

A

(1) Water, (2) Glucose, (3) Sucrose, (4) Starch + Molisch reagent or C10H8OH + conc. H2SO4

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13
Q

A.3. What is the purpose of conc. H2SO4?

A

It is used as a hydrolyzing & dehydrating agent of monosaccharides in carbohydrates

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14
Q

A.4. Results of Molish Test

A
  • With water: No reaction—no carbohydrates
  • With Glucose: Purple ring forms at junction—positive reaction
  • With Sucrose: Purple ring forms at junction—positive reaction
  • With Starch: Slight purple ring forms at junction—positive reaction
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15
Q

A.5. How does purple ring form in Molisch Test?

A
  1. Carbohydrates are detected because they are hydrolyzed in the solution, being broken down into monosaccharides
  2. Monosaccharides are then dehydrated by conc. H2SO4 which form furfural derivatives
  3. Furfural derivatives interact with the a-napthol in Molisch reagent, causing a purple ring to form
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16
Q

B.1. It is the general test for carbonyl group and reducing sugar

A

Phenylhydrazine Test

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17
Q

B.2. Phenylhydrazine Test process:

A

Glucose + H2NNHC6H5 or phenylhydrazine

  1. Shake.
  2. Boil.
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18
Q

B.3. What forms in Phenylhydrazine test?

A

Yellow precipitate crystals called Osazone crystals

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19
Q

B.4. What is the purpose of Phenylhydrazine?

A

It is a derivatizing agent

20
Q

B.5. How is osazone crystals formed?

A
  1. The H2NNHC6H5 reacts with the carbonyl group in Glucose to form glucose phenylhydrazone.
  2. The glucose phenylhydrazone further reacts into osazone.
21
Q

C.1. It is a test for the action of alkalines and presence of reducing sugars

A

Moore’s Test

22
Q

C.2. Moore’s Test process:

A

(1) Glucose, (2) Sucrose + 25% NaOH

  1. Boil
23
Q

C.3. What kind of substance is NaOH? What was its function in Moore’s Test?

A

It is alkaline, or basic, used for polymerization

24
Q

C.4. Results of Moore’s Test:

A
  • With Glucose: Brown solution forms, emitting a caramel scent; positive reaction
  • With Sucrose: No reaction
25
Q

C.5. In Moore’s Test did positive reaction show in Glucose, but not in Sucrose?

A

The color change and formation of resinous caramel is caused by the polymerization of the free aldehydes from the reducing sugar, which is Glucose

Sucrose is not a reducing sugar, thus doesn’t have free aldehydes; therefore doesn’t react

26
Q

D.1. What are Reducing Sugars?

A

These are sugars that contain reducing properties because of the presence of their free aldehyde or ketone group.

27
Q

D.2. Which classifications of sugars are reducing and non-reducing?

A

All monosaccharides are reducing sugars.

Lactose and maltose are reducing disaccharides.

Sucrose and polysaccharides are non-reducing sugars.

28
Q

D.3. What do reducing sugars reduce?

A

They reduce alkaline solutions of copper and silver, which are converted to cuprous oxide

29
Q

D.4. Benedict’s Test process:

A

(1) Glucose, (2) Lactose, (3) Sucrose, (4) Starch + Benedict’s reagent

  1. Boil, then cool
30
Q

D.4.2. What is Benedict’s reagent composed of?

A
  • Copper sulfate
  • Sodium carbonate
  • Sodium citrate
31
Q

D.5. Results of Benedict’s Test:

A
  • With Glucose & Lactose: Blue to red precipitates; reducing sugars detected
  • With Sucrose & Starch: No reaction; no reducing sugars detected
32
Q

D.6. How are reducing sugars detected in Benedict’s Test?

A
  1. Benedict’s solution contains copper.
  2. In the presence of reducing sugars, the copper in the reagent is reduced to red cuprous oxide / Copper (I) ions.
33
Q

E.1. What is Hydrolysis?

A

It is the addition of water to disaccharides and polysaccharides to break them apart into their component monosaccharides.

34
Q

E.2. Sucrose Hydrolysis process:

A

Sucrose + HCl, then boil

Add NaOH to make it alkaline

Test half with Benedict’s reagent, the other with Seliwanoff’s reagent

35
Q

E.3. What kind of substance is HCl?

A

It is a non-oxidizing acid

36
Q

E.4. What happens when HCl is added to Sucrose?

A

HCl hydrolyzes Sucrose, breaking it down into separate Glucose & Fructose molecules

37
Q

E.5. What happens when the alkaline hydrolyzed sucrose was added with Benedict’s reagent?

A

A dark orange-yellow color formed.

This is because the freed Glucose molecules–which are reducing sugars-reduced the copper in the reagent to cuprous oxide

38
Q

E.6. It is a specific test for ketoses

A

Seliwanoff’s Test

39
Q

E.6. What are ketoses?

A

Ketoses are sugars with the presence of a ketone group

40
Q

E.7. What is Seliwanoff’s reagent made of?

A

C6H6O2 (Resorcinol) & HCl

41
Q

E.8. What happens when the alkaline hydrolyzed sucrose was added with Seliwanoff’s reagent?

A

It turned mahogany red because Fructose, a ketose, was detected

42
Q

F.1. Starch Hydrolysis process:

A

Starch + HCl, then boil

Add I2 drops on test plate, then add starch solution drop on each I2 drop until no color change is detected

43
Q

F.2. Upon addition of HCl, what is starch hydrolyzed into?

A

Multiple glucose forms

44
Q

F.3. The point at which starch no longer gives the blue color and is colorless is called _____

A

Achromatic point; starch no longer detected

45
Q

F.4. Stages of Starch Hydrolysis:

A
  1. Starch stage / dark blue
  2. Soluble Starch / dark blue
  3. Amylodextrin / purple
  4. Erythrodextrin / red
  5. Achrodextrin / colorless; the achromatic point
  6. Maltose / colorless
  7. Glucose / colorless

As starch is catabolized and converted to sugars, there will be less and less starch to react with the iodine

46
Q

F.5. During the hydrolysis of starch, there is a decrease in _____

A

Molecular Weight

47
Q

F.6. What happens when the neutralized starch is added with NaOH and Benedict’s reagent?

A

Red-orange precipitate forms

This is because Glucose, a reducing sugar, reduces the copper in Benedict’s reagent to copper oxide

OrgBio Chem (29 decks)

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