Quiz 3

Question 1

Define carbohydrates

Answer 1

Contain carbon, hydrogen, and oxygen which can directly or indirectly after hydrolysis, reduce alkali solutions of heavy metal salts

Question 2

What are the different types of carbs?

Answer 2

Monosaccharide
Oligosacchrides
Polysacchrides
Homosaccharides: contains the same monosacchrides unit
Heteropolysacchrides: contain different monosacchrides

Question 3

What are some naturally occurring monosacchrides?

Answer 3

Trioses: D-glyceraldehyde, dihydroxyaceton
Pentose: bêta-D-ribofuranose, bêta-D-deoxyribofuranose
Hexoses: D-glucose, D-mannose

Question 4

How do you determine alpha animer from beta anomer?

Answer 4

Alpha anomer: OH is projecting downwards

Beta anomer: OH is projecting upwards

Question 5

What are the different reactivity of carbs?

Answer 5

1. Potential reducing group: an unreacted OH group is a potential reducing group, forming a straight chain molecule with an aldehyde grouping on the end
2. High capacity to rotate plane polarized light (polarimèter): translated into sugar units
3. Seperation by chromatography
4. High capacity to interact with water: hydrophilic

Question 6

What is a pyranose?

Answer 6

Contains 5 to 6 carbons and 1 oxygen
Alford and ketose forms
The oxygen is placed between carbons at the position C1 and C5

Question 7

What is a furanose?

Answer 7

Contains 4-5 carbons and 1 oxygen
Contain aldose and ketose forms
Oxygen is placed between the carbons at the position C1 and C4

Question 8

How do you determine number of isomers?

Answer 8

Aldose= 2^(n-2)
Ketose= 2^(n-3)

n = # of carbons

Question 9

Describe starch

Answer 9

Poly D glucose

1,4-alpha glycosidic bond and 1,6-alpha glycosidic bond

Question 10

Lost some naturally occurring saccharides

Answer 10

Starch
Trehalose: glucose and glucose (1-1* linkage)
Turanose: glucose and fructose (1*-3 linkage)
Maltose: glucose and glucose (a-glycosidic linkage)
Sucrose: glucose and fructose (ab-glycosidic linkage)

Question 11

Describe the iodine test

Answer 11

Distinguishes starch and glycogen from other polysacchrides
Starch= dark blue
Glycogen= brown
No colour change = polysacchrides
Iodine atoms fit into helices to form starch-iodine complexes or glycogen-iodine complexes

Question 12

Describe benedicts test

Answer 12

Red precipitate = reducing sugars
No colour change = non reducing sugar
Reducing sugars are oxidized by the copper ion in solution to form a carboxylic acid and a reddish precipitate of copper oxide

Question 13

Describe barfoeds test

Answer 13

Also uses Cu2O
Dark blue= monosacchrides
Light blue= disaccharides
A reddish precipitate shows up as a positive result
The precipitate shows up much sooner with monosacchrides than disaccharides

Question 14

Describe seliwannoffs test

Answer 14

Differentiates between ketohexoses and aldohexoses
When a ketose is heated with strong mineral acid, 5-hydroxymethylfulfural is formed
Forms a red complex with recorcinol
Aldoses - occurs more slowly

Question 15

Describe HPLC

Answer 15

Identifies monosacchrides
Dilute HCl hydrolyses oligosacchrides into their consituant monosacchrides 
Mobile = liquid phase
Stationary = solid
Normal = stationary phase is more polar 
Reverse = stationary phase is less polar

Question 16

What does treatment with sodium borohydride do?

Answer 16

Aldehyde group in terminal ring is reduced to a hydroxyl group

Question 17

What is the anthrone reaction?

Answer 17

Concentrated sulfuric acid and heat hydrolyses all the inter-ring links (glycisidic bonds)
Sulfuric acid also oxidized each of the monomers and produces a hydroxymethyk furfural
A momifier monomeric product reacts with the anthrone reagent to produce m moles of coloured product
Sodium borohydride will cause terminal aldose ring to be reduced to hydroxyl group and become inert
Leads to the production of oxidized monomers of coloured product following the same procedure