carbohydrates Flashcards
Classification by number of Monosaccharide units:
● Monosaccharides (1) - glucose, fructose, galactose (GFG)
● Disaccharides (2) - maltose, lactose, sucrose (MLS)
● Oligosaccharides (2-10) - raffinose, stachyose
● Polysaccharides (10 or more) - starch, glycogen, cellulose
Simplest sugar and cannot be hydrolyzed further
Monosaccharide
Classification by number of Carbon atoms:
● Pentoses: five carbon atoms
○ Aldopentoses: ribose and xylose
● Hexoses: six carbon atoms
○ Aldohexoses: glucose, galactose
○ Ketohexoses: fructose
Converts pentoses into furfural and hexoses into 5-hydroxymethylfurfural which then reacts with phenolic compounds
Dehydrating acids
Reducing sugars include aldoses containing either a free aldehyde group or a cyclic hemiacetal
Copper (II) ions containing solutions
Objective of Benedicts Test
To determine the presence or absence of reducing sugar in the solution.
● All monosaccharides are reducing sugars
● A reducing sugar has a free aldehyde group or a free ketone group
Sodium carbonate: _____ g
Sodium citrate: _____ g
Distilled water: _____ mL
Copper sulfate pentahydrate: _____ g
Sodium carbonate: 10g
Sodium citrate: 17.3g
Distilled water: 100 mL
Copper sulfate pentahydrate: 1.73g
Na carbonate: provides ________
Na citrate: forms ________
Na carbonate: provides alkaline medium
Na citrate: forms complexes with Cu^2+ ions
(Benedict’s Test) Interpretation of Result
● Blue - 0, negative/no sugar
● Green - 0.5-1%, traces of reducing sugar
● Yellow - 1-1.5%, low amount of reducing sugar
● Orange - 1.5-2%, moderate amount of reducing sugar
● Brick red - >2%, large amount of reducing sugar
(Benedict’s Test)
Positive color:
Variable color:
Positive color: brick red precipitate
Variable color: green (+/-)
Barfoed’s Test Objectives
used to detect the presence of reducing monosaccharides
distinguish reducing monosaccharides from disaccharides
(Barfoed’s Test) Interpretation of Result
● Positive Result: Brick red precipitate at the bottom of the tube.
● Monosaccharide + barfoed’s reagent = 5 minutes (brick red/red/brown precipitate)
● Disaccharide + barfoed’s reagent = 10 minutes (any color)
(Barfoed’s Test)
Positive color:
Barfoed’s reagent:
Positive color: brick red/brown
Barfoed’s reagent: copper sulfate & acetic acid
In Barfoed’s Test, Acetic acid - provides _______
condition that ________ pH
acidic, decreases
Seliwanoff’s Test Objective
● To detect the presence of ketohexoses in a given sample.
● To distinguish ketoses from aldoses.
Seliwanoff’s Test | Interpretation of Result
Ketose Color
Aldose Color
● Ketose reacts to produce a deep cherry red color
● Aldoses may react slightly to produce a faint pink to cherry red color if the test is prolonged.
In Seliwanoff’s Test, ______ and _______also give a positive result for this test as these are hydrolyzed by acid to give fructose.
Sucrose and Insulin
Bial’s Orcinol Test Objective
● To detect the presence of carbohydrates.
● To distinguish the pentoses and pentosans from other derivatives of carbohydrates like the hexoses.
Bial’s Test Interpretation of Result
Positive color:
Negative color:
Positive color: blue-green
Negative color: any color besides blue-green
The presence of a blue-green complex indicates the presence of _________ in the sample.
pentoses
Bial’s Solutions
5% fructose, 5% sucrose, 5% ribose, 5% glucose
Purpose of Mucic Acid Test
● Detects galactose and lactose in a
given sample.
● Distinguish galactose containing
saccharides and other sugars.
Each test’s objective
Benedict’s Test:
Barfoed’s Test:
Seliwanoff’s Test:
Bial’s Orcinol Test:
Benedict’s Test: amount of sugar
Barfoed’s Test: if monosaccharide or disaccharide
Seliwanoff’s Test: if aldose or ketose
Bial’s Orcinol Test: if pentose or hexose
What is Mucic Reagent and Nitric Acid
● Mucic Reagent is a concentrated
Nitric Acid.
● Nitric Acid causes the formation of
crystals in a solution.
(Mucic’s Test) Interpretation of Result
● Positive Mucic Acid Test - Crystals are present and the indication is that galactose is present.
● Negative Mucic Acid Test - No crystals are present and the indication is that galactose is absent.
Purpose of PHENYLHYDRAZONE TEST
● The objective of this test is to detect reducing sugars from non-reducing sugars.
● This is also used to distinguish reducing sugars from each other.
MATERIALS AND REAGENTS OF PHENYLHYDRAZONE TEST
● Phenylhydrazine HCl
● CH COONa
● Distilled water
● Test tubes
● Carbohydrate solutions (glucose, fructose, xylose, lactose, sucrose and starch)
● Microscope
MATERIALS AND REAGENTS OF MUCIC ACID TEST
● Carbohydrate Solution (Galactose and Lactose)
● Concentrated HNO3
● Alcohol Lamp
● Microscope
● Mucic Reagent
● Test sample
● Distilled Water
● Test tube
● Test tube stand
● Pipette
What is Mucic acid test
a test that is highly specific and is used for the detection of the presence of galactose and lactose.
Other term for Mucic Acid
galactaric acid
What is Phenylhydrazone Test
a chemical test used to detect and differentiate reducing sugars
Phenylhydrazone Test
Differentiation of reducing sugars is based on the ____________________________ and ________________________.
Differentiation of reducing sugars is based on the time of appearance of the complex and relative solubility in hot water.
Examples of reducing sugars are
glucose, fructose, glyceraldehyde and galactose.
Buffer is a combination of ?
weak acid and weak base.
Phenylhydrazone Test is based on the fact that carbohydrates with free or potentially free carbonyl groups react with _______________ to form _______________
phenylhydrazine to form osazone.
The condensation-oxidation-condensation reaction between three molecules of phenylhydrazine and carbon one and two of aldoses and ketoses yields
1, 2-diphenylhydrazine, which is known as osazone.
Osazone appears as _______________ of characteristic shape, solubility, melting point, and time of formation.
yellow-colored crystals
Reaction for Mucic Acid Test
CH2OH - (CHOH)4 - CHO + HNO3 -> CH2OH - (CHOH)4 -CHO - NO3 + H^+
Limitation of Mucic Acid
● It cannot distinguish between the monosaccharide and disaccharide kind of galactose.
● False-positive results occur due to impurities of carbonyl groups at the terminal end.
Lactose also yields a _________, due to the _______ of the
________ between the __________ and ________ subunits of the carbohydrate.
Lactose also yields a mucic acid, due to the hydrolysis of the glycosidic bond between the glucose and galactose subunits of the carbohydrate.
Other monosaccharides like glucose also have a similar structure; however, the resultant precipitate Formed in glucose is ____________ under _______ temperature.
water-soluble, room
Aldohexoses (monosaccharide) upon treatment with potent oxidizing agents like nitric acid yield _____________________.
saccharic acids (dicarboxylic acids)
Nitric acid has the capacity to oxidize both aldehyde and primary alcoholic groups present at C1 and C6 respectively of galactose to yield an _____________________ of mucic acid under ______________.
insoluble precipitate (rod-shaped crystals), higher temperature.
