CARBOHYDRATES SEMIS Flashcards
A polyhydroxy aldehyde, a polyhydroxy ketone, or a compound that yields polyhydroxy aldehydes or polyhydroxy ketones upon hydrolysis.
CARBOHYDRATES
Also known as simple sugars
Highly soluble in water
Less soluble in ethanol
Insoluble in ether
MONOSACCHARIDES
Monosaccharides may also be classified into:
Tetroses
Pentoses
Hexoses
Formed by two molecules monosaccharides
Disaccharides
Are abundant in germinating barley
Maltose
Also known as cane sugar or beet sugar
Sucrose
This does not taste very sweet and is not fermented by yeast
Lactose
Found in nature function either as structural units or for storage such as starch, dextrin, glycogen, insulin
Polysaccharides
Give the 4 Polysaccharides for storage
Starch
Dextrin
Glycogen
Insulin
Give the 3 general tests for carbohydrates
Molisch test
Bial’s orcinol test
Seliwanoff’s test
The general test for carbohydrates
Molisch test
In Molisch test the sugars are with a ____
A-naphthol
The concentrated H2SO4 will dehydrate the sugar allowing it to react with the alcohol forming a _____
Furfural or hydroxymethyl-furfural
When the Molisch test result is colorless, the result is?
Negative
When the Molisch test result has a purple/violet ring, the result is?
Positive
Used to determine the presence of pentoses and nucleotides and nucleotides that contain pentose sugars
Bial’s Orcinol Test
When pentoses are treated with orcinol, furfurals are formed and they will yield a _____ compound in the presence of ferric ion
Blue-green compound
Hydroxymethyl furfural is formed from hexoses to give ________ condensation products.
Yellow-brown
In Bial’s Orcinol Test what color indicates pentoses
Blue-green color
In Bial’s Orcinol Test what color indicates hexoses (negative)
Yellow-brown color
This test is used to differentiate keohexoses from aldohexoses
Seliwanoff’s test
This react faster with the solution containing hydrochloric acid and resorcinol
Ketohexoses
The dehydrated positive ketohexoses form a ______
Bright cherry red condensation product
Aldohexose yields a ______ that is a negative result
Pale pink color
Any sugar that, in a solution, has an aldehyde or a ketone group
Reducing sugar
Name the 8 reducing sugars
Glucose
Galactose
Fructose
Ribose
Glyceraldehyde
Xylose
Cellobiose
Lactose
Give the 3 test based on reducing property of sugars
Benedict’s test
Barfoed test
Tollen’s test
It is a very sensitive test done in mildly alkaline conditions
Benedict’s test
Benedict’s reagent are composed of;
CuSO4
Na2CO3
Sodium citrate
When the Benedict’s reagent changes color the result is?
Positive
Used to test the presence of glucose in urine
Benedict’s test
Benedicts solution and simple carbohydrates are heated, the solution changes to what color?
Orange red/brick red
What is the color of the Benedict’s solution when there are traces of reducing sugar?
Green/yellow
What is the color of the Benedict’s solution when there are moderate amount of reducing sugar?
Orange red
What is the color of the Benedict’s solution when there are large amount of reducing sugar?
Brick-red
A copper reduction test in which heating a mixture of a monosaccharides in a given time interval results in the conversion of cupric ions in the reagent to cuprous ions with the formation of copper (I) oxide seen as a brick red precipitate in the mixture
Barfoed Test
Copper reduction in Barfoes’s test occurs in an
Acidic medium (pH 4.6)
In Barfoed test when red precipitate is formed faster what is present?
Monosaccharides
In Barfoed test when red precipitate is formed slower what is present?
Disaccharide
Also known as silver mirror test
Tollen’s test
Sugars with ________ are capable reducing Tollen’s reagent
Aldehyde groups
What is the Tollen’s reagent?
Ammoniacal solution of silver
What is the color of a positive result Tollen’s test?
Gray - black precipitate (silver mirror)
Reducing sugars that reduce silver ions in the test reagent to elemental silver
Glucose & lactose
Common dietary monosaccharides
Glucose
Galactose
Fructose
Examples of Pentose
Ribose & cellobiose
2 Examples of Pentose
Ribose & cellubiose
4 Examples of hexoses
Glucose, fructose, galactose, maltose
Most important sugars
Pentoses & hexoses
3 Examples of aldehyde
Glucose, maltose, galactose
Example of ketone
Fructose
Molisch test is based on dehydration by ____
Sulfuric acid
