15 Questions
What is the purpose of Benedict’s test in biochemistry?
To detect the presence of monosaccharides and some disaccharides
Which types of saccharides have an aldehyde group?
Only monosaccharides with aldehyde or ketone groups
What type of saccharides can open into aldoses?
Mono and some di-saccharides with a hemiacetal group
What is the characteristic feature of all monosaccharides?
Hemiacetal group
Why can some di-saccharides not open into aldoses?
They are 'locked' in a form of acetal
Which reagent is used to detect the presence of monosaccharides and some disaccharides directly in a urine sample?
Benedict's test
Which type of saccharides can be isomerized in an alkaline medium to give an aldehyde?
Ketoses
Which group of saccharides has a characteristic feature that allows them to open into aldoses?
Cyclic saccharides with hemiacetal group
Why do some di-saccharides test negative with Benedict’s reagent?
They are in a locked form of acetal
What characteristic feature do all monosaccharides have that allows them to be isomerized to aldehydes?
Hemiacetal group
Which monosaccharide will give a positive result in Seliwanoff's test after more than 7 minutes?
Glucose
What is the characteristic feature of the monosaccharide that allows it to be isomerized to fructose and then dehydrated to give a positive Seliwanoff's test result?
Aldehyde group
Which disaccharide should be digested to monosaccharides of fructose before it can give a positive Seliwanoff's test result?
Sucrose
What is the minimum time it takes for fructose to dehydrate and give a positive result in Seliwanoff's test?
More than 7 minutes
What is the minimum concentration of fructose (ketose) that the Seliwanoff's test is sensitive to, in the absence of glucose (aldose)?
0.1 gm%
Study Notes
Seliwanoff's Test
- Used to differentiate between ketoses and aldoses in mono and disaccharides
- Uses HCl as a dehydrating agent and resorcinol as a condensing agent
Reaction Principle
- Involves a dehydration reaction due to the hydroxyl groups of the sugar
- Seliwanoff's reagent consists of resorcinol in dilute hydrochloric acid
- Ketoses (e.g. fructose) are more readily dehydrated by HCl than aldoses
Test Results
- Produces a clear colored solution with intensity proportional to the amount of ketoses
- Can be coupled with spectrophotometric measurement to quantify the amount of ketoses in solution
Test your knowledge about the reactions of carbohydrates, including Benedict’s test and the types of saccharides based on their functional groups.
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