biomolecules Flashcards
what is carbohydrates
the carbohydrates may be defined as
optically active polyhydroxy aldehydes or ketones or the compounds
which produce such units on hydrolysis
why is carbohydrates, are also called sugars
Some of the carbohydrates,
which are sweet in taste, are also called sugars
the sugar present in milk is known as
lactose
Carbohydrates are also called
saccharides
what are Monosaccharides
A carbohydrate that cannot be hydrolyzed further to give simpler unit of polyhydroxy aldehyde or ketone is called a
monosaccharide. About 20 monosaccharides are known to occur in
nature
what are Oligosaccharides
Carbohydrates that yield two to ten
monosaccharide units, on hydrolysis, are called oligosaccharides. They
are further classified as disaccharides, trisaccharides, tetrasaccharides,
etc., depending upon the number of monosaccharides, they provide
on hydrolysis. Amongst these the most common are disaccharides.
The two monosaccharide units obtained on hydrolysis of a disaccharide
may be same or different
what are reducing sugars
All those carbohydrates which reduce Fehling’s solution and Tollens’ reagent are referred to as reducing sugars All
monosaccharides whether aldose or ketose are reducing sugars.
what are Polysaccharides
Carbohydrates which yield a large number of monosaccharide units on hydrolysis are called polysaccharides. Some common examples are starch, cellulose, glycogen, gums, etc. Polysaccharides are not sweet in taste, hence they are also called non-sugars
what are aldose
If a monosaccharide contains an aldehyde group, it is known as an aldose
what are ketose
If a monosaccharide contains an aldehyde group and if it contains a keto group, it is known as a ketose
Preparation of Glucose
From sucrose (Cane sugar)
From starch:
Preparation of Glucose From sucrose (Cane sugar)
If sucrose is boiled with dilute HCl or
H2SO4 in alcoholic solution, glucose and fructose are obtained in equal amounts.
Structure of Glucose
Glucose is an aldohexose and is also known as dextrose. It is the monomer of many of the larger carbohydrates, namely starch, cellulose.
Preparation of Glucose From starch:
glucose is obtained by hydrolysis of
starch by boiling it with dilute H2SO4
at 393 K under pressure.
how we get to know that glucose has five OH groups
Acetylation of glucose with acetic anhydride gives glucose pentaacetate which confirms the presence of five –OH groups. Since
it exists as a stable compound, five –OH groups should be attached
to different carbon atoms.
how we get to know that glucose is straight chain
On prolonged heating with HI, it forms n-hexane, suggesting that all the six carbon atoms are linked in a straight chain
how we get to know that glucose has carbonly group
Glucose reacts with hydroxylamine to form an oxime and adds a molecule of hydrogen cyanide to give cyanohydrin. These reactions confirm the presence of a carbonyl group (>C = O) in glucose
how we get to know that glucose has presence of a primary alcoholic (–OH) group in glucose.
On oxidation with nitric acid, glucose as well as gluconic acid both yield a dicarboxylic acid, saccharic acid. This indicates the presence of a primary alcoholic (–OH) group in glucose.
how we get to know that glucose has aldehydic group.
Glucose gets oxidised to six carbon carboxylic acid (gluconic acid) on reaction with a mild oxidising agent like bromine water. This indicates that the carbonyl group is present as an aldehydic group.
what The letters ‘D’ or ‘L’ before the name of any compound indicate
The letters ‘D’ or ‘L’ before the name of any compound indicate the relative configuration of a particular stereoisomer of a compound with respect to configuration of some other compound
