As competition is getting tougher day by day, students don’t want to waste their precious time in reading the topics from the book just before any engineering entrance examination. They want to study only the concepts which are very important from the examination point of view.
To fulfil this need of engineering aspirants we bring the study notes and important previous years’ solved questions of chapter Bimolecules for coming UPSEE/UPTU examination.
Read about the following topics here:
1. Definition of Bimolecules
2. Examples of some common biomolecules like Carbohydrates, Proteins, Lipids, Nucleic acids, ATP molecules
3. Types of carbohydrates like Monosaccharide, Disaccharides and Polysaccharides
4. Some important chemical reactions of Monosaccharides
UPSEE: Important Questions and Preparation Tips – Solid State
Important Concepts:
Bimolecules
They are the organic molecules that are involved in the maintenance and metabolic processes of living organisms. Thus, they build up the living system and are responsible for their growth and maintenance.
Some of the common biomolecules are given below:
• Carbohydrates
• Proteins
• Lipids
• Nucleic acids
• ATP molecules
Carbohydrates:
On the basis of hydrolysis, carbohydrates are classified as follows:
(a) Monosaccharide
(b) Disaccharides
(c) Polysaccharides
Monosaccharide: These are the simpler carbohydrates which cannot be hydrolysed further to its constituent aldehyde or ketone.
For example glucose,fructose, galactose etc.
Disaccharides: It is a sugar which can be hydrolysed into two monosaccharides.
For example sucrose, lactose, maltose.
Polysaccharides: These are carbohydrates which on hydrolysis yield many monosaccharide units.
For example starch, cellulose, glycogen, gums, etc.
Monosaccharides and oligosaccharides are crystalline solids, soluble in water and sweet in taste. These are called sugars. Polysaccharides are amorphous, insoluble in water and tasteless. These are called non-sugars.
D and L configuration of Sugar:
For defining D and L configuration of sugar the compound glyceraldehydes, HOCH2CH(OH)CHO was chosen as the standard.
Compounds that resembles D-glyceraldehyde at one terminal is known as D-sugar. Similarly, compound that resembles L-glyceraldehyde at one terminal is known as L-sugar.
Note: Natural sugar are D-sugar and synthetic sugar are L-sugar.
Cyclic Structure of Monosaccharides:
Some monosaccharides adopt cyclic structures. This conversion occurs because of the ability of aldehydes and ketones to react with alcohols:
Reactions of monosaccharides
Oxidation Reaction:
(a) Reaction with Br2 – H2
The oxidation of monosaccharides with Br2 – H20 is shown as follows:
Note: Ketose is not oxidized by Br2 – H20 because it causes epimerization.
(b) Reaction with dilute HNO3
The oxidation reaction of monosaccharide with dilute HNO3 is as follows:
(c) Tollen’s Test:
Ammonical AgNO3 is called Tollen’s reagent. It oxidizes aldehyde group of sugar into carboxylic acid.
Note: Ketose also give Tollen’s test because of basic medium. In basic medium Ketose is first of all epimerized to aldose and aldose gives Tollen’s test.
Reducing and non reducing Sugars:
Reducing Sugar: Those sugar which reduces Tollen’s reagent are called reducing sugar.
Non Reducing Sugars: Those sugar which fail to reduce Tollen’s reagent are called non reducing sugar.
Reaction with Phenylhydrazine:
Both glucose and fructose react with phenylhydrazine whose chemical formula is C6H5NHNH2 to form osazone.
Glucose and Fructose react as shown below:
Reduction: Sugar are reduced either with NaBH4 or with H2/Ni into sugar-alcohol.
Some previous years’ solved questions are given below:
Question 1:
Solution 1:
Hence, the correct option is (B).
UPSEE: Important Questions and Preparation Tips – Solutions
Question 2:
A solution of D-glucose in water rotates the plane of polarised light
(A) To the left
(B) To the right
(C) To either side
(D) None of these.
Solution 2:
D-glucose rotates the plane polarised light to the right.
Hence, the correct option is (B).
UPSEE: Important Questions and Preparation Tips – Thermodynamics (Part 1)
Question 3:
Which of the following pairs give positive Tollen’s test?
(A) Glucose, Sucrose
(B) Glucose, Fructose
(C) Hexanal, Acetophenone
(D) Fructose, Sucrose
Solution 3:
Aldehyde gives positive Tollen’s test. However under the strongly basic condition of the test α-hydroxy ketones can isomerise to aldehydes so that’s why they also give a positive Tollen's test α - hydroxy ketones.
Hence, the correct option is (B).
UPSEE: Important Questions and Preparation Tips – Equilibrium
Question 4:
The two forms of D-glucopyranose obtained from the solution of D-glucose are called
(A) enantionier
(B) epimer
(C) anomer
(D) isomer
Solution 4:
The two forms of D-glucopyranose obtained from the solution of D-glucose are called anomers. They are: α-D(+) glucopyranose and β-D(+)-glucopyranose. Anomers are a pair of stereoisomer which differs in configuration only around first carbon atom.
Hence, the correct option is (C).
UPSEE: Important Questions and Preparation Tips – States of Matter
Conclusion:
Students will find every important topic related to Bimolecules here. They can refer the topics mentioned in these notes instead of reading the complete theory from the books to save their time. It is presented in a systematic manner to help students in grasping the content easily.
