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WBJEE: Study Notes & Important Questions for Bimolecules

Jan 18, 2018 16:33 IST
    WBJEE 2018: Bimolecules
    WBJEE 2018: Bimolecules

    To secure a good rank in engineering entrance exam does not depend on how much students study during their preparation. It totally depends on how much students can recall when they actually appeared for the examination. 

    In Chemistry subject, students have to remember more theory as compared to Physics and Mathematics. But it is impossible for students to study from the text books before few days of the examination as the syllabus is very vast but the time is very limited. All students should try to focus only on important concepts or theory.

    In this article, students can find important concepts related to chapter Biomolecules in a very concise form for WBJEE 2018.

    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

    Important Concepts:


    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


    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.

    WBJEE Bimolecules Concepts 1

    Disaccharides: It is a sugar which can be hydrolysed into two monosaccharides.

    For example sucrose, lactose, maltose.

    WBJEE Bimolecules Concepts 2

    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.

    WBJEE Bimolecules Concepts 3

    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:

    WBJEE Bimolecules Concepts 4

    Reactions of monosaccharides

    Oxidation Reaction:

    (a) Reaction with Br2 – H2

    The oxidation of monosaccharides with Br2 – H20 is shown as follows:

    WBJEE Bimolecules Concepts 5

    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:

    WBJEE Bimolecules Concepts 6

    (c) Tollen’s Test:

    Ammonical AgNO3 is called Tollen’s reagent. It oxidizes aldehyde group of sugar into carboxylic acid.

    WBJEE Bimolecules Concepts 7

    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:

    WBJEE Bimolecules Concepts 8

    Reduction: Sugar are reduced either with NaBH4 or with H2/Ni into sugar-alcohol.

    WBJEE Bimolecules Concepts 8

    WBJEE: Important Questions and Preparation Tips for Alcohol

    Some solved questions are given below:

    Question 1:

    Which of the following is disaccharide?

    (a) Ribose

    (b) 2-deoxyribose,

    (c) Maltose,

    (d) Galactose

    Solution 1:

    Ribose, 2-deoxyribose, Galactose are Monosaccharides while Maltose is Disaccharide.

    Hence, the correct option is (c).

    Question 2:

    Natural sugar is:

    (a) D-sugar

    (b) L-sugar

    (c) Either D or L sugar

    (d) None of these

    Solution 2:

    Natural sugar is D-sugar while synthetic sugar is L-sugar.

    Hence, the correct option is (a).

    Question 3:

    DNA and RNA contain four bases each. Which of the following bases in not present in RNA?

    (a) Adenine    

    (b) Uracil        

    (c) Thymine    

    (d) Cytosine

    Solution 3:

    DNA contain four bases adenine, guanine, thymine and cytosine. While RNA contain four bases adenine, uracil, guanine and cytosine. Thus, RNA does not contain thymine.

    Hence, the correct option is (c).

    Question 4:

    Which of the following acids is a vitamin?

    (a) Aspartic

    (b) Ascorbic acid        

    (c) Adipic acid           

    (d) Saccharic acid

    Solution 4:

    Ascorbic acid is the chemical name of vitamin C. While others are not vitamins aspartic acid is an amino acid. Adipic acid is a dicarboxylic acid having 8 carbon chain. Saccharic acid is a dicarboxylic acid obtained by oxidation of glucose using HNO3.

    Hence, the correct option is (b).

    Question 5:

    Proteins can be classified into two types on the basis of their molecular shape, i.e., fibrous proteins and globular proteins. Examples of globular proteins are

    (a) insulin       

    (b) keratin       

    (c) albumin     

    (d) myosin

    The structure of protein which results when the chain of polypeptides coil around to give a spherical shape are known as globular protein. These proteins are soluble in water, e.g., insulin and albumin are globular protein. Hence, (a) and (c) are correct choices.

    Solution 5:

    Ascorbic acid is the chemical name of vitamin C. While others are not vitamins aspartic acid is an amino acid. Adipic acid is a dicarboxylic acid having 8 carbon chain. Saccharic acid is a dicarboxylic acid obtained by oxidation of glucose using HNO3.

    Hence, the correct options are (a) and (c).


    The content is presented in a systematic manner which will help students to grasp the things very easily. Students can refer these notes for the revision instead of reading text books to save their precious time when exams are around the corner.

    WBJEE 2018: Notification, Application, Dates, Eligibility, Exam Pattern, Syllabus

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