CBSE Class 12 Chemistry Biomolecules Notes Set D

BIOMOLECULES

POINTS TO REMEMBER

1. Carbohydrates are optically active polyhydroxy aldehydes or ketones or molecules which provide such units on hydrolysis.

2. Corbohydrates are classified into three groups    (i) monosaccharides,

(ii) oligosaccharides and         (iii) polysaccharides.

3. Glucose, the most important source of energy for mammals, is obtained by the digestion of starch.

4. Monosaccharides are held together by glycosidic linkages to form disaccharides or polysaccharides.

5. Proteins are the polymers of about twenty different amino acids which are linked by peptide bonds. Ten amino acids are called essential amino acids because they can not be synthesised in our body, hence must be provided through diet.

6. Proteins perform various structural and dynamic functions in the organisms. Proteins which contain only amino acids, are called simple proteins.

7. The secondary or tertiary structure of proteins get disturbed on change of pH or temperature and they are not able to perform their functions. This is called denaturation of proteins.

8. Enzymes are biocatalysts which speed up the reactions in biosystems. They are very specific and selective and efficient in their actions and chemically all enzymes are proteins.

9. Vitamins are necessory food factors required in the diet. They are classified as fat soluble (A, D, E and K) and water soluble (B group and C).

10. Nucleic acid are responsible for the transfer of characters from parents to offsprings.

11. There are two types of nucleic acids DNA and RNA. DNA contains a five carbon sugar molecule called 2-deoxyribose and RNA contains ribose.

12. Both DNA and RNA contain adenine, guanine and cytosine. The fourth base is thymine in DNA and uracil in RNA. The structure of DNA is double stranded while that of RNA is a single stranded molecule.

13. DNA is the chemical basis of heredity and has the coded message for proteins to be synthesised.

14. There are three types of RNA, i.e., m-RNA, r-RNA and t-RNA which actually carry out the protein synthesis in the nucleus.

15. Human stomach does not have any enzyme capable of breaking cellulose molecules and thus we cannot digest cellulose.

QUESTIONS

VSA TYPE QUESTIONS (1 - MARK QUESTIONS)

1. Name polysaccharide which is stored in the liver of animals.

2. What structural feature is required for a carbohydrate to behave as reducing sugar?                             [Hint : The carbonyl group of any one monosaccharide present in carbohydrate should be free]

3. How many asymmetric carbon atoms are present in D (+) glucose?

4. Name the enantiomer of D-glucose.                                                                                                    [Hint : L-glucose]

5. Give the significance of (+)-sign in the name D-(+)-glucose.                                                                 [Hint : (+) sign indicates dextrorotatory nature of glucose].

6. Give the significance of prefix ‘D’ in the name D-(+)-glucose.                                                                [Hint : ‘D’ Signifies that –OH group on C-5 is on the right hand side]

7. Glucose is an aldose sugar but it does not react with sodium hydrogen sulphite. Give reason.                 [Hint : The –CHO group reacts with –OH group at C–5 to form a cyclic hemiacetal].

8. Why is sucrose called invert sugar?                                                                                                     [Hint : When sucrose is hydrolysed by water, the optical rotation of solution changes from                                                                                                                                                                                                                                 positive to negative.]

9. Name the building blocks of proteins.

10. Give the structure of simplest optically active amino acid.

11. Name the amino acid which is not optically active.

12. Write the Zwitter ionic form of aminoacetic acid. stranded while that of RNA is a single stranded molecule.

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