CBSE Class 12 Chemistry Biomolecules Notes Set 03

Chemistry Concept Notes for Class 12: Unit 10 Biomolecules

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Bio molecule

Gist Of The Chapter

1.Carbohydrates‐ These are optically active polyhydroxy aldehydes or ketones due to presence of chiral `C’ or the compounds which produce these on hydrolysis except dihydroxy acetone is not optically active.

2. Classification

i) Monosaccharide’s – Those carbohydrates which cannot get hydrolysed e.g. glucose ,fructose, galactose etc.

(ii) OligosaccharidesThose carbohydrates which give to or more monosaccharide’s on hydrolysis e.g. sucrose on hydrolysis gives glucose and fructose. Raffinose on hydrolysis gives glucose, fructose and galactose.

(iii) Polysaccharides‐ Those carbohydrates which on hydrolysis give large number of monosaccharide’s hydrolysis.eg starch, cellulose, glycogen.

3. Sugar-

i)Reducing SugarsThose which reduce Fehling’s or Tollen’s reagent. They have free aldehydic groups, eg , glucose, fructose , galactose

(ii)Non Reducing SugarsThose which do not reduce Fehling’s or Tollen’s reagent. They do not have free functional group ,e.g., sucrose

4. Glucose‐ It is a monosaccharide’s with molecular formula C6H12O6

5. Preparation

(i)F mSucrose

C12H22O11 + H2O ‐‐‐‐‐‐‐> C6H12O6 + C6H12O6 ( Only from sucrose)

(ii)From tarch

(C6H10O5)n + nH2O ‐‐‐‐‐‐‐> C12H22011 + H20 ‐‐‐‐‐‐> 2C6H12O6

6.Structure

(i)Fischer structure –

CHO — (CHOH)4 — CH2OH

(+) Glucose has `D’ configuration as shown

 class_12_chemistry_concept_36

`D’ means —OH group on first chiral `C’ from the bottom is on right hand and + means it is dextro rotator, i.e, it rotates plane polarized light towards right.

(ii) Cyclic Structure OF Glucose: the straight chain is unable to explain the following reactions.

(a) It does not give the 2, 4‐DNP test, Schiff’s Test and does not form the hydrogensulphide product with NaHSO3 .

(b) The pentacetate of glucose does not react with NH2OH, indicating the absence of free aldehydic group.

(iii) Glucose exist in 2 different crystalline forms α and β forms. These are called anomers. They differ in optical rotation, they also differ in melting point.

Anomers are isomers which have a different configuration across C‐1 (first chiral ‘C’ atom).

7. Glycosidic Linkage: The linkage between two monosaccharide units through oxygen is called the glycosidic linkage. 

8. Proteins: These are micro molecules made up of amino acids joined via a peptide link ( ‐(‐CONH‐)‐ is the peptide linkage). These are required for growth and development of the body. 
 
9. Amino Acids: These contain an amino (‐NH2) and an acidic (‐COOH) group and are therefore amphoteric in nature. In solution they exist in the form of zwitter ion. 
 
10. Classification
 
CBSE Class 12 Chemistry notes and questions for Biomolecules Part B 1
 
11. Structure And Shape of Protein
 
CBSE Class 12 Chemistry notes and questions for Biomolecules Part B 2
CBSE Class 12 Chemistry notes and questions for Biomolecules Part B 3
12. Denaturaion of Protein: The protein in native state, when subjected to a physical change like temperature, pH etc undergoes uncoiling and looses it’s biological activity. The 2o and 3o structures are destroyed, only 1o structure is retained.
 
Renaturation of Protein:
Some proteins regain their biological activity by reversible process it is called Renaturation of Proteins. In such a cases, when temperature in pH of a denatured proteins is brought back to conditions in which the native protein is stable, secondary and tertiary structures of proteins are restored to which leads to recovery of biological activity.
 
13. Enzymes: These are biocatalyst and generally globular proteins e.g., invertase,zymase,phenyl, alaninehydroxylase, urease etc.
 
14. Vitamins: They are organic compounds required in the diet in small amounts to perform specific biological functions for maintenance of optimum growth and health of the organism. They are classified as follows
(i) Fat Soluble Vitamins: Vitamin A,D,E and K. They are stored in liver and adipose tissues. 
(ii) Water Soluble Vitamins: B group vitamins and vitamin C. They need to supplied regularly in diet as they are excreted in urine and cannot be stored(except vitamin B12) in our body.
Their deficiency causes diseases.Biotin (Vit H) is however neither fat nor water soluble. It’s deficiency leads to loss of hair. 
 
15. Nucleic Acids: These are biomolecules which are long chain polymers of nucleotides. They are: 
(i) Deoxyribonucleic acid (DNA) 
(ii) Ribonucleic acid (RNA) 
They are responsible for protein synthesis and transfer of genetic characteristics to offspring’s. 
 
16. Composition of Nucleic Acid:
They are made up of pentose sugar(β‐D‐2‐deoxyribose in DNA and β‐Dribose in RNA), phosphoric acid and a nitrogen containing heterocyclic compound(base). 
DNA‐ Bases present are Adenine(A), Thymine(T),Guanine(G) and Cytosine(C). 
RNA‐ contains Adenine(A), Guanine(G), Cytosine(C) and Uracil(U). 
 
17. Nucleoside: The unit formed by the attachment of a base to n1’‐ position of sugar (Base+Sugar). 
 
18. Nucleotide: Nucleoside and phosphoric acid at 5’‐position.Nucleotides are bonded by phosphodiester linkages between 5’ and 3’ carbon atoms of pentose sugar (Base+ Sugar+ Phosphoric Acid). 
 
19.DNA : has a double helical structure with AT and GC linked together through 2 and 3 hydrogen bonds respectively. It is responsible for transfer of genetic characteristics. 
 
20. RNA: is of three types‐ messenger RNA(m‐RNA), ribosomal RNA(r‐ RNA) and transfer RNA (t‐RNA). RNA helps in protein synthesis. 
 
21. Biological Functions of Nuclei Acid: DNA is chemical basis of hereditary and have the coded message for proteins to be synthesized in the cell. RNA carry out the protein synthesis in the cell.

 

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