Biomolecules

14. Biomolecules

Carbohydrates:

Most carbohydrates have the general formula C x(H2O)y Classification of carbohydrates: Three groups (on the basis of their behaviour on hydrolysis)  Monosaccharides: Cannot be hydrolysed further to yield simpler units; Example: glucose, fructose  Oligosaccharides: On hydrolysis, give two to ten units of  monosaccharides  Disaccharides (give two units) Example: sucrose (gives glucose and fructose) maltose (gives two molecules of glucose)  Trisaccharides (give three units)  Tetrasaccharides (give four units), etc.  Polysaccharides: On hydrolysis, give a large number of units of  monosaccharides  Called non-sugars as they are not sweet to taste The carbohydrates which are sweet to taste are also called sugars.

All monosaccharides are reducing sugars Classification of monosaccharides  Aldose (contains an aldehyde group)  Ketose (contains a keto group) Different types of Monosaccharides Carbon atoms General term Aldehyde

3 4 5 6

Triose Tetrose Pentose Hexose

Aldotriose Aldotetrose Aldopentose Aldohexose

Ketone

Ketotriose Ketotetrose Ketopentose Ketohexose

7

Heptose

Aldoheptose

Ketoheptose

Glucose:

Evidences for the given structure  Molecular formula, C 6H12O6  The six C-atoms are linked in a straight chain.



Presence of a carbonyl



Presence of carboxyl groups as an aldehydic group



Presence of five  – OH groups attached to different carbon atoms

group



Presence of a primary alcoholic ( – OH) group

Spatial arrangement of  – OH groups

Cyclic structure of glucose  Reactions that are not explained by the open-chain structure  Does not give 2, 4 – DNP test, Schiff’s test, and does not form hydrogensulphite addition product with NaHSO 3  There is no reaction between pentaacetate of glucose and hydroxylamine (i.e., free  – CHO group is absent) and  There are two different crystalline forms of glucose,   – form and -form are called anomers  Haworth structure

Fructose:

Molecular formula, C 6H12O6 Structure

Cyclic structure (Haworth structure)

Disaccharides:

Glycosidic linkage Sucrose



Linkage between two monosaccharide units through oxygen atom

Invert sugar Maltose

The product of the hydrolysis of sucrose

Lactose It is also know as milk sugar (as it is found in milk)

Polysaccharides:

Starch 

Main storage polysaccharide of plants  Two components – Amylose and amylopectin Cellulose Predominant constituent of cell wall of plant cells Glycogen  Storage carbohydrates of animals  Known as animal starch Proteins:

Amino acids

Name of the amino acids

Characteristic feature of side chain, R

Three-letter symbol

Oneletter code

Glycine Alanine Valine* Leucine*

H  – CH3 (H3C)2CH –  (H3C)2CH – CH2 – 

Gly Ala Val Leu

G A V L

Ile

I

Arg

R

Lys

K

Glu Asp

E D

H 3C

CH 2

Isoleucine*

CH

| CH 3 HN

Arginine*

C

NH

CH 2

3

|

–  

NH 2

Lysine* Glutamic acid Aspartic acid

H2 N

HOOC

CH 2

CH2

4

CH

HOOC – CH2 – 

2

Glutamine

Gln

Q

Asparagine

Asn

N

Thr Ser Cys Met Phe Tyr

T S C M F Y

Tryptophan*

Trp

W

Histidine*

His

H

Proline

Pro

P

Threonine* Serine Cysteine Methionine* Phenylalanine* Tyrosine

H3C – CHOH –  HO – CH2 –  HS – CH2 –  H3C – S – CH2 – CH2 –  C6H5 – CH2 –  ( p)HO – C6H4 – CH2 – 

*essential amino acid, a = entire structure Classification of amino acids  Essential amino acids (cannot be synthesised in the body and must be obtained through diet) Example: valine, bucine, isoleucine, phenylalanine  Non-essential amino acids (can be synthesised in the body) Example: glycine, alanine, cysteine, aspartic acid In aqueous solution, amino acid exists as zwitter ion (a dipolar ion)

Structure of proteins:

Peptide linkage group

Amide formed between – COOH group and – NH2

Insulin contains 51 amino acids. Classification of proteins (based on their molecular shape)  Fibrous protein Parallel polypeptide chains are held together by hydrogen and disulphide bonds. Generally, they are insoluble in water. Example: keratin, myosin  Globular protein Coil of polypeptide chains of spherical shape. Generally, they are soluble in water. Example: insulin, albumin  Primary structure of protein  –  Sequence of amino acids in polypeptide chain  Secondary structure of protein  –  Due to regular folding of polypeptide chain on account of  H-bonding  – helix

 – pleated



Tertiary structure of protein  –  Overall folding of the polypeptide chains  Quaternary structure of protein  –  Spatial arrangement of subunits with respect to each other Denaturation of protein: Loss of biological activity by a protein as a result of unfolding of globules and uncoiling of helix. Example: coagulation of egg on  boiling, curdling of milk Enzymes: Biocatalysts C12 H 22 O11

Maltase

2C6 H12 O6 Glucose

 

Oxidoreductase: Enzymes which simultaneously catalyse the oxidation of one substrate and the reduction of another substrate Enzymes reduce the magnitude of activation energy of a reaction

Vitamins:

Organic compounds required in small amounts in the diet, whose deficiency causes specific diseases. Classification of vitamins  Fat-soluble vitamins: Vitamins A, D, E and K  Water-soluble vitamins: Vitamin C and B group vitamins Sl. No.

Name of  vitamins

Sources

1

Vitamin A

Fish, liver, oil, carrots, butter and milk

2.

Vitamin B1 (Thiamine)

Yeast, milk, green vegetables

Deficiency diseases

Xerophthalmia (hardening of cornea of eye), night  blindness Beri beri (loss of  appetite, retarded

and cereals

3.

Vitamin B2 (Riboflavin)

4.

Vitamin B6 (Pyridoxine)

5.

Vitamin B12

6.

Vitamin C (Ascrobic acid)

7.

Vitamin D

8.

Vitamin E

9.

Vitamin K

growth) Cheilosis (fissuring at corners of mouth Milk, egg white, and lips), digestive liver, kidney disorders and  burning sensation of  the skin Yeast, milk, egg yolk, cereals and Convulsions grams Pernicious anaemia Meat, fish, egg (RBC-deficiency in and curd haemoglobin) Citrus fruits, Scurvy (bleeding amla and green gums) leafy vegetables Rickets (bone deformities in Exposure to children) and sunlight, fish osteomalacia (soft and egg yolk  bones and joint pain in adults) Vegetable oils Increased fragility of  like wheat germ RBCs and muscular oil, sunflower weakness oil, etc. Green leafy Increased blood vegetables clotting time

Nucleic acids: Polymers of nucleotides

Mainly two types Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) Chemical composition of nucleic acid A pentose sugar Phosphoric acid Base (nitrogen-containing heterocyclic ring)  DNA Sugar moiety  – D – 2 – Deoxyribose Bases adenine (A), guanine (G), cytosine (C) and thymine (T)  RNA  – D – ribose Sugar moiety Bases adenine (A), guanine (G), cytosine (C) and uracil (U)

Structure of nucleic acid:

Formation of dinucleotide

Primary structure  – 

Sequence of nucleotides in the chain Secondary structure  –   Double-strand helix structure for DNA: The two strands are complimentary. This is because H –  bonds are formed between specific pairs of bases. A – T C – G



RNA is single stranded  Classification of RNA on the basis of their functions Messenger RNA (m – RNA) Ribosomal RNA (r – RNA) Transfer RNA (t – RNA) Biological functions of nucleic acids  DNA  Maintains the identity of different species





Stores the message for the synthesis of a particular protein



Carries out protein synthesis in the cell

RNA

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