Biomolecules

{tocify} $title={Table of Contents}

Classification of Carbohydrates

Based on no of products on Hydrolysis

• Monosaccharides: Doesn't undergo Hydrolysis
• Oligosaccharides: Undergo Hydrolysis and give 2-10 units
• Polysaccharides: Undergo Hydrolysis and give more than 10 units

Based on no of Carbon atoms

• Classified as: Triose, Tetrose, Pentose, Hexose for 3, 4, 5, 6 Carbons respectively
• Aldo suffix used if it has -CHO group otherwise Keto for -CO- groups

Based on Reducing properties

• Reducing Sugars: Reduce Tollen's reagent, Fehling's Solution, and Benedict's Solution. It possess a free Hemiacetal or Hemiketal group. Eg: All monosaccharides, Maltose, Lactose
• Non-Reducing Sugars: Doesn't Reduce Tollen's reagent, Fehling's Solution, and Benedict's Solution. It doesn't possess a free Hemiacetal or Hemiketal group. Eg: Few oligosaccharides and polysaccharides, Starch, Cellulose, Sucrose

Sugar Molecule tree

The simplest Carbohydrate known was Glyceraldehyde. D & L isomers are taken based on the reference of C2 of Glyceraldehyde. If the lowermost chiral carbon contains \(\text{OH/NH}_{2}\) on its right then it is called D-isomer otherwise it is called L-isomer

Monosaccharides

Glucose

• Molecular formula of Glucose is \( \text{C}_{6}\text{H}_{12}\text{O}_{6} \)

• This implies that all carbons are on a straight line

• This implies that all carbonyl group is present in Glucose as it forms Cyanohdrin & Oxime

• This implies that all carbonyl group is present in Glucose is Aldehyde because ketone is not oxidized by Bromine. On reaction with \(\text{Con. HNO}_{3}\) it forms Glucaric acid and this shows that there is on group \(\text{2}^{\theta}\text{OH}\)

• It forms pentacetate derivative. This implies that there are \(\text{ 5OH }\) groups on different carbon atoms
• The structure of Glucose
• Failures of Structure of Glucose: The pentacetate derivative formed doesn't react with \(\text{NH}_{2}\text{OH}\). It doesn't give positive test with 2-4-DNP Test, Schiff's base test, \(\text{NaHSO}_{3}\) addition product.
• Epimers: The carbohydrates that differ in the position of \(\text{OH}\) group at only one chiral carbon are known as Epimers. Its conversion is known as Epimerisation.
• Fisher & Haworth Cyclic projection:

• Since these are similar to Pyran it is also called α-D-Glucopyranose or β-D-Glucopyranose
• Comparison of α-D-Glucose or β-D-Glucose

• Anomers:The carbohydrates that differ in its structure only at the anomeric carbon ( newly formed chiral carbon )

• Mutarotation: The specific rotation of α-D-Glucose or β-D-Glucose changes over time to reach equilibrium and this phenomenon is known as Mutarotation 

Fructose

• Fisher & Haworth Cyclic projection:

• Since these are similar to Furan it is also called α-D-Fructofuranose or β-D-Fructofuranose 

Preparation of Glucose

1. Hydrolysis of Cane Sugar:
               Boiling in the presence of alcohol or using enzyme Invertase can cause this reaction

2. Commercial Preparation:

              Commercially it is obtained by the Hydrolysis of Cellulose

                

Properties of Glucose

1. Reduction by HI:

2. Reduction by Catalyst:

3. Reaction with HCN:

4. Reaction with \(\text{NH}_{2}\text{OH}\):

5. Oxidation of Glucose:

6. Reaction with Periodic Acid

7. Ozasone formation:

              Using 3 moles of Phenyl Hydrazine oxidizes C2 to Ketone and then forms Ozasone.

8. Monoalkylation & Polyalkylation:

10. Acylation:

Glycosidic Linkage

A Glycosidic Linkage or Glycosidic bond is a covalent bond that joins two or more carbohydrates together

Disaccharides

Sucrose

                                      Sucrose is a disaccharide carbohydrate consisting of α-1,2-Glycosidic bond. It is non reducing sugar because the anomeric carbon itself involved in the Glycosidic bond. On hydrolysis it yields Glucose and Fructose in equal amount. It is named as α-D-glucopyranosyl-β-D-fructofuranoside. The optical activity of Glucose is  \(\text{ +52.5}^{\theta}\) and that of Fructose is \(\text{-92.4}^{\theta}\), therefore the optical activity of Glucose is \(\text{ +66.6}^{\theta}\)

Lactose

                                            Lactose is a disaccharide carbohydrate consisting of β-1,4-Glycosidic bond. It is a reducing sugar. On hydrolysis it yiels equal amount of Galactose and Glucose. It is named as β-D-galactopyranosyl-(1--->4)β-D-glucopyranose.

Maltose

                                              Maltose is a disaccharide carbohydrate consisting of  α-1,4-Glycosidic bond. It is also a reducing sugar. It is named as α-D-glucopyranosyl-(1--->4)α-D-glucopyranose.

Polysaccharides

Starch

It is the main storage polysaccharide of plants. It is a polymer of α-D- Glucose and consist of two components amylose and amylopectin

Amylose

It is a straight-chain compound and there is no branching. It is water soluble and consists of only C1-C4 bonds. It is a non-reducing sugar

Amylopectin

It contains a branched-chain structure and has a C1-C4 bond and only one C1-C6 bond. It is insoluble in water. It is a non-reducing sugar

Cellulose

It is polysaccharide occurs in plants. It consists of β-D-Glucose which are joined together by glycosidic linkage of C1 C4 carbons respectively. It is non reducing sugar

Test for Carbohydrates

Molisch Test

This test can detect all types of carbohydrates, i.e. monosaccharides, disaccharides, and polysaccharides. Molisch reagent (1% alcoholic solution of a-naphthol) is added to the aqueous solution of a carbohydrate followed by \(\text{Con. H}_{2}\text{SO}_{4}\) along the sides of test tube. A violet ring is formed at the junction of two layers

Barfoed Test

This test is used to distinguish monosaccharides from reducing disaccharides. Monosaccharides usually react in about 1-2 min while the reducing disaccharides take much longer time between 7 - 12 min to get hydrolysed and then react with the reagent. Brick red color is obtained in this test which is due to the formation of cuprous oxide.

Seliwanoff Test

This test is used to distinguish aldohexose from ketohexose. Ketoses undergo dehydration to give furfural derivatives, which condense with resorcinol to form a red complex. Prolonged heating will hydrolyze disaccharides and other monosaccharides will also eventually give color.

Iodine test

Iodine forms colored adsorption complexes with polysaccharides. Starch gives blue color with iodine, while glycogen reacts to form reddish brown complex. Hence it is useful, convenient and rapid test for detection of amylose, amylopectin and glycogen.

Amino acids & its Structure

Amino acids contains a \(\text{-NH}_{2}\) amino group and a \(\text{-COOH}\) carboxyl functional groups. Depending upon the relative position of amine group it is classified as α,β,γ amino acids respectively. On hydrolysis of protein α amino acid is obtained, where X is the Side chain

It is water soluble and has high melting points. Except Glycine all the amino acids are optically optive. Few amino acids based on different X groups are as follows

Essential Amino acids

Leucine, Methionine, Isoleucine, Phenylalanine, Valine, Threonine, Histidine, Tryphtophan, Lysine

Non-Essential Amino acids

Alanine, Glutamine, Arginine, Glycine, Proline, Asparagine, Aspartic acid, Serine, Cysteine, Tyrosine, Glutamic acid

Zwitter ion

It is a compound that has a positive charge and a negative but it has no net charge so that it is neither attracted by cathode nor by anode. Isolelectric point is the value of pH at which maximum of the amino acid exist as Zwitter ion

For a Zwitter, if it has more \(\text{-COOH}\) group than \(\text{-NH}_{2}\) it is called an Acidic amino acid and its pH is approximately 3. If it has more \(\text{-NH}_{2}\) group than\(\text{-COOH}\) group then it is called a basic amino acid and its pH ranges from 7.6-10.8

Peptide bond

Peptide linkages are amide linkages or covalent bond formed between amine group and carboxyl group. When two α-amino acids forms the linkage it is called dipeptide, if three α-amino acids then it is a tripeptide and so on. A polypeptide is formed when there are many α-amino acids

Preparation of Amino acids

1. From α-Halo Carboxylic acid

2. From aldehyde

3. Cyclic amino acids

4. Polymer of Amino acids

Proteins & its Classification

A protein is poly-peptide with more residues of α-amino acid that has molecular mass greater than 10,000 amu

Based on molecular shape

Globular proteins

These are cross-linked condensed polymers of acidic and basic α-amino acids. This structure results when the chains of polypeptides coil around to give a spherical shape. These are usually soluble in water. Insulin and albumins are the common examples of globular proteins.

Fibrous proteins

When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, then fibre– like structure is formed. Such proteins are generally insoluble in water. Some common examples are keratin (present in hair, wool, silk) and myosin (present in muscles), etc.

Nucleic acid and its components

There are two types of nuclei acids: Deoxyribose Sugars and Ribonucleic acids. These on hydrolysis gives pentose sugars, phosphate ester, nitrogenous bases

Chemical composition of nucleic acid

Pentose sugars

Nucleic acids contains contain only its β form. In RNA ribose sugar is present is present whereas in DNA deoxyribose sugar is present

Phosphoesters

Nitrogenous bases

It is of two types: Purines & Pyrimidines. In DNA Adenine, Thymine , Cytosine, Guanine whereas RNA contains Adenine, Uracil , Cytosine, Guanine

Nucleosides & Nucleotide

Nucleoside is the combination of a nitrogenous base and a pentose sugar, formed by the attachment of 1' of sugar to the nitrogenous base.

When a nucleoside is attached to phosphoric acid at 5' position nucleotide is formed. Nucleotides join through 5' & 3' phosphate linkages and yield polynucleotides

Structure of DNA

Vitamins

Vitamins are organic compounds required in the diet in small amounts to perform specific biological functions for normal maintenance of optimum growth and health of the organism. Vitamins are designated by alphabets A, B, C, D, etc. Some of them are further named as sub-groups e.g. B1, B2 , B6 , B12, etc. Excess of vitamins is also harmful and vitamin pills should not be taken without the advice of doctor

Classification of Vitamins

(i) Fat soluble vitamins: Vitamins which are soluble in fat and oils but insoluble in water are kept in this group. These are vitamins A, D, E and K. They are stored in liver and adipose (fat storing) tissues. 

(ii) Water soluble vitamins: B group vitamins and vitamin C are soluble in water so they are grouped together. Water soluble vitamins must be supplied regularly in diet because they are readily excreted in urine and cannot be stored (except vitamin B12) in our body.

Sources and Deficiency diseases of Important Vitamins

S/No	Vitamins	Sources	Deficiency diseases
1	Vitamin A	Fish liver oil, carrots, butter and milk	Xerophthalmia (hardening of cornea of eye) Night blindness
2	Vitamin B1 (Thiamine)	Yeast, milk, green vegetables and cereals	Beri beri (loss of appetite, retarded growth)
3	Vitamin B2 (Riboflavin)	Milk, eggwhite, liver, kidney	Cheilosis (fissuring at corners of mouth and lips), digestive disorders and burning sensation of the skin.
4	Vitamin B6 (Pyridoxine)	Yeast, milk, egg yolk, cereals and grams	Convulsions
5	Vitamin B12	Meat, fish, egg and curd	Pernicious anaemia (RBC deficient in haemoglobin)
6	Vitamin C (Ascorbic acid)	Citrus fruits, amla and green leafy vegetables	Scurvy (bleeding gums)
7	Vitamin D	Exposure to sunlight, fish and egg yolk	Rickets (bone deformities in children) and osteomalacia (soft bones and joint pain in adults)
8	Vitamin E	Vegetable oils like wheat germ oil, sunflower oil, etc.	Increased fragility of RBCs and muscular weakness
9	Vitamin K	Green leafy vegetables	Increased blood clotting time