paper: vii paper code: che 523

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CHEMISTRY CHE523:CHEMISTRY OF BIO-MOLECULES

PG SEMESTER:- II, PAPER: - VII

M.Sc. Chemistry: Second Semester

CHEMISTRY OF BIO MOLECULES

Paper: VII Paper Code: CHE 523

UNIT-II

Lipids

Staturated and unsaturated fatty acid

Essential fatty acid

Structure and function of triglycerides

Glycerophospholipids

Lipo Protien

Biological Membrane

Lipid Metabolism

𝛽-oxidation of fatty acid

UNIT-III

Amino acid ,peptides and protiens

Amino acid essential

Non Essential amino acids

Isoelectric point

Primary structure of protein

Secondary structure of protein

Force responsible for secondary structure of protein

𝛼-helix and 𝛽–sheet structure of protein

Tertiary and Quaternary structure of protein

UNIT-IV

Nucleotides and nucleic acid

Chemical syntheses of Purine and Pyrimidine derivatives present in nucleic acid

Structure of ribonucleic acid(RNA) and deoxyribonucleic acid(DNA)

Double helical model of DNA

Chemical and Enzymatic hydrolysis of Nucleic acid

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UNIT - II

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Dr. S.K Choudhary

Professor of Chemistry

C.M. Sc. College, Darbhanga

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LIPIDS

These are the heterogeneous group of organic compounds but placed in one class on the basis of their common functions. These are the main constituent of plant and animal tissues soluble in organic solvents such as either chloroform, benzene and carbon tetrachloride and insoluble in water. In recent years, the role of lipids in diet has received attention because of their apparent connection between saturated fats and blood cholesterol associated with arterial disease.

Biological functions: -

Lipids are biologically important compounds and play following functions.

1. These are main components of cell membrane and therefore, associated with transportation across cellular membranes.

2. They provide insulation for the vital organs, protecting them from mechanical shock and in maintaining optimum body temperature also.

3. These are the important energy storage compounds. The food taken above normal requirement of the animal is converted into fat as reserve product in the form of fat body.

4. Glycolipids and lipoproteins are essential for maintaining cellular integrity.

5. The compound lipid like phosphatides of blood platelets are associated in the production of thromboplastin, which is essential in the primary stage of blood clotting.

6. Some vitamins (A and B) and hormones (steroids) necessary for proper functioning of our body are lipids.

7. Lipids like waxes form protective covering in plants.

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Classifications of lipids:-

These are classified on the basis of their hydrolysis products and also according to their similarities in molecular structures

1. Simple lipids: - (a) Fats and oils:- These give fatty acids and glycerol on hydrolysis. Oils are liquids at ordinary temperature and containing large proportion of unsaturated fatty acid unit, whereas fats are solid glycerides of saturated fatty acids. Lipids obtained from animal origin are generally fats. Ex-batter, lard, beef tallow etc. whereas those obtained from vegetable origin are oils. Ex- cotton seed oil, ground nut oil, linseed, corn oil, coconut oil, rapeseed oil, soya bean oil etc. (b) Waxes: - These are the esters of fatty acids and long chain alcohols. These give fatty acids on hydrolysis. These give protective coatings on the surface of plants. This coating protect plants from infection, adhesive damage and loss of water on transpiration.

Example :- C15H31COOC30H61 C25H51COOC30H61

Myricylpalmitate Myricylcerotate

(Bees wax) (Carnuba wax) C15H31COOC16H33

(Cetylpalmitate) (Spermaceti)

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2. Conpound lipids:-

(a) Phospholipids / phosphatides:- These give fatty acids, glycerol,

phosphoric acid and a nitrogen containing alcohol on hydrolysis.

Example :-

CHOLINE UNIT

α - LECITHEN

I – SERINE UNIT

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Fatty acids most commonly found in lecithin’s are palmitic stearic, oleic, linoleic and archiodonic acids. Whereas cepholines usually contain stearic, oleic, linoleic and archiodonic acids. Braain and nerve tissues are rich in phospholipids. Phosphatides are often found associated with proteins and glycolipids. (b) Sphingolipids :- These give fatty acid, phosphoric acid, sphingosine and an alcohol component on hydrolysis. The sphingolipids with proteins and a protective coating that encloses nerve fibres or oxons. The oxons of nerve cells carry electrical nerve impulses. Ex :-

SPHINGOSINE

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(C) GLYCOLIPIDS: - These produce fatty acids, sphingosine or glycerol and a carbohydrate on hydrolysis. For example, glactolipid found on brain tissue is name as ganglioside.

The cerebroside is an example of glycolipid.

CH3(CH2)11 – CH2 – C – H

H – C - CHOH

CH – NH – C – (CH2)22 CH3

CH2 CH2OH

=o

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CEREBROSIDE

Oils and fats are mostly triglycerides. These triglycerides are triesters of three long chain fatty acids (C12 to C22) with glycerol a trihydroxy alcohol.

Acid + Alcohol → Ester + Water

RCOOH HO – CH2

RICOOH + OH – CH catalyst

RII COOH HO - CH2

These triglycerides are further classified on the basis of their physical states at room temperature. It is called fat, if solid at room temperature.

Whereas oil, if liquid at the same temperature. It is found that fats containing a greater proportion of saturated fatty acid, whereas oils contain a greater percentage of unsaturated fatty acids. Oils and fats are generally mixed triglycerides oil contain more of short – chain saturated acid residues and unsaturated acid residues, whereas fats contain more of long - chain saturated acid residues. These acids associated with glycerides of oil and fats are generally straight chain acids (C4 to C20) containing an even member of carbon atoms. The major acids associated with oils and fats are palmitic (C17H33COOH) oleic (C17H33COOH) etc.

Fats and oils make up over 90 percent of the lipid of adipose tissue in mammal’s. Fats and oils are predominantly the glyceryl esters of various higher fatty acids mainly palmitic, stearic, oleic, linoleic and linolenic. Fats and oils

|

|

3H2O

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generally differentiated by their melting range.

Chemically fats contain larger portion of saturated fatty acids. For example steric and palmitic acids and melt at higher temperature, while the oils contain a larger portion of unsaturated acid. For example oleic acid.

Production of Higher Fatty Acids: - The hydrolysis of fats to free fatty acids many be carried out by batch and continuous process. However, as compared to the batch saponification process, production of soaps by fat – splitting followed by neutralization with sodium – hydroxide as much shorter since the fatty acids are always refined by distillation, they are produced from low – grade fats viz. bone and skin grease, low grade tallow, acid oils unsuitable for soap manufacture, and low grade vegetable oils. Before the fat is subjected to the actual fat splitting process, it is usually refined by agitating with dil. Sulphuric acid, and are then washed with water.

The modern fat splitting process are carried out at higher pressures and in the absence of a catalyst. In a typical non – catalytic process, the auto clave is two third filled with the purified fat, and air free condensate from a previous hydrolysis is added. The VALVES of the autoclave are closed and steam is injected. The process is generally carried in two stage, the glycerol – water produced in the first stage is replaced by water continuous fat splitting processes are more recent and are performed at temperature and pressure higher than those used in batch processes.

The hydrolysis is carried out in tall towers provided with a number of perforated plates. The preheated fat is pumped into the bottom of the tower through a distributor while the preheated water is pumped into the top of the

tower. Superheated steam is injected into the tower to bring the pressure up to 600-700 1b/in2 and temperature to about 280°C

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The fatty acids produced pass out from the top of the tower. while the glycerol comes downwards along with water.

The fatty acids produced by either of the above process are dried by heated under reduced pressure and then refined by distillation under high vacuum

Properties of fats: -

Fats and oils impure from are colorless or pale yellow. fats are insoluble in water and polar solvents, but soluble in non- polar solvents.

1. Hydrolysis: - The ester linkages of the fats are cleaved by sodium hydroxide to give glycerol and sodium hydroxide to give glycerol and sodium salt of long chain fatty acids (soap)

CH2OCOR CH2 - OH

│ │

CHOCOR + 3NaOH → CH – OH + 3RCOONa

│ │

CH2OCOR CH2 - OH

From the biological stand point the enzyme hydrolysis of fats is of interest. A fat splitting enzyme is called lipase.

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Rancidity: - Fresh fats and oils are nearly colorless and are neutral in reaction. However, if they are exposed to moisture and the action of aerobic bacteria, they are oxidized or hydrolyzed into aldehydes and ketones, acids etc. and are called rancid. Thus two types of rancidity are recognized namely as hydrolytic and oxidative Hydrolytic rancidity is caused hydrolysis and are very common in fats like butter, having a high percentage of volatile fatty acids. thus butter becomes unpalatable when even very small amount of butyric acid is produced by the hydrolysis glyceryl butyrate. On the other hand, the more the more common oxidative rancidity is caused by the oxidation of unsaturated fatty acid at their double bonds with the formation of shorter – chained acids, aldehydes and ketones. In the dairy industry tallowy butter is result of oxidative rancidity. Different fats vary in their ability to with stand oxidative rancidity. The time require for the rapid oxidation is known as induction periods of some fats may be due to the presence of traces of substances, called antioxidants. The important artificial antioxidants used in food stuffs are Gallic acid and its esters, nordihydro guaiaretic acid, 3-tertiary butyl - 4 – hydroxyl anisole etc.

GALLIC ACID HYDROXY ANISOLE

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Drying: - Certain oils, when exposed to air becomes thick and finally harden to resin like solid substances, this effect is known as drying and is of immense importance when these oils are incorporated into paints and vanishes. Probably, the drying effects involves the addition of oxygen to the unsaturated linkages presents in the esters of the oils and some amount of polymerization. Drying is catalyzed by the addition of driers like salt of manganese, lead etc. The non – drying oils like palm oil, coconut oil, olive oil, almond oil consist of triolein. Hydrogenation: - Certain oils, especially the drying and semidrying oils add on hydrogen atoms to the unsaturated linkage of the glycerides after hydrogenation, the oil is cooled and the catalyst is removed by filtrations. This process is frequently used by the Vanaspati ghee manufacturers. Physical Constants: - The important physical constants of facts and oils are the specific gravity, the refractive index, the viscosity and the melting point. Chemical Constants: - Acid Value It is the number of milligrams of potassium hydroxide required to neutralize the free fatty acids in one gram of the oil or fat. The acid value of a fat is determined by dissolving a weighed amount of the fat in alcohol and titrating the solution against standard alkali solution using phenol ethylene is on indicator. A high acid value would be expected in a rancid fact

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Saponification Value It is the number of milligrams of potassium hydroxide required to completely saponify one grams of oil and fat. The saponification value indicates the quantity of alkali which must be used to the convert a blend of facts to soap. It is also of use of for detecting adulteration of a given fat one of the higher or lower saponification value. Iodine Value The Iodine value is defined as the number of grams of iodine that combine with 100 grams of an oil and fats. The iodine value is a measure of the degree of unsaturation of a fat or oil, and thus allows its classification into non- drying, drying and semidrying oils. Ester value The ester value is defined as the number of milligrams of KOH necessary to combine with the fatty acids which are in combination with glycerol in 1 gm of fat. It is determined by subtracting acid number from the saponification number. Physiological importance of facts and oils: - Fats and oils act on storage of energy in plants and animals. in the animal body, fats are stored in

fatty tissues which are almost pure fats. Fats give about 21

4 times as

much energy as carbohydrates or proteins fat is poor conductor of heat , hence the fat layer under the skin serves to prevent losses of heat from the body.

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UNIT - III

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Dr. Abdus Samad Ansari

Associate professor of Chemistry

University Department L.N.M.U Darbhanga,

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A. AMINO ACID, PEPLIDES AND PROTEIN

Amino acid- essential, non-essential amino acids, isoelectric point, primary structure of protein, secondary structure of protein, force responsible for secondary structure of protein α-helix and β-sheet structure of protein, tertiary and quaternary structure of protein

B. Nucleotides and nucleic acid

Chemical synthesis of purine and pyrimidine, derivatives present in nucleic acid, structure of ribonucleic acid (RNA) deoxyribonucleic acid (DNA) double helical of DNA

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The term protein is derived from Greek word ‘PROTEIOS’ meaning ‘PRIMARY’. Or “holding first place “proteins are indeed extremely important constituent of living cells. Chief sources of protein are milk, meat, fish, pulses, and peanuts etc. They are present in every part of the body and form the fundamental basis of structure and function of life; besides the structural protein, other proteins having capital biological functions, especially the enzymes which are

biological catalyst responsible for the reaction in cells of living organism.

All protein contains C, H, O and N mainly and S, P in some.

CLASSIFICATION OF PROTEINS

protein are large molecules in macromolecule formed by the condensation of a large number of unit (from 50 to several thousand) called amino acid. They are two types: -

1. SIMPLE PROTEIN (HOLOPROTEIN) which have amino acid chain only

2. CONJUGATED PROTEIN (HETEROPROTEIN) which have besides one or several amino acid chain, a PROSTHETIC gp., (non protein gp.) like carbohydrates, lipids, nucleic acids etc.

AMINO ACIDS If is the basic unit of protein. As the name implies it has one acidic group and one primary mino gp. in α postion w.r.t the carboxylic acid group except proline and hydroxyproline, their genral formula is

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-COOH

All amino acid constituting the protein belongs to L-series or S configuration but they may be D or R also in some cases. In some cases, it may be β, 𝛾, δ etc. Amino acids but hydrolysis of protein yield on α-amino acids

CLASSIFICATION OF AMINO ACID

1.ESSENTIAL OR INDISPENSABLE AMINO ACIDS:- Amino acids which cannot be synthesised in the body and must be obtained from outside i.e from diet called essential amino acids. There are 10 essential amino acids.

1. Arginine, (required for young, but not for adult) 2. Histidine, 3. Isoleucine 4. Leucine 5. Lysine 6. Methionine 7. Phenylalanine 8. Threonine 9. Tryptophan and 10. Valine.

these amino acid required in diet. Plants, of course must be able to prepare all amino acids.

N

H N

H

COOH

OH

Proline Hydroxy proline

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NON ESSENTIAL/DISPENSABLE AMINO ACIDS.

Amino acids which can be synthesized in the body are called non-essential amino acids. Out of 20 standard amino acids 12 are non-essential. They are: -

1. Alanine 2. Asparagine 3. Aspartate 4. Cystein 5. Glutamate 6. Glutamine 7. Glycine 8. Proline 9. Serine 10. Tyrosine 11. Arginine & 12. Histidine

Arginine and histidine form the group of so called semi essential amino acids.

SOURCES OF ESSENTIAL AMINO ACIDS Dairy products such as milk, yoghurt, cheese meat, egg, etc. contain essential amino acids

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ANOTHER CLASSIFICATION OF AMINO ACID

A. ALIPHATIC AMINO ACIDS

A. HYDROCARBON CHAIN AMINO ACIDS

i. Glycine (Gly),(G)

ii. Alanine (Ala),(A)

iii. Valine(Vla),(V)

iv. Leucine (Leu),(L)

v. Isolencine (Ile),(I)

B. HYDROXYAMINO ACIDS

i. Serine (Ser) (S) α-amino- β- hydroxypropionic

acid

ii. Threonine (Thr) (T) α- amino-β- hydroxybutyric

acid

α- amino acetic acid

α-aminopropanoic

acid

α- amino inovaleric

acid

α- amino iso caproic

acid

α- amino β methyl

valiric acid

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C. SULPHUR CONTANING AMINO ACIDS

(i) Cysteine (Cys),(C) , α- amino –β- thiopropionic acid

CH2 – C - COOH

SH NH2

(ii) Methionine (Met),(M) α-amino – 𝛾 – methylmercapto butyric acid

CH2 – CH2 – CH – COOH

S NH2

CH3

D. DICARBOXYLIC AMINO ACIDS AND THEIR AMIDES

i. Aspartic acid (Asp),(D), amino succinic acid and its amide β-amide

asparagine (Asn)(N)

HOOC – CH2 – CH – COOH H2NOC – CH2 – CH - COOH

NH2 NH2

| |

| |

|

| |

α β

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CH2-CH-COOH

ii. Glutamic acid (Glu) (Q) α-amino glutaric acid or its amide, 𝛾-amide,

glutamine

HOOC – CH2 – CH2 - CH – COOH H2NOC – CH2 – CH2 - CH - COOH

NH2 NH2

E. BASIC AMINO ACIDS

(i) Lysine (Lys)(K) α-ε diamino- caproic acid

(ii) Arginine (Arg)(R) α- amino – δ – quanidino valeric acid

H2N – C- NH – CH2-CH2-CH2-CH-COOH

(iii) Histidine (His)(H) α- amino – β – imidazole propionic acid

| |

ǁ |

NH

|

N

NH NH2

NH2

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HO-

COOH

B. CYCLIC AMINO ACIDS

i. Phenylalanine (Phe)(F) α-amino acid-β-phenyl propionic acid

ii. Tyrosine (Tyr)(Y) α-amino acid –β-perhydroxyphenyl propionic acid

iii. Tryptophan(Trp)(W), α- amino-β-indolepropionic acid

2. HETEROCYCLIC AMINO ACIDS

i. Proline (Pro)(P) pyrrolidine – 2 – carboxylic acid

CH2-CH-COOH

NH2

|

|

CH2-CH-COOH

NH2

|

CH2-CH-COOH

NH2

|

N

NH

H

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ZWITTER IONS

Since in amino acids both COOH and NH2 gp. exists, therefore in aqueous solution the H+ ion shifts from COOH gp. to –NH2 gp. forming dipolar ion called Zwitter ion. It is considered both electrically charged and electrically neutral, the net charge of Zwitter ion is zero

ISOELECTRIC POINT / ISOIONIC POINT

An isoelectric point is the pH at which an amino acid exits primarily in its zwitter ion form i.e its neutral form (no net change) and does not migrate when placed in an electric field. At the isoelectric point, almost all amino acid molecules in a solution (more than 99%) are present in Zwitter ion. Every amino acid has different isoelectric point. Those with non polar neutral side chain have isoelectric point 4.8-6.3 (pH). The three basic amino acid have higher isoelectric point (more basic hence high (pH). The two acidic amino acid have lower isoelectric point (more acidic hence low pH).

. .

Zwitter ion

+

-

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1. PRIMARY STRUCTURE OF PROTEN

Primary structure of protein refers to the linear sequence of amino acid in the polypeptide chain. Since protein are polymers of α-amino acids which are connected with each other through amide bond formed between – COOH and NH2 gp. and is called peptide bond or peptide linkage.

The two amino acids form peptide linkage is called dipeptide. Three amino acid from two peptide linkage called tripeptide and so on. When the number is more than ten it is called polypeptide.

Polypeptide having more than 100 amino acids with molecular mass 10,000u is called protein through the difference is not very clear The primary structure of protein is encoded in DNA. In order to make a protein first copy of DNA is made. This process is called TRANSCRIPTION. This copy is called messenger RNA ( mRNA). The copy is sent out of nucleus to the cytoplasm. Once the cytoplasm ribosome will interact with mRNA, they can read the mRNA sequence

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and create a protein (POLYPEPIDE) from individual amino acid. This process is called translation.

2. SECONDARY STRUCTURE OF PROTEINS X-ray diffraction pattern provide the data for this structural study. There are mainly two main type of secondary structures A. STRETCHED STATE OR PLEATED SHEET STRUCTRES B. HELICOIDE STATE OR α-HELIX

A. STRETCHED STATE OR PLEATED SHEET STRUCTRUE

In this type two antiparallel polypeptide chains (“moving” in opposite directions united by inter chain hydrogen bonds. The atoms of the peptide linkage are situated in the same plane but the α-carbon belongs simultaneously to two different planes.

e.g. The fibrous proteins or scleroprotein, often found as structural protein (β-keratin, silk fibrous)

R

R

R R

R

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B. Helicoid state or α-helix: - In this type the peptide chain is maintained in this helicoidal configuration by intra chain hydrogen bond. The helix has 3.7 amino acid residue per turn. The plane of peptide linkage form between them an angle of about 800. The side chain is directed outward and can react with each other or with the medium.

3.TERTIARY STRUCTRE OF PROTEIN: - The tertiary structures have a single polypeptide chain “backbone” with one or more protein secondary structure the protein demains. Amino acid side chains may interact and bond in a number of ways.

Helicoid state or α Helix

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The interactions & bonds of side chain with a particular protein determines its tertiary structure.

1° Order of amino acid 2° Due to interaction of backbone 3° Due to side chain interaction 4° Arrangement of multipeptide

4. QUATENARY STRUCTURE OF PROTEIN

Quaternary structures result in the assembly of identical peptide units and in other cases from the different sub-unit For eg.: - Haemoglobin which transports oxygen from lung to different tissues consists of 4-sub units generally 2 α-chain and 2β-chain each of these chain has tertiary structure

PRIMARY

STRUCTURE secondary structure tertiary structure

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Forces responsible / influencing primary & secondary structures

1. HYDROGEN BOND: - Structural studies of folded protein indicate the hydrogen bonding gp. almost always find an appropriate partner. Hydrogen bonding gp. include the main chain carbonyl and amide gp. and as well as polar side chain. Polar gp. exposed on surface of protein. often have water as their hydrogen bonding partner. Polar gp. within the core region usually form H-bond with other gp. within the protein

2. HYDROPHOBIC INTERACTION: - A primary driving force for protein folding involves the removal of non-polar side chain from solvent exposure. This accomplished by sequestering them within core region example: -Vander Waals forces. Some non-polar gp are still found on the surface of folded protein.

Quaternary structure

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UNIT - IV

32



Dr. Shashi Ranjan Kumar

Professor and former Head

University Department of Chemistry

L.N. Mithila University Darbhanga,

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NUCLEIC ACIDS

Nucleic acids are complex high molecular weight polymers which occur in living cell. They were first discovered by Miescher (1869) and named by Altman (1889). These play important roles in the synthesised of protein and serve as hereditary material.

CHEMISTRY OF NUCLEIC ACIDS: - Nucleic acids are composed of chain of nucleotides i.e they are polymers of nucleotides. Each nucleotides composed of the following three components.

(i) A nitrogeneous base (ii) A pentose sugar and (iii) A compound phosphate

The combination of molecules of nitrogenous base with pentose sugar component lead to the formation of nucleoside

nitrogenous base+ pentose sugar →nucleoside

The combination of nucleoside with phosphate component lead to the formula of nucleotide

Nitrogeneous base+ pentose sugar+ phosphate →nucleotide

Or nucleoside+phosphate→nucleotide

Nitrogeneous bases are present in the form of purines and pyrimidines Pentose sugar molecules are present in the form of deoxyriboes and ribose. Depending upon type of sugar molecules and nitrogenous base, the nucleic acids are categorized as:-

(a) DEOXYRIBOSE NUCLEIC ACIDS (DNA) which contain, adenine, thymine, cytosine guanine and deoxyribose sugar

(b) RIBOSENUCLEIC ACIDS (RNA) which contain uracil instead of thymine and ribose sugar i.e adenine, cytosine, guanine, uracil and ribose

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HOH2C HOH2C

NH2

(1) Hetero cyclic nitrogen basic compound

2.Pentose sugar component: - sugar component of nucleic acid is present in the form of ribose sugar with five carbon atoms. The carbon atom of the

ring is numbered as 1’,2’,3’ and 4’ the carbon of –CH2 is numbered 5’

NH2

CH3

NH2

H H

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3. PHOSPHATE COMPONENT. It is phosphoric acid united with pentose sugar

molecule.

NUCLEOSIDE: - when the nitrogen base component is linked to 1-position of

ribose sugar by β-glycosidic bond it is called a nucleoside

nucleotide

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NUCLEOTIDE:- When a nucleoside is linked to phosphoric acid at 5-position of ribose sugar, it is called nucleotide i.e. it is phosphate ester of nucleoside

Replication of DNA:

As DNA is a primary hereditary material, it has to duplicate to produce exact copies of itself every time cell divisor takes place. This process is called replication. Besides replication DNA also synthesises RNA and this process is called transcription. Both these functions are named differently. When DNA guides the synthesis of DNA it is called Autocatalysis, whereas when it guides the synthesis of RNA and protein then it is called hetreocatalysis.

There are different methods proposed for the replication of DNA like:

(i) Conservative methods, (ii) Dispersive which are discarded (iii) Semi-conservative method: This method was proposed by

Watson & Crick & experimentally supported by Meselson & Stahl (1958).

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(iv) According to this method only half part of the newly formed DNA molecule is synthesized & half original part is retained.

Mechanism of DNA replication: The two polynucleotide strands of DNA molecule needs to be separated to act as a template for the synthesis of its complimentary partner. As the two strands are joined together by hydrogen bond, their separation needs removal of the bond. The weak H-bond joining are

broken by the enzyme helicase. Further, the two polynuclectids strands are interwined in a helix, their separation also needs unwinding. The problem of unwinding is solved by the enzyme topoisomerases. To overcome the tension of interwining, the unwined portion of the strand is broken into pieces & resealed by the enzyme topoisomerases. It has been also suggested that this problem is solved by simultaneous unwinding and rewinding with newly formed strands of DNA by assuming fork like shape is forming a “Y” with the parent strand which is referred as replication fork.

Mechanism in DNA Replication: DNA replication is an important process resulting with the production of another copy of DNA strand.

1. First Enzyme called Helicase unzips the double helix, beginning at the replication fork is small opening of DNA by breaking up the hydrogen bond between the nitrogen bases. The unwinding is carried out by enzyme topoisomerase.

2. Then, DNA polymerase adds nucleotides to the lagging strands , which is synthesized continuously, and it goes in the 5’ to 3’ direction.

3. On the lagging strand, the RNA primase synthesize RNA Primer.

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4. DNA polymerase III adds deoxyribonucleotides to the end of the RNA Primer.

5. DNA polymerase I replaces DNA polymerase III then removes RNA & replaces with DNA. The synthesis on the lagging strand is discontinuous, unlike the leading strand & has okazaki fragments/segments that are not connected.

6. Ligase connect the Okazaki fragments with phosphodiester bond.

Watson – crick model for semi conservation D.N.A replication

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paper: vii paper code: che 523

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