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There is a subject called Biology.
The most interesting topic of my Biology book is Mechanism of DNA replications.Mechanisms of DNA replications are:1.Activation of Deoxyribonucleotides: They occur freely in the nucleoplasm.They are of four types-deAMP,deGMP,deCMP and deTMP.2.Exposure of DNA strands:Enzyme helicase acts and opens the two strands of DNA . The whole strands however does not opens at one stretch  but the point of separation proceeds slowly towards the direction hence giving it a Y-shaped structure called replication fork.3.RNA Primer: It is essential for the formation of new DNA chains. 4.DNA Polymerases: Prokaryotes have three major types of DNA synthesizing enzymes  called DNA Polymerases III, II and I. All of them add nucleotides in 5'-->3' direction on 3-->5 strand. 5.Base Pairing: The two separated DNA strands in the replication fork function as templates. Deoxyriboribonucleoside triphosphates come to lie opposite the nitrogen bases of exposed DNA templates. 6.Chain Formation: It requires DNA Polymerase III in prokaryotes and Polymeraseδ/ε in eukaryotes.7.Proof Reading and DNA repair: A wrong base is sometimes introduced during replication. The frequency is one in ten thousand. DNA Polymerase III is able to sense the same. It goes back, removes the wrong base, allows addition to proper base and proceeds forward.
It also gives us knowledge of human, plant and animal anatomy.
Science is interesting for every class i.e 4th class because it is very joyful to learn our world around us. We can know about the our universe , our body , plants feature , kinds of organisms and much more . It includes biology , chemistry and physics . Science is very easy that anyone can learn and understand it and can use it for research . Everyone can be benefited by this .

Through the biology we can able to know about our surrounding . Biology also tell us about us . Our human system , the structure of plants and animals  . We study different organs in our body . We can know about our each body organs system and functions such as heart transfer as blood .

Now the subject is Chemistry . We use chemical in every our work . We use salt   ( Nacl) in our food , we use detergent to wash our clothes , we use fertilizers and pesticides for the good crops etc . Most importantly all the medicines are made up of chemical process . Hence it also give life to organisms . 

And the last is physics . Physics is the most important subject in the science . We can calculate speed of anything , we can calculate heat of anything etc . Through physics we can know  evolution of the universe and atoms.
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