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InterviewSolution
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Question : Describethe process of transcription in protein synthesis. |
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Answer» Solution :(1) Transcription is the process in whichall the TYPES of RNA moleculesare formed. It is the friststep in the protein synthesis . In this,m -RNAstrand is formed fromDNAtemplate. (2)Initiatingthe process of transcription requiredthe presence of an enzyme called DNAdependentRNApolymerase. Genticinformation fromDNAis copiedinto m-RNAduringthe step, (3) A transcription unithas a promoter,the structuralgeneand a terminator. Thistranscripitonunithelpsin thetranscription process. The DNAstrandwhich is used for thesynthesisof RNA is calledtemplatestrand or antisencestrand. Thisis oriented in ` 3' to 5'`direction . The otherstrandwhich is no involvedin RNAsynthesisis calledcodingstrandor sense strand . THS strandhas theorientation` 5' to 3'` . A smallDNAsequence is usedas a binding site for RNApolymerase.thisregionis calledpromoter. Promoteris presenttowards 5 end.Towardsthe 3' end there is anothersmall DNAsequence called terminator.5' endis calledupstreamwhilethe 3' endis called downstream. (4)structural gene is generallymonocistronicin eukaryotes and polycistronic in prokaryotes. This gene getstranscribed. In eukaryotes. the geneshaveintronsand exons. In theexons, DNAsequences are expressedin the mature or processedRNA. Duringtranscription , the enzyme RNApolymerase bindsto the promoter site.it initiates the process . Dueto thistwostrandsof DNAseparate . ComplementaryRNA nucleotides arejoined to form the m-RNAstrand. Thisprocess is calledelongation . (5)A smallpartof RNAremainsattached to theenzyme RNA polymerase.This partreaches the terminator region and then bothenzyme and NEWLY synthesized m-RNAfalloff.Thisis called terminationof the transcription.  (6) Forthe process of transcription. initiation fator (` gamma` sigma) and temination factor(`rho` rho) are ESSENTIAL . In prokaryotesfurtherprocessingof RNAdoes notnot takeplacebut in eukaryotes , there is anelaborate process of RNAprocessing . Thereare three types of RNApolymeraseenzymesfor this purpoe. These are RNApolymerase I , II and III. (7) (i) r-RNAis formedis formedby RNApolymerase I. (ii) hn-RNA (het- eroncuclear RNA)is formedby RNApolymerase II and (iii) t-RNAand sn-RNA (small nuclear) are formedby RNApolymerase III. (8)The RNAformedby transcriptioon is non functionalin eukaryotes. It undergoesfurther processing for becoming active. Thisprocess consistsof splicing, cappingand TAILING (9) Suchhn-RNA whichundergoessplicing , cappingand tailingnow becomes m-RNA. In eukaryotic cellsthe m-RNA molecular leavesnucleusand goes toribosomes to carryout the further process of protein synthesis. |
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