EAPCET | Botany - Transcription | T-SAT

Added: 2026-05-05

[00:00:00]Today's topic is molecular basis of inheritance in that transcription.

[00:00:06]Transcription means synthesis of RNA from DNA.

[00:00:13]Transcription means synthesis of RNA from DNA.

[00:00:25]This is what is called transcription.

[00:00:27]And how many types of RNAs are there?

[00:00:30]This is the DNA. [clears throat] And we have at least three kinds of RNAs.

[00:00:36]mRNA, rRNA, tRNA.

[00:00:44]Of course, we have snRNAs and also subunits of rRNA.

[00:00:52]And for this there is an enzyme. The required enzyme is DNA dependent RNA polymerase.

[00:01:09]This is the enzyme required for the process.

[00:01:13]The synthesis of RNA from DNA is called transcription. We have different kinds of RNAs.

[00:01:19]And synthesis of all of them comes under transcription.

[00:01:24]And mRNA, rRNA, tRNA, they can be synthesized by the catalytic activity of DNA dependent RNA polymerase. And earlier we have seen central dogma of molecular biology, that is DNA.

[00:01:46]And it will produce DNA. And this is called replication.

[00:01:52]And here we have mRNA.

[00:01:57]And from this proteins are obtained.

[00:02:03]And this part is called translation.

[00:02:07]This part is called transcription.

[00:02:15]And this is called replication.

[00:02:18]If we add one more RNA then DNA then mRNA followed by protein.

[00:02:31]So, this is what is already written here, from here.

[00:02:36]And so, from RNA DNA is produced. So, this step we have named this already.

[00:02:43]This is called transcription.

[00:02:46]And this part is called translation.

[00:02:51]And this is called this must be called reverse transcription.

[00:03:02]The enzyme required here is RNA dependent DNA polymerase.

[00:03:15]Here it is DNA dependent RNA polymerase.

[00:03:28]And for this step we require DNA dependent DNA polymerase.

[00:03:37]Transcription >> [snorts] >> Central dogma of molecular biology and DNA mRNA e mRNA translation and transcription and translation and translation mRNA protein and protein and protein translation and translation retrovirus and retrovirus RNA DNA protein DNA reverse transcription and reverse transcription DNA RNA DNA polymerase enzyme enzyme DNA DNA DNA DNA DNA DNA polymerase polymerase DNA mRNA DNA dependent RNA polymerase enzyme enzyme mRNA translation protein protein Now, let us consider the differences between replication of DNA and transcription.

[00:05:13]About replication This is synthesis of DNA from DNA.

[00:05:21]And about transcription this is synthesis of RNA.

[00:05:27]DNA producing RNA.

[00:05:31]And this is DNA producing DNA.

[00:05:36]DNA is double stranded.

[00:05:39]And it is producing two double stranded DNA molecules.

[00:05:45]It is producing two double stranded DNA molecules.

[00:05:49]DNA is double stranded. But it is producing ssRNA.

[00:05:55]And it can be mRNA, rRNA, or tRNA.

[00:06:05]Whole DNA is copied.

[00:06:13]Only a part of three five strand is copied.

[00:06:25]Only a part of a three five strand is copied.

[00:06:32]Whole DNA is copied.

[00:06:35]That is both strands are copied.

[00:06:45]Only one strand is copied.

[00:06:57]Only a part of three five strand is copied. And that means only one strand.

[00:07:02]And a part only.

[00:07:08]So, these are the differences between replication where DNA produces DNA, two molecules of DNA.

[00:07:19]And DNA produces RNA, that is transcription. And the dsDNA produces single stranded RNA. Only a part of a the DNA strand is copied, never whole.

[00:07:34]And only one strand. And this is one a small part only. Whole DNA is copied.

[00:07:42]Once it begins, it ends with the formation of two daughter DNA molecules.

[00:07:50]DNA replication and DNA translation and translation and translation DNA DNA and DNA replication and DNA DNA and DNA DNA DNA and DNA DNA and DNA replication and replication and replication DNA DNA and DNA and DNA and DNA and DNA and DNA DNA and DNA and DNA DNA and DNA and DNA and DNA and DNA and DNA translation and translation DNA and DNA and DNA and DNA DNA DNA and DNA and DNA and DNA and DNA rRNA mRNA and tRNA and tRNA and tRNA and tRNA DNA DNA and DNA and DNA and DNA and DNA and DNA and DNA and DNA and DNA and DNA and DNA and DNA DNA DNA and DNA and DNA and DNA and DNA and DNA and DNA and DNA DNA DNA and DNA and DNA DNA DNA and DNA and DNA and DNA DNA DNA and DNA and DNA and DNA DNA DNA and DNA and DNA DNA DNA and DNA and DNA DNA dependent DNA polymerase DNA DNA dependent DNA dependent RNA polymerase DNA dependent RNA polymerase is required here. DNA dependent DNA polymerase is required here. This is restricted to S subphase in eukaryotes.

[00:09:53]This occurs all throughout life.

[00:10:01]except during division.

[00:10:29]Complimentary copying means this is a strand of DNA.

[00:10:36]A T G C are here.

[00:10:38]And this is the other strand.

[00:10:41]T A C G And when replication occurs, it will synthesize its complementary strand. It will synthesize its complementary strand. It is copied in complementary manner. So, A is complementary to T, T is complementary to A, G is complementary to C, C is complementary to G. In similar manner, T is complementary to A, and A is complementary to T, C is complementary to G, G is complementary to C.

[00:11:15]So, this is how the replication of DNA occurs.

[00:11:20]When one strand of DNA is acting as template and let this be the sequence A T G C and this is sequence of DNA template and the RNA produced should be since there is no thymine thymidylic [clears throat] acid in RNA there is no thymidylic acid in RNA, U will be here.

[00:11:44]U will be here. And thymine this is complementary to A, and G is complementary to C, C is complementary to D. And there is a difference here.

[00:11:57]Here we have deoxyribose sugar.

[00:12:04]Here we have ribose sugar.

[00:12:10]So, instead of T U will be here in case of RNA.

[00:13:18]Instead of T is replaced by U.

[00:13:26]And deoxyribose sugar is replaced by ribose sugar.

[00:13:41]So, this is the difference.

[00:13:46]Now, let us consider why only one strand of DNA is transcribed especially in the form of mRNA.

[00:13:55]This is one strand of DNA where the sequence of nucleotides is triple A, triple G triple C triple T.

[00:14:08]And the other strand is having triple T.

[00:14:16]A is complementary to T.

[00:14:18]G is complementary to C, triple C. C is complementary to G.

[00:14:24]And T is complementary to A.

[00:14:28]This is one strand of DNA, this is other strand of DNA. If this is transcribed basing on principle of complementarity, it will be producing an mRNA. I will draw this as dotted line. It will be having triple U. And this will be having triple C. This will be having triple G.

[00:14:48]This will be having triple A.

[00:14:51]And this triple U is codon for phenylalanine. This is for proline. This is for glycine. This is for lysine. So, this is the sequence of amino acids joined because of this particular sequence of nucleotides in the dictator molecule DNA and this is mRNA. Now, if this is acting as a template and basing on the principle of complementarity, the nucleotides formed here on this is our mRNA and this is our supposed protein where amino acid residues are joined. So, triple T, this will be A A, this will be synthesizing coding for lysine, and this is G G G, triple G.

[00:15:59]This will be coding for glycine, and this will be triple C coding for proline, and this is triple A that will be triple U coding for phenylalanine.

[00:16:15]And this is our second mRNA, and this is our second protein. And the two proteins are different because the amino acid sequence is different. The two proteins are different because the amino acid sequence is different. This is the first problem.

[00:16:36]So, two different kinds of proteins are produced.

[00:16:45]Two different kinds of proteins are formed.

[00:16:49]This is the first problem.

[00:16:51]And we have yet another problem, and what is that? Let me draw copy these two mRNAs again here. This is U U U, and this is C C C, and this is followed by triple G, and this will be triple A. And let me copy this. This is triple A, and this is triple G, and this is triple C.

[00:17:17]And this is triple U. And A is complementary to U, so the two will be bonded by two H bonds, two H bonds, two H bonds. G is complementary to C, and we have triple bond between G and C of opposite strands, and double bond between A and U of opposite strands. So, a dsRNA is produced. This is not suitable for translation. There is no protein synthesized. The cell cannot produce any protein if both strands are transcribed at the same time.

[00:18:03]Now, DNA mRNA protein mRNA triple A, triple G, triple C, triple U lysine, glycine, proline, phenylalanine amino amino amino mRNA mRNA mRNA >> Now let us consider what is a transcriptional unit. Transcriptional unit is a portion of DNA with a This is a portion of DNA.

[00:20:38]This is 35.

[00:20:42]And this is 35.

[00:20:46]The transcribed portion is called template.

[00:20:53]And this is called The other one is called coding strand. This is called template strand. This is structural gene.

[00:21:09]This is transcribed in whole.

[00:21:13]And we have a promoter at upstream and there is a terminator at downstream.

[00:21:25]And the RNA DNA dependent RNA polymerase polymerizes in the direction of a 53 only.

[00:21:46]So this is direction of polymerization.

[00:21:51]Then what is the direction of template?

[00:21:55]So template polarity must be 35 only.

[00:22:07]Template polarity must be 35 only.

[00:22:13]And this is template strand. This is actually copied in complementary manner.

[00:22:19]And So whatever copy RNA is produced is similar to coding strand. RNA produced will be similar to coding strand. Let me draw few nucleotides here. ATGC CTG. This is what is in 35 strand, a small portion. And what is in the other strand will be TACG GAC.

[00:22:47]This is what is in the 53 strand. And on transcription, this will be producing U A C G G A C. Let us compare these two strands.

[00:23:04]The coding strand and mRNA formed are similar except the uracil replacing thymine. This is the reason for calling the other strand as coding strand. And this is also called sense strand and also can be called non-template strand.

[00:23:30]Since this is called sense strand, this template strand can be called antisense strand.

[00:23:43]And the coding strand and mRNA produced are RNA produced are similar except for thymine. It can be considered as code copy also.

[00:23:57]This also can be called code copy.

[00:24:00]Because this is called code copy, this can be called code complement.

[00:24:07]This can be called code complement.

[00:24:12]So mRNA is produced from the strand template strand only.

[00:24:18]And to produce an mRNA from the other strand, a promoter should be here and a terminator must be here. So if the position of promoter and terminator are interchanged, this can be acting as a template. So this is the template strand. It has a polarity of 35 direction. What is the reason for this polarity of 35 direction? The RNA polymerase can add nucleotides in 53 direction only. So this is 35 direction and this will be showing 53 direction. So this is the reason. The template polarity is always 35 only.

[00:25:05]And what is the location of promoter gene or promoter? The promoter is described as upstream or five end.

[00:25:23]Five end of what? Five end of coding strand. All references are made from coding strand only. So initially it was explained like this and those who followed understood. That is the reason it became a convention to call the template non-template strand as coding strand. And then where is the What is the location of terminator?

[00:25:50]Where the process of transcription will end. This is downstream or at three prime end.

[00:26:09]Eppudu anulakan pramanani parsil dam anulakan pramanamu DNA lo konta bagamu idi anulakanamuku lonayadi moodu aidu duravatvani kaliguntundi three prime five prime duravatvani kaliguntundi diniki karnam emitante DNA adharita RNA polymerase enzyme kunjikarana RNA nucleotide kunjikarana aidu moodu five prime three prime disalo matrame cheyagalugutundi dinivalana e moosa palakamu ellapudu moodu three prime five prime duravatvani matrame kaligundali e moodu aidu duravatvam kaliginantuvanti e structural jenuvu structural gene mundu bagamulo promoter venaka bagamulo terminator untai e perulu annintini coding strand coding strand paramga chebutaru anaga template moosa palakamu three five duravatvam kaligina palakamulo e rakamaina natrajeni charala varasa kramam unnapudu e rakamaina mRNA erpadutundi leda RNA erpadutundi idi coding strand sanketa posalo e rakamainadi untundi sanketa posa erpadina RNA okavidinga unnai t badulu u tappinchi a a c c g g g g a a c c so t badulu u tappinchi migilina vishayalo okavidinga undatam valana dinni sanketa posa and dinni moosa posa alage dinni ardhavantavaina posa idi prati antisense posa adere kanga e perulato pilustaru e promoter stanam ekkadundi promoter promoter anulakananiki lonukadu terminator kuda anulakananiki lonukadu kani promoter terminator panicheyani edala e anulakanam jaragadu kabatti vitini kuda jenuvulani pilustaru so promoter stanamedi promoter yuguva disalo undi yuguva disa ante emiti aidu prime end deniki sambandinchina aidu prime end idi sanketa posaku sambandinchina aidu end nizanikidi moosa palakaniki sambandinchina moodu prime end kani acharang diniprakaram perulu pettatam jarigindi so promoter jenuvo stanamu yuguva disa leda five prime end lo undi terminator stanamedi terminator three prime end leda diguvu disalo unnadi Now let us consider what is the relation between transcriptional unit and gene? Relation between transcriptional unit and gene.

[00:29:26]A transcriptional unit is a structural gene.

[00:29:33]This codes for This codes for one polypeptide.

[00:29:41]This will be coding for one polypeptide.

[00:29:52]>> So, transcriptional unit is a structural gene.

[00:29:55]It codes for one polypeptide. This is normally called cistron.

[00:30:03]It has a promoter and a terminator.

[00:30:06]Promoter upstream, terminator downstream.

[00:30:10]Now, this kind of transcriptional unit is called monocistronic.

[00:30:23]And this is seen in case of eukaryotes.

[00:30:29]In case of prokaryotes, in case of prokaryotes, many cistrons will be there.

[00:30:41]Many cistrons will be there.

[00:30:44]Say this is promoter and this is terminator.

[00:30:54]So, we have many genes here and all are required by the cell at the same time. So, this will be producing one polypeptide, another, another, another, another, and another, and another. So, this kind of gene is called polycistronic gene.

[00:31:16]In case of prokaryotic organisms, it is polycistronic genes.

[00:31:22]Many genes have common promoter and common terminator.

[00:31:28]All are required. The gene products of all these are required by the cell at the same time. So, they have common switch on and common switch off. So, prokaryotic genes are commonly polycistronic genes and these polycistronic genes are normally called operons. And example for some operons are lac operon, tryptophan operon, similarly, valine operon, histidine operon, etc. In eukaryotic organisms, the ancestral sequence is also present in the transcriptional unit or monocistronic gene and those intervening sequences are called introns. They represent the ancestral genes and they are removed during splicing.

[00:32:34]Now, let us consider the types of RNA and how they are synthesized, transcribed. In case of prokaryotic organisms, in case of prokaryotic organisms, there is only one kind of RNA polymerase, DNA-dependent RNA polymerase.

[00:33:04]It will be transcribing for mRNA, it will be transcribing for rRNA, it will be transcribing for tRNA.

[00:33:15]All three kinds of RNAs are transcribed from the DNA and the three types are produced by the catalytic action of same enzyme, RNA polymerase.

[00:33:29]So, this is transcription, this is also production of this is transcription, this is transcription, and this is also considered as transcription. To produce any of these three, three stages are required, that is initiation, elongation, and termination.

[00:33:57]And RNA DNA-dependent RNA polymerase can do only this and not the first and the last steps.

[00:34:05]And for this, it requires sigma factor.

[00:34:12]And for this, it requires rho factor.

[00:34:17]So, with the help of sigma factor, it can begin initiation. With the help of rho factor, it can end the process of transcription. And it is on its own, it is capable of elongation only. Many aspects of transcription are not well understood even today.

[00:34:39]So, in case of prokaryotic organisms, RNA DNA-dependent RNA polymerase transcribes for mRNA, rRNA, and tRNA.

[00:34:49]And it is three steps are required in any kind of transcription. And what are they? Initiation, elongation, and termination. And on its own, DNA-dependent RNA polymerase can perform elongation only and not initiation and termination. For initiation, sigma factor is required.

[00:35:14]For termination, rho factor is required.

[00:35:21]In eukaryotic organisms, there is a clear-cut division of labor.

[00:35:35]We have three RNA polymerases, DNA-dependent RNA polymerases.

[00:35:48]We have one, two, and three.

[00:35:52]And what is the function of DNA-dependent RNA polymerase one?

[00:35:59]It mainly transcribes for rRNA.

[00:36:03]You have 28S rRNA and 18S rRNA and also 5.8S rRNA.

[00:36:19]So, there is a division of labor in RNA polymerases. RNA polymerase one transcribes for rRNA.

[00:36:31]RNA polymerase two, this transcribes for hnRNA.

[00:36:40]This is precursor for mRNA. This is precursor for mRNA. After processing, hnRNA will change into mRNA.

[00:36:55]Next, we have RNA polymerase three.

[00:37:00]This mainly transcribes for different kinds of tRNAs. The minimum number is 55 22 and maximum number is 55.

[00:37:12]So, different kinds of tRNAs, 5S rRNA, similarly, sn RNA.

[00:37:23]sn stands for small nuclear RNAs.

[00:37:31]These are useful in splicing.

[00:37:37]These are useful in splicing.

[00:37:40]So, there is a division of labor in eukaryotic RNA polymerases and DNA-dependent polymerase one, two, three are there. And one mainly synthesizes rRNA, whereas two synthesizes mRNA, its precursor, hnRNA.

[00:37:59]And RNA polymerase three, it mainly synthesizes tRNAs and also 5S rRNA and snRNA. sn stands for small nuclear RNAs. They are useful in splicing.

[00:38:19]Now, let us consider the process of transcription in prokaryotic organisms.

[00:38:24]This is a segment of DNA undergoing transcription.

[00:38:35]And this is the RNA polymerase and this is the sigma factor.

[00:39:01]So, somehow it opens the somehow it opens the double-stranded DNA and it binds near the promoter region.

[00:39:13]It binds near the promoter region.

[00:39:24]And this is what is taken as initiation.

[00:39:31]Then, the process will continue.

[00:39:46]>> This is newly formed mRNA and this is the RNA polymerase.

[00:39:59]This is elongation performed by the RNA polymerase on its own.

[00:40:09]Now, let us consider the termination.

[00:40:18]Here, and this is called termination.

[00:40:51]The transcription process, the transcription process in prokaryotic organisms is simple. Here, somehow, with the help of sigma factor, RNA polymerase gets the double-stranded DNA open up at promoter region it will bind and the process of transcription will continue in 5-3 direction on a template of 3-5 and then the sigma factor is released and the RNA polymerase on its own continue elongation. So, the mRNA strand is formed. Then, what happens? Once it reaches the terminator region, rho factor binds to the RNA polymerase and it is released. The newly formed mRNA also released into the cytoplasm.

[00:41:46]In prokaryotic organisms, there is no nucleus and compartmentalization.

[00:41:51]As a result, while the process of transcription is going on, translation also may begin and in many cases, both appear to be simultaneous. So, when this is being produced, ribosomes get attached to this and the process of protein synthesis also may continue. So, translation and transcription and translation are simultaneous in case of prokaryotic organisms.

[00:42:25]The important point to remember in case of prokaryotic transcription is transcription and translation and translation can be simultaneous because there is no nuclear membrane separating the nucleus and cytoplasm.

[00:43:00]Now, the transcription process in eukaryotic organisms and this is the DNA and this is the RNA polymerase and this is the mRNA formed.

[00:43:29]This is the mRNA formed.

[00:43:32]This is called hnRNA.

[00:43:35]This is called hnRNA.

[00:43:38]So, there is a promoter and there is a terminator and the process will continue like this and the gene here is monocistronic genes are here.

[00:43:53]The gene here is monocistronic.

[00:43:56]Okay, the process is completed.

[00:43:59]Initiation, elongation, termination also completed. Now, let us consider this and this is the hnRNA formed and this hnRNA immediately requires capping and a methylated guanine cap is attached at the beginning at five end. A methylated guanine cap is attached and here So, this is let me write this as exon intron exon intron exon intron exon intron exon intron So, this is a methylated guanine cap is added at five end.

[00:45:04]And now, what happens is the intron portions represent intervening sequences of nucleotides.

[00:45:15]They are of ancestral origin. These are not normally expressed. If they are expressed, it may produce what is called atavism. So, they must be removed. At the beginning and ending of intron portions, snRNA will bind. At beginning and ending of introns, snRNA will bind.

[00:45:39]So, this is five end we are referring to and this is the So, same calibration.

[00:45:52]Now, we have at the beginning and ending of intron, there is binding of snRNA and this is the So, this is intron portion and this is intron portion. This is also intron portion. And at the beginning and ending we have and then this is the beginning and at this step, a poly-A tailing is done.

[00:46:28]A poly-A tail is attached at three end.

[00:46:34]And this capping and tailing are independent of a template. They are added in template-independent manner.

[00:46:42]If we observe, these sequences are not there in the DNA. That is what is meant by template-independent manner. Now, this undergoes processing and this is what is left and this is poly-A tail.

[00:47:02]This is three end and this is our methylated guanine cap.

[00:47:10]Methylated guanine cap at five end.

[00:47:17]This removal of intron portions are removed. Intron portion is removed, removed, removed, removed, removed.

[00:47:24]So, due to removal of intron portions, we have what is left. mRNA is present here and this mRNA has this hnRNA has undergone processing producing mRNA and in this mRNA, this and this part, cap and tail are template-independent.

[00:47:52]Cap and tail are template-independent, whereas this part is template-dependent but modified. The intron portions are removed because this is coding for one polypeptide only and the original sequence has introns also not expressed in the form of amino acids polymerized to form a protein. This requires ancestral sequence. This is called a splicing. So, after processing, hnRNA is changed into mRNA. The methylated guanine cap helps in coming out of the nucleus and well functioning of the mRNA. Poly-A tail gives protection from exonucleases of cytoplasm and this is translated inside endoplasmic reticulum, rough endoplasmic reticulum.

[00:49:08]Heterogeneous nuclear RNA will be called Here, it can be called hnRNA.

[00:49:37]Methylated guanine methylated guanine and so on.

[00:49:48]nucleotide processing processing law intron are in the more s n r loop only sun Bhagavad only d n a cap in the tail a poly a tail three prime a poly a d n d other it could d intron x on garlic antar d m r n a is not directly formed. h n r n a processing are splicing capping and also tailing then we have what we call m r n a.

[00:51:23]This processing is essential for m r n a. The process of m r n a or transcription occurs in nucleus.

[00:51:37]It's a translation into protein.

[00:51:40]It's translation into protein.

[00:51:43]This occurs in cytoplasm.

[00:51:48]Specifically inside luminal part of rough endoplasmic reticulum translation process occurs.

[00:51:57]So, h n r n a and during splicing what is removed?

[00:52:02]During splicing there is a removal of intron portions.

[00:52:08]During capping there is a addition of methylated guanine triphosphate. And in this case we have the addition of poly a tail.

[00:52:25]So, this represents processing and only after this we have m r n a and this m r n a is a translated in the cytoplasm because nucleus and cytoplasm are separated by nuclear envelope or membrane in eukaryotic organisms. In mitochondria and plastids the transcription occurs and translation also occurs in mitochondrial matrix.

[00:53:02]We have both transcription and translation and in plastids stroma in stroma of plastids also the process of transcription and translation occur.

[00:53:23]And here we have three kinds of r n a polymerases in this case only one kind of r n a polymerase because these are similar to prokaryotic organisms only one kind of r n a polymerase will be present.

[00:53:39]h n r n a h n r n a capping law methylated guanine tri guanylic acid or guanosine triphosphate the I do go and join up to the tailing number tailing number poly a tail 200 to 300 edilic amla our session will carry now poly a tail and so on about 200 transcription kind of camel is there going to be and what I do more and I got protein less some solution garlic endoplasmic reticulum occur luminal Bhagavad is there with only other than the major kind of kind of one day mitochondrial matrix law transcription translation render matrix number plastid law one day our indicator could I transcription Mario and what I can do more and what I do okay peria and I got to tell me government job and you can I got to be kind of for the same amount of money since introns are removed the type of gene in eukaryotic organisms is called split gene.

[00:55:06]Why this is called split gene? The intron portions are removed. The primary transcript is not undergoing translation. It is subjected to processing where certain portions are removed certain portions are added. So, the eukaryotic genes are monocistronic and also split genes.

[00:55:30]need need a kind of a gene law one day gene you will do monocistronic gene you will do Mario split split kind of splicing law intron Bhagavad kind of a day primary transcript mother to study problem number 18 and and what I can do more protein number intron e gene you will do split gene you will do and what I can do more Now, let us try to conclude what is discussed up to now. The copying of some portion the copying of some portion or a small portion of d n a into r n a is called transcription. It may be production of m r n a r r n a t r n a h n r n a s n r n a any kind of r n a and this is only a small part of d n a is one of the d n a strands is acting as template so that a portion is transcribed. For this d d n a dependent r n a polymerase enzyme is essential.

[00:56:47]Only one kind of d n a dependent r n a polymerase is present in prokaryotic organisms whereas in eukaryotic organisms three kinds of d n a dependent r n a polymerases are there and r n a polymerase one is responsible for synthesis of r r n a r n a polymerase two is responsible for synthesis of h n r n a the precursor for m r n a and r n a polymerase three is responsible for synthesis of different kinds of t r n a s useful for carrying amino acids to site of protein synthesis and the trans primary transcript can immediately undergo translation in prokaryotic organisms whereas in eukaryotic organisms it requires some processing in whatever m r n a is produced inside nucleus requires processing that is called h n r n a it undergoes splicing capping tailing and whereas in the same eukaryotic cells inside mitochondria transcription and translation are simultaneous inside plastids of plant cells and also mitochondria of plant cells it occurs in the stroma and transcription and translation are simultaneous.