Similarities: Show
Comparisons between bacterial and RNA polymerase II have been performed. Similarity in sequence has been shown between alpha, Rpb3, and Rpb11. Alpha2 binds beta to form a subcomplex that then binds beta’ that form the core enzyme. Rpb3 and Rpb11 also form a subcomplex with Rpb2. The Rpb3 and Rpb11 show the same fold as the alpha subunit in bacterial polymerase. Beta and Rpb2 as well as beta’ and Rpb1 show sequence homology. The pore in which RNA exits and where NTPs comes into the polymerase are conserved as well (4). Differences: Prokaryotes only contain three different promoter elements: -10, -35 promoters, and upstream elements. Eukaryotes contain many different promoter elements: TATA box, initiator elements, downstream core promoter element, CAAT box, and the GC box to name a few. Eukaryotes have three types of RNA polymerases, I, II, and III, and prokaryotes only have one type. Eukaryotes form and initiation complex with the various transcription factors that dissociate after initiation is completed. There is no such structure seen in prokaryotes. Another main difference between the two is that transcription and translation occurs simultaneously in prokaryotes and in eukaryotes the RNA is first transcribed in the nucleus and then translated in the cytoplasm. RNAs from eukaryotes undergo post-transcriptional modifications including: capping, polyadenylation, and splicing. These events do not occur in prokaryotes. mRNAs in prokaryotes tend to contain many different genes on a single mRNA meaning they are polycystronic. Eukaryotes contain mRNAs that are monocystronic. Termination in prokaryotes is done by either rho-dependent or rho-independent mechanisms. In eukaryotes transcription is terminated by two elements: a poly(A) signal and a downstream terminator sequence (7). Prokaryotic and eukaryotic translation are involved in the synthesis of proteins by decoding the genetic instructions carried by the mRNAs. During translation, nucleotide triplets, known as codons, on the mRNA are translated into a sequence of amino acids. Both prokaryotic and eukaryotic translation share a similar basic plan throughout the processes. However, there are several differences that can be observed in these translation processes. The main difference between prokaryotic and eukaryotic translation is that prokaryotic translation occurs synchronously with its transcription whereas eukaryotic translation occurs asynchronously with its transcription. This article explains, 1.
What is Prokaryotic Translation
What is Prokaryotic TranslationIn prokaryotes, translation is the process of simultaneously synthesizing proteins with transcription. Translation begins just after transcribing the 5′ end of the gene into mRNA. Prokaryotic translation basically occurs in three steps: initiation, elongation and termination. In order to initiate the translation, the two subunits 50S and 30S are assembled. The three initiation factors, IF1, IF2 and IF3 help to assemble the initiation complex. N-formylmethionine is the first added amino acid in translation. GTP is used as the energy source for the peptide bond formation between the remaining and incoming nucleotides. The translation initiation factor is EF-P. The selection of the start codon is facilitated by the binding of the ribosome with the Shine-Dalgarno sequence. The Shine-Dalgarno sequence is a purine-rich region located upstream of the AUG start codon. This sequence is complementary to the pyrimidine-rich region on 16S rRNA. The 16S rRNA is a component of 30S subunit. These two complementary nucleotides pair together, forming a double-stranded RNA structure. This pairing brings the initiation codon into the P-site of the ribosome. The first amino acid binds with the P site. A ribosome consists of three active sites: A site, P site and E site. Incoming aminoacyl tRNAs, other than the first aminoacyl tRNA, binds with the A site. The peptide bond formation occurs at the P site. Exit site for the uncharged tRNA is the E site.  Figure 1: Transcription initiation in prokaryotes’ 70S ribosome The two elongation factors are EF-G and EF-Tu. The translation elongates until the ribosome reaches to one of the three stop codons: UAA, UGA, UAG. Release factors other than the tRNAs, recognise the stop codon. The mRNA with the termination codon at A site is referred to as the termination complex. Three release factors can be identified: RF1, RF2 and the RF3. RF1 and RF2 recognise the UAA/UAG and UAA/UGA and hydrolyze the ester bond in peptidyl-tRNA to release the nascent polypeptide chain. RF3 catalyses the releasing of RF1 and RF2. Once the new protein releases, the ribosome undergoes recycling. The Ribosome Recycling Factor and EF-G, are involved in releasing mRNA and tRNAs from the ribosome and dissociation of 70S ribosome into 30S and 50S subunits. IF3 releases the mRNA by replacing the deacylated tRNA. When bacteria enter the stationary phase, the translation is downregulated by the dimerization of ribosomes. Ribosome dimerization is facilitated by RMF, HPF and YfiA. The ribosome-dissociation factors are RsfA and HflX. What is Eukaryotic TranslationTranslation is the second step of eukaryotic gene expression, a separate event from eukaryotic transcription. Transcription and translation occur in two different compartments in eukaryotes. Therefore, the two processes can not occur simultaneously. Eukaryotic mRNAs are monocistronic and are processed in the nucleus by adding a 5′ cap, poly A tail and splicing out of introns before they are released to the cytoplasm. Ribosomal pausing also affects the translation by co-translational folding of the newly synthesising polypeptide chain on the ribosome. This process delays translation, giving time for the translation. Eukaryotic mRNAs consist of a 5′ cap and poly A tail. Therefore, the initiation of translation occurs in two different ways: cap-dependent initiation and cap-independent initiation. During cap-dependent initiation, the initiation factors bind to the 5′ end of the mRNA. These initiation factors hold the mRNA in the small subunit of the ribosome. During cap-independent initiation, internal ribosome entry sites allow the ribosome trafficking to the start site by direct binding. In eukaryotes, the first binding amino acid is methionine. 40S subunit associates with 60S subunit to form 80S ribosome. Two elongation factors are involved in eukaryotic translation: eEF-1 and eEF-2. Elongation occurs in a similar way to that of prokaryotes. Termination of the translation is also the same as in the prokaryotic system. But the universal release factor eRF1 is capable of recognising all three stop codons. The release factor, eRF3 helps eRF1 to release the polypeptide chain. Basic steps of the translation are shown in figure 2. Figure 2: Generalised translation
Difference Between Prokaryotic and Eukaryotic TranslationTimingProkaryotic Translation:Prokaryotic transcription and translation are simultaneous processes. Eukaryotic Translation:Eukaryotic transcription and translation are discontinuous processes. RibosomesProkaryotic Translation:30S and 50S = 70S ribosomes Eukaryotic Translation: 40S and 60S = 80S ribosomes Messenger RNA SourceProkaryotic Translation:Porkaryotic mRNAs occur in the cytoplasm. The mRNA is polycistronic. Eukaryotic Translation: Eukaryotic mRNAs occur in the nucleus. After the post-transcriptional modifications they are released to the cytoplasm via nuclear pores. The mRNA is monocistranic. Life Span of mRNAProkaryotic Translation: The mRNAs are unstable and live for few seconds to two minutes. Eukaryotic Translation:The mRNAs are quite stable, and live for about few hours to days. LocationProkaryotic Translation: This is performed by 70S ribosomes in the cytoplasm. Eukaryotic Translation: This is performed by the 80S ribosomes attached with the ER. Localization in the Cell CycleProkaryotic Translation: There is no definite phase for the occurrence. Eukaryotic Translation:This occurs in G1 and G2 phases in the cell cycle. Sequences in the Untranslated RegionProkaryotic Translation:Shine-Dalgarno sequence is found in the 5′ UTR, ~10 nucleotides upstream to the start codon. Eukaryotic Translation: Kozak sequence is found in the 5′ UTR, a few nucleotides upstream to the stat codon. Translation InitiationProkaryotic Translation: Cap- independent initiation. Eukaryotic Translation: Both cap-dependent and cap-independent initiation. Initiation FactorsProkaryotic Translation: Three initiation factors are involved: IF1, IF2 and IF3. Eukaryotic Translation:Nine initiation factors are involved: elF 1, 2, 3, 4A, 4B, 4C, 4D, 5 and 6. First Amino AcidProkaryotic Translation:N-formylmethionine is the first amino acid added to the polypeptide chain. Eukaryotic Translation:Methionine is the first amino acid added to the polypeptide chain. Elongation FactorProkaryotic Translation:Two elongation factors are involved: EF-G and EF-Tu. Eukaryotic Translation: Two elongation factors are involved: eEF-1 and eEF-2. SpeedProkaryotic Translation: Prokaryotic translation is a faster process which adds twenty amino acids per second. Eukaryotic Translation: Eukaryotic translation is a slower process which adds a single amino acid per second. Fate of First Amino AcidProkaryotic Translation: The formyl group is removed from first amino acid, retaining methionine in the polypetide chain. Eukaryotic Translation: The whole methionine is removed from the polypeptide chain. Release FactorProkaryotic Translation:Two released factors are involved: RF1 (for UAG and UAA) and RF2 (for UAA and UGA). Eukaryotic Translation: A single release factor is involved: eRF1. ConclusionTranslation is the universal process of synthesizing proteins as the second step in gene expression. Both prokaryotic and eukaryotic ribosomes decode mRNAs in fundamentally similar methods. Ribosomes are the machinery of the protein synthesis. All twenty essential amino acids are shared in both prokaryotic and eukaryotic translation processes. Both processes occur in the cytoplasm, completing the four processes: initiation, elongation, translocation and termination. The tRNA, brings the correct amino acid, allowing peptide bonds to form between two amino acids. The main difference between prokaryotic and eukaryotic translation is that prokaryotic translation is a simultaneous process with transcription whereas eukaryotic translation is a separate process from its transcription. Reference: Image Courtesy: How is transcription and translation different in prokaryotes?Prokaryotic transcription occurs in the cytoplasm alongside translation. Prokaryotic transcription and translation can occur simultaneously. This is impossible in eukaryotes, where transcription occurs in a membrane-bound nucleus while translation occurs outside the nucleus in the cytoplasm.
Is transcription the same in prokaryotes and eukaryotes?Both prokaryotes and eukaryotes perform fundamentally the same process of transcription, with the important difference of the membrane-bound nucleus in eukaryotes. With the genes bound in the nucleus, transcription occurs in the nucleus of the cell and the mRNA transcript must be transported to the cytoplasm.
How does the process of translation in prokaryotes differ from translation in eukaryotes quizlet?In a eukaryotic cell, transcription occurs in the nucleus, and translation occurs in the cytoplasm. In a prokaryotic cell, transcription and translation are coupled; that is, translation begins while the mRNA is still being synthesized.
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Difference between transcription and translation in prokaryotes and eukaryotes
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