Molecular structure of prokaryotic and eukaryotic gene
Answers
Answer:
Explanation:
Abstract Genes consist of multiple sequence elements that together encode the functional product and regulate its expres-sion. Despite their fundamental importance, there are few freely available diagrams of gene structure. Presented here are two figures that summarise the different structures found in eukaryotic and prokaryotic genes. Common gene structural elements are colour-coded by their function in regulation, transcription, or translation. Introduction GThe structure of eukaryotic genes includes features not found in prokaryotes. Most of these relate to post-transcriptional modification of pre-mRNAs to produce mature mRNA ready for translation into protein. Eukaryotic genes typically have more regulatory elements to control gene expression compared to prokaryotes.[5] This is particularly true in multicellular eukaryotes, humans for example, where gene expression varies widely among different tissues.[11]
A key feature of the structure of eukaryotic genes is that their transcripts are typically subdivided into exon and intron regions. Exon regions are retained in the final mature mRNA molecule, while intron regions are spliced out (excised) during post-transcriptional processing.[22] Indeed, the intron regions of a gene can be considerably longer than the exon regions. Once spliced together, the exons form a single continuous protein-coding regions, and the splice boundaries are not detectable. Eukaryotic post-transcriptional processing also adds a 5' cap to the start of the mRNA and a poly-adenosine tail to the end of the mRNA. These additions stabilise the mRNA and direct its transport from the nucleus to the cytoplasm, although neither of these features are directly encoded in the structure of a gene.[18]
Prokaryotes
Prokaryote gene structure diagram
Polycistronic operonRegulatory sequenceRegulatory sequenceEnhancerEnhancer/silencer/silencerOperatorPromoter5'UTRORFORFUTR3'UTRStartStartStopStopTerminatorTranscriptionDNARBSRBSProtein coding regionProtein coding regionmRNATranslationProtein
The image above contains clickable linksThe structure of a prokaryotic operon of protein-coding genes. Regulatory sequence controls when expression occurs for the multiple protein coding regions (red). Promoter, operator and enhancer regions (yellow) regulate the transcription of the gene into an mRNA. The mRNA untranslated regions (blue) regulate translation into the final protein products.[17]
The overall organisation of prokaryotic genes is markedly different from that of the eukaryotes. The most obvious difference is that prokaryotic ORFs are often grouped into a polycistronic operon under the control of a shared set of regulatory sequences. These ORFs are all transcribed onto the same mRNA and so are co-regulated and often serve related functions.[23][24] Each ORF typically has its own ribosome binding site (RBS) so that ribosomes simultaneously translate ORFs on the same mRNA. Some operons also display translational coupling, where the translation rates of multiple ORFs within an operon are linked.[25] This can occur when the ribosome remains attached at the end of an ORF and simply translocates along to the next without the need for a new RBS.[26] Translational coupling is also observed when translation of an ORF affects the accessibility of the next RBS through changes in RNA secondary structure.[27] Having multiple ORFs on a single mRNA is only possible in prokaryotes because their transcription and translation take place at the same time and in the same subcellular location.[23][28]
The operator sequence next to the promoter is the main regulatory element in prokaryotes. Repressor proteins bound to the operator sequence physically obstructs the RNA polymerase enzyme, preventing transcription.[29][30] Riboswitches are another important regulatory sequence commonly present in prokaryotic UTRs. These sequences switch between alternative secondary structures in the RNA depending on the concentration of key metabolites. The secondary structures then either block or reveal important sequence regions such as RBSs. Introns are extremely rare in prokaryotes and therefore do not play a significant role in prokaryotic gene regulation.[31]ene structure
Answer:
Prokaryotes typically contain a single circular chromosome that occupies a nucleoid area of the cytoplasm. They may also include plasmids, which are tiny rings of double-stranded extra-chromosomal DNA.
Gene structure in eukaryotic cells. Most eukaryotic genes include coding sequences (exons) separated by noncoding regions (introns). Exons and introns are both transcribed to produce a lengthy main RNA transcript.
Explanation:
The structure and chemical makeup of DNA varies between eukaryotic and prokaryotic organisms. Prokaryotic cells lack a nucleus, organelles, and a limited quantity of DNA. Eukaryotic cells, on the other hand, have nuclei and cell organelles, as well as a huge quantity of DNA.
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