Role Of Rna Polymerase In Post
RNA polymerase plays a very crucial role in all steps including post-transcriptional changes in RNA.
As shown in the image in the right it is evident that the CTD is a tail that changes its shape this tail will be used as a carrier of splicing, capping and polyadenylation, as shown in the image on the left.
Regulation Of Rna Processing
When a eukaryotic gene is transcribed in the nucleus, the primary transcript isnt yet considered a messenger RNA. Instead, its an immature molecule called a pre-mRNA.
The pre-mRNA has to go through some modifications to become a mature mRNA molecule that can leave the nucleus and be translated. These include splicing, capping, and addition of a poly-A tail, all of which can potentially be regulated sped up, slowed down, or altered to result in a different product.
Most pre-mRNA molecules have sections that are removed from the molecule, called introns, and sections that are linked or together to make the final mRNA, called exons. This process is called splicing.
In the process of alternative splicing, different portions of an mRNA can be selected for use as exons. This allows either of two mRNA molecules to be made from one pre-mRNA.
Figure 7. Image modified from Eukaryotic Post-transcriptional Gene Regulation, by OpenStax College, Biology .
Alternative splicing is not a random process. Instead, its typically controlled by regulatory proteins. The proteins bind to specific sites on the pre-mRNA and tell the splicing factors which exons should be used. Different cell types may express different regulatory proteins, so different exon combinations can be used in each cell type, leading to the production of different proteins.
What Does Transcription Mean In Biology
Transcription is the process by which the information in a strand of DNA is copied into a new molecule of messenger RNA . Meanwhile, mRNA is comparable to a copy from a reference book because it carries the same information as DNA but is not used for long-term storage and can freely exit the nucleus.
What is transcription vs translation in biology?
Transcription is the synthesis of RNA from a DNA template where the code in the DNA is converted into a complementary RNA code. Translation is the synthesis of a protein from an mRNA template where the code in the mRNA is converted into an amino acid sequence in a protein.
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Dna Rna And Protein Synthesis
The genetic material is stored in the form of DNA in most organisms. In humans, the nucleus of each cell contains 3 × 109 base pairs of DNA distributed over 23 pairs of chromosomes, and each cell has two copies of the genetic material. This is known collectively as the human genome. The human genome contains around 30 000 genes, each of which codes for one protein.
Large stretches of DNA in the human genome are transcribed but do not code for proteins. These regions are called introns and make up around 95% of the genome. The nucleotide sequence of the human genome is now known to a reasonable degree of accuracy but we do not yet understand why so much of it is non-coding. Some of this non-coding DNA controls gene expression but the purpose of much of it is not yet understood. This is a fascinating subject that is certain to advance rapidly over the next few years.
The Central Dogma of Molecular Biology states that DNA makes RNA makes proteins .
The Language Of Rna A U G C
To transcript DNA into mRNA, the rule is the same. The only difference is that Uracil replaces Thymine . So, G C, A U, and T A. In our cell, the transcription is done by an enzyme called RNA polymerase in the nucleus, which can synthesize mRNA from a DNA template.
Nitrogenous base options for DNA and RNA.Image source: wiki
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Modification Of Mrna In Eukaryotic Cells
Creating a completed mRNA molecule isnt quite as simple in eukaryotic cells. Like prokaryotic cells, the end of a transcription unit is signalled by a certain sequence of nucleotides. Unlike prokaryotic cells, however, RNA polymerase continues to add nucleotides after transcribing the terminator sequence.
Proteins are required to release the RNA polymerase from the template DNA strand and the RNA molecule is modified to remove the extra nucleotides along with certain unwanted sections of the RNA strand. The remaining sections are spliced together and the final mRNA strand is ready for translation.
In eukaryotic cells, transcription of a DNA strand must be complete before translation can begin. The two processes are separated by the membrane of the nucleus so they cannot be performed on the same strand at the same time as they are in prokaryotic cells.
Differences Between Prokaryotic And Eukaryotic Transcription
The obvious difference between prokaryotic and eukaryotic transcription is the presence of a nuclear membrane in eukaryotes. Eukaryotic RNA transcripts need to be exported from the nucleus, whereas prokaryotes conduct coupled transcription and translation in the cytoplasm. This is possible because the prokaryotic transcript does not undergo extensive modification and prokaryotes do not need transcription factors for initiation. Therefore, the transcription machinery is simpler and can simultaneously accommodate the enzymes of translation.
Prokaryotes also have only one RNA polymerase to catalyze all the transcription reactions of the cell and a single RNA transcript can direct the synthesis of multiple proteins. These mRNA are called polycistronic mRNA. Often, all the genes involved in one biochemical pathway are transcribed and translated together, allowing the entire pathway to be regulated as a single unit. In eukaryotes, polycistronic mRNA can be found in chloroplasts.
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What Kinds Of Rna Can Be Transcribed
When talking about RNA and transcription, we usually refer to messenger RNA . An mRNA is transcribed from a protein-encoding gene and subsequently is translated to a protein. But there is a whole set of other RNAs that get transcribed, like transfer RNA and ribosomal RNA , that do different functions in the cells.
Types of RNA molecules.
Transcription produces RNAs that functionally are either for protein-coding or non-coding . At least six functional types of RNA genes exist:1. Transfer RNA During translation, tRNAs transfer specific amino acids to the growing polypeptide chains in the ribosomes for protein synthesis.2. Ribosomal RNA rRNAs and ribosomal proteins assemble into ribosomes.3. Small nuclear RNA snRNAs help the splicing of pre-messenger RNAs in the nucleus.4. Micro RNA miRNAs can regulate gene activity. Some miRNAs bind to mRNAs and block the translation. Scientists use the same principle to synthesize small interfering RNA , which can be used as a drug.5. Catalytic RNA Ribozymes are RNA molecules but have enzymatical activities.6. Long non-coding RNAs lncRNAs are RNA transcripts of more than 200 nucleotides that are not translated into any protein. lncRNA was discovered to regulate gene functions. However, the actual mechanisms are still unclear.Note: Different types of RNAs are transcribed by different RNA polymerases. We will cover this topic in the next section.
Mistakes In Dna Replication
DNA replication is not perfect. Errors occur in DNA replication, when the incorrect base is incorporated into the growing DNA strand. This leads to mismatched base pairs, or mispairs. DNA polymerases have proofreading activity, and a DNA repair enzymes have evolved to correct these mistakes. Occasionally, mispairs survive and are incorporated into the genome in the next round of replication. These mutations may have no consequence, they may result in the death of the organism, they may result in a genetic disease or cancer or they may give the organism a competitive advantage over its neighbours, which leads to evolution by natural selection.
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How Dna Transcription Works
selvanegra / Getty Images
DNA consists of four nucleotide bases that are paired together to give DNA its double helical shape. These bases are: adenine , guanine , cytosine , and thymine . Adenine pairs with thymine and cytosine pairs with guanine . Nucleotide base sequences are the genetic code or instructions for protein synthesis.
Lesson Explainer: Transcription Biology
In this explainer, we will learn how to describe the process of transcription and to outline the roles of DNA, mRNA, and RNA polymerase.
Do you like mushrooms? When picking wild mushrooms, you need to be careful about which ones you select to eat. This one in particular needs to be avoided at all costs.
In the picture above, we see the so-called death cap mushroom, which can lead to death within a few days of ingestion. The poison inside the mushroom, called -amanitin, is able to inhibit transcription by interacting with the enzyme RNA polymerase. Without transcription, cells cannot produce the proteins necessary for their survival, and they die.
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Nucleotide Bases Are Translated Into 20 Different Amino Acids
RNA molecules only contain four different types of nitrogenous bases but there are 20 different amino acids that are used to build proteins. In order to turn four into 20, a combination of three nitrogenous bases provides the information for one amino acid.
Each three-base word is called a codon and the series of codons holds the information for the production of the polypeptide chain. There are a total of 64 different codons and more than one codon translates into each amino acid.
A strand of mRNA obviously has multiple codons which provide the information for multiple amino acids. A tRNA molecule reads along one codon of the mRNA strand and collects the necessary amino acid from the cytoplasm.
The tRNA returns to the ribosome with the amino acid, binds to the complementary bases of the mRNA codon, and the amino acid is added to the end of polypeptide chain as the RNA molecules move through the ribosome.
Control Transcription Control Gene Expression
A gene has been traditionally viewed as the basic molecular unit of heredity . In the form of DNA or RNA, it carries the raw genetic information that can be turned into functional products, usually proteins. However, the number of genes does not reflect the complexity of the organism. For example, a human has about 20 000 protein-coding genes, which is 6000 more than a fruit fly, 2000 more than Caenorhabditis elegans, and 14 000 more than budding yeast, but 10 000 less than a lab mouse, 5000 less than the model plant Arabidopsis, and 17 000 less than rice. Clearly, the level of complexity of the organism is achieved by regulating available genes, not simply by introducing more genes.
The central dogma of gene expression includes two sequential steps: transcription and translation . Transcription is the key step that controls the on and off of genes and subsequently underlines the identity and the status of the cell . For example, when I compare a string of my hair and my finger tip, they appear so different, as if they are made from different genetic materials. However, the fact is that all the different tissues and cells in my body contain the same DNA and it is the differential expression profiles that created the functional diversity. Understanding the mechanism of gene expression will help us to understand the formation and evolution of life and to find possible cures for diseases.
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Key Takeaways: Dna Transcription
- In DNA transcription, DNA is transcribed to produce RNA. The RNA transcript is then used to produce a protein.
- The three main steps of transcription are initiation, elongation, and termination.
- In initiation, the enzyme RNA polymerase binds to DNA at the promoter region.
- In elongation, RNA polymerase transcribes DNA into RNA.
- In termination, RNA polymerase releases from DNA ending transcription.
- Reverse transcription processes use the enzyme reverse transcriptase to convert RNA to DNA.
Directionality Of Dna Strands
As shown in the diagram above, the two ends of a strand of DNA or RNA strand are different. That is, the directionality to read a DNA or RNA strand.At the 5 end of the chain, the phosphate group of the first nucleotide in the chain sticks out. The phosphate group is attached to the 5 carbon of the sugar ring, which is why this is called the 5 end.At the 3 end, the hydroxyl of the last nucleotide added to the chain is exposed at the other end. The hydroxyl group is attached to the 3 carbon of the sugar ring, which is why this is called the 3 end.Many processes, such as DNA replication and transcription, can only take place in one particular direction, from 5 end to 3 end.
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Types Of Rna Transcripts
Traditionally, three types of RNA transcripts were known â messenger RNA , tRNA and rRNA â and all three are intimately associated with protein synthesis . While mRNA determines amino acid sequence, tRNA and rRNA are crucial for the mechanism of translating the mRNA code.
mRNA polymerization from DNA containing protein coding genes is catalyzed by RNA polymerase II. Occasionally, proteins that are used together are coded as a single unit, in one long mRNA molecule and this is particularly common among prokaryotes. DNA sequences upstream of the coding sequence contain docking sites for the transcription machinery as well as regulatory factors that modulate the timing and quantity of transcriptional activity. mRNA is then modified and processed to give rise to the final transcript used for translation.
rRNA constitutes nearly fifty percent of the RNA of a cell and is transcribed by RNA polymerase I in specialized regions of the nucleus called the nucleolus. Nucleoli appear as dense spherical structures around the loci that code for rRNA. Prokaryotic rRNA is of three types and eukaryotic ribosomes are made of four types of rRNA with the largest one containing over 5000 nucleotides. These RNA molecules determine the three-dimensional structure of ribosomes.
Transcription Biology For Dummies
The range of copies of the various components of DNA rides on the cells need for the corresponding proteins. There are many versions of RNA. Depending on what precisely the shift is it could have different effect on the subsequent amino acid.
It uses a strand of DNA as a template to build a molecule called RNA. It is the first step in the process known as protein synthesis, the way that a cell takes a set of instructions in its DNA known as a gene and uses that set of instructions to build a protein so that it can carry out a particular function or make a structure for the cell. In bacteria, when the transcription is finished, the comprehensive mRNA is prepared for protein synthesis.
For that reason, its thought that polymerase pausing must be an evolved mechanism that was positively selected-for. This bit of RNA is called the important transcript. 1 strand of DNA is known as the coding strand and the other one is the template strand.
No further modifications are necessary for the mRNA molecule and its feasible for translation to begin immediately. It produces polypeptides as a consequence of decoding of mRNA.
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S To Measure And Detect
For Transcription, RT-PCR, DNA microarray, In-situ hybridization, Northern blot, RNA-Seq is quite often used for measurement and detection.For Translation, western blotting, immunoblotting, enzyme assay, Protein sequencing, Metabolic labeling, proteomics is used for measurement and detection.
Cricks central dogma: DNA —> Transcription —> RNA —> Translation —> Protein
Genetic code used during translation:
The Regulation Of Individual Genes
Not all genes are transcribed all the time. Instead, transcription is controlled spatially and temporarily for each gene. For example, some growth hormones express only when we are young. Some proteins which can wake our immune system up will only be produced when our bodies sense pathogen invasion. Cells carefully regulate transcription, just transcribing the genes whose products are needed at a particular moment.
Diagram showing an imaginary cells RNAs at a given moment. In this cell, genes 1, 2, and 3, are transcribed, while gene 4 is not. Also, genes 1, 2, and 3 are transcribed at different levels, meaning that different numbers of RNA molecules are made for each.Image credit: Khan Academy
Like building a dam upstream of a river, our cells control gene expressions at the beginning of transcription. There are many ways to regulate the transcription:1. The initiation of transcription for some genes requires the binding of assistant proteins, called transcription factors, together with RNA polymerases, to their promoters.2. Some rarely used genes have their promoters covered by inhibitory proteins or hidden deeply in folded chromosomes, which make these genes inaccessible for transcription. This is called epigenetic regulation.3. Some genes are regulated by the stability of their mRNA. Some mRNA have pretty short half-lives and break down even before the translation happens. Only when a stimulus kicks in and makes the mRNA stable can these genes function.
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