The Molecular Mechanisms of Transcription and Translation in Prokaryotes (PDF Download)
- How are they different in prokaryotes and eukaryotes? - Why are they important for prokaryotic gene expression? H2: Transcription in Prokaryotes: The Process - The components of prokaryotic RNA polymerase - The stages of transcription: initiation, elongation, and termination - The types of prokaryotic promoters and terminators - The regulation of transcription by sigma factors and other factors H2: Translation in Prokaryotes: The Process - The components of prokaryotic ribosomes - The stages of translation: initiation, elongation, and termination - The types of prokaryotic codons and anticodons - The regulation of translation by riboswitches and other factors H2: Coupling of Transcription and Translation in Prokaryotes: The Advantages - The spatial and temporal proximity of transcription and translation - The formation of polysomes and operons - The coordination of gene expression and protein synthesis - The adaptation to environmental changes and stress responses H2: Transcription and Translation in Prokaryotes: The Applications - The use of prokaryotic transcription and translation systems for biotechnology and synthetic biology - The use of prokaryotic transcription and translation inhibitors for antimicrobial therapy - The use of prokaryotic transcription and translation models for evolutionary and comparative studies H2: Transcription and Translation in Prokaryotes: The Summary - A recap of the main points of the article - A conclusion that highlights the significance and implications of the topic # Article with HTML Formatting Transcription and Translation in Prokaryotes: An Overview
Transcription and translation are two fundamental processes that enable living cells to express their genetic information. Transcription is the synthesis of RNA from a DNA template, while translation is the synthesis of proteins from an RNA template. Both processes are essential for prokaryotes, which are single-celled organisms that lack a membrane-bound nucleus and other organelles. However, transcription and translation in prokaryotes differ from those in eukaryotes, which are multicellular organisms that have a membrane-bound nucleus and other organelles. In this article, we will explore the similarities and differences between transcription and translation in prokaryotes and eukaryotes, as well as their importance for prokaryotic gene expression.
transcription and translation in prokaryotes pdf download
Transcription in Prokaryotes: The Process
Transcription in prokaryotes is carried out by a single type of RNA polymerase, which is a complex enzyme composed of five subunits: two alpha (α), one beta (β), one beta prime (β'), and one sigma (σ). The core enzyme consists of α2ββ', which can synthesize RNA from a DNA template, but lacks specificity. The holoenzyme consists of α2ββ'σ, which can recognize specific sequences on the DNA called promoters, where transcription begins.
Transcription in prokaryotes can be divided into three stages: initiation, elongation, and termination. Initiation involves the binding of the holoenzyme to the promoter, forming a closed complex. Then, the DNA strands are separated, forming an open complex. Next, the RNA polymerase starts to synthesize a short RNA transcript, called the abortive transcript, which is released from the enzyme. This process is repeated several times until a longer RNA transcript, called the productive transcript, is formed. This marks the transition from initiation to elongation.
Elongation involves the continuous synthesis of RNA from the DNA template by the core enzyme, which moves along the DNA strand in a 3' to 5' direction. As the RNA polymerase moves forward, it unwinds the DNA ahead of it and rewinds it behind it, creating a transcription bubble. The RNA transcript is complementary to the DNA template strand and has the same polarity and sequence as the DNA coding strand, except that uracil (U) replaces thymine (T).
Termination involves the release of the RNA transcript and the dissociation of the core enzyme from the DNA template. There are two types of termination mechanisms in prokaryotes: intrinsic and extrinsic. Intrinsic termination relies on specific sequences on the DNA template that form a hairpin loop and a string of uracils on the RNA transcript. The hairpin loop destabilizes the interaction between the RNA transcript and the core enzyme, while the string of uracils weakens the interaction between the RNA transcript and the DNA template. As a result, the RNA transcript is released from the transcription complex. Extrinsic termination relies on a protein factor called rho (ρ), which binds to a specific sequence on the RNA transcript called the rut site. The rho factor moves along the RNA transcript in a 5' to 3' direction until it reaches the transcription complex, where it interacts with the core enzyme and causes it to release the RNA transcript.
Transcription in prokaryotes is regulated by various factors that can enhance or inhibit the binding of the holoenzyme to the promoter. One of these factors is the sigma factor, which determines the specificity of the holoenzyme for different promoters. There are several types of sigma factors in prokaryotes, each recognizing a different set of promoters. For example, σ is the most common sigma factor in E. coli, which recognizes promoters with two conserved sequences: -35 (TTGACA) and -10 (TATAAT). Other sigma factors, such as σ, σ, and σ, recognize different promoters that are associated with heat shock response, nitrogen metabolism, and stationary phase, respectively. By switching between different sigma factors, prokaryotes can adjust their gene expression according to their environmental conditions.
Translation in Prokaryotes: The Process
Translation in prokaryotes is carried out by ribosomes, which are complex structures composed of ribosomal RNA (rRNA) and ribosomal proteins. Prokaryotic ribosomes are smaller than eukaryotic ribosomes, having a sedimentation coefficient of 70S. Each ribosome consists of two subunits: a large subunit (50S) and a small subunit (30S). The large subunit contains two rRNA molecules (23S and 5S) and about 34 proteins, while the small subunit contains one rRNA molecule (16S) and about 21 proteins.
Translation in prokaryotes can be divided into three stages: initiation, elongation, and termination. Initiation involves the assembly of the translation machinery on the mRNA template, which is facilitated by several initiation factors (IFs). First, IF-3 binds to the small subunit and prevents it from associating with the large subunit. Then, IF-1 and IF-2 join IF-3 on the small subunit. Next, a special tRNA molecule, called the initiator tRNA, carrying the amino acid formylmethionine (fMet), binds to a specific sequence on the mRNA template called the start codon (AUG). The start codon is recognized by a complementary sequence on the initiator tRNA called the anticodon (CAU). The initiator tRNA also binds to a specific site on the small subunit called the P site. Then, IF-3 is released from the small subunit, allowing it to join with the large subunit, forming an intact ribosome. Finally, IF-1 and IF-2 are released from the ribosome, completing the initiation stage.
Elongation involves the sequential addition of amino acids to the growing polypeptide chain by the ribosome, which moves along the mRNA template in a 5' to 3' direction. As the ribosome moves forward, it exposes a new codon on the mRNA template, which is recognized by a complementary anticodon on a new tRNA molecule carrying an amino acid. The new tRNA molecule binds to another site on the ribosome called the A site. Then, a peptide bond is formed between the amino acid on the tRNA molecule in the A site and the amino acid on the tRNA molecule in the P site, extending the polypeptide chain. Next, the tRNA molecule in the P site leaves the ribosome, while the tRNA molecule in the A site moves to the P site, carrying the polypeptide chain with it. This process is repeated until UAG, or UGA) is encountered on the mRNA template, which is recognized by a protein factor called the release factor (RF), which triggers the termination stage.
Termination involves the release of the polypeptide chain and the dissociation of the ribosome from the mRNA template, which is facilitated by several termination factors (TFs). First, the release factor binds to the stop codon in the A site of the ribosome, mimicking the shape of a tRNA molecule. Then, the release factor interacts with the peptidyl transferase enzyme in the large subunit and causes it to hydrolyze the bond between the polypeptide chain and the tRNA molecule in the P site. As a result, the polypeptide chain is released from the ribosome and folds into its functional shape. Next, another termination factor, called RF3 in bacteria and eRF3 in eukaryotes, binds to the ribosome and stimulates the release of the first release factor from the A site. Finally, a ribosome recycling factor (RRF) and elongation factor G (EF-G) bind to the ribosome and catalyze its dissociation into the large and small subunits, which are ready for another round of translation.
Translation in prokaryotes is regulated by various factors that can enhance or inhibit the initiation, elongation, or termination stages. One of these factors is the riboswitch, which is a regulatory segment of mRNA that can bind to a specific ligand, such as a metabolite or an ion, and change its conformation. Depending on the type of riboswitch, this conformational change can either expose or hide the ribosome binding site (RBS) on the mRNA, which is needed for the initiation stage. For example, if a riboswitch binds to a ligand that signals abundance of a certain metabolite, it may hide the RBS and prevent the translation of an enzyme that produces that metabolite. Conversely, if a riboswitch binds to a ligand that signals scarcity of a certain metabolite, it may expose the RBS and allow the translation of an enzyme that produces that metabolite.
Coupling of Transcription and Translation in Prokaryotes: The Advantages
One of the distinctive features of prokaryotes is that they can couple transcription and translation, meaning that they can translate an mRNA while it is still being transcribed from DNA. This is possible because both processes occur in the same cellular compartment, the cytoplasm, and because prokaryotic mRNAs do not undergo extensive processing steps before translation. Coupling of transcription and translation has several advantages for prokaryotes, such as:
The spatial and temporal proximity of transcription and translation allows for faster and more efficient gene expression, as there is no delay or transport required between the two processes.
The formation of polysomes and operons enables coordinated synthesis of multiple proteins from a single mRNA molecule. A polysome is a complex of multiple ribosomes attached to an mRNA molecule, each translating it at different positions. An operon is a set of genes that are transcribed together into a single mRNA molecule, usually encoding proteins that are involved in a common pathway or function.
The coordination of gene expression and protein synthesis allows for rapid adaptation to environmental changes and stress responses. For example, prokaryotes can modulate their translation rate by altering their ribosome content or activity in response to nutrient availability, temperature, pH, or other factors.
Transcription and Translation in Prokaryotes: The Applications
The knowledge of transcription and translation in prokaryotes has many applications for biotechnology, synthetic biology, antimicrobial therapy, evolutionary and comparative studies. Some examples are:
The use of prokaryotic transcription and translation systems for biotechnology and synthetic biology. Prokaryotic cells can be engineered to produce recombinant proteins or metabolites of interest by introducing foreign genes or modifying native genes. Prokaryotic transcription and translation systems can also be used in vitro to synthesize proteins or RNA molecules for research or therapeutic purposes.
The use of prokaryotic transcription and translation inhibitors for antimicrobial therapy. Many antibiotics target specific components or stages of prokaryotic transcription or translation, such as RNA polymerase, ribosomes, tRNAs, or initiation, elongation, or termination factors. These antibiotics can selectively kill or inhibit the growth of pathogenic bacteria without affecting eukaryotic cells.
The use of prokaryotic transcription and translation models for evolutionary and comparative studies. Prokaryotic transcription and translation are more ancient and conserved than eukaryotic transcription and translation, and they reflect the origin and diversification of life on Earth. By comparing the similarities and differences between prokaryotic and eukaryotic transcription and translation, as well as between different groups of prokaryotes, such as bacteria and archaea, we can gain insights into the molecular evolution and adaptation of living organisms.
Transcription and Translation in Prokaryotes: The Summary
In this article, we have learned about the processes of transcription and translation in prokaryotes, which are single-celled organisms that lack a membrane-bound nucleus and other organelles. We have seen how prokaryotes use a single type of RNA polymerase and ribosome to synthesize RNA and proteins from DNA templates, and how they regulate these processes by various factors. We have also explored the advantages of coupling transcription and translation in prokaryotes, which allows for faster and more efficient gene expression and adaptation. Finally, we have discussed some of the applications of prokaryotic transcription and translation for biotechnology, synthetic biology, antimicrobial therapy, evolutionary and comparative studies.
Transcription and translation are two fundamental processes that enable living cells to express their genetic information. By understanding how they work in prokaryotes, we can appreciate the diversity and complexity of life on Earth, as well as the potential for innovation and discovery.
FAQs
What are the main differences between transcription and translation in prokaryotes and eukaryotes?
Some of the main differences are:
Prokaryotes have a single type of RNA polymerase and ribosome, while eukaryotes have multiple types of RNA polymerases and ribosomes.
Prokaryotes transcribe and translate in the same cellular compartment (cytoplasm), while eukaryotes transcribe in the nucleus and translate in the cytoplasm.
Prokaryotes transcribe multiple genes into a single mRNA molecule (polycistronic), while eukaryotes transcribe one gene into one mRNA molecule (monocistronic).
Prokaryotic mRNAs do not undergo extensive processing steps before translation, while eukaryotic mRNAs undergo capping, splicing, polyadenylation, and export.
Prokaryotes use formylmethionine as the first amino acid in every protein, while eukaryotes use methionine.
What are the roles of sigma factors in prokaryotic transcription?
Sigma factors are proteins that bind to RNA polymerase and confer specificity for different promoters. There are several types of sigma factors in prokaryotes, each recognizing a different set of promoters that are associated with different functions or conditions. By switching between different sigma factors, prokaryotes can adjust their gene expression according to their environmental conditions.
What are the roles of riboswitches in prokaryotic translation?
Riboswitches are regulatory segments of mRNA that can bind to a specific ligand, such as a metabolite or an ion, and change their conformation. Depending on the type of riboswitch, this conformational change can either expose or hide the ribosome binding site (RBS) on the mRNA, which is needed for the initiation stage. By modulating the accessibility of the RBS, riboswitches can regulate the translation of their downstream genes.
What are the benefits of coupling transcription and translation in prokaryotes?
Coupling transcription and translation in prokaryotes has several benefits, such as:
The spatial and temporal proximity of transcription and translation allows for faster and more efficient gene expression, as there is no delay or transport required between the two processes.
The formation of polysomes and operons enables coordinated synthesis of multiple proteins from a single mRNA molecule.
The coordination of gene expression and protein synthesis allows for rapid adaptation to environmental changes and stress responses.
What are some applications of prokaryotic transcription and translation?
Some applications of prokaryotic transcription and translation are:
yotic transcription and translation systems for biotechnology and synthetic biology. Prokaryotic cells can be engineered to produce recombinant proteins or metabolites of interest by introducing foreign genes or modifying native genes. Prokaryotic transcription and translation systems can also be used in vitro to synthesize proteins or RNA molecules for research or therapeutic purposes.
The use of prokaryotic transcription and translation inhibitors for antimicrobial therapy. Many antibiotics target specific components or stages of prokaryotic transcription or translation, such as RNA polymerase, ribosomes, tRNAs, or initiation, elongation, or termination factors. These antibiotics can selectively kill or inhibit the growth of pathogenic bacteria without affecting eukaryotic cells.
The use of prokaryotic transcription and translation models for evolutionary and comparative studies. Prokaryotic transcription and translation are more ancient and conserved than eukaryotic transcription and translation, and they reflect the origin and diversification of life on Earth. By comparing the similarities and differences between prokaryotic and eukaryotic transcription and translation, as well as between different groups of prokaryotes, such as bacteria and archaea, we can gain insights into the molecular evolution and adaptation of living organisms.
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