Biological Sciences
Transcription and Translation in Prokaryotes
Transcription in prokaryotes is the process of synthesizing RNA from a DNA template, carried out by RNA polymerase. Translation is the process of converting the information in RNA into a sequence of amino acids to form a protein. In prokaryotes, both transcription and translation occur in the cytoplasm, allowing for simultaneous gene expression and protein synthesis.
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10 Key excerpts on "Transcription and Translation in Prokaryotes"
eBook - PDFKarp's Cell and Molecular Biology
Concepts and Experiments
- Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
Now that we have described the basic events of transcription and translation, it is fitting to close the chapter with a picture show- ing both processes in a prokaryotic cell (FIGURE 11.51 ). Unlike eukaryotic cells, in which transcription occurs in the nucleus and translation occurs in the cytoplasm with many intervening steps, the corresponding activities in bacterial cells are tightly coupled. Thus protein synthesis in bacterial cells begins on mRNA templates well before the mRNA has been completely synthesized. The synthesis of an mRNA proceeds in the same direction as the movement of ribo- somes translating that message, that is, from the 5 ′ to 3 ′ end. Consequently, as soon as an RNA molecule has begun to be pro- duced, the 5 ′ end is available for attachment of ribosomes. The micrograph in Figure 11.51 shows DNA being transcribed, nascent mRNAs being synthesized, and ribosomes that are translating each of the nascent mRNAs. This single micrograph thus displays the entire central dogma in action. RNA Polymerase RNA Polymerase Ribosome Ribosome DNA DNA FIGURE 11.51 Visualizing transcription and translation. Electron micrograph of portions of an E. coli chromosome engaged in transcription. The DNA is seen as faint lines running the length of the photo, whereas the nascent mRNA chains are seen to be attached at one of their ends, presumably by an RNA polymerase molecule. The particles associated with the nascent RNAs are ribosomes in the act of translation; in bacteria, transcription and translation occur simultaneously. The RNA molecules increase in length as the distance from the initiation site increases. SOURCE: From Oscar L. Miller, Jr., Barbara A. Hamkalo, and C. A. Thomas, Science 169:392, 1970; © 1970, reprinted with permission from AAAS.
eBook - ePub- Chang-Hui Shen(Author)
- 2019(Publication Date)
- Academic Press(Publisher)
Chapter 3Gene Expression: Transcription of the Genetic Code
Abstract
The central dogma of molecular biology is that DNA makes RNA, and RNA makes proteins. This process is called gene expression, and the genetic information is used within a cell to produce the proteins needed for the cell to function. The process of making RNA from DNA is transcription, a process of RNA biosynthesis. It is the first step in gene expression, and it is a vital control point in the expression of genes and production of proteins. In this process, one of the strands of the double-stranded DNA molecule (a template strand) is transcribed into a complementary sequence of RNA. The RNA sequence differs from DNA in three respects: (1) the DNA base thymine (T) is replaced by the RNA base uracil (U); (2) the sugar ring of RNA has a hydroxyl group in the 2′-position, whereas the sugar ring of DNA has a hydrogen group in the 2′-position; and (3) DNA exists as double helix, whereas RNA is single stranded. In this chapter, we discuss the mechanism of transcription in both prokaryotes and eukaryotes. Different types of RNA are also discussed in this chapter.
eBook - PDF- Joseph W. Lengeler, Gerhart Drews, Hans G. Schlegel(Authors)
- 2009(Publication Date)
- Wiley-Blackwell(Publisher)
called sigma. This subunit confers genetic information contained in DNA and protein biosynthesis. All RNAs in the bacterial cell are synthesized by transcription. In most cases, portions of the DNA are transcribed separately and independently of each other. Some phages can, however. produce a single transcript from their entire genome. Transcriptional units can comprise one or, in operons. several cisrrons. Transcrip- tion is the DNA-template-directed polymerization of ribonucleoside (riphosphates to a polymeric ribonucleic acid. whereby a pyrophosphate is released for every phosphodiester formed. like any other synthesis of a biological macromolecule. transcription proceeds in three functionally distinct steps: initiation. elongation. and termination. Transcription is catalyzed by DNA- dependent RNA polymerase (RN?). As the nascent mRNA emerges from the synthesizing protein-nucleic acid complex. the signals for protein biosynthesis are exposed and are recognized by the translation machin- ery. and protein biosynthesis takes place on the nascent mRNA This direct coupling of transcription and transla- tion is typical for gene expression in bacteria. Thus. the growing mRNA is incorporated into polysomes and becomes part of a very complex multicomponent ultrastructure that moves with respect to the DNA template (Figs. 15.1 and 15.4). Seve", topological consequences for the usually supercoiled template DNA result from the limited rotational freedom of the nascent mRNA in that complex: the template is over- wound in front of. and underwound behind the locus of transcription. As a result, the overClIl efficiency of transcription depends also on the superheJical status of the template and on the ability of the cell to remove the introduced supemelicity efficiently from the tem- plate. 15.2.1 Initiation of Transcription Is Linked to Promoter Structure and Function
eBook - PDF- D. Peter Snustad, Michael J. Simmons(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
Unlike mRNAs, which specify polypeptides, the final products of tRNA, rRNA, snRNA, and miRNA genes are RNA molecules. Transfer RNA, ribo- somal RNA, snRNA, and miRNA molecules are not translated. ◾ Figure 11.3 shows an overview of gene expression in eukaryotes, emphasizing the transcriptional origin and functions of the five types of RNA molecules. The process is similar in prokaryotes. However, in prokaryotes, the DNA is not separated from the ribosomes by a nuclear envelope. In addition, prokaryotic genes seldom contain noncoding sequences that are removed during RNA transcript processing. The central dogma of molecular biology is that genetic information flows from DNA to DNA during chromosome replication, from DNA to RNA during transcription, and from RNA to protein during translation. Transcription involves the synthesis of an RNA transcript complementary to one strand of DNA of a gene. Translation is the conversion of information stored in the sequence of nucleotides in the RNA transcript into the sequence of amino acids in the polypeptide gene product, according to the specifications of the genetic code. KEY POINTS Information stored in the nucleotide sequences of genes is translated into the amino acid sequences of proteins from unstable intermediaries called messenger RNAs. The Process of Gene Expression How do genes control the phenotype of an organism? How do the nucleotide sequences of genes direct the growth and development of a cell, a tissue, an organ, or an entire living creature? Geneticists know that the phenotype of an organism is produced by the com- bined effects of all its genes acting within the constraints imposed by the environment. In this and the following chapter, we focus on the mechanisms by which genes direct the synthesis of their products, namely, RNAs and proteins.
eBook - ePub- William M. Brown, Philip M. Brown(Authors)
- 2001(Publication Date)
- CRC Press(Publisher)
2Transcription, The Process
- Overview
- The transcriptional process
- Post-transcriptional processing of eukaryotic mRNA
- Transcription and translation occur simultaneously in prokaryotes
- Sequence-specific DNA-binding proteins or “transcription factors”
OBJECTIVES- introduce the three steps in the transcriptional process
- introduce other processes that occur co-transcriptionally or posttranscriptionally
1.OVERVIEW
The process of transcription can be thought of as a three-step process: initiation, elongation, and termination of the RNA transcript. Logically and economically, the major control point ought to be at the first step of the process, that of initiation. It is therefore not surprising that this is exactly where the cell primarily regulates transcription, but it is not the only point. In the eukaryotic cell, further levels of control are possible via mRNA processing (capping, tailing, and splicing), mRNA transport (out of the nucleus to the ribosomes), mRNA degradation, and protein translation at the ribosome.2.THE TRANSCRIPTIONAL PROCESS
An operon is a set of functionally related genes under a common control mechanism, commonly found in bacteria.There are three primary steps in the process of transcription: initiation, elongation, and termination of the RNA transcript. Initiation involves assembling a multi-protein complex on a gene’s promoter, upstream of the transcriptional start site. Elongation involves the complex moving down the DNA strand, “copying” -by base pairing-the DNA into RNA. Termination involves the complex recognising the end of the gene or operon and disassembling.3.POST-TRANSCRIPTIONAL PROCESSING OF EUKARYOTIC MRNA
Transcription is a three-step process: initiation, elongation, and termination.In eukaryotes, in addition to the transcription process itself, there is much processing of the nascent RNA transcript (sometimes referred to as hnRNA, heterogeneous nuclear RNA) before it passes to the cytoplasm for translation at the ribosome. Eukaryotic mRNA has a long half-life, is monocistronic (i.e.,
eBook - PDF- Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
486 CHAPTER 11 The Central Dogma: DNA to RNA to Protein Figure 11.8b, which shows the homologous regions of the bac- terial and eukaryotic enzymes at much higher resolution. Our understanding of transcription in eukaryotes was greatly advanced with the 2001 publication of the X-ray crys- tallographic structure of yeast RNA polymerase II by Roger Kornberg and colleagues at Stanford University. As a result of these studies, and those of other laboratories in subsequent years, we now know a great deal about the mechanism of action of RNA polymerases as they move along the DNA, transcribing a complementary strand of RNA. A major distinction between transcription in prokaryotes and eukaryotes is the requirement in eukaryotes for a large variety of accessory proteins, or tran- scription factors. These proteins play a role in virtually every aspect of the transcription process, from the binding of the polymerase to the DNA template, to the initiation of transcrip- tion, to its elongation and termination. Although transcription factors are crucial for the operation of all three types of eukary- otic RNA polymerases, they will only be discussed in regard to the synthesis of mRNAs by RNA polymerase II (Section 11.4). All three major types of eukaryotic RNAs—mRNAs, rRNAs, and tRNAs—are derived from precursor RNA molecules that are considerably longer than the final RNA product. The ini- tial precursor RNA is equivalent in length to the full length of the DNA transcribed and is called the primary transcript, or pre-RNA. The corresponding segment of DNA from which a primary transcript is transcribed is called a transcription unit. Primary transcripts do not exist within the cell as naked RNA but become associated with proteins even as they are synthe- sized. Primary transcripts typically have a fleeting existence, being processed into smaller, functional RNAs by a series of “cut-and-paste” reactions.
eBook - PDF- Lizabeth A. Allison(Author)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
This chapter focuses on the process of transcription in bacteria. The lactose operon, a classic example of the process of induction, is highlighted because of the many important and universal principles this operon illustrates, and for its relevance to molecular biology research. Other key features of transcriptional regulation in bacteria are illustrated by the arabinose and tryptophan operons. 234 Ch 8 Transcription in Bacteria The mode of action of transcriptional regulators is addressed, focusing in particular on the cooperative binding of proteins to DNA, allosteric modification of protein activity, and how distant DNA regulatory sites are brought together by protein–protein interactions that cause DNA looping. These classical paradigms of transcriptional regulation are simple and elegant. But as the control of individual genes is examined in greater detail, the process often becomes remarkably complex. Bacterial gene transcription may require input from multiple DNA-binding proteins, elaborate regulatory cascades, differential folding of RNA, or even sensing of metabolites by RNA transcripts. Finally, bacteria do not live in isolation. They can com-municate with each other through the production of diffusible signaling molecules. Once a critical concentration of signaling molecules is reached, these signals can activate or repress a number of target genes in the population of bacteria. Before delving into the intricacies of gene regulation, let’s first explore the general mechanism of transcription. 8.2 Mechanism of transcription By 1967 it was clear that RNA polymerase is the enzyme that catalyzes RNA synthesis. Using DNA as a template, this multisubunit enzyme joins, or “polymerizes,” nucleoside triphosphates (NTPs) by phosphodiester bonds from 5 ′ to 3 ′ . In archaea and in bacteria such as Escherichia coli , there is one type of RNA polymerase.
- Aniruddha Datta, Edward R. Dougherty(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
The transfer RNAs (tRNAs) form the adaptors that select amino acids and hold them in place on a ribosome for their incorporation into proteins. In eucaryotes, each gene coding for a single protein is typically transcribed into a separate mRNA molecule. In bacteria, a single mRNA is often tran-scribed from several adjacent genes and, therefore, contains information for several different proteins. The way in which transcription is initiated differs somewhat between pro-caryotes and eucaryotes. Here, we will focus on procaryotes. Transcription 66 Introduction to Genomic Signal Processing with Control initiation in eucaryotes is more complicated and will be discussed later in the next chapter. In procaryotes, the RNA polymerase molecules slide rapidly along the DNA and tightly latch on to it when they encounter a region called a promoter which contains a sequence of nucleotides indicating the starting point for RNA synthesis. After the RNA polymerase makes contact with the promoter DNA and binds it tightly, it opens up the double helix immediately in front of it to expose the nucleotides on a short stretch of DNA on each strand. One of the two exposed DNA strands then acts as a template for synthesis of the complementary RNA. The RNA chain elongation continues until the RNA polymerase encounters a second signal in the DNA, the terminator (or stop site), where the polymerase halts and releases both the DNA template and the newly made single-stranded RNA chain. A subunit of bacterial polymerase, called sigma ( σ ) factor , is primarily responsible for recognizing the promoter sequence on DNA. Once the RNA polymerase has latched onto the promoter and has synthesized approximately 10 nucleotides of RNA, the sigma factor is released. The RNA polymerase moves forward and continues the transcription process.
eBook - PDF- Jelena Kuši?-Tišma, Jelena Kušić-Tišma, Jelena Kušić-Tišma(Authors)
- 2011(Publication Date)
- IntechOpen(Publisher)
16 Relations Between Replication and Transcription Daniel Castro-Roa and Nikolay Zenkin Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences Newcastle University, Newcastle upon Tyne United Kingdom 1. Introduction In the cell, RNA polymerase (RNAP) and the replisome share the same template DNA for their respective functions. The rate of replication is typically 20 times faster than transcription and six or more replication forks may be present at the same time on the chromosome (Gotta et al. 1991; Hirose et al. 1983). This implies that collisions between the two machineries are inevitable. In this chapter we will discuss the recent findings on the outcome of collisions between transcription and replication and their consequences, as well as cooperation between the two machineries. 2. Stability of RNA polymerase complexes with nucleic acids In all living organisms transcription, the first step in gene expression, is accomplished by multisubunit RNAP. RNAP is highly evolutionary conserved, both structurally and functionally, in all three domains of life. Although there are differences in the mechanisms of initiation and regulation of transcription, mechanisms of catalysis are remarkably similar in all living organisms. Fully functional eukaryotic and archeal models involve 12-14 subunits (depending on the polymerase type and organism) with a total molecular weight greater than 500 kDa (Cramer et al. 2001). The simplified versions found in bacteria are composed of five subunits (subunits composition 2 α , β ’, β and ω ) with a molecular mass of approximately 400 kDa. Transcription is a cyclic pathway roughly composed of three steps: initiation, elongation and termination. RNAP is a flexible machine able to adopt different states required for various transcription stages and the mode and stability of binding of the enzyme to DNA at these stages are different.
eBook - PDF- Donald Voet, Judith G. Voet(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
The peculiar use of the word “dogma,” one definition of which is a religious doctrine that the true believer can- not doubt, stemmed from a misunderstanding. When Crick formulated the central dogma, he was under the impres- sion that dogma meant “an idea for which there was no rea- sonable evidence.” We begin this chapter by discussing experiments that led to the elucidation of mRNA’s central role in protein synthesis. We then study the mechanism of transcription and its control in prokaryotes. Finally, in the last section, we consider post-transcriptional processing of RNA in both prokaryotes and eukaryotes. Translation is the subject of Chapter 32. Note that these subjects were outlined in Sec- tion 5-4. Here we shall delve into much greater detail. 1 THE ROLE OF RNA IN PROTEIN SYNTHESIS The idea that proteins are specified by mRNA and synthe- sized on ribosomes arose from the study of enzyme induc- tion, a phenomenon in which bacteria vary the synthesis rates of specific enzymes in response to environmental changes. In this section, we discuss the classic experiments that explained the basis of enzyme induction and revealed the existence of mRNA. We shall see that enzyme induc- tion occurs as a consequence of the regulation of mRNA synthesis by proteins that specifically bind to the mRNA’s DNA templates. There are three major classes of RNA, all of which partici- pate in protein synthesis: ribosomal RNA (rRNA), transfer RNA (tRNA), and messenger RNA (mRNA). All of these RNAs are synthesized under the direction of DNA tem- plates, a process known as transcription. RNA’s involvement in protein synthesis became evident in the late 1930s through investigations by Torbjörn Caspersson and Jean Brachet. Caspersson, using micro- scopic techniques, found that DNA is confined almost ex- clusively to the eukaryotic cell nucleus, whereas RNA oc- curs largely in the cytosol.
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