The Central Dogma of Molecular Biology

Module 13: Proteinsynthesis: The Flow of Information from DNA to RNA to Protein Key Terms: Central dogma, Genes, Genetic code, Transcription, Translation, Protein, Initiation, Elongation, Termination, Amino acid, RNA Polymerase, Promoter, mRNA, tRNA, mutation, Codon, Anticodon, Ribosomes, Promoters, mRNA splicing, intron, exon. Learning Outcomes: 1. 2. Explain the “central dogma” of DNA-protein synthesis. Describe the genetic code and how the nucleotide sequence prescribes the amino acid and the protein sequence. 3. Describe and compare protein synthesis in prokaryotes and eukaryotes. 4. List the different steps in prokaryotic and eukaryotic transcription. 5. Discuss the role of promoters in prokaryotic transcription. 6. Discuss the role of RNA polymerase in eukaryotic transcription. 7. Describe how and when transcription is terminated. 8. Know the general functions of the three major types of RNA (mRNA, rRNA, tRNA). 9. Describe the DNA sequence motifs and proteins required to initiate transcription. 10. Predict the RNA transcribed from a DNA sequence identified as either the template strand or the coding strand. 11. Use the genetic code to predict the protein amino acid sequence translated from an mRNA sequence. 12. Describe the process of and key components required for translation. 13. Predict the likely effects of mutations in DNA on protein amino acid sequence, structure and function. 14. Describe the genetic code and how the nucleotide sequence prescribes the amino acid and the protein sequence Getting Started! Before starting your journey with this module, test yourself first with your current knowledge about chromosomes, mitosis and meiosis. Answer the following questions by encircling the correct letter that corresponds to the option that best answers the question. 1. Control of gene expression in eukaryotic cells occurs at which level(s)? A. only the transcriptional level B. epigenetic and transcriptional levels C. epigenetic, transcriptional, and translational levels D. epigenetic, transcriptional, post-transcriptional, translational, and posttranslational levels 2. The binding of ________ is required for transcription to start. A. a protein C. RNA polymerase B. DNA polymerase D. a transcription factor 3. What will result from the binding of a transcription factor to an enhancer region? A. decreased transcription of an adjacent gene B. increased transcription of a distant gene C. alteration of the translation of an adjacent gene D. initiation of the recruitment of RNA polymerase 4. Post-translational modifications of proteins can affect which of the following? A. protein function C. chromatin modification B. transcriptional regulation D. all of the above 5. Prokaryotic cells lack a nucleus. Therefore, the genes in prokaryotic cells are: A. all expressed, all of the time B. transcribed and translated almost simultaneously C. transcriptionally controlled because translation begins before transcription ends D. b and c are both true 6. Post-translational control refers to: A. regulation of gene expression after transcription B. regulation of gene expression after translation C. control of epigenetic activation D. period between transcription and translation 7. How does the regulation of gene expression support continued evolution of more complex organisms? A. Cells can become specialized within a multicellular organism. B. Organisms can conserve energy and resources. C. Cells grow larger to accommodate protein production. D. Both A and B. 8. Which of the following are involved in posttranscriptional control? A. control of RNA splicing C. control of RNA stability B. control of RNA shuttling D. all of the above 9. Binding of an RNA binding protein will ________ the stability of the RNA molecule. A. increase C. neither increase nor decrease B. decrease D. either increase or decrease 10. Cancer causing genes are called ________. A. transformation genes C. oncogenes B. tumor suppressor genes D. mutated genes Introduction Regardless of what kind of organism, (bacteria, archaea, or eukaryotes), the primary role of DNA is to store heritable information that encodes the instruction set required for creating the organism in question. While we have gotten much better at quickly reading the chemical composition like the sequence of nucleotides in a genome and some of the chemical modifications that are made to it, we still don't know how to reliably decode all of the information within and all of the mechanisms by which it is read and ultimately expressed. Since the rediscovery of Mendel’s work in 1900, the definition of the gene has progressed from an abstract unit of heredity to a tangible molecular entity capable of replication, expression, and mutation. Now, genes are composed of DNA and are linearly arranged on chromosomes. Further, genes specify the sequences of amino acids, which are the building blocks of proteins. In return, proteins are responsible for orchestrating nearly every function of the cell. Together, genes and the proteins they encode are absolutely essential to life. There are, however, some core principles and mechanisms associated with the reading and expression of the genetic code whose basic steps are understood and that need to be part of the conceptual toolkit for all biologists. Two of these processes are transcription and translation, which are the coping of parts of the genetic code written in DNA into molecules of the related polymer RNA and the reading and encoding of the RNA code into proteins, respectively. The basic flow of genetic information in biological systems is often depicted in a scheme known as "the central dogma". This states that information encoded in DNA flows into RNA via transcription and ultimately to proteins via translation. Processes like reverse transcription (the creation of DNA from and RNA template) and replication also represent mechanisms for propagating information in different forms. This scheme, however, doesn't say anything per se about how information is encoded or about the mechanisms by which regulatory signals move between the various layers of molecule types depicted in the model. Therefore, while the central dogma is a nearly required part of the lexicon of any biologist, perhaps left over from old tradition, students should also be aware that mechanisms of information flow are more complex as we'll learn about some as we go, and that "the central dogma" only represents some core pathways.