Abstract
Publisher Summary This chapter presents the concept of gene expression. The concept of the central dogma of molecular biology, formulated in the late 1950s by Francis Crick may be summarized as DNA (deoxyribonucleic acid) →RNA (ribonucleic acid) →protein. Transcription is the process in which RNA is synthesized by enzymes called DNA-directed RNA polymerases. These enzymes use ribonucleoside triphosphates as substrates and DNA as a template. Specific base sequences signal the termination of transcription. Transcription produces RNA molecules. Translation involves two compartments: the cytosol in which individual amino acids are enzymically attached to their specific tRNAs by amino-acid-tRNA ligases and the ribosomes in which the amino acids are correctly positioned according to the base sequence of a mRNA template and polymerized into polypeptide chains. As there are four major bases in mRNA, 43 different codons are possible. The 64 triplets constitute the genetic code. The genetic code applies to prokaryotes and eukaryotic nuclear and chloroplast mRNAs but not to mitochondrial mRNAs. Therefore, the genetic code is quasi-universal.
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