![]() ![]() Although each cell in an organism contains the same DNA, the regulated expression of certain genes causes the cells to specialize and assume different functions, e.g., muscle cells or hepatocytes. There are also regulatory mechanisms at a translational level. The newly formed RNA may also be degraded after transcription by various mechanisms before use in protein synthesis. Genes can undergo activation or silencing, and transcription depends on the presence of specific DNA-binding proteins. Other genes are only active in certain cells their expression is regulated by a variety of mechanisms. Some genes are expressed in all cells and are required as housekeeping genes for basic cellular functions (i.e., constitutive expression). Gene expression is strongly regulated at all levels. ![]() In eukaryotes, the newly formed primary transcript is further modified to be, for example, available for protein synthesis. The strand is synthesized until the end of the DNA segment (termination site) is reached. RNA polymerase moves along the template strand of the double-stranded DNA. Transcription factors are required to recognize the promoter. These enzymes synthesize the RNA molecule based on the genes encoded in DNA, which contain starting sites ( promoters) where transcription begins. Key enzymes involved in transcription are DNA-dependent RNA polymerases. RNA is then used to synthesize proteins during translation. During transcription, DNA is copied into RNA. Gene expression occurs in two stages: transcription and translation. The conversion of the information stored within DNA into a functional molecule, or RNA and proteins, is termed gene expression. A relatively small percentage of DNA codes for proteins and ribonucleic acids (RNAs), while a large amount of the genome is composed of sequences without a clear function. This information is stored as a sequence of bases in DNA. The genome contains the hereditary information of the structure and function of a cell or organism. ![]()
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