MCB 150 Lecture Notes - Lecture 22: Tandemly Arrayed Genes, 5.8S Ribosomal Rna, 28S Ribosomal Rna
13 Mar 2017
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4 types of rrna, designated 5s, 5. 8s, 18s, 28s rrna. Actively growing mammalian cells have 5-10 million ribosomes that must be synthesized each time the cell divides. To meet this demand, all cells have multiple copies of their rrna genes. Human cells have about 280 copies of 5. 8, 18, and 28s and about 2000 copies of the 5s rrna genes. Tandem arrays of genes for 5. 8s, 18s, and 28s rrnas are transcribed by: Ribosomal genes are found in tandem arrays. 45s gene array (will be processed into 5. 8s, 18s, and 28s rrna) are found on 5 different human chromosomes rrna genes found in huge array on chromosome. The nucleolus forms around the arrays of 45s rrna genes which are therefore called nucleolar organizing regions, or nor. Transcription of the rrna genes is very active and very efficiently initiated when needed. Replication, trans, and translation all depend on accurate complementary base pairing, but none are perfect.
