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Unformatted text preview: X X X X X X V V V I I I . . . P P P r r r o o o t t t e e e i i i n n n S S S y y y n n n t t t h h h e e e s s s i i i s s s I I I : : : T T T r r r a a a n n n s s s c c c r r i i i p p p t t t i i i o o o n n n The synthesis of proteins from genes is a two-stage process. As in house construction, first the plans must be found in the library and photocopied transcribed then the copied blueprints are taken to a construction site, read, and translated into brick walls. In a cell the first stage, copying the plans stored in DNA into a building-site set of blueprints (stored in RNA) is called transcription. The second stage, the actual building is called translation. DNA DNA mRNA mRNA protein protein transcription transcription translation translation TRANSCRIPTION TRANSLATION DNA mRNA Ribosome Polypeptide (a) Bacterial cell Nuclear envelope TRANSCRIPTION RNA PROCESSING Pre-mRNA DNA mRNA TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell T T T h h h e e e P P P l l l a a a y y y e e e r r r s s s Only the genetic library is made of DNA, the remaining players are various kinds of RNA: Abbreviation Name Function Structure mRNA messenger RNA it functions as a blueprint; its a code for a single protein (or polypeptide chain) single-stranded, tRNA transport RNA the translator, capable of reading the mRNA language and binding corresponding amino acid to a growing peptide chain cloverleaf rRNA ribosomal RNA the factory, an "enzyme" of sorts complexed with proteins G G G e e e n n n e e e t t t i i i c c c C C C o o o d d d e e e How is the information stored? There are 4 letters (bases), but they must encode 20 amino acids. The solution is in the word length. W W W o o o r r r d d d l l l e e e n n n g g g t t t h h h A 1-letter code would code for 4 words (amino acids)....
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