Chain Termination

Chain Termination

Chain Termination - Chain elongation continues until a termination codon (UAA, UAG or UGA) reaches the ribosome. The chain is then terminated and released from the ribosome. This process requires release factors (RF I, RF 2 and RF 3 in prokaryotes and RF in eukaryotes)

a.The termination codon provides signals to the ribosome for the attachment of release factors

b. The release factors interact with peptidyl transferase causing hydrolysis of the bond between tRNA and the polypeptide chain, and the chain is released from the ribosome.

c. Hydrolysis of GTP results in the dissociation of the release factors from the ribosome. The tRNA is also unloaded. The ribosomal subunits dissociate and mRNA is released, for breakdown to nucleotides.

d. Processing of the polypeptide chain, e. g. cleavage of the formyl residue or of methionine, takes place after release. In some cases internal cleavage cuts the polypeptide chain into two or more pieces.

During transcription a messenger RNA strand is copied or transcribed from a DNA strand. The mRNA is formed on the DNA of the chromosomes. In eukaryotes it then makes its way through the nuclear membrane to the cytoplasm where it forms a complex with a group of ribosomes. In prokaryotes the mRNA strand is pulled away from the DNA by a ribosome.

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