Question

describe on detail the procesa of translation. please remeber to list the key players (proteins, molecules and emzymes)

Answer 1

Translation is the process by which the four letter nucleotide language of mRNA is translated into the 20 letter amino acid language of proteins. In a eukaryotic cell it occurs in the cytoplasm and the organelle that translates the mRNA is Ribosome. In an mRNA a set of three adjacent nucleotides (codon) represents an amino acid and the codon is decoded by the anticodon of tRNA by complementary base pairing. Translation is a tree step process - i) Initiation ii) Elongation and iii) Termination

Initiation - The initiation codon in eukaryotes is always AUG and in bacteria it is often AUG. Meaning of AUG in bacteria depends on its context. In bacteria, as the initiation codon the meaning of AUG is N-formy Methionine and at internal positions AUG represents methionine. Two types of tRNAs carry methionine in bacteria - tRNAfMet  is used for initiation and tRNAmMet is used for reading AUG codons at internal positions. In eukaryotes the initiator tRNA is tRNAiMet. Initiation of translation in bacteria needs three initiation factors - IF1, IF2 and IF3. Eukaryotes use more initiation factors to initiate translation - eIF1, eIF2, eIF3, eIF4A,B,D,E,G,F, and eIF5. The ribosome binding site of bacterial mRNA is Shine -Dalgarno Sequence and that of eukaryotes is the methylated cap of mRNA. The amino acids enter into the ribosome as amino acyl tRNAs with the help of the initiation/elongation factor.

Elongation - Includes all the processes starting from the formation of first peptide bond to the formation of the last peptide bond. Elongation factor of bacteria is EF-TU-EF-TS and in eukaryotes the factors needed for elongation include eEF1α and eEF1βγ. All amino acyl tRNAs enter into the A-site of ribosome. An exception is the initiator tRNA which directly enters into the P- site. When both A and P- sites of the ribosome are occupied by amino acyl tRNAs peptide bond formation occurs, which is catalyzed by the peptidy transferse centre in the ribosome. Peptide bond formation creates a peptidyl tRNA in the A-site and deacylated tRNA in the P-site. The incorporation of an amino acid into the growing peptide chain is completed by translocation. During which the ribosome advances to the next codon creating a new A-site, the deacylated tRNA is expelled from the P- site and the peptidy tRNA is transferred from the A-site to the new P-site. The transloctaion in bacteria needs a translocation factor which is EF-G and the translocation factor of eukaryotes is eEF2.

Termination - Termination occurs when a stop codon comes in the A-site of the translating ribosome. Termination involves release of the completed peptide chain from peptidyl tRNA, release of mRNA, dissociation of ribosome into subunits and the release of the deacylated tRNA. Termination requires factors called termination factors. Bacterial termination factors are RF1 RF2 and RF3. RF1 and RF2 are condon specific. Eukaryotic termination factors are eRF1 and eRF2.