Question

Translation can be considered to have three phases or steps: initiation, protein synthesis, and termination. Please give a detailed summary of the factors and molecules involved with each step and, where appropriate, compare/contrast the differences between prokaryotic and eukaryotic translation.

Answer 1

# Translation :

1. Initiation ; first tRNA is activated by adding 20 amino acids to there respective tRNAs by an enzyme aminoacyl tRNA synthetase.

In prokaryotes, ribosomes have three sites that bind tRNAs, the aminoacyl (A) site, the peptidyl (P) site, and the exit (E) site. Smaller subunit Ribosome scans the mRNA for the codon AUG which is start sequences and Met-tRNA adds at the P site ofbthe ribosome. Certain proteins called initiation factors are required for initiation.

** for initiation factor i am sending a table, due to limited time. Sorry.

2. Elongation; after attaching the larger subunit upcomming next aminoacyl-tRNA enters at the A site of ribosome. In bacteria, the appropriate incoming aminoacyl-tRNA binds to a complex of GTP-bound EF-Tu. The resulting aminoacyl-tRNA–EF-Tu–GTP complex binds to the A site of the 70S initiation complex. The GTP is hydrolyzed and an EF-Tu–GDP complex is released from the 70S ribosome. The EF-Tu–GTP complex is regenerated in a process
involving EF-Ts and GTP. The enzymatic activity that catalyzes peptide bond formation is catalysed by peptidyl transferase. Movement of the ribosome along the mRNA requires EF-G (also known as translocase) and the energy provided by hydrolysis of another molecule of GTP. In eukaryotes, 3 eukaryotic elongation factors (eEF1, eEF1, and eEF2) have functions analogous to those of the bacterial elongation factors (EF-Tu, EF-Ts, and EF-G, respectively).

3. Termination ; it is signaled by the presence of one of three termination codons in the mRNA (UAA, UAG, UGA) also called stop codon. In bacteria three termination factors, or release factors—the proteins RF-1, RF-2, and RF-3—contribute to (1) hydrolysis of the terminal peptidyl-tRNA bond, (2) release of the free polypeptide and the last tRNA, now uncharged, from the P site, and (3) dissociation of the 70S ribosome into its 30S and 50S subunits, ready to start a new cycle of polypeptide synthesis . RF-1 recognizes the termination codons UAG and UAA, and RF-2 recognizes UGA and UAA. Either RF-1 or RF-2

In eukaroytes, eRF recognises all three termination codon.

# In prokayotes ribosomes used is 70S (30S and 50S) an in eukaryotes the ribosome used is 80S (40S and 60S).

In prokaryotes, ribosomes have three sites that bind tRNAs, the aminoacyl (A) site, the peptidyl (P) site, and the exit (E) site. The A and P sites bind to aminoacyl-tRNAs, whereas the E site binds only to uncharged tRNAs that have completed their task on the ribosome. Eukaryotes donot have E site , the uncharged tRNA is released from P site.

In prokaryotes the initiating (5')AUG is positioned at the P site and codes for fromylated methionine, fMet-tRNAfMet but in eukaryotes, start codon AUG codes for normal methionine, Met-tRNAMet.

In prokaryotes translation occurs during transcription is still udergoing, while in eukaryotes translation is done outside the nucleus and in cytoplasm ( after complete trasncription).

In prokaryotes, the peptides are not modified and doesnot undergo post translation modification, while in eukaryotes post translational modification occurs.

and the initiation factor, elonagtion factors and release/termination factors are mentioned above.

**Table for initiation factor