Describe the process of translation (initiation, elongation, termination)

Question 1

Initiating translation

Answer 1

-first stage in assembling a protein uses mRNA as a template
-translation is initiated when large and small ribosomal subinits associate with an mRNA molecule at the 5’cap, and the first aminoacyl-tRNA of the new protein chains becomes bound to the AUG start codon.
-this start codon get regonized by the aniticodon of Met-tRNA. The large ribosomal subunit binds to the complete ribsosome, at the end of initiation, the initiator Met-tRNA is on the P site.
-after the initiator tRNA pairs with AUG initiator codon, the subsequent stages of translation reads the nucleotide bases, and can be read in three different ways depending on where the ribosome behims. A correct initiator tRNA-AUG pairing establishes the correct reading frame:the series of codons for the polypeptide that is encoded in the mRNA.

Question 2

Elongating the polypeptide chain

Answer 2

Step one
- A site is empty
Step two
-the second tRNA with the appropriate anticodon and amino acid binds to the codon in the A site of the ribosome. A GTP rather than ATP is hydrolyzed to provide energy for this step.
-Next the amino acid Met is cleaved from the tRNA in the P site and forms a peptide bond with the amino acid on the tRNA in the A site. (catalyzed by peptidyl transferase)
-next the new polypeptide chain is attachted to the tRNA in the A site and an empty tRNA remains in the P site.
Step 3
-then the ribosome moves along the mRNA to the next codon. The next two rRNA’s stay bounded to their respective codons, this step positions the newly made peptidyl tRNA in the P site leaving A site empty
-the appropriate tRNA moves into the A site and the first two steps are repeated, after they are repeated the empty tRNA that was in the P site moves to the E site,
-in step 4 RNA is released from the ribosome.

Question 3

Termination of protein synthesis

Answer 3

-translation goes from elongation to termination when the A site of a ribosome arrives at one of the stop codons (UAA,UAG,UGA) on the mRNA
-when a stop codon appears on the A site, a protein release factor binds to this site instead of an aminoacyl-tRNA at the P site as usual.
-Because no amino acid is present at the ribosome the freed polypeptide is released from the ribosome. The ribosomal subunits will detach from the mRNA, and the empty tRNA and the release factor alsp detach.

Question 4

Polypeptide to protein

Answer 4

-The formed polypteiride is still not functional, the protein exists in an inactive state. Protein shape determines function so it must be folded into the correct shape.
-processing reactions occur, carried out by enzymes
-they remove amino acids and add other structure where necessary to give the protein a function and activate it