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Translation
Key Events:
1. mRNA enters cytoplasm and attaches to ribosome
A site
P site
E site
- aminoacyl site
- peptidyl site
- exit site
2. ribosome holds mRNA and tRNA together for accurate reading
and assembly of proteins
3. tRNA molecules in cytoplasm link up with specific amino acid
specified by their sequence
-- each tRNA molecule has an anticodon sequence,
complementary to the mRNA transcript
-- tRNA joins to amino acid via enzyme aminoacyl tRNA
synthetase (20 different enzymes!) and ATP is
required
4. tRNA comes in and attaches to start site on mRNA strand
(AUG = start codon)
(binding site called "P site" or peptidyl site)
5. a second tRNA comes in and attaches to second codon
(This is the "A site" or aminoacyl site.)
-- the two adjacent amino acids are bonded together by
peptidyl transferase enzyme
6. tRNA is released from P site and the ribosome moves down
one codon.
7. Polypeptide chain synthesized by adding amino acids to the
carboxyl end of the last amino acid in the peptide chain
8. Ribosome continues to move down mRNA in 5' to 3' direction
9. release factors recognize UAG, UAA, or UGA
(STOP CODONS) and cause the polypeptides to be released
from the tRNA and ribosome
10. polypeptide folds into its tertiary structure
11. ribosome detaches from mRNA and is free to translate
another mRNA strand
Summary Diagram
Main Nucleic Acids Involved in Transcription