case 1

case 1


….translating mRNA into a protein

1. The smaller ribosomal subunit binds to a leader sequence of the mRNA
2. The ribosomal subunit ‘reads’ along the mRNA until it reaches a start codon (AUG)
a. AUG is the start codon and also translates to the amino acid methionine (met)
3. At the start codon, transfer RNA (tRNA) that has the corresponding anticodon (UAC) binds by hydrogen binding
a. This tRNA has the anticodon at one end, and binds the proper corresponding amino acid at the other end
b. This tRNA will have met bound to it (initiator tRNA)
4. Next, the larger subunit bind the complex
a. mRNA is ‘sandwiched’ in a groove between the rRNA subunits
5. The rRNA has 3 binding sites; when tRNA-met binds, it occupies the aminoacyl (A) location
6. rRNA moves to the next codon
a. tRNA-met moves to the second location – the peptidyl (P) site
7. The A site becomes bound by a tRNA with the corresponding anticodon and carries the amino acid specific for the mRNA codon being read
8. Peptide bonds form between the amino acids; the amino acid in the P site is transferred to the amino acid on the A site
9. The ribosome travels to the next codon and the corresponding amino acid moves in attached to its tRNA
10. The tRNA that occupied the P site is now in the E site (exit site); it is released
11. Peptide bonds form between the amino acids in the A site and P site, amino acid is transferred to the A site
12. The entire process continues to repeat until the rRNA reaches a termination sequence
a. There are 3 stop sequences (UAA, UAG, UGA)
b. Upon recognition of one of these codons, the polypeptide chain is released from the ‘groove’ and the subunits detach from each other

13. Notes/terms
a. mRNA may be read by several different ribosomes simultaneously, thus numerous copies of protein may be produced from one mRNA
b. tRNA and rRNA are long-lived; mRNA is short-lived
c. DNA codes for proteins (1), largely enzymes, that are synthesized...

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