1. Outline 12-3B Protein Synthesis
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Outline 12-3B
Protein Synthesis

2. I. Genetic Code B. Codons: 1. Codons are 3-letter sequences on mRNA
A. The code for a particular protein is the sequence of the nucleotides in the DNA and resulting mRNA.
B. Codons:
1. Codons are 3-letter sequences on mRNA
2. Each codon signifies an amino acid or a “start” or “stop” signal
3. There are 64 different codons
C. The genetic code is universal. It can be read by ALL life forms.
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4. Genetic Code

5. II. Codon Practice (p. 303 ) mRNA codon Amino acid 1. AUG 1. 2. AAU 2.
3. UUU 3.
4. CUG 4.
5. GGU 5.
6. UGG 6.
7. CGU 7.
8. GAA 8.
9. UAA 9.
methionine
asparagine
phenylalanine
leucine
glycine
tryptophan
arginine
glutamic acid
stop
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6. III. Translation A. Proteins are made of chains of amino acids.
1. Amino acids must be arranged in the correct sequence for the protein to function properly.
B. The process of assembling amino acids into proteins is called translation
1. The code is changing:
RNA codons  amino acids
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7. C. Steps of Translation:
1. mRNA moves out of nucleus & goes to a ribosome

8. a. The ribosome has 2 sites inside of it:  P site = primary site
 A site = adjacent site
b. The mRNA “start” codon will fit into the P site
c. The second codon will end up in the A site
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9. Process of Translation
P site
A site

10. 2. tRNAs carrying their specific amino acids will arrive at the site
a. The anticodons of the tRNAs are complementary to codons on the mRNA
b. The tRNAs will come to the site & bind with the complementary codons on the mRNA
 First amino acid is always methionine, since the “start” codon, AUG, codes for it
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11. Process of Translation
P site
A site

12. 3. Once 2 tRNAs are sitting next to each other in the ribosome:
a. Enzymes form a peptide bond between the adjacent amino acids
b. The tRNA in the P site can now detach & go out and find another amino acid
c. The ribosome shifts over to leave the A site empty
d. A new tRNA comes in to fill the empty A site
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13. Protein Synthesis

14. 4. Steps 2 & 3 are repeated until a “stop” codon is reached
a. The polypeptide chain (protein) is then released from ribosome
b. Meanwhile, another ribosome might have attached to the mRNA at its start codon
 This allows many copies of the same protein to be made from a single mRNA molecule
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15. Protein Synthesis

16. Protein
Synthesis
Summarized