1. Section 8-5 “Translation”

2. Transcription
KEY CONCEPT Translation converts an mRNA message into a polypeptide, or protein.
Translation

3. The basic building block of a protein is the amino acid.
There are 20 amino acids; each one differs in its R group.
Below are four amino acids showing the differences in R groups

4. 20 Amino Acids

5. Amino acids are joined together in proteins by peptide bonds.
A peptide bond forms between the carboxyl group of one amino acid (amino acid 1 in the figure below) and the amino group of the adjacent amino acid (amino acid 2)

6. Amino acids are coded by mRNA base sequences
A codon is a sequence of three nucleotides
that codes for an amino acid.
codon for
Methionine (Met)
Leucine (Leu)

7. START codon – signals the start of translation.
One START codon: AUG (methionine)
START codon for
Methionine (Met)
codon for
Leucine (Leu)

8. STOP codon – signals the end of translation.
Three STOP codons: UAA, UAG, UGA

9. mRNA (Messenger RNA)
Messenger RNA consists of leader, reading frame, and trailer sequences.
mRNAs vary in length. Sequences of mRNAs vary because amino acid coding sequences (reading frames) differ, and because leader and trailer sequences differ

10. A three-nucleotide sequence that codes for an amino acid
- three stop codons signal the end of the amino acid chain
Signals start of translation always begins with amino acid: methionine. (AUG)

11. Codons are read, without spaces, as a series of three nonoverlapping
A change in the order in which codons are read changes the resulting protein
READING FRAME
Codons are read, without spaces, as a series of three nonoverlapping
nucleotides.
Regardless of the organism, codons code for the same amino acid

12. COMMON LANGUAGE:
The genetic code is shared by almost all organisms—and even viruses.
The “language” of proteins uses 20 amino acids
Each code word is a unique combination of three letters (like the ones shown above) that will eventually be interpreted as a single amino acid in a polypeptide chain. There are 64 code words possible from an 'alphabet' of four letters
Translation 2

14. The genetic code shared by almost all organisms—
“language” of proteins uses 20 amino acids
Codons are read, without spaces, as a series of 3 nonoverlapping
nucleotides.

15. Amino acids are linked together to become a protein
An anticodon is a set of three nucleotides that is complementary (opposite) to an mRNA codon
An anticodon is carried by a tRNA
Codon
Translation 3

17. Ribosomes consist of two subunits
The large subunit has three binding sites for tRNA
The small subunit binds to mRNA

18. For translation to begin, tRNA binds to a start codon and signals the ribosome to assemble
A complementary tRNA molecule binds to the exposed codon, bringing its amino acid close to the first amino acid

19. The ribosome helps form a polypeptide bond between the amino acids
The ribosome pulls the mRNA strand the length of one codon

20. The tRNA molecule (now empty) exits the ribosome
A complementary tRNA molecule binds to the next exposed codon
Once the stop codon is reached, the ribosome releases the protein and disassembles (gets taken apart)

21. large subunit binds to tRNA small subunit binds to mRNA
Type of RNA that carries amino acids from cytoplasm to ribosome. One end has specific anticodon and the other a specific amino acid
Matching set of 3 nucleotides complementary
to an mRNA codon.
large subunit
binds to tRNA
small subunit
binds to mRNA

22. Use the chart in textbook on page 244 to decode the mRNA.
Group in sets of 3’s then use chart to determine what amino acid each would be.

23. Use the chart in textbook on page 244 to decode the mRNA.
Group in sets of 3’s then use chart to determine what amino acid each would be.
Ile ____ ____

24. Use the chart in textbook on page 244 to decode the mRNA.
Group in sets of 3’s then use chart to determine what amino acid each would be.
Ile ____ ____
Gln

25. Use the chart in textbook on page 244 to decode the mRNA.
Group in sets of 3’s then use chart to determine what amino acid each would be.
stop
Ile ____ ____
Gln

26. Amino acid (start – methionine. AUG
Peptide bond
tRNA
Large ribosomal subunit
Anticodon
mRNA
Small ribosomal subunit
codons

27. Ribosome assembles at the start codon
Ribosome assembles at the start codon. Complementary tRNA molecule pairs with exposed codon
Ribosome helps bond the new amino acid to start codon and breaks bond between the amino acid and first tRNA
Ribosome pulls the mRNA strand the length of one codon. The first tRNA strand returns to cytoplasm as another codon is exposed (opened up) for tRNA binding