8.5 Translation

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

8.5 Translation

Recap:

• Translation = RNA to Protein

• Replication = DNA to DNA• Transcription = DNA to RNA• Translation = RNA to Protein

codon formethionine (Met)

codon forleucine (Leu)

8.5 Translation

Amino acids are coded by mRNA base sequences. Amino Acids link up to form a protein • Translation converts mRNA messages into polypeptides.• A codon is a sequence of three nucleotides that codes for

an amino acid.

codon formethionine (Met)

codon forleucine (Leu)

8.5 Translation

• The genetic code matches each codon to its amino acid or function.

– three stop codons

– one start codon, codes for methionine

The genetic code matches each RNA codon with its amino acid or function.

8.5 Translation

Practice:

• -What amino acid is coded by GGA?• UGG?• ACU, ACC,ACA, ACG? • -What happens when a ribosome reads the codon AUG?• -What happens when a ribosome reads the codon UGA?

8.5 Translation

Bell Ringer

• 1-How do cells help ensure that DNA replication is accurate?

• 2-What happens in Replication?• 3-What happens in Transcription?• 4-What happens in Translation?

• Find your lab handout from Friday and log about our DNA extraction lab!

8.5 Translation

• A change in the order in which codons are read changes the resulting protein.

• Regardless of the organism, codons code for the same amino acid.

8.5 Translation

Amino acids are linked to become a protein.

• An anticodon is a set of three nucleotides that is complementary to an mRNA codon.

• An anticodon is carried by a tRNA.

8.5 Translation

• Ribosomes consist of two subunits.

– The large subunit has three binding sites for tRNA.– The small subunit binds to mRNA.

8.5 Translation

• 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.

8.5 Translation

– The ribosome helps form a polypeptide bond between the amino acids.

– The ribosome pulls the mRNA strand the length of one codon.

8.5 Translation

– The now empty tRNA molecule 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.

8.5 TranslationLook at figure 8.16 in the text on page 246 to help you answer the following questions and label the diagram on the next page.

• -What is the function of mRNA?• -What is the function of tRNA?• -What is the function of ribosomes?• -In step 1 what is the codon?• -In step 1 what is the anticodon?• -In step 1 what is the amino acid?