8.5 Translation

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

8.5 Translation

Amino acids (protein building blocks) are coded for by mRNA base sequences.

• 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 signal the end of a chain of amino acids.

– one start codon, codes for methionine and to start translation

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

8.5 Translation• Reading frame: multiple codons that code for a chain of

amino acids• A change in the order in which codons are read changes

the resulting protein – this is why having a clear “start” and “stop” is important

• Common language: 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. tRNA carries amino acids from cytoplasm to the ribosome to become part of the growing protein. EXAMPLE:

mRNA codon=GUUtRNA anticodon=CTTAmino acid=Valine

8.5 Translation• Ribosomes are the site of protein synthesis. They are

located in the cytoplasm & on the rough ER.• Ribosomes are made of rRNA & proteins. They have a

large & small subunit.• Helps form peptide bonds between amino acids.

8.5 Translation

1. For translation to begin, tRNA binds to a start codon (Met in picture) and signals the ribosome to assemble.

– A complementary tRNA molecule binds to the exposed codon (Leu in picture), bringing its amino acid close to the first amino acid.

8.5 Translation

2. 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

3. 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 Translation