Step 3 in Protein Synthesis Notes: TRANSLATION Step 3 in Protein Synthesis (Copy everything that is underlined.)

KEY CONCEPT Translation converts an mRNA message into a “polypeptide”, or protein - a chain of amino acids.

Amino acids are coded by mRNA base sequences. Translation converts mRNA messages into “polypeptides”. A CODON is a sequence of three nucleotides in the mRNA. Each codon codes for an Amino Acid. codon for methionine (Met) leucine (Leu) Copy the Picture 

Amino Acids are the building blocks (subunits/monomers) of proteins.

The Genetic Code matches each codon to its amino acid. The genetic code matches each RNA codon with its amino acid or function. There is 1 start codon(methionine) There are 3 stop codons

What Amino Acid does each of the following Codons “code for”? AUG? AAA? CUU? GAC? The genetic code matches each RNA codon with its amino acid or function.

Answers: AUG = methionine (START) AAA = lysine CUU = leucine UGA = STOP The genetic code matches each RNA codon with its amino acid or function.

A change in the order in which codons are read changes the resulting protein = mutation. Copy Diagrams  In all organisms, codons code for the same amino acid. (DNA is the “universal code”.)

Mutation can be caused by … Insertion or deletion of one or more nucleotides Substitution of one or more nucleotides. This causes a “Frame Shift” – or shift in the way the mRNA is read (by the ribosome).

Amino acids are linked to become a protein. Anticodon - a set of three nucleotides that is complementary to an mRNA codon. - an anticodon is carried by a tRNA. Copy Diagram 

Ribosomes consist of two subunits (parts). Large subunit has three binding sites where tRNA molecules attach. Small subunit binds to the mRNA. Copy Diagram 

Steps of translation: (see handout of slides 12 & 13) 1. tRNA binds to a start codon and signals the ribosome to assemble. 2. A complementary tRNA molecule binds to the exposed codon, bringing its Amino Acid close to the first amino acid.

3. The ribosome helps form a “polypeptide” bond between the Amino Acids. 4. The ribosome pulls the mRNA strand the length of one codon.

5. Empty tRNA molecule exits the ribosome. 6. A complementary tRNA molecule binds to the next exposed codon. 7. At the stop codon, the ribosome releases the protein and disassembles.