Translation Genetic code converted from the “language” of mRNA to the “language” of protein. - a protein is a string of amino acids

Translation Proteins “carry out instructions” found in the genetic code. The primary structure of a protein is encoded in the mRNA base sequences.

Codon Codons are the essential units of translation of mRNA. A. Is a group of 3 adjacent nucleotides 1. each nucleotide contains one of 4 bases (A, U, G, C)

Codon 2. the mRNA is “read” codon by codon 3. each codon specifies one amino acid

Codon 4. the codon “tells” the ribosome which amino acid goes next in the protein chain.

Each amino acid (20) coded for by at least one codon. 1. all but two amino acids have more than one codon 2. three codons are STOP codons 3. START codon = AUG (also codon for methionine)

mRNA = a series of codons to be translated into chains of amino acids

Mutation A change in a single nucleotide (either on DNA or RNA) can “scramble” the message. When translated, the affected protein may remain unimpaired or may function abnormally or not at all, leading to disease.

Small changes in DNA or mRNA can cause big changes in the protein. mutagens: chemicals radiation viruses

tRNA Bring amino acids to the growing polypeptide chain

tRNA: Structure

tRNA: Key Regions 1. amino acid attachment site (very specific)

2. anticodon a. one per tRNA b. three adjacent nucleotides c. complementary to a codon on mRNA

Which amino acid would be carried by the tRNA with the anticodon CGC? How about GAG? How about ACU?

Polypeptide Synthesis Ribosome is the “workbench” on which the peptide is constructed. Ribosome has one large and one small subunit. 1. Subunits must come together in cytoplasm for protein synthesis.

Polypeptide Synthesis (cont.) 2. mRNA binds to small subunit via its leader sequence. 3. Small subunit then binds to large. 4. Large subunit has enzymes for amino acid linkage.

Polypeptide synthesis = bringing appropriate amino acids together in the proper sequence.