1. 11/17/08
Lecture 30 - Molecular Genetics 5
 Initiation
 Initiation is the process of bringing together mRNA with the two sub-units of the ribosome and the first
tRNA (bearing the amino acid, methionine).
 The first codon in mRNA will be AUG.
 The first anticodon in tRNA will be UAC.
 Assembly of the protein proceeds from the N terminal end to the C terminal end.
 Elongation
 Basically, amino acids are added one at a time and a peptide bond attaches each amino acid to the last
one in the forming chain.
 GTP → GDP (releasing energy).
 Termination
 The elongation process continues until a STOP codon (UAG, UAA, or UGA) is reached.
 As soon as a STOP codon arrives at the “A site” of the large ribosome sub-unit, it stops elongation.
 A release factor fits into the “A site”.
 Instead of an amino acid being attached, a water molecule is attached.
 The polypeptide chain is released.
 Post translation modification of the polypeptide: sometimes certain modifications must be done before
the protein is functional.
 Proper folding of the protein.
 Attach other molecules to the chain (often lipids or carbohydrates).
 Turning a straight strand of the protein into a quaternary structure. (ie. the protein insulin).
 The protein molecule is divided into half.
 Then, the two pieces are joined (one on top of the other) with sulfur bonds)
 Finally, the protein needs to be transported to the proper location.
 Polyribosomes
 The mRNA can interact with several ribosomes in the sequence to make several copies of the same
polypeptide (when necessary).
 Mutation: changes in the genetic message in a cell (changes in DNA).
 Large scale (mutation): involves large portions of DNA mutated
 Deletion: removal of a chromosome segment.
 Duplication: a repetition of a segment.
 Inversion: a particular segment is reversed.
 Translocation: where a piece gets moved from a place to another (within the chromosome or to
another chromosome).
 Point mutation (small scale)
 Usually one pair of bases in the DNA is changed.
 Normally occurs during DNA replication.
 Sickle cell anemia is a disease resulting from a point mutation.
 Glutamic acid is replaced by Valine producing sickle cell hemoglobin.

- Gene: the region of DNA who's final produce is a specify polypeptide or RNA.