1. Unit 7: Molecular Genetics
7.4 Protein Synthesis: Translation

2. Types of RNA
Messenger RNA (mRNA): a form of RNA that carries the instructions from the DNA in the nucleus to the site of protein synthesis in the cell: the ribosome!
The instructions are written as 3 nucleotide sequences called codons
Each codon corresponds to an amino acid or a start or stop signal for translation
Ribosomal RNA (rRNA): a type of RNA that is found in the ribosome and accounts for 80% of the RNA found in the cell. Carries instructions for the enzyme that binds amino acids together.
Transfer RNA (tRNA): single strands of RNA that temporarily carries a specific amino acid on one end.
Contains the anticodon: a 3 nucleotide sequence on a tRNA that is complementary to a codon on the mRNA strand.

3. Translation The process in which cellular ribosomes create proteins.
Takes place at the ribosome (in the cytoplasm of the cell), which attach to the mRNA and travel its length.

4. Steps of Translation
mRNA leaves the nucleus and joins to rRNA subunits in the ribosomes.
The tRNA that carries the amino acid Methionine binds to the start codon on the mRNA strand, AUG.
AUG signals the start of translation.
The next codon on the mRNA strand binds to the anticodon on the tRNA strand carrying a specific amino acid.
An enzyme binds the two amino acids carried by the tRNA, forming a peptide bond.
The tRNA detaches, leaving behind its bonded amino acid.

5. Steps (cont.)
The ribosomes, containing rRNA, moves down the mRNA strand to the next codon. A tRNA carrying the amino acid specified by the new codon arrives.
The new amino acid is bonded to the amino acid chain and the tRNA in the detaches again.
Steps 2-6 are repeated until a stop codon is reached.
Stop codons are: UAG, UAA, or UGA
There is no complementary anticodon to these stop codons so there will be no tRNA to fit into this spot. When that happens, the amino acid chain is released into the cell.

7. Summary of Protein Synthesis:
In the nucleus, DNA uncoils and unzips  RNA nucleotides pair up with DNA bases to form mRNA  mRNA travels to the ribosomes  tRNA adds amino acids using the mRNA strand  a protein is formed
All cells have the same DNA, but differ due to some genes being expressed in some cells and not others.