Genetics 4: Translation

Transfer RNA tRNA molecules are made of a single strand of RNA that folds into a 2-dimentional cloverleaf-like shape It has 3 stem-loops and 2 functional areas: one contains the anticodon (complementary to the mRNA codon) and at the 3’ end is the acceptor stem where an appropriate amino acid is attached. Aminoacyl-tRNA synthetase enzymes attach the correct amino acid onto the tRNA according to the anticodon. There are 20 different enzymes (one for each amino acid) Anticodons are written in the 3’ to 5’ direction tRNA molecules are made of a single strand of RNA that folds into a 2-dimentional cloverleaf-like shape It has 3 stem-loops and 2 functional areas: one contains the anticodon (complementary to the mRNA codon) and at the 3’ end is the acceptor stem where an appropriate amino acid is attached. Aminoacyl-tRNA synthetase enzymes attach the correct amino acid onto the tRNA according to the anticodon. There are 20 different enzymes (one for each amino acid) Anticodons are written in the 3’ to 5’ direction

Ribosomes Made of protein and rRNA Made of 2 subunits: small and large subunits and they look like a hamburger bun, with the mRNA fitting in between the two subunits. In the large subunit, it has 3 binding sites (E- site, P-site and A-site) where the tRNA molecules can fit. Numerous ribosomes can fit on a single strand of mRNA. Made of protein and rRNA Made of 2 subunits: small and large subunits and they look like a hamburger bun, with the mRNA fitting in between the two subunits. In the large subunit, it has 3 binding sites (E- site, P-site and A-site) where the tRNA molecules can fit. Numerous ribosomes can fit on a single strand of mRNA.

Translation Phase 1: Initiation All components come together Proteins called initiation factors assemble the small subunit, mRNA, initiator tRNA and large subunit to start protein synthesis. The small subunit attaches near the start codon AUG and the first tRNA with the anticodon UAC will bind on. Then the large subunit joins on to form the active ribosome so that the P-site (peptide) is filled with the first tRNA All components come together Proteins called initiation factors assemble the small subunit, mRNA, initiator tRNA and large subunit to start protein synthesis. The small subunit attaches near the start codon AUG and the first tRNA with the anticodon UAC will bind on. Then the large subunit joins on to form the active ribosome so that the P-site (peptide) is filled with the first tRNA

Initiation Diagram

Translation Phase 2: Elongation Here is where protein synthesis occurs. The next codon is read in the A-site (amino acid) and a new tRNA fits in A peptide bond forms between the first and second amino acids and the dipeptide is attached to the second tRNA (in the A-site) The mRNA then moves along one codon (or 3 bases) at a time and the tRNA that was in the P- site will move over to the E-site (exit) and the A- site tRNA moves to the P-site. The tRNA in the E-site exits the ribosome and there is now room for another tRNA in the A-site This process continues while the ribosome makes the polypeptide chain. Here is where protein synthesis occurs. The next codon is read in the A-site (amino acid) and a new tRNA fits in A peptide bond forms between the first and second amino acids and the dipeptide is attached to the second tRNA (in the A-site) The mRNA then moves along one codon (or 3 bases) at a time and the tRNA that was in the P- site will move over to the E-site (exit) and the A- site tRNA moves to the P-site. The tRNA in the E-site exits the ribosome and there is now room for another tRNA in the A-site This process continues while the ribosome makes the polypeptide chain.

Elongation Diagram

Termination A stop codon on the mRNA signals to the ribosome to stop making the polypeptide Components of the translation machinery are separated. A protein called the release factor then cleaves the polypeptide from the last tRNA. Polypeptide then forms its 3D shape. A stop codon on the mRNA signals to the ribosome to stop making the polypeptide Components of the translation machinery are separated. A protein called the release factor then cleaves the polypeptide from the last tRNA. Polypeptide then forms its 3D shape.

Questions: Page 260 #13, 16, 18 Page 261 Activity 6.2 Page 266 # 2, 3, 4. Page 260 #13, 16, 18 Page 261 Activity 6.2 Page 266 # 2, 3, 4.