30. Protein synthesis. Proteasomes

Question 1

Protein synthesis? detailed?

Answer 1

Transcription

The process of making pre – mRNA from DNA as a template. The process is as follows:

1. DNA helicase breaks the hydrogen bond in a specific region of the DNA molecule thus exposing the unpaired bases
2. The enzyme RNA polymerase moves along a template DNA strand and causes nucleotides in the DNA strand to bond with pre-existing free nucleotides in the nucleus
3. As RNA polymerase moves along the molecule causing complementary bases to join up with one another, the DNA molecule recombines behind it
4. Eventually DNA polymerase reaches a stop codon on the DNA molecule and detaches and com-pletes the production of pre – mRNA

Translation

The process of polypeptide formation is as follows:

1. A ribosome becomes attached to the starting codon at one end of the mRNA molecule
2. The tRNA molecule with the complementary anticodon sequence binds with the mRNA with the correct code whilst having an amino acid attached to it
3. Another tRNA molecule with its anticodon binds on to the next codon on the mRNA stand whilst carrying another amino acid
4. The ribosome moves along the mRNA, bringing together two tRNA molecules at any one time
5. Enzymes along with ATP join together the amino acids on adjacent tRNA molecules
6. The ribosome moves along to the third codon and links the amino acids on the second and third tRNA together
7. As this happens the first tRNA is released from the amino acid and is now free to collect a new amino acid
8. The process continues as the polypeptide chain is built up
9. The synthesis continues until a ribosome reaches a stop codon. At this point the ribosome, mRNA and the tRNA all separate leaving behind the polypeptide

Ribosomes are attached to the ER to form RER. The process explained above then occurs creating proteins for folding and packaging within the ER.

Question 2

Proteasomes?

Answer 2

Proteasomes are protein complexes inside all eukaryotes and archaea, and in some bacteria. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds.