VIDEO: Protein Synthesis in Biology

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Part 1 of protein biosynthesis: transcription

Transcription is the process by which a gene is copied from DNA. It represents the first stage of protein synthesis. The mRNA, the messenger ribonucleic acid, plays a key role in this. The aim of the transcription is to read the information of the gene and then to transport it to a ribosome in a processable state.

  • RNA polymerase, a protein complex, settles on the promoter of the DNA on the gene that is being read. The promoter consists of a base sequence that shows the RNA polymerase where transcription begins and, as a key principle, is the only way to which it can bind.
  • The RNA polymerase is now on the promoter and from this point begins to uncoil a part of the DNA strand (double helix). At least 10 bases are exposed.
  • All now free bases of the codogenic strand (DNA single strand) are occupied by complementary nucleotides. Together these form the mRNA.
  • It is only read from 3 'to 5' direction (because of the polarity). In addition, thymine is paired with uracil, which replaces the otherwise common adenine in the RNA. Instead of deoxyribose, ribose also acts as a stabilizer.
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  • The promoter was the beginning, the terminator the end. Once the RNA polymerase has reached the terminator base sequence, it stops working. The mRNA newly created by the nucleotides is now released.
  • If this process took place within a eukaryote, the mRNA is once again "revised" by splicing - useless pieces of the base sequence are removed in order to allow the following translation to proceed smoothly.

The translation of protein synthesis

  • After the mRNA has left the cell nucleus at the end of the transcription and has migrated towards the ribosomes, it is ready for translation. Here, in turn, another RNA is added, the tRNA (transfer).
  • In the ribosome, the tRNAs are now merged with the appropriate location from the mRNA. Only one tRNA that has the three complementary bases fits on any three bases of the mRNA. Here, too, there is a special starting point, the start codon. It has the base sequence A-U-G and is occupied by the start tRNA.
  • Starting from this point, the next tRNAs begin. Amino acids of the tRNA that are at the top end are linked by a peptide bond - an amino acid chain is created.
  • The tRNA now leaves the ribosome, but without its amino acid. This process continues until the stop codon (U-G-A) is reached.
  • The resulting chain of amino acids ultimately detaches from the ribosome and folds into a more complex structure: a peptide or protein - protein synthesis is complete.
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