VIDEO: Protein synthesis in prokaryotes and eukaryotes

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Protein biosynthesis in prokaryotes and eukaryotes

  • Protein biosynthesis differs in some details between prokaryotes and eukaryotes. In eukaryotes like humans, for example, it takes place outside the cell nucleus.
  • Prokaryotes do not have a nucleus, their DNA lies unprotected in the cytoplasm. DNA plays an essential role in protein biosynthesis

The course of protein synthesis in eukaryotes

The first step in protein synthesis in prokaryotes and eukaryotes is called transcription. The cell represents a copy of the genes to be read (mRNA) and transports it through the nuclear pores to the ribosomes.

  1. At the beginning of protein synthesis, the DNA strand opens at a certain point. This point represents the gene which is to be copied and which codes for a specific protein.
  2. Free RNA nucleotides are deposited on the complementary bases of the DNA. These nucleotides also consist of a phosphate and a base. They differ from the DNA in the sugar. The sugar in RNA is ribose and not deoxyribose, as is the case with DNA. In prokaryotes and eukaryotes, the nucleotides only attach to the codogenic strand. This is the strand of DNA that contains the genetic information.
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  3. Once the strand has been copied completely, the mRNA becomes detached from the DNA.
  4. The mRNA contains exons and introns. Introns are areas that do not contain any genetic information and are therefore superfluous. They are removed during so-called splicing.
  5. It is brought through the cell pores to the ribosomes through the mediation of the poly-A tail and the cap (both enzymatic means of transport).

Translation takes place on the ribosomes, the second step in protein synthesis in prokaryotes and eukaryotes. During translation, the sequence of base triplets of the mRNA is translated into a sequence of amino acids.

  1. At the beginning of translation, the mRNA is stored in the ribosome with its start codon. The start codon consists of a specific base triplet which initiates translation.
  2. After the mRNA has been attached, there are now two base triplets in the ribosome. Free transport RNA molecules with a specific anticodon now bind to these base triplets. There is also an amino acid attached to the tRNA, which forms the basis of a protein chain. When the tRNA molecules have joined the mRNA in a complementary manner, the two amino acids are also bound to one another by a peptide bond.
  3. The mRNA moves through the ribosome in triplet steps. If the two binding sites of the ribosome are occupied, the first amino acid resp. Amino acid chain connected to the following and the mRNA migrates a piece from the ribosome. A tRNA dissolves and a binding site is released. A new tRNA settles in the ribosome and the amino acid chain is lengthened step by step.
  4. Protein synthesis comes to an end when a stop codon enters the ribosome. No matching tRNA can be found for this base triplet. The ribosome falls apart and the amino acid chain is released.
  5. The amino acid chain is further processed enzymatically in the cell until it has found its specific final structure.

There are, however, differences in the protein synthesis of prokaryotes and eukaryotes

  • In prokaryotes, protein biosynthesis is basically the same. However, there are small differences to the eukaryotes.
  • The peptide bonds of the prokaryotes are somewhat different than those of the eukaryotes.
  • There are no introns in prokaryotes. Splicing is no longer necessary.
  • The eukaryotes have a cap and a poly-A tail, which protects the mRNA from enzymatic degradation, among other things. This is absent in the prokaryotes. The lifespan of your mRNA is therefore shorter.
  • The DNA of the prokaryotes is free in the cytoplasm and is not stored in the cell nucleus. Protein biosynthesis therefore takes place in the immediate vicinity of the DNA and the mRNA does not first have to be fetched from the cell nucleus. This speeds up protein synthesis in prokaryotes.
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