Bacterial Protein Synthesis Steps

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Bacterial Protein Synthesis

The process through which bacteria manufacture new proteins that they need for fundamental metabolic functions, reproduction and repair are known as bacterial protein synthesis. Proteins produced by bacteria can be utilised to reproduce bacteria by binary fission, repair and maintain cellular structures or produce enzymes for metabolising food.

The method of protein synthesis in both prokaryotes and eukaryotes can be broken down into the following three major steps:

  1. Initiation
  2. Elongation
  3. Termination

Steps Involved in Bacterial Protein Synthesis

Bacteria lack a nucleus and instead have a free-floating circular DNA structure called a nucleoid. Thus, protein synthesis takes place in the cytoplasm of the bacteria. However, ribosomes are responsible for the actual process of synthesising proteins from amino acids during translation.

In bacteria, protein synthesis takes place when mRNA is copied from DNA during transcription and subsequently converted into proteins during translation. Although bacteria lack the intermediate processing stages found in eukaryotic organisms between transcription and translation, proteins may nonetheless go through further maturation after translation.

Step 1 – Initiation

A functionally competent ribosome is formed at the proper location on an mRNA during initiation, preparing to start protein synthesis. The binding of mRNA to ribosomes, choice of the start codon, activation of amino acids, transfer of activated amino acids to tRNA and binding of acylated tRNA containing the first amino acid are the primary characteristics of the initiation phase.

  • In bacteria, the commencement of protein synthesis is initiated by the interaction of one 30S ribosomal subunit, an mRNA molecule, a Met-tRNA, three initiation factors (IFs) and guanosine 5′-triphosphates (GTP). The 30S preinitiation complex is made up of these components.
  • AUG codons are also found in coding sequences and protein synthesis starts at an AUG start codon.
  • The untranslated section of bacterial mRNA molecules contains a specific base sequence known as the ribosome binding site. This location, also known as the Shine-Dalgarno sequence, is close to the AUG codon.
  • The 30S subunit binds to the tRNA fMet at the P site with three ribonucleotides when it is charged with the first amino acid.
  • The 50S component joins the 30S initiation complex during the successive stages of translation to create the 70S initiation complex.
  • A GTP molecule that was delivered to the initiation complex in connection with the initiation process is hydrolysed to provide energy for this union.

Explore:What is Translation in Biology?

Step 2 – Elongation

The two processes that make up the stage of elongation are the production of a peptide bond between two amino acids and the movement of the mRNA and ribosomes so that the codons can be translated sequentially. The proper amino acid is thus delivered to the ribosome through elongation and linked by the nascent polypeptide chain. Finally, the complete assembly shifts one position along the mRNA.

  • The P site, in the centre of the ribosome, is the first location which carries methionine. A new codon is exposed in a different slot, known as the A site, right next to it.
  • The following tRNA, whose anticodon is a perfect (complementary) match for the exposed codon, will land at the A site.
  • Now the production of the peptide bond happens which joins one amino acid to another after the matching tRNA has arrived at the A site.
  • In this phase, the amino acid of the second tRNA’s A site is joined to the methionine from the first tRNA. The polypeptide’s N-terminus is made up of methionine, and its C-terminus is made up of another amino acid.
  • One codon pulls the mRNA through the ribosome once the peptide bond has been created. The E site or exit site of the first, empty tRNA can now drift away as a result of this shift. Additionally, it opens up a new codon at the A site, allowing the cycle to continue.

Step 3 – Termination

The finished polypeptide or protein is released from the synthetic machinery during the termination stage and the ribosomes are made available to start a new cycle of synthesis. When the stop codon has been reached, an amino acid cannot be added and the freshly produced polypeptide is released from the ribosome.

  • A stop codon (UAG, UAA or UGA) in the mRNA causes termination when it enters the A site.
  • Release factors are proteins that fit into the P site and identify stop codons. The activity of these factors causes the termination of translation, the release of the polypeptide from the tRNA and dissociation of the 70S ribosome into its 30S and 50S subunits which leave the mRNA.

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Frequently Asked Questions

What are elongation factors?

A group of proteins called elongation factors work on the ribosome during the synthesis of proteins to speed up the elongation. The most prevalent elongation factors of prokaryotes are EF-Tu, EF-G and EF-Ts. Elongation factors used by bacteria and eukaryotes are mostly similar but have different structures.

What is the Shine-Dalgarno sequence?

A ribosomal binding site known as the SD or Shine-Dalgarno sequence is often found eight bases upstream of the initiation codon (AUG) in bacterial mRNA. The RNA sequence aids in attracting the ribosome to the mRNA and matches it with the start codon on the mRNA to start protein synthesis.

What is the difference between the A-site and the P-site of a ribosome?

On the ribosome, there are 4 binding sites – 3 for tRNA and 1 for mRNA. A, P and E are the three t-RNA sites. The P site or peptidyl site binds to the tRNA that is holding the developing polypeptide chain of amino acids. The A or acceptor site binds to the aminoacyl tRNA, which holds the newly added amino acid to the polypeptide chain.
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