Microbial genetics

Overview of Translation and Regulation

Translation Process

  • Codon Definition:

    • Explanation of Codon as a set percentage (5%) involved in coding during translation.

  • Initiation Phase:

    • The initiation phase of translation involves the assembly of the small ribosomal subunit with mRNA and associated amino acids.

    • Key components:

    • Small Subunit: Binds to the mRNA at the start codon, often at a specific sequence.

    • Peptide Chain Position: The first amino acid, known as the lead, is positioned before the growing peptide chain, which is situated in the middle of the ribosome.

  • Elongation Phase:

    • During elongation, amino acids are added to the growing peptide chain sequentially, moving towards the stop codon.

    • The process of elongation continues until the ribosome encounters a stop codon, ending the translation.

  • Termination Phase:

    • The translation process terminates once a stop codon is reached, signalling the end of protein synthesis.

    • Discussion clarifies that simply altering components does not ensure correct or functional proteins due to folding requirements.

Protein Folding During Translation

  • Importance of Folding:

    • As proteins are synthesized, they begin to fold into their functional three-dimensional structures concurrently with translation.

    • Correct folding is essential for proper enzyme function and structure stability.

  • Chemical Groups Involvement:

    • Certain chemical groups may remain shielded or available, influencing how proteins interact and fold.

Polyribosome Formation

  • Multiple Translations:

    • In prokaryotic systems, translation results in multiple ribosomes translating a single mRNA strand simultaneously, creating a polyribosome.

    • This allows for efficient protein synthesis, as several ribosomes can produce multiple protein products at the same time.

Operon Systems

  • Definition of Operon:

    • An operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter, typically seen in prokaryotes.

  • Structure of Operon:

    • An operon consists of:

    • Regulatory Gene: This gene produces a protein related to the regulation of the operon.

    • Operator: A segment where regulatory proteins can bind to influence promoter activity.

    • Structural Genes: These encode proteins and are transcribed into a single mRNA molecule leading to the synthesis of proteins.

  • Cis and Trans Regulations:

    • Cis-acting elements: Operators and promoters are located adjacent or nearby to one another on the DNA strand.

    • Trans-acting factors: Regulatory proteins that can act from a distance, potentially on different loci within the genome.

Catabolic Regulation

  • Lac Operon Example:

    • Discussed the lac operon in detail:

    • Repressor Protein Dynamics:

      • In absence of lactose, a repressor protein binds to the operator, blocking transcription.

      • Binding of lactose changes the shape of the repressor, preventing it from binding to DNA, thus allowing transcription.

    • Presence of Glucose:

      • The operon is silenced in the presence of glucose due to metabolite control, which prioritizes glucose utilization over lactose.

      • Cyclic AMP Role:

      • Cyclic AMP activates the CAP protein, which assists RNA polymerase in binding to the promoter, promoting transcription.

  • Metabolite Catabolite Repression:

    • When glucose is present, cyclic AMP levels drop; thus, the lack of cyclic AMP prevents transcription activation of operons responsible for breaking down alternative sugars.

Tryptophan Operon Regulation

  • Regulation Mechanism:

    • Discussed the Trp operon illustrating feedback inhibition:

    • Tryptophan Levels:

      • High levels of tryptophan signal for the repressor to bind the operator, inhibiting transcription.

    • Attenuation Process:

      • Attenuation is a unique regulatory mechanism which depends on coupled transcription and translation seen only in prokaryotes.

      • The presence of tryptophan alters ribosome activity, affecting the formation of secondary structures in mRNA that dictate transcription termination or continuation.

  • Translation Coupling:

    • The ribosome directly influences the formation of anti-terminator or terminator structures based on tryptophan levels, creating a regulatory loop that modulates transcription of the operon.

The trp operon is regulated by attenuation as well as the trp repressor. This type of regulation will not work  in eukaryotes    organisms.