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Related Concept Videos

Plasmids01:28

Plasmids

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Plasmids are extrachromosomal DNA molecules found in bacteria, archaea, and some eukaryotic microbes like yeast. These small, circular DNA structures typically contain fewer than 30 genes, although some may exist linearly. Plasmids vary in their number within a cell, known as copy number. Single-copy plasmids are present in one copy per cell and multi-copy plasmids are present in multiple copies, reaching over 100 copies per cell.Plasmids usually replicate independently of the chromosomal DNA...
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Genomic DNA in Prokaryotes00:46

Genomic DNA in Prokaryotes

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The genome of most prokaryotic organisms consists of double-stranded DNA organized into one circular chromosome in a region of cytoplasm called the nucleoid. The chromosome is tightly wound, or supercoiled, for efficient storage. Prokaryotes also contain other circular pieces of DNA called plasmids. These plasmids are smaller than the chromosome and often carry genes that confer adaptive functions, such as antibiotic resistance.
Genomic Diversity in Bacteria
Although bacterial genomes are much...
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Bacterial Transformation01:33

Bacterial Transformation

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In 1928, bacteriologist Frederick Griffith worked on a vaccine for pneumonia, which is caused by Streptococcus pneumoniae bacteria. Griffith studied two pneumonia strains in mice: one pathogenic and one non-pathogenic. Only the pathogenic strain killed host mice.
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Prokaryotic Transcriptional Activators and Repressors01:58

Prokaryotic Transcriptional Activators and Repressors

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The organization of prokaryotic genes in their genome is notably different from that of eukaryotes. Prokaryotic genes are organized, such that the genes for proteins involved in the same biochemical process or function are located together in groups. This group of genes, along with their regulatory elements, are collectively known as an operon. The functional genes in an operon are transcribed together to give a single strand of mRNA known as polycistronic mRNA.
Transcription of prokaryotic...
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Conjugation01:19

Conjugation

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Conjugation is a form of horizontal gene transfer that primarily occurs in bacteria and some archaea, promoting genetic diversity and adaptation. Bacteria can acquire resistance genes through conjugative plasmids, allowing them to survive antibiotic treatments that would otherwise be lethal. This process involves direct contact between cells through specialized structures such as the sex pilus and is mediated by conjugative plasmids, including the F (fertility) factor.Conjugation requires...
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Antibiotic Selection00:57

Antibiotic Selection

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Overview
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Related Experiment Video

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Quantification of Plasmid-Mediated Antibiotic Resistance in an Experimental Evolution Approach
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Quantification of Plasmid-Mediated Antibiotic Resistance in an Experimental Evolution Approach

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Why There Are No Essential Genes on Plasmids.

Samuel J Tazzyman1, Sebastian Bonhoeffer2

  • 1Theoretical Biology, Institute of Integrative Biology (IBZ), ETH Zürich, CH 8092, Zürich, Switzerland.

Molecular Biology and Evolution
|December 26, 2014
PubMed
Summary

Essential genes are generally favored on bacterial chromosomes over mobile plasmids due to more stable inheritance. Plasmids can host essential genes only if chromosomal genes degrade faster.

Keywords:
antibiotic resistancegenetic architecturehorizontal gene transfermobile genetic elementsplasmids

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Area of Science:

  • Evolutionary biology
  • Microbial genetics
  • Population genetics

Background:

  • Mobile genetic elements like plasmids play a crucial role in prokaryotic evolution.
  • Differences exist between genes on mobile elements (plasmids) and the core genome (chromosomes).
  • Essential genes, vital for basic cellular functions, are typically found in the core genome.

Purpose of the Study:

  • To investigate whether natural selection favors chromosomal locations for essential genes in bacteria.
  • To model the competition between bacteria with different gene locations (plasmid vs. chromosome).

Main Methods:

  • Developed a mathematical model simulating bacterial population competition.
  • Incorporated genotypic variation and the concept of gene 'degradation' rate (mutation, deletion, translocation).
  • Analyzed selection pressures favoring essential genes on either plasmids or chromosomes.

Main Results:

  • Chromosomal locations for essential genes are generally favored by selection.
  • Stable inheritance of chromosomes makes them a more reliable location for essential genes.
  • Plasmids can host functioning essential genes only if chromosomal genes degrade at a significantly higher rate.

Conclusions:

  • Bacterial chromosomes provide a more stable environment for essential genes compared to plasmids.
  • The rate of gene degradation is a critical factor determining the location of essential genes.
  • Selection generally favors essential genes on chromosomes unless plasmid stability is exceptionally high relative to chromosomal gene loss.