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Genomic DNA in Prokaryotes

Genomic DNA in Prokaryotes

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...

Genome Size and the Evolution of New Genes

Genome Size and the Evolution of New Genes

While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.

Bacterial RNA Polymerase

Bacterial RNA Polymerase

Unlike eukaryotes, bacteria use a single RNA Polymerase (RNAP) to transcribe all genes. The different subunits of bacterial RNAPhave distinct functions. The multisubunit structure of the bacterial RNAP helps the enzyme to maintain catalytic function, facilitate assembly, interact with DNA and RNA, and self-regulate its activity.
In most genes, the transcription site is a single base present upstream of the coding sequence. Though RNAP is a catalytically efficient enzyme, it does not recognize...

Gene Duplication and Divergence

Gene Duplication and Divergence

The seminal work of Ohno in 1970 popularized the idea of gene duplication and divergence. DNA sequence comparison studies reveal that a large portion of the genes in bacteria, archaebacteria, and eukaryotes was generated by gene duplication and divergence, indicating its critical role in evolution.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are characterized.

Prokaryotic Gene Structure and Organization

Prokaryotic Gene Structure and Organization

Prokaryotic genomes exhibit a streamlined organization of coding and non-coding regions essential for gene expression and protein synthesis. While coding regions contain the genetic instructions for proteins or functional RNAs, non-coding regions regulate the precise transcription and translation of these genes.Coding Regions: Proteins and RNAsThe primary coding regions, known as structural genes, include sequences transcribed into messenger RNA (mRNA) and ultimately translated into...

Coordination of Gene Expression Processes in Bacteria

Coordination of Gene Expression Processes in Bacteria

The DNA replication, transcription, and translation processes are intricately coupled in bacteria, allowing efficient gene expression and rapid protein synthesis. While this physical and functional coordination is advantageous, it introduces challenges that bacteria overcome through specific regulatory mechanisms.Coupling of Replication, Transcription, and TranslationThe coupling of replication, transcription, and translation is a hallmark of bacterial gene expression. As the replisome unwinds...

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Related Experiment Video

Updated: Jul 17, 2026

Replication of the Ordered, Nonredundant Library of Pseudomonas aeruginosa strain PA14 Transposon Insertion Mutants

Replication of the Ordered, Nonredundant Library of Pseudomonas aeruginosa strain PA14 Transposon Insertion Mutants

Published on: May 4, 2018

Where are the pseudogenes in bacterial genomes?

J G Lawrence¹, R W Hendrix, S Casjens

¹Pittsburgh Bacteriophage Institute and Dept of Biological Sciences, University of Pittsburgh, PA 15260, USA. jlawrenc+@pitt.edu

Trends in Microbiology

|February 5, 2002

Summary

Most bacteria maintain high DNA deletion rates to purge harmful genetic elements. Intracellular parasites, shielded from these elements, exhibit lower deletion rates and more pseudogenes.

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Generation of In-Frame Gene Deletion Mutants in Pseudomonas aeruginosa and Testing for Virulence Attenuation in a Simple Mouse Model of Infection

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Area of Science:

Genomics
Microbial Evolution

Background:

Bacterial genomes are typically compact with few pseudogenes.
Intracellular parasites like Rickettsia prowazekii and Mycobacterium leprae are notable exceptions with higher pseudogene loads.

Purpose of the Study:

To investigate the evolutionary pressures shaping bacterial genome size and pseudogene accumulation.
To propose a model explaining the difference in pseudogene content between free-living and intracellular bacteria.

Main Methods:

Comparative genomic analysis of bacterial genomes.
Theoretical modeling of DNA influx and deletion rates.

Main Results:

Most bacterial genomes maintain a balance between DNA influx and deletion.
Free-living bacteria face constant influx of mobile genetic elements (transposons, phages).
Intracellular parasites experience a reduced influx of dangerous genetic elements due to their sheltered environment.

Conclusions:

High deletion rates in most bacteria act as a selective pressure against detrimental genetic elements.
The sheltered lifestyle of intracellular parasites reduces the need for high deletion rates, leading to pseudogene accumulation.