Bacterial DNA Replication: 3 Important Concepts


How is bacterial DNA replication different from eukaryotic DNA replication?

Contrast features among bacterial DNA replication steps (prokaryotic) and eukaryotic DNA replication processes are primarily identified with the difference in complexity and size of the DNA and cell.

In prokaryotic cells, there is just one starting place for the replication process to happen in two opposites headings simultaneously and in the cell cytoplasm, unlike Eukaryotic cells, which have numerous areas of origin of replication and utilize unidirectional replication inside the nucleoplasm.

Prokaryotic DNA ReplicationEukaryotic DNA Replication
Site of Replication is CytoplasmSite of Replication is Nucleus
Origin of replication: SingleOrigin of replication: Multiple
DNA Gyrase: RequiredDNA Gyrase: Not Required
Replication occurs very fast (Usually within 20 min)Replication process takes much longer time
Very long (1-2 kilo base pairs) Okazaki fragments are formedOkazaki fragments are very short
Telomeres are not replicated since prokaryotic DNA is circularTelomeres are present and replicated since the eukaryotic DNA is not circular
Table 1: Contrasting features of prokaryotic and eukaryotic replication steps

Other important facts related to the replication process:

  • In comparison to the prokaryotes, Eukaryotes has 25 times more DNA content.
  • Eukaryotic cells generally has double number of DNA polymerases as compared to the prokaryotic cells (normally has two DNA polymerases) Replication additionally occurs at a lot quicker rate in prokaryotic cells, as compared to the eukaryotes. They usually require just 40 minutes, while humans might need as long as 400 hours.
  • Eukaryotes likewise have a particular interaction for replicating telomeres at their chromosome‘s closures (end). While prokaryotes have circular chromosomes, hence no telomere is present.
  • The short replication in prokaryotes happens persistently, But in eukaryotic cells DNA replication during the cell cycle more precisely in the synthetic (S-Phase).
bacterial DNA replication steps
Figure: Formation of replication fork is the key step for DNA replication. Image Credit: AWS Commons

Where does DNA replication occur in bacteria?

The bacterialDNA replication process occurs in the cytoplasm.

The “cell cycle” of bacterium starts with the commencement of Replication at the single replication origin. Replication takes relying upon the length of a chromosome, which is followed by some time until the division is finished.

Other important facts about bacterial growth and DNA replication:

  • Microorganisms grow overall under two unique conditions, either under limited nutrient supply. This is alluded to as static microbial growth (no increment of the populace) or in abundant nutrient supply, where populace (population) growth is swift and implied to as logarithmic microbial growth.
  • This is the way it happens when bacterial cultures are denser or some different variables resist the populace’s growth.

DNA replication in a bacterium during the log phase happens continuously. This is a fundamental supposition dependent on the accompanying four basic facts:

  • The genome of E. coli is about 4.5 Million base pairs long.
  • The speed of Replication is around 1000 bases/sec.
  • Replication takes 15 min to complete
  • There is just a single replication origin in the genome.

To duplicate 4.5 million bases of a bacterium will require 4.500 sec or 75 minutes (if the replication speed is 1000 bp/sec). The DNA replication, even at a sluggish duplication rate, will take about an hour if the DNA replication process is continuous.

Now a question arises in mind, how might an E.coli bacterium copy its DNA under 75 min?

  • The explanation is that the replication origin initiates before the Replication of the chromosome is finished. On the off chance that the ori starts every 15 min when the primary Replication is completed after 75 min, the chromosome will contain additional extra replication forks.
  • Consequently, in microscopic organisms, there isn’t something very similar to the “cell cycle” as in eukaryotic cells. We additionally don’t allude to mitosis concerning nucleated cells, yet cell division. Additionally, reproduction is a term not frequently utilized in microbial science.

How do bacterial cells divide and reproduce?

Binary fission is the type of reproduction process through which most of the microorganism multiply their number.

Bacterium separates into two daughter cells. The phenomenon of Binary fission starts when the DNA of the bacterium replicates. Bacterial cell first elongates and then give rise to two daughter cells by splitting the DNA content of the parent cell. Each daughter cell is the clone of a parent cell.

Binary Fission and other Forms of Reproduction in Bacteria:

Binary Fission

Most microscopic organisms are dependent on binary fission for reproduction. It’s an elementary form of reproduction:

  • A cell grows in size (most of the time, double its initial size) and afterward split in two.
  • Every daughter cell a complete replica of its fundamental hereditary material (genome).

Bacterial cell division is analyzed in many exploration research centers globally. These examinations uncover the genetic mechanisms that control bacterial cell division—understanding the mechanics of this cycle and considering producing new substances or antibiotics that explicitly target bacterial cell division.

binary fission
Figure: Key steps involved in the process of binary fission. Image Credit: AWS Commons

Some Unusual Forms of Reproduction in Bacteria:

  • There are microbes that utilization unusual forms of cell division to multiply.
  • The microbes grow over two times their initial cell size and afterward utilize subsequent divisions to form multiple daughter cells.
  • Some bacterial species multiply by the process of budding.
  • Others forms structure (internal) that form inside the cytoplasm of a more giant “mother cell.”
  • There are few examples of these surprising types of bacterial reproduction processes.

Baeocyte production in the cyanobacterium Stanieria

Baeocyte production takes place in the following steps:

  • Stanieria never adopts the process of binary fission for multiplication. It begins as a tiny spherical cell roughly 1 to 2 μm in width. This cell is alluded to as a baeocyte (which means “a little cell”).
  • The baeocyte starts to grow, ultimately forming a vegetative cell up to30 μm in size. As it develops, the cell DNA is duplicated again and again, and the cell creates a dense extracellular matrix.
  • The vegetative cell ultimately changes into a useful stage where it goes through a quick progression of cytoplasmic divisions to deliver multiple baeocytes.
  • The extracellular framework in the end tears open, releasing the baeocytes. Different individuals from the Pleurocapsales (an Order of Cyanobacteria) utilize surprising examples of division in their propagation.

Budding in bacteria

  • Budding has been seen in individuals from the Firmicutes, Cyanobacteria, Planctomycetes (a.k.a. the Low G+C Gram-Positive Bacteria), and the prosthecate Proteobacteria.
  • Albeit the mechanism of budding has been extensively studied in the yeast (Saccharomyces cerevisiae) which is a eukaryotic system, the mechanism of bud development is still under research and exploration.

Intracellular offspring production by some Firmicutes

  • Metabacterium polyspora, Epulopiscium species, and the Segmented Filamentous Bacteria (SFB) structures numerous intracellular offsprings.
  • For some microbes, this cycle seems to be the best way to multiply. Intracellular offspring growth in these microscopic organisms imparts similarities with endospore development in Bacillus subtilis. 

In giant Epulopiscium species, this extraordinary regenerative system starts with unequal cell division. Rather than setting the FtsZ ring at the cell center, as in the process of binary fission: 

  1. Z rings are put close to both cell terminals in Epulopiscium. 
  2. Division shapes a giant mother cell and two tiny daughter cells. 
  3. The small cells contain DNA and become inundated entirely by the giant mother cell. 
  4. The inside offspring develop inside the cytoplasm of the mother cell. 
  5. Once offspring growth is finished, the mother cell degrades and deliveries the posterity.

What is the basic difference between bacterial genomic DNA and plasmid DNA?

Genomic DNA and plasmid DNA are two sorts of DNA exhibited by living organisms.

Genomic DNA is the chromosomal DNA of living life forms that contain genetic data. Then again, plasmid DNA is extrachromosomal DNA present in microscopic organisms, archaea, and a few eukaryotes.

  • The major difference between the plasmid DNA and genomic DNA is that genomic DNA is fundamental for the endurance of life forms.
  • Plasmid DNA isn’t essential for the persistence of living organisms. Likewise, genomic and plasmid DNA also differ in their sizes. Genomic DNA is ordinarily bigger than plasmid DNA.
  • Genomic DNA contains crucial genes that produce all primary and valuable proteins. However, plasmid DNA contains genes that give extra benefits to the creatures. Subsequently, this is likewise a distinction between genomic and plasmid DNA.
Figure: Fate of plasmid DNA (Extra-Chromosomal). Image Credit: Wikimedia Commons
CharacteristicsPlasmid DNAGenomic DNA
DefinitionIt’s a type of Extra chromosomal DNA present in prokaryotes and some eukaryotesIt is present in the form of genetic material which harbours the genetic information of an individual
OrganismIt is frequently present in prokaryotes and in some eukaryotes as wellIt is present in all living beings
SizeSmaller in size (Few kilobase pairs)Generally larger in size
TypeExtra-chromosomal in naturePresent in chromosomes
Encoding genesEncodes additional proteins such as antibiotic resistance which provides additional survival capabilities to the organismEncodes for proteins that are essential for the survival of organism (involved in carrying out life processes)
Gene TransferHorizontal gene transfer (Transformation) is possible, but cell division is not requiredHorizontal gene transfer is not possible, only vertical gene transfer is possible (form parents to offspring)
VectorOften used as a vector for genetic engineering experimentsNot much promising to be used as a vector
Rate of ReplicationVery highLow
Table 2: Differences between plasmid and Genomic DNA

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