We all have heard about bacteria, right? These are prokaryotic cells and find their place in both Botany and Zoology.
Bacteria (singular: bacterium) are those microorganisms that don’t have any kind of a nucleus. In fact, they have a nucleoid which is a thin and transparent area within the bacteria’s prokaryotic cell, that contains loops of circular DNA.
Unlike the true nucleus of eukaryotic cells, the prokaryotic cells of bacteria have a nucleoid that is not membrane-bound.
This nucleoid is an irregularly shaped region within the central portion of the prokaryotic cell. This central portion contains all or most of the genetic materials that bacteria need in order to synthesize proteins and survive.
Bacteria are very small living cells typically with a length of 0.5 to 5.0 micrometres each. So, small that most of them are about one-tenth the size of the general eukaryotic cells.
Due to their micron size, it is not so easy to view them under a microscope. So, you’ll need a light microscope with the lens of at least a 400x magnification just to see many of the bacteria at once in the medium they are.
On the other case, if you use a light microscope with 1000x to 2000x magnification then you can see bacteria in very amazing details.
But, if you want to see the nucleoid part of the bacteria with the single circular DNA loop, then you will definitely need an electron micrograph at a high magnification between 1 and 50 million times depending on which type you use and how precise you want to see.
Let’s know more about this topic and get the queries cleared. Keep reading and you’ll learn so many things. So, let’s get started…
Do bacteria have nucleus?
Bacteria don’t have any kind of nucleus. In fact, they have an irregularly shaped nucleoid that contains their genetic materials within no definite membrane-bound boundary.
Bacteria are the most primitive and first formed living single cells that contain DNA as the genetic material. In fact, the DNA is simple, double-stranded, and circular in nature.
Bacterial cells are those ancestor cells from where the present-day eukaryotic cells have evolved over the course of millions of years of evolution.
The bacterial DNA is very much simple and is contained totally equipped within a single circular molecule, called the bacterial chromosome.
It is also to be noted that most bacteria have a single circular chromosome. However, there are many bacteria that contain two circular chromosomes as well.
Bacterial DNA can contain anywhere between 1 million to 5 million base pairs which constitute anywhere between 500 to 3000 genes.
Just, for example, the E. coil bacteria contains 4.6×106 bp (Four million six hundred thousand base pairs) in its 1.36mm length of DNA that makes their single circular chromosome.
Do bacteria have nucleoid?
Yes, bacteria have nucleoids but no nucleus because they are prokaryotic cells. This nucleoid can in no way be compared with a nucleus because it is that central region of the bacterial cell that stores all the genetic material and controls cellular activities within a no boundary region.
A nucleus is actually a membrane-bound structure within a eukaryotic cell that assembles and arranges the genetic materials within a well-definite structure.
But, as the bacteria are considered prokaryotes so, they have their genetic materials concentrated in the center of the prokaryotic cell with the lack of a protective membrane, and so the genetic materials remain in open contact with the cytoplasm of the cell.
Also that, in the nucleus of eukaryotes you will find nucleoplasm and nucleolus. But, nucleoplasm and nucleolus can in no way be found in the nucleoid.
No such protective membrane can be seen around the single circular loop of DNA in the bacterial cell, and also that the single circular loop of DNA is not separated at all from the other cellular components of the bacterial prokaryotic cells like cytoplasm, plasmids, mitochondria, chloroplasts, ribosomes, etc.
So, this very clearly indicates that nucleoid is present in bacteria, and not the nucleus.
What is a Nucleoid in bacteria? Let’s learn more about the nuceloid of a bacterial cell…
Nucleoids in bacteria or in other prokaryotes like Archaea are not true-nucleus. In fact, these are irregularly shaped nucleus-like primitive holding of the genetic materials that include one or two circular chromosomes (mostly a single circular chromosome) that are made up of DNA, RNA, histones, and other cellular proteins.
Nucleoid in bacteria is very poorly organized, irregularly shaped, very small, lacks a protective membrane to hold the genetic materials inside. It also lacks nucleoplasm and nucleolus.
In the most simple words, if we say, this nucleoid is nothing more than the loop of genophore fibres consisting of DNA, along with the various architectural proteins and RNA molecules that have coiled and supercoiled itself in order to fit itself to the center of the bacterial cell making it look concentrated in nature.
It was in the year 1971 when the nucleoid or the so previously called nuclear-like bodies were first discovered in bacteria using the light microscope and DNA-specific stains such as the Feulgen or Giemsa stains.
And there were almost five decades of scientific research that were being conducted starting from the year 1971, which has revealed that there is DNA in the nuclei forming the genophore and it is not membrane-bound.
And during these researches it was also discovered that inside the nucleoid there is well-organize.
In eukaryotes, genophore fibres are termed chromatin fibres due to their various structural and biomolecular differences.
It is to be estimated that the nucleoid contains about 80% DNA, 10% protein, and 10% RNA by weight. This has been estimated in accordance with the various studies conducted on E. coli bacteria.
Most of the bacterial cells are considered haploid as the majority of them have a single circular chromosome. However, a few species of bacteria are also called diploids as they have two copies of circular chromosomes in them.
However, I don’t think that terminology of haploid and diploid is appropriate here in this case of bacteria, as also reported by many researchers because bacteria also have plasmids that are a few closed loops of DNA present outside of the nucleoid.
In order to view the nucleoid clearly, with the DNA strands, we need an electron micrograph at a higher magnification between 1 and 50 million times.
However, using a light microscope with magnification of anywhere between 1000x to 2000x we can blurry see the DNA contents of the nucleoid by staining the cell with Feulgen stain, which specifically stains DNA so that it is visible.
ANSWERED: What is Nucleoid composed of?
Nucleoid is composed of about 80% DNA, 10% protein, and 10% RNA by weight that makes genophore. The genophore is the chromosome of the prokaryotic cells that lacks chromatin.
In the case of a eukaryotic cell, the chromatin fibre is the material that is composed of DNA, RNA, and proteins that supercoils itself to form chromosomes.
But, here in the case of prokaryotic cells, the genophore is the total genomic material that is is composed of DNA, RNA, and proteins that supercoils itself to form chromosomes.
Genophore is made up of nucleic acids, DNA or RNA but has no histone proteins. But, chromatin fibres has histone proteins along with nucleic acids, DNA or RNA to give the fibre its “beads on a string” appearance.
The nucleoid in bacteria is composed of:
- Genophore: It is the bacterial genomic material composed of DNA, RNA, and Proteins that supercoils and condenses itself to form the single circular chromosome that is seen in the nuceloid of the cell.
- DNA: The DNA of most bacteria is contained in a single circular, double-stranded DNA molecule, called the bacterial chromosome. As compared to eukaryotes that have 98% of non-coding DNA sequence in the total DNA of the cell, bacteria are those prokaryotes that have relatively low amounts of repetitive and non-coding DNA that is only about 12% of the total DNA of the cell.
- RNA: They have Messenger RNA (mRNA), Ribosomal RNA (rRNA), and Transfer RNA (tRNA). Here, the synthesis of mRNA from DNA and the synthesis of proteins by reading mRNA with the help of tRNA and rRNA occurs in the cytoplasm itself.
- Proteins: Their genetic code is a degenerate, non-overlapping set of 64 codons that encodes for 21 amino acids and 3 stop codons. These 21 amino acids can code for about 500 to about 10,000 different types of proteins that will be associated with the nucleoid of the bacteria.
That’s all folks! Hope you got your queries cleared in detail.