Do all cells have DNA? Do all body cells have the same DNA?
Do all cells have DNA?
No, not all cells of the human body have DNA, but nearly a majority of the cells have DNA contained within the nucleus.
The cells like the mature Red Blood Cells (RBCs) have no DNA at all. Other cells like the Blood Platelets (Thrombocytes in mammals), and Sieve tube elements in the phloem of plants lack genetic DNA within the nucleus.
The requirement of DNA as the genetic material is very much necessary for almost all of the cells. The DNA as the genetic material translates to mRNA and then transcripts from mRNA to Proteins.
The proteins are the building blocks of life. The cell that contains genetic materials will produce proteins all of the time.
The proteins help in cell signaling, cell growth, cell division, endocytosis, exocytosis, cell structure maintenance, immunity, the formation of enzymes and hormones, etc.
So, it is very much clear that almost all of the living cells require genetic material for proper functioning. So, there’s no way that there won’t be any type of genetic material in the cells.
But still, with some exceptions, there are cells like the mature Red Blood Cells that totally lack genetic materials.
Yes, we are speaking about mature RBCs, not the newly formed RBCs. The mature RBCs lose their genetic material because they lose their nucleus as they mature.
It’s because as the young RBC reaches its maturity the nucleus inside is swallowed by macrophages (one of the immune system’s quick-response cells) and thus the RBC becomes devoid of the nucleus. The genetic materials that are the DNA segments inside the nucleus also get swallowed.
Because of the lack of nuclei and organelles, mature red blood cells do not contain DNA and cannot synthesize any RNA, and so no protein production is done, and so they consequently cannot divide and have limited repair capabilities.
Thus, the mature RBCs become unable to carry out protein synthesis, and so the only work they can do is the proper transportation of O2 and CO2 in our body.
Other cells like the Blood Platelets (Thrombocytes) in mammals also lack the nucleus and so the genetic DNA. However, they do contain mitochondria and mitochondrial DNA, as well as Endoplasmic reticulum fragments and granules.
In plants, the Sieve tube elements in phloem lack nucleus at maturity and so no DNA in the nucleus. But, they do contain some amount of DNA in their mitochondria and plastids.
Do all body cells have the same DNA?
Yes, all cells of the body have the same DNA structure, but not all cells of the body have the same quantity of DNA.
All cells of the body don’t have the same DNA quantity because some cells are haploid, some are diploid, and some don’t even have DNA.
Although a majority of the cells contain the same DNA contents, with some exceptions, there are cells that do not contain DNA as well. Just like the RBC cells in mammals that don’t have any DNA.
In general, most of the body cells are diploid that is containing two complete sets of chromosomes.
For your information, chromosomes are made of DNA, and DNA is of the same double helix structure in most cells.
So, each diploid cell contains about 6.6 x 109 base pairs of DNA that include about 23 pairs of chromosomes (46 chromosomes).
Some, cells like the reproductive cells (sperm cell and egg cell) are haploid in nature, that is containing only one complete set of chromosomes.
So, each haploid cell contains about 3.3 x 109 base pairs of DNA that includes only 23 chromosomes.
In simple words, in human the somatic cells are all diploid with 2n number of chromosomes. And, all gametic cells are haploid with n number of chromosomes.
Also all cells of the body have the same DNA but different functions. Why?
This is because all of the cells in our bodies are formed from a single fertilized egg that forms the diploid zygote (2n) after the fusion of one haploid sperm cell (n) with one haploid egg cell (n).
And so, as the diploid zygote (2n) cells divide and grow into an embryo and then into a mature human, different genes are expressed, resulting in different cell types.
Is there DNA in dead cells?
Yes, there is DNA in dead cells. It doesn’t matter if the cell is living or non-living, if the cell had DNA during the time it was alive then surely it will have DNA once it’s dead.
But, not all cells of the body will have DNA after the cells are dead. It’s because in some cells the DNA is degraded during the time of cell death by apoptosis or necrosis.
Just for instance, take the example of malignant cells. As the tumor grows, the malignant cells die and are replaced by new ones. When the cells die, the dead cells get broken down and their contents, including DNA, are released into the bloodstream.
Circulating tumor DNA (ctDNA) are those DNAs that were once alive inside the nucleus of the malignant cell. The ctDNA level increases in the bloodstream and refers to DNA that comes from cancerous cells and tumors.
So, that’s why it is also said that some dead and dying cells have usually been considered the source of blood DNA. So, if you evaluate some cells like those of the malignant dead cells you won’t find the DNA.
But, a majority of the dead will have DNA, just take the example of fossils and stromatolites which are million years old, that are definitely dead cells. From these dead cells, DNA is well-extracted for various evolutionary studies.
What about the viruses, have you ever thought of? Viruses are considered to be intermediate between living and non-living. And, DNA can also be extracted from viruses too.
Now, also take the example of crime scenes. In many murder cases, you will often see the forensic people collecting DNA samples of the dead body like hairs, blood, skin, etc. to detect the crime scene and the criminal of course.
They are doing so because DNA can also be extracted from the cells of the dead body. That’s you have often come across in media and television of how and when it’s done.
Other cells like the mature RBC cells and the dead plant sclerenchyma cells, also do not contain DNA in them. And so, no DNA or any cell material can be extracted from them.
How big is the DNA in a human cell?
To answer this we need to first under the relationship DNA, genes, and chromosomes.
The main relationship between DNA, genes, and chromosomes is that genes are made up of segments of coiled DNA, and chromosomes are long supercoiled chains composed of various genes.
In humans, a single gene can contain about 1 million base pairs of DNA and a chromosome can contain about 1,000 such genes, and a single cell has 46 of such chromosomes.
On average, a single human chromosome consists of a coiled DNA molecule that is about 2 inches (5 cm) long.
And, if we consider the whole length of DNA in one haploid cell then it is estimated to be about 2 meters long. That’s how big the DNA is.
If you see more precisely, then it is clear that if all the DNA in all your cells are put together would be about twice the diameter of the Solar System. That’s how long all of the cells uncoiled DNA is, if added together.
DNA is so compressible that a DNA helix with a diameter of 2nm (2 x 10-9 m) can be supercoiled to become a chromatid of 700nm (700 x 10-9 m) diameter or so. A chromosome consists of two chromatids attached together.
On average, a single human chromosome consists of a coiled DNA molecule that is about 2 inches long. And, if that same 2 inches long DNA molecule gets uncoiled then it can gain 109 times more length than that of a chromosome.
Considering the length if you see, the smallest human chromosome is Chromosome Y which has a length of 20 mm with 57,227,415 bp of DNA.
And, the largest human chromosome is Chromosome 1 which has a length of 85 mm with 248,956,422 bp of DNA.
Can DNA be taken from hair?
Yes, it’s absolutely possible to get DNA from a sample of hair. It’s because the hair contains samples of DNA that can be experimentally evaluated in order to solve various maternity and paternity disputes, and also the various crime scenes.
The hair is made up of keratin and is divided into two parts- the shaft which is what we see above the surface of your skin, and the root or follicle which remains below the surface of the skin.
In simple words, the shaft is made up of dead cells that have been pushed up through the root. At the base of the hair root, is a small ball-like formation called a bulb.
So, if we consider the cut hair samples without the root of the hair, then those can only be used to extract mtDNA (mitochondrial DNA). The mtDNA is present in the dead cells that make up the hair shaft.
On the other case, if we consider the plucked out hair samples with the root of the hair, then those can be used to extract nuDNA (nuclear DNA). Such hair samples can only be collected if the hairs have been ripped or torn from the scalp or plucked out.
The most common difference between mtDNA and nuDNA is that the Mitochondrial DNA (mtDNA), unlike nuclear DNA (nuDNA) is inherited from the mother, while nuclear DNA is inherited from both parents.
So, in hair DNA testing with the freshly plucked hair with both shaft and root, is of course always better for DNA analysis. And so, a minimum of 5 hairs is recommended for lab testing of the nuDNA.
Where actually is the DNA inside the cell?
In animal cells, DNA is present inside the nucleus, and inside the mitochondria. In plant cells, DNA is present inside the nucleus, inside the mitochondria, and also inside the chloroplasts.
In prokaryotic cells, like those of the bacterial cells, a single circular chromosome is present in the cytoplasm as they don’t have a nucleus, and a double-stranded DNA is present inside the Plasmids.
DNA is always present inside the nucleus of the cell in eukaryotes. This DNA is also known as nuclear DNA (nuDNA).
The nuDNA inside the nucleus remains in a more compressed and packaged way in the form of chromosomes and is the main genetic material carrying the genetic information from generation after generation.
Mitochondria also have a small amount of their own DNA. This genetic material is known as mitochondrial DNA or mtDNA.
The mtDNA is critically important to synthesize proteins for many of the metabolic pathways happening inside the mitochondria that produce energy for the cell.
In plants, the chloroplast contains Chloroplast DNA (cpDNA). cpDNA is also referred to as plastosome to refer to the genome of the chloroplasts as well as other plastids as a whole.
Chloroplast DNA (cpDNA) contains genes that are involved with aspects of photosynthesis and with components of the special protein-synthesizing apparatus that is active within the chloroplast.
In prokaryotic cells, the plasmid DNA is a small, circular, double-stranded DNA molecule that is distinct from a cell’s chromosomal DNA.
The genes carried in plasmid DNA provide the bacteria with genetic advantages, such as antibiotic resistance, and also carry genes that benefit the survival of the organism.
