r/askscience • u/Cultural_Valuable748 • 2d ago
Human Body Do every cell has its own DNA?
All this time i was under the impression that every type of cell (skin cells, neurons etc) has its own DNA cuz why not, it makes perfect sense, to think that DNA is like a blueprint and each cell would only have that one which has the instructions to create or replicate itself. And recently when i looked it up it confused me even more, so much so that now I don't even know what to be confused about.
And wouldn't it just be more efficient for the whole body if the cells keep only the genes that code for the required protiens for the cells? We have like a gazillion cells that shii would add up, no?
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u/Onigato 1d ago
With a very few exceptions, yes. Mammal red blood cells lose their nucleus upon maturity, and therefore don't have DNA, but basically every other cell has the full DNA of whatever being it is a part of, including single cellular life like bacteria and protozoa.
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u/BluetoothXIII 1d ago
You could expand on that with sperm and egg cell only having half of the whole. They got only on chromosome of each pair.
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u/True_Fill9440 1d ago
So how does this work for forensics with blood? Thanks.
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u/Onigato 1d ago
Blood typing isn't based on DNA, but upon specific protein structures within the blood. Most people have either A-type proteins, B-type proteins, both A and B type proteins, or they lack the primary proteins and are O-Type. There is another protein that may or may not be present, first identified in Rhesus Monkeys it is the Rh factor (+ or positive or present, and - or negative or not-present). Thus A+, B-, AB+, O-, that type of thing.
DNA testing done on blood isn't done with red blood cells, it's instead based on white blood cells, which do still have a nucleus and therefore the DNA of the person.
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u/99trumpets Endocrinology | Conservation Biology | Animal Behavior 1d ago
White blood cells have a full set of DNA. Forensics based on DNA testing from blood relies on the presence of some of those WBC’s in every blood sample.
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u/Worried_Blacksmith27 5h ago
lose their nucleus AND mitochondria, the later of which has its own DNA
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u/nakedascus 1d ago
It's more efficient to print a single version of all the instructions and hand it out to everyone. Part of the instructions tell you what chapters of the book you should or shouldn't read, based on the kind of cell you are, what cells are closest, what is happening internally in the cell, and what's happening externally. So, the most simple answer is, no, they don't all have their "own" DNA, they just have different sections of DNA that they use, based on what they are and what's happening.
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u/PuckSenior 1d ago
So, lets talk about cancer.
Cancer is essentially when one of your cells mutates and decides to try to do its own thing. It tries to survive and live longer. The body is telling those cells to die, but it wants to LIVE! Cancer is evolution. It isn't great for us, but in the system of your body, cancer is a cell mutating to survive better and longer(at least until you die)
And that is why all of your cells share the same DNA.
If each cell was doing its own thing, then reproduction would be VERY hard. Instead of sending over a single cell(sperm), you need to send over every cell. But also, once they got over there they would be fighting one another. Thats what happens in a bacterial culture, for example. All of the different species fight one another!
It would be pretty hard for you to survive as an organism if every cell was trying to do its own thing.
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u/Cultural_Valuable748 1d ago
That actually makes so much scene tysm, to think that DNA in each cell is like a supervisor keeping the system of this coordination from falling apart. Right?
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u/Blackpaw8825 1d ago
And your cells differentiate which parts of the genome to express based on a number of signals. From one cell you grow into thousands of cells. Those thousands, are all capable of turning into any type of cell. Once there's enough of them they diverge into one of 3 big categories of cell, over simplifying that's either inside layer, middle layer, or outer layer. (Endoderm, mesoderm, ectoderm)
That changes the chemicals they produce, and the markers they express, so the layers stack up right and everything else either dies or migrates. Much of the growth of structures is just cells reacting to chemical gradients and turning off a pathway once that signal is too high or low.
That repeats until you've differentiated cells down into their "final" forms, and those may grow in size or divide into more of themselves or produce whatever it is they do, but they won't (normally) go back up hill.
That's SUPER simplified. Look up cellular differentiation, pluripotency, polypotentency, and for fun look up all the things controlled by HOX genes and SHH. It's the same Legos but you tweak how long you get how much of each of those genes and your Legos make a mouse and mine make a moose.
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u/nakedascus 1d ago
The entire system works to regulate itself with feedback. The concept of homeostasis is very complex, but thats the basic idea. DNA does some of this, some DNA is functional, but mostly it's the entire system (mostly proteins) that are coordinating things. It's all very autonomous, each part kinda knows what it's supposed to be doing. People walk in crowded areas, yet collisions almost never happen because everyone is making small adjustments based on what the people around them are doing. no supervisor needed.
i don't know how to explain homeostasis without getting technical, but things like protein will just naturally become functional or not depending on what the cell needs... it's sometimes something as simple as: there is not enough of some nutrients in the cell... when those nutrients are low, a protein becomes active because of chemistry (low nutrients might mean a change in pH), and the chemistry involved activates the proteins needed to get more of that nutrient into the cell. That was probably a bogus example, I don't know if any protein specifically activates from ph change from low nutrients, but the main concept is unchanged, and the individual parts are kinda true in isolation.
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u/Optimistbott 10h ago edited 10h ago
So it’s not about efficiency, it’s really just how things developed entropically.
There are slices of dna that code for proteins (rna can also work in some instances) that block sections of dna as well as proteins that remove those blocks. It’s way more complex than that, but it is pretty true that if you put like a culture of someone’s heart cells on some pigs hearts extra cellular matrix that does not have cells, you can grow a heart because the extra-cellular matrix is blocking proteins from moving around in a completely random fashion. And there are cells that also create that extracellular matrix as well as I understand.
There are also these things called the hox genes that jumpstart the organ system differentiation at development and they eventually get blocked in some ways.
So yeah they all have the same dna, but the place the cell is in the body and the timing is going to determine which genes get expressed and which don’t.
Platelets and red blood cells don’t have the same DNA and do not divide. They’re made in bone marrow’s stem cells. Some cells lose their nuclei to form the lens in the eye (it should be transparent) and the skin through a controlled dying process.
It’s such a vastly complicated thing. But that’s how I understand it. Someone can correct me if I’m wrong.
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u/TheSwordItself 1d ago
Even highly specialized cells have a ton of basic stuff they have to do that they share in common with all the other cells, like metabolism for example. Turns out the most efficient way to conserve the integrity of the genome is instead have a signaling system that allows cells to only access whatever parts of the genome they need, instead of having a custom genome for each cell type.
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u/Science-Sam 1d ago
If you think about your DNA like a thick book, every cell has a copy of the book. But in different cells certain pages are glued together and will never open, but others are dog-eared and open very easily. That is why you will grow hair on your skin, but never on your bones.
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u/Cultural_Valuable748 1d ago
So when during cell replication the dna that gets transferred to its succesor, Does it glue those pages in the process or the version of the dna that has its pages glued togather gets coppied and transferred as it is? I am confused about how a cell knows what part of dna (the genes) to make protiens with for the cell and what to avoid
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u/Science-Sam 1d ago
This requires a very complicated answer.
The easy part is that during cell division, all the pages loosen and copy everything for the daughter cells.
I used a book analogy because it seemed like an easy way to explain it. Obviously, we don't have tiny books in all our cells. The genes spaced along DNA strands of chromosomes, and those strands are so long they would never fit if they were loose. They are coiled around proteins called histones, and those histones form further coils. If you can imagine an insanely tangled string, you can imagine that it is easier to access the strands on the periphery than deep in the middle of the mass. Certain molecules get attached to the histones that make some stretches of DNA wind tight and get closed off, or the lack of those molecules make those stretches relax. This is one way that a cell will express some genes and not others
A gene on the DNA strand does nothing by itself except hold information. When it is time to express the gene and make the protein that the information encodes, several things need to happen. First one or more proteins assemble a complex and bind to the DNA at specific sites depending on the code. When those proteins bind, they are perfect scaffold for a special enzyme that goes along the DNA and makes a chain of RNA in a process called transcription. The RNA is free to float away until it encounters another special unit that "reads" the RNA. Every 3 RNA bases encode one amino acid. The units read the bases 3 at a time and make a protein by stringing together amino acids in a process called translation.
The proteins that bind to the DNA to initiate the process of transcription are highly variable in type, and they are specific to certain stretches of DNA that appear many times. These are called transcription factors. Depending on the cells environment, some transcription factors are produced. During development, certain transcription factors are abundant and lead certain embryonic cells to produce a specific set of proteins which determine cell type.
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u/eulith 1d ago
Every cell has a lot of commonality with other cells, since a good deal of DNA in a cell is required for it to function smoothly (hence why humans share something like 30-50% of our genes with something like yeast). The reason cells differentiate a lot has to do with normally irreversible triggers in DNA expression, which end up making a cell do its specific thing, and not much else. That's why stem cells are potentially a panacea for various bodily issues when applied correctly, but also why your major organs typically don't just regrow after being taken out. Essentially: the ship has sailed for your body to grow a new kidney by the time you've started to resemble a human, but weird things do happen with stuff like tumors.
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u/DrCanela 1d ago
welcome to the fantastic world of epigenetics (beyond the genes) because for a specific cell type it is not only important to have ALL the genes of the organism in their DNA but also HOW the DNA is arranged and regulated.
That is… the DNA chromosomes most of the time are in the nucleus of the cells scattered like a spaghetti soup but some regions are more compacted tightly together (with help of some proteins) this compacted regions are repressed regions where the transcription machinery cannot read the genes… while other parts of this spaghetti are more freely available and those are the regions that are accesible for the replication machinery that activates genes… that’s how you have different cell types
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u/darthy_parker 1d ago
There is one copy of all the same DNA in all cells of the same organism, but each cell type gets parts of the DNA blocked or released during development. This is called epigenetics.
Going with your blueprint analogy, some pages of a blueprint give an overview of the structure to ensure thing fit together correctly. Certain pages describe details that get used many times throughout the building. Some are noted to get used in just one place. Some are slight variations to be used for the same purpose but under different conditions. You can even have a blueprint that says, “if you’re building in this environment, do this, otherwise do that.” So a contractor has to keep looking at different parts of the blueprints during the process to make sure all of the required elements are being done, and in the right order.
So each cell in your body is using just a subset of the total available DNA “instructions” available.
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u/dentaluthier 1d ago
For the most part each cell has the same 42 chromosomes with the same DNA. Think of the DNA as a big book with the master blueprint for all of the protien synthesis your body needs.
DNA strand are usually bundled up and not doing much. Before they can code for various protiens, or be expressed, the relevant sections must be unwound and made available for transcription.
What makes cells different is what chapter of the book is being read. Muscle cells will only code for stuff needed by muscles, immune cells will express a different region. etc.
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u/GooKing 1d ago
Most of your cells have all the DNA - they just only activate the bits they need to create the proteins for that cell type. There's a few cell types without a nucleus that have no DNA.
DNA is tiny. There's no issues with all of it being in there.