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Why do cells die?

by NextElement
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NextElement
#1
Oct8-13, 05:57 PM
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I'm a high school student in AP Biology, and we are learning about how cells can absorb nutrients they need through the plasma membrane, as well as break down glucose into ATP for use.

So why do cells (and organisms, for that matter) all of the sudden.... Die? Why can't the cell just keep diffusing oxygen, absorbing glucose and other organic molecules, and continue doing this forever? What causes the cell to stop these processes and quit working?
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besulzbach
#2
Oct8-13, 06:23 PM
P: 28
A lot of reasons kill cells.
Trauma, lack of oxygen, starvation... and there is also programmed cell death (probably what you wanted).
Apoptosis (a.k.a. programmed cell death) is a cell's self-destruction (i.e. suicide).

1. Chromosomal DNA and nucleus break.
2. The cell shrinks.
3. It breaks into vesicles that can be "phagocytosed" (I'm not sure this word exists) by other cells.

If this didn't happen, you would not have your fingers apart from each other (unless you cut the skin between them with a knife, I think).
Pythagorean
#3
Oct8-13, 06:30 PM
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complex processes relying on potential gradients degrade over time and the gradients run down. Signaling between cells begins to malfunction more. Foreign contaminates cause signalling disruption. Errors in translation and transcription accumulate.

Cells can die by apoptosis or necrosis. Apoptosis, programmed cell death, is usually done in the name of the organism's survival. Necrosis is cell death by injury (acid, freezing, burning, being torn open, etc).

Cancer is the case of apoptosis failing... cancer cells can't be programmed to die gracefully because some pathway in apoptosis has become disrupted, so programmed cell death is a nice thing to have.

Borek
#4
Oct9-13, 02:21 AM
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Why do cells die?

Technically some cells live forever - think about bacteria for example. If you don't treat division as a death, bacteria cells are immortal (as long as the environment doesn't kill them).
Ryan_m_b
#5
Oct9-13, 05:05 AM
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Assuming a healthy human cell (I.e non-cancerous) and well maintained culture environment a cell will die eventually due to cellular senescence. This does not refer to an individual cell, as borek says cells will replicate over time but with each replication a section of their DNA located at the very end of the chromosomes will be shortened. These are called telomeres and they give rise to a limit known as the Hayflick limit. Essentially each cell will only be able to replicate a certain number of times before it can no longer replicate due to telomere shortening.

Aside from embryonic stem cells no healthy cell avoids this though different cells will have shorter or longer limits depending on how often they are expected to replicate. This whole system is a defence mechanism against diseases like cancer as with every replication errors occur which could eventually give rise to immortalised cells that replicated uncontrollably.
Borek
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Oct9-13, 05:34 AM
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Quote Quote by Ryan_m_b View Post
This does not refer to an individual cell, as borek says cells will replicate over time but with each replication a section of their DNA located at the very end of the chromosomes will be shortened. These are called telomeres and they give rise to a limit known as the Hayflick limit. Essentially each cell will only be able to replicate a certain number of times before it can no longer replicate due to telomere shortening.
I have a feeling you are - probably by accident - suggesting telomeres are present and shortened in each cell. Do they exist in unicellular organisms?

In general: most of the things written so far seems to be focusing on cells in multicellular organisms. These behave differently from unicellular organism, and as far as I can tell nothing in the original question suggested multicellular organisms.
Ryan_m_b
#7
Oct9-13, 05:44 AM
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You're correct Borek I had assumed the OP was asking about human cells.
Ygggdrasil
#8
Oct9-13, 09:45 AM
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Quote Quote by Borek View Post
I have a feeling you are - probably by accident - suggesting telomeres are present and shortened in each cell. Do they exist in unicellular organisms?
Telomeres exist in most eukaryotes, whether they are multicellular or unicellular. For example, unicellular yeasts, such as the budding yeast used in much of biological research Saccharomyces cerevisiae, have telomeres. These yeast and other similar unicellular organisms do not obey the Hayflick limit because they activate telomerase to extend their telomers to counteract the shortening that occurs upon DNA replication. Many cancer cells use a similar strategy to evade the Hayflick limit.

Most prokaryotes have circular chromosomes and therefore avoid the end replication problem.
Norseman
#9
Oct11-13, 12:11 AM
P: 24
So why do cells (and organisms, for that matter) all of the sudden.... Die? Why can't the cell just keep diffusing oxygen, absorbing glucose and other organic molecules, and continue doing this forever? What causes the cell to stop these processes and quit working?
This is a very good question. The simple answer is that cells die just like how anything else dies: something permanently damages them in a way that prevents them from continuing to function. Unsurprisingly, cells can die in many different ways, just like how the people who are built up from cells can die in many different ways. Since you asked about organisms and cells, let's start with people and work our way down to cells.

Most commonly, people die because of hypoxia, which means a shortage of oxygen. Hypoxia kills cells, and that cell death is what kills people. When someone has a heart attack, the blood vessels which deliver oxygen to the heart are blocked. The cells in the heart become hypoxic, which can make the heart pump ineffectively, and eventually stop pumping at all (cardiac arrest). As a result, they will no longer have oxygen circulating in their blood very effectively and then the cells in the rest of their body will begin to die of hypoxia. Not good!

Ischemic stroke is quite similar to a heart attack, except that it's a blockage of blood vessels to the brain instead of the heart (ischemic means a shortage of blood supply). Even if nothing else were injured by this ischemia, brain death is still a form of death, and just like cardiac arrest, it will lead to the rest of the body's cells dying if life support is not provided, since the brain is what keeps the lungs breathing.

I should be clear that ischemic strokes and heart attacks can have different levels of severity, so they're not always fatal, but they are still serious medical emergencies. Strokes and heart attacks are the top two causes of death in the United States. I should also point out that, although most strokes are ischemic, not all of them are. Some strokes involve bleeding in the brain, but I'll stick to the topic of hypoxia.

So, how does hypoxia kill cells? The short answer is that it kills through acidosis, meaning a disease where there's too much acid. It sounds like you may have already learned about the two different pathways for cellular respiration, and that's important. As you probably know, as long as you have oxygen, which is normal, your cells will use aerobic respiration and you'll produce CO2 as a byproduct. Your body needs to get rid of CO2. When you have a lot of CO2 in your blood, your blood becomes more acidic, and this is dangerous. The opposite is true as well - if you have a panic attack and breathe off too much CO2, your pH can get too high, so you might need a paper bag to help you rebreathe your own CO2. Your body has to maintain a delicate balance in pH, and it can usually do that as long as it body has access to oxygen.

When your body is deprived of oxygen, hypoxia sets in and that delicate pH balance is thrown off. Instead of the normal aerobic respiration, your cells begin using glucose and producing lactic acid. As this process continues, it results in lactic acidosis. The buildup of acid is a problem because it interferes with and potentially destroys proteins. For example, your stomach is acidic because acid helps to break down proteins. The problem here is that proteins are used for almost every structure in your cells. They are the machinery that make your cells work. Ribosomes, membrane channels and enzymes are just a few examples of cellular structures made of proteins, and they're all vitally important for the continued function of your cells. You can imagine pouring acid into a car engine to have some idea of what it's like to expose proteins to a buildup of acid. Pretty quickly, those cells aren't working so well anymore, and it's not long before they stop working at all.

We've talked about the most common way that people die, but what about cells? Usually, individual cells die usually die from apoptosis instead of hypoxia. It might sound bad, but apoptosis is a very good thing, because it prevents old cancer-prone cells from potentially causing cancer, and it also allows new, healthy better-functioning cells to take their place. It's also essential for your immune system. Your body is constantly creating new antibodies to protect you against viruses and bacteria. This is how you can develop antibodies to fight off almost any infection you can imagine - your body is pretty much just making them at random and seeing what works. However, you don't want your body to attack itself. To avoid this, certain types of white blood cells will produce antibodies and stick them on the outside of their membrane. They'll try to see if they can stick to anything inside a 'safe' area (like your bone marrow). If they stick to anything in that safe area, it means those antibodies would attack your own body, so the cell kills itself rather than producing a lot of 'children' and spreading. This doesn't always work, and sometimes people have an immune system which attacks their own body, but usually it's effective.

I've hardly scratched the surface, but now you've got answers for the main causes of death for people and for cells. I've probably left you with more questions than answers, but that's what always happens when you learn about a new subject. There's a whole world of information out there about how cells die, and it's an absolutely fascinating topic. I'd strongly recommend learning more about it if you're interested, and feel free to ask more questions if you have a sudden craving for information! I'll post some links to get you started:

Videos:Reading:
DrDu
#10
Oct11-13, 06:46 AM
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Death is one of the most important inventions of evolution. Dead parents can't consume resources which their eventually fitter ofspring is in need off.


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