What is the biological reason for why things die?

[Megalodon]

Many theories involve the DNA. We have a protein in our cell called telomerase, that makes sure our DNA is big as needed after each cell division. This is needed because a small amount of DNA is lost after each division, and without telomerase this won't be regained. This only works in some of our cells, and those who doesnt have it, will only be able to divide themselves for a set amount of times (around 50.)

Over the years we accumulute mutations in our DNA. We have 3.2 DNA molecules in our genome, and for each cell division a few will be wrongly copied. This can lead to cancer, or to the decline in cell functionality which might cause aging.

Cells can divide far more than 50 times before they run out of telomeres, the telomeres are massive, thousands of nucleotides long. The telomerase enzyme is only expressed in the fetus and immortal cells, primarily the germ cells and cancer.

3.2 DNA molecules? This makes absolutely no sense. Not sure how big you think a DNA molecule is (neither an I to be honest, DNA is rarely referred to in molecules), but given that we have 46 individual chromosomes in our genome, the figure of 3.2 is ludicrous.

Because as thing grow and age the clones of your cells degrade with every batch, this is due to the fact transposons and centromeres occasionally "lose" a peptide or some phosphate groups are lost, so mainly as your cells essentially clone themselves the degradation carries down the line, until the degradation causes dangerous defects and mutations. There more to it but I don't know the exact specifics and I'm too lazy to type them anyway.

I'm sorry, but none of the terminology you used is correct. Transposons are involved in transporting sections of DNA between individual chromosomes and have no role in DNA replication. Centromeres hold the pairs of chromosomes together and have a structural role in cell replication as part of the spindle, getting each copy of the DNA to opposite ends of the cell for when it divides. DNA does not contains peptides, and at no point in DNA replication are nucleotides dephosphorylated (the loss of phosphate groups). Instead the strand loses some nucleotides, in their entirety.

 

[Hawk of Battle]

I think you are refering to telomeres. These are lengths of additional DNA on the ends of the DNA double helix. Every time a cell replicates, the telomeres are shortened by a small amount. This occurs because the DNA polymerase enzyme that replicates the DNA does not run the full length of the DNA strand. Once the telomeres are fully depleted, the cell will die.
This process results in the symptoms of aging. UV light accelerates the telomere degradation because free radicals generated by the UV radiation oxidise the telomeres, meaning that a greater section of DNA is lost at each replication, so the affected cells grow "old" before their time.

Basically this.

Cells divide in order to replace other cells because they degrade over time. Every time they are "copied" the new cell is a slightly worse version of the previous cell (a copy of a copy of a copy of a copy, etc. Throw in all the radiation we're exposed to all through our lives (light, thermal energy, electromagentc, microwave, gamme, beta, etc) and even a 0.001 degradation every time your cells divide is eventually going to result in the complete breakdown of said cell.

Eventually you just can't copy those cells anymore, hence death by old age. Whether the actual cause of death is a breakdown of the heart muscles, a breakdown of the ateries in the brain resulting in hemorage, liver cell breakdowns, whatever, it all comes down to the same thing; too many cells wore worn out and could no longer funtion, so something had to give.

 

[Yudas]

Many theories involve the DNA. We have a protein in our cell called telomerase, that makes sure our DNA is big as needed after each cell division. This is needed because a small amount of DNA is lost after each division, and without telomerase this won't be regained. This only works in some of our cells, and those who doesnt have it, will only be able to divide themselves for a set amount of times (around 50.)

Over the years we accumulute mutations in our DNA. We have 3.2 DNA molecules in our genome, and for each cell division a few will be wrongly copied. This can lead to cancer, or to the decline in cell functionality which might cause aging.

Cells can divide far more than 50 times before they run out of telomeres, the telomeres are massive, thousands of nucleotides long. The telomerase enzyme is only expressed in the fetus and immortal cells, primarily the germ cells and cancer.

3.2 DNA molecules? This makes absolutely no sense. Not sure how big you think a DNA molecule is (neither an I to be honest, DNA is rarely referred to in molecules), but given that we have 46 individual chromosomes in our genome, the figure of 3.2 is ludicrous.


When I said 3.2 I meant to say 3.2 billion but forgot that last word. My message was abit rushed so thats my mistake and I will correct it in my original thread to not confuse people. Thanks for noticing. As to the amount of divisions before it halts, the estimate I listed is what is generally accepted. It is known as the Hayflick limit, if you want to look it up for confirmation.
[/quote="Megalodon" post="18.236975.8463370"]

EDIT: By DNA molecules I mean base pairs. The teminology I used was a bit sloppy, as a base pair ofcourse consist of two molecules of DeoxyriboNucleiAcid.

 

[robinkom]

Analogy for everyone's DNA-related answers:

It's like copying a piece of footage across several VHS tapes over and over. Each time, the quality degrades a little. Eventually, you cannot decipher what is on screen anymore as it will be a garbled mess.

 

[cheeseraven]

The CIIRRRCALLLLL of LIIIIIIIIFE *dadummm!*

Thank you for that. You just made my day.

 

[Megalodon]

I think you are refering to telomeres. These are lengths of additional DNA on the ends of the DNA double helix. Every time a cell replicates, the telomeres are shortened by a small amount. This occurs because the DNA polymerase enzyme that replicates the DNA does not run the full length of the DNA strand. Once the telomeres are fully depleted, the cell will die.
This process results in the symptoms of aging. UV light accelerates the telomere degradation because free radicals generated by the UV radiation oxidise the telomeres, meaning that a greater section of DNA is lost at each replication, so the affected cells grow "old" before their time.

Basically this.

Cells divide in order to replace other cells because they degrade over time. Every time they are "copied" the new cell is a slightly worse version of the previous cell (a copy of a copy of a copy of a copy, etc. Throw in all the radiation we're exposed to all through our lives (light, thermal energy, electromagentc, microwave, gamme, beta, etc) and even a 0.001 degradation every time your cells divide is eventually going to result in the complete breakdown of said cell.

Eventually you just can't copy those cells anymore, hence death by old age. Whether the actual cause of death is a breakdown of the heart muscles, a breakdown of the ateries in the brain resulting in hemorage, liver cell breakdowns, whatever, it all comes down to the same thing; too many cells wore worn out and could no longer funtion, so something had to give.

A given tissue will not malfunction fatally because the component cells cannot be replicated by mitosis. The function of cells does degrade as mutations build up in the DNA because DNA replication is not 100% accurate, this process is made worse by radiation exposure/smoking/generally being alive. Death by "old age" is something of a misnomer anyway, you die because of some problem brought about by being old. It's like how AIDS doesn't kill you directly, merely crippling you immune system something else can kill you.

 

[spartan231490]

shortening of telmeers(no idea how it's spelled) cause cell mutation to become more likely with each division. these mutations usually lead to the cell failing in it's purpose, when this happens enough, the tissues are compromised and organ function degrades until it fails. another common result is cancerous tumor cells.

 

[deathninja]

I'm having to cram for an exam on cell death, cancer and senescence in a few weeks, I'm having nightmares about this stuff.

Anyways, there's several mechanisms; Necrosis is when cells die through toxic insult, apoptosis is controlled cell death (kill signals basically, like if it's compromised), there's also another way to get rid of cells in a controlled manner (autophagosis) where they basically break themselves down.

Cell ageing is due to telomere shortening, as has been brought up already. Once the telomeres are too short, the cell stops replicating as a safeguard against mutation (there's a link between some cancers and bypassing this safety net).

There's probably more, but I'm trying to do this off the top of my head, someone smarter than me feel free to shoot holes in this.

 

[Tasachan]

I did a project on cloning last year. I read that cells are programmed to only divide x amount of times, and once they run out of those, you're not getting any new cells - that's why organs slow down and stop working.
Assuming you don't die of organ failure from drinking, or from being unhealthy, I'm pretty sure that is the reason.

Edit: Upon further investigation, this has already been said. This is what I get for posting while in class. -_-

 

[sp86]

It's not biology, it's physics. Entropy is the inalienable true state of the universe, all systems fail eventually.

 

[Ren3004]

Basically what some people already said. Every time your cells replicate a little piece at the end of the chromosomes can't be copied and as such, becomes shorter. When it gets too short the cell will start having an abnormal set of chromosomes, which eventually lead to its death.

Another reason is that we have some sort of functional reserve... For example, our kidneys have way more nephrons than needed. As we get older, we lose these reserves, making it more difficult to adapt to disease, environmental changes, etc...

 

[mageroel]

It is because your cells can only have a limited number of copies of your DNA used in mitosis & meiosis. So you can only reach a certain age, you die when your cells cannot 'refresh'. Actually, you're dying all the time. It's just that you keep making new cells at a faster or at the same rate as you lose cells (except for certain cells like brain cells, who die off slowly [luckily, you have enough to last.. well, a lifetime]).

 

[Megalodon]

As to the amount of divisions before it halts, the estimate I listed is what is generally accepted. It is known as the Hayflick limit, if you want to look it up for confirmation.

Fair enough, I did, my text books list it at around 60 times which is close enough. With about 1000 repeats of a six nucleotide sequence and 100 or so being lost every replication. I initially forgot that cells with very fast turn over, like the skin for bone marrow for red blood cells, come from lines of stem cells that do not undergo telomre degradation.

 

[theevilsanta]

So yeah, all the people posting "entropy" are stupid. Entropy might make sense if you asked why all life in the universe might someday end, but why a single human being dies has a lot more to do with molecular biology. Specifically, the people that talk about telomeres. Also, we don't need any carcinogenics to eventually get cancer - we'll never get far past 100 as long as we dont have DNA repairing therapies.

 

[SlayerN]

The biological reason is that after a certain point the electrons in you brain cease to function because they eventual will balance out and contain a neutral charge and stop having reactions with the ions and atoms around them. after this happens it will happen to everything that your brain kept functioning this happens in a 0.000000000001 of a second though as it grows less and less you will grow weaker and this is what death of old age is. (also why dead things don't ave body heat the electrons stop reacting giving off no heat) and this is coming from a biology textbook I think I was supposed to return to my 9th or 10th grade teacher about 8 years ago

 

[Caliostro]

Think of a car, or a computer. Why do they stop working? They're worn out. Our bodies start out like brand new machines. In fact, they start out like unfinished machines that slowly finish themselves. So, actually, when we're born, we're "more" than brand new. As we age, we give our body lots of use. If we're careful, do a lot of proper maintenance, try not to abuse it too much, it lasts longer than if we never do any maint and always push it till it breaks, but nothing lasts forever. Eventually things start wearing down, failing, which includes the mechanisms that help you regenerate... Some parts of our body cannot be self-regenerated... Things start breaking down, until eventually and inevitably, something critical goes beyond your body's capacity to fix it, and we break down. We stop functioning.

 

[ninjapenguin981]

The point is so that species can evolve with fresh brains. If there were the old people around for millennia there would be no evolution as there'd be no random mutations and survival of the fittest. There'd just be the old organisms slowly plodding away inefficiently and unintelligently.

 

[Killercheesepuff]

Actually Immortality would be possible..... If it was at all practical. A species would die Out if it never passed its genes on and simply continued to live. (It would be eaten, killed ect.)For there to be an evolution to immortality, It would requier a extreme need for long or permanent life and lets face it, besides from our own desires, there isn't any. Parents have to die out so the next generation can survive with the resources we have. So even if there was immortality by staying healthy (still assuming you have to eat which is really unavoidable) You wouldnt have enough food. Also If reproduction stopped then so would evolution and the species would go into a standstill of no improvements. And If you've noticed, when people get old they tend not to have kids. And nature has no use for people who can't have kids.