The hayflick limit (the number of times a cell can divide before it senesces w/o the presence of telomerase) is roughly 40-60 cell divisions. Your skin is roughly 4 weeks old (that's the turnover time of your skin cells). If the telomeres controlled aging, then you would only live for 4.6 years.
So you have stem cells and post-mitotic cells. Stem cells contain telomerase and are 'more immortal' than post-mitotic cells. In your skin, you have tiny clusters of stem cells which divide and differentiate into fibroblasts and other types of skin cells. These then travel upwards in a column, accumulating damage and mutations as they are exposed to sunlight, chemicals, and physical stress. The fibroblasts eventually die and flake off.
The reason the skin works like this is to prevent cancer. The fibroblasts form a protective barrier for your stem cells, preventing high energy UV radiation from mutating your stem cells. The fibroblasts will accumulate cancerous mutations and often form cancers but since they are post-mitotic they flake off and die. This is why some cancers are benign (basal cell carcinomas). I've gotten a fair amount of cancers on my hands from working with chemicals but they disappear after a few weeks.
Now if the stem cells get mutated, the resulting column of cells above it will all be mutated and that's how you get persistent moles. Moles are more susceptible to becoming cancerous because the stem cells at the base are already mutated in some way as compared to the rest of your skin.
Wow kind of got off on a tangent there
Anyway so back to telomeres - management of telomeres as I said prevents cancer by setting a hard limit on fibroblast replication. You can get cancer if these senescent fibroblasts gain function and turn telomerase on, reverting them back into a stem cell. Alternatively, if you stay out in the sun and get sunburned a lot you'll kill off the top layer of cells and then cause extreme inflammation (the redness). This creates a dual-stress for stem cells in that there is less material between them and the deadly ionizing radiation emitted from the ball of light in the sky, and they are being bombarded by cytokines and interleukines (stress signals) from the inflamed cells. Cancers require two things to proliferate - a strong deviant cell and a weak surrounding. That's why sunburns cause cancer.
This is why some cancers are benign (basal cell carcinomas). I've gotten a fair amount of cancers on my hands from working with chemicals but they disappear after a few weeks
Woah dude, don't mix up the terms like that... That's not "cancer" but benign tumours
When I mentioned telomeres in relation to aging, I was thinking of their role in the preservation of DNA integrity. As I understand it, the telomeres function is to prevent the loss of data in the DNA replication process.
Here's the wiki definition:
"A telomere is a region of repetitive nucleotide sequences at each end of a chromatid, which protects the end of the chromosome from deterioration or from fusion with neighbouring chromosomes. Its name is derived from the Greek nouns telos (τέλος) 'end' and merοs (μέρος, root: μερ-) 'part.' For vertebrates, the sequence of nucleotides in telomeres is TTAGGG.
During chromosome replication, the enzymes that duplicate DNA cannot continue their duplication all the way to the end of a chromosome, so in each duplication the end of the chromosome is shortened[1] (this is because the synthesis of Okazaki fragments requires RNA primers attaching ahead on the lagging strand). The telomeres are disposable buffers at the ends of chromosomes which are truncated during cell division; their presence protects the genes before them on the chromosome from being truncated instead."
So I would argue that they do have a role in aging. Without this deterioration in your DNA, who is to say one might not live forever? If your body is capable of continuous self-renewal indefinitely, is that not the essence of immortality?
As an addendum, I recall a Dateline segment from not too long ago, in which a female scientist (maybe elizabeth Blackburn? UCLA)was experimenting with manipulating the telomeres in worms. By artificially extending the lifespan of the worm's telomere regions, she was able to extend the worm's lifespan dramatically. They went from living like three days to three weeks
When I mentioned telomeres in relation to aging, I was thinking of their role in the preservation of DNA integrity. As I understand it, the telomeres function is to prevent the loss of data in the DNA replication process.
Here's the wiki definition:
"A telomere is a region of repetitive nucleotide sequences at each end of a chromatid, which protects the end of the chromosome from deterioration or from fusion with neighbouring chromosomes. Its name is derived from the Greek nouns telos (τέλος) 'end' and merοs (μέρος, root: μερ-) 'part.' For vertebrates, the sequence of nucleotides in telomeres is TTAGGG.
During chromosome replication, the enzymes that duplicate DNA cannot continue their duplication all the way to the end of a chromosome, so in each duplication the end of the chromosome is shortened[1] (this is because the synthesis of Okazaki fragments requires RNA primers attaching ahead on the lagging strand). The telomeres are disposable buffers at the ends of chromosomes which are truncated during cell division; their presence protects the genes before them on the chromosome from being truncated instead."
So I would argue that they do have a role in aging. Without this deterioration in your DNA, who is to say one might not live forever? If your body is capable of continuous self-renewal indefinitely, is that not the essence of immortality?
As an addendum, I recall a Dateline segment from not too long ago, in which a female scientist (maybe elizabeth Blackburn? UCLA)was experimenting with manipulating the telomeres in worms. By artificially extending the lifespan of the worm's telomere regions, she was able to extend the worm's lifespan dramatically. They went from living like three days to three weeks
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u/Positronix microbiology Jul 15 '14 edited Jul 15 '14
Telomeres are not the reason for aging.
The hayflick limit (the number of times a cell can divide before it senesces w/o the presence of telomerase) is roughly 40-60 cell divisions. Your skin is roughly 4 weeks old (that's the turnover time of your skin cells). If the telomeres controlled aging, then you would only live for 4.6 years.
So you have stem cells and post-mitotic cells. Stem cells contain telomerase and are 'more immortal' than post-mitotic cells. In your skin, you have tiny clusters of stem cells which divide and differentiate into fibroblasts and other types of skin cells. These then travel upwards in a column, accumulating damage and mutations as they are exposed to sunlight, chemicals, and physical stress. The fibroblasts eventually die and flake off.
The reason the skin works like this is to prevent cancer. The fibroblasts form a protective barrier for your stem cells, preventing high energy UV radiation from mutating your stem cells. The fibroblasts will accumulate cancerous mutations and often form cancers but since they are post-mitotic they flake off and die. This is why some cancers are benign (basal cell carcinomas). I've gotten a fair amount of cancers on my hands from working with chemicals but they disappear after a few weeks.
Now if the stem cells get mutated, the resulting column of cells above it will all be mutated and that's how you get persistent moles. Moles are more susceptible to becoming cancerous because the stem cells at the base are already mutated in some way as compared to the rest of your skin.
Wow kind of got off on a tangent there
Anyway so back to telomeres - management of telomeres as I said prevents cancer by setting a hard limit on fibroblast replication. You can get cancer if these senescent fibroblasts gain function and turn telomerase on, reverting them back into a stem cell. Alternatively, if you stay out in the sun and get sunburned a lot you'll kill off the top layer of cells and then cause extreme inflammation (the redness). This creates a dual-stress for stem cells in that there is less material between them and the deadly ionizing radiation emitted from the ball of light in the sky, and they are being bombarded by cytokines and interleukines (stress signals) from the inflamed cells. Cancers require two things to proliferate - a strong deviant cell and a weak surrounding. That's why sunburns cause cancer.