211 replies to this topic

[John Schloendorn]

Heh, Don :-) I think if you actually drop the "negligibly senescent" you end up with "mature", which hits the point quite well by itself, don't you think?

[DJS]

Well, the idea I was trying to go for was on going mental maturation, coupled with biological agelessness.

[psudoname]

How do organisms with no brain exibit stimulus-and-responce behaviour?

[randolfe]

I'm not so well versed in anatomy. However, organisms with no brain can exhibit stimulus-and-response behavior. A frog's leg that has been severed from the body and hung from a line of string will twitch when touched for several days.

Having seen that happen in High School biology classes, I've always suspected that cremation is not actually painless. Corpses sit up in fires and are ritually beaten down by relatives (in India) until their skulls explode.

Likewise, perhaps being cryonically suspended involves some sort of sensatory stimulation and/or awareness since the body's entire nervous system remains intact.

[DJS]

How do organisms with no brain exibit stimulus-and-responce behaviour?

hhhm, do you mean "running like a chicken with its head cut off"? I'll let a real scientist go for a more nuanced response, but common sense would dictate that certain aspects of coordination and reflexive response are/can be stored in areas of the central nervous system outside of the brain. This would make sense both in terms of optimizing response time and distributing work load.

I'm not sure if this is germane, but my favorite childhood plant, the Venus Flytrap also comes to mind.

[randolfe]

Don, your example of the chicken running around with its head cut off shows that actual organized activity (one foot in front of the other, etc.) can spring from some other center of the nervous system outside of the brain.

I think the Venus Flytrap example is more akin to the twitching of a frog's leg. Doesn't it automatically close even when it is your finger touching it?

[zoolander]

common sense would dictate that certain aspects of coordination and reflexive response are/can be stored in areas of the central nervous system outside of the brain

and indeed they do. Try to consciously inhibit the patella reflex. You can't. Unless you tighten your hamstrings before the hammer hits

[psudoname]

Ok, thanks for the responses, but I didn't phrase the question quite right. I meant how does an organism with no central nervious system at all exhibit stimulus-and-response behavior. I'm thinking more of single celled organisms (especially preaditors), but it also applied to plants I suppose.

Having seen that happen in High School biology classes, I've always suspected that cremation is not actually painless.  Corpses sit up in fires and are ritually beaten down by relatives (in India) until their skulls explode.

Likewise, perhaps being cryonically suspended involves some sort of sensatory stimulation and/or awareness since the body's entire nervous system remains intact.

*screams in terror*

I don't think this would apply in cryonics, as allthough the CNS is intact it's kinda frozen and not doing anything.

[John Schloendorn]

Why would one need a nervous system for stimulus-response behavior? Your car responds very well to the stimulus of turning the steering wheel, doesn't it?

[DJS]

psudoname

Ok, thanks for the responses, but I didn't phrase the question quite right. I meant how does an organism with no central nervious system at all exhibit stimulus-and-response behavior.  I'm thinking more of single celled organisms (especially preaditors), but it also applied to plants I suppose.

I had a feeling you were going for something different. As per my venus flytrap example, a CNS is not necessary for a cybernetic system to exist.

Cybernetics = The theoretical study of communication and control processes in biological, mechanical, and electronic systems, especially the comparison of these processes in biological and artificial systems.

These links may also be helpful:

en.wikipedia.org/wiki/Cybernetics

en.wikipedia.org/wiki/Feedback

and if mathematics is more to your taste...

en.wikipedia.org/wiki/Control_theory

[MichaelAnissimov]

Having seen that happen in High School biology classes, I've always suspected that cremation is not actually painless. Corpses sit up in fires and are ritually beaten down by relatives (in India) until their skulls explode.

It is painless, because they've already died. The "sitting up" motion is purely a mechanical response. It is not an electrochemically-modulated reflex as in a healthy nervous system. The frog response exists because (presumably) the nerve cells have not shriveled up and died yet.

[123456]

1. Do each of the Deoxyribonucleic Acid bases (Adenine, Thymine, Guanine, Cytosine) have the ability to give instructions by themselves without pairing up with their counterpart/equal?

2. Regardless of the pairs ("Adenine and Thymine" or "Guanine and Cytosine"); A particular pair can be associated to one precise instruction or perhaps it, the pair, is responsible for more than one instructions? Same question below, attempting to phrase better. A pair of one Adenine molecule and one Thymine molecule located at any given point on the chromosome; does it have multiple functions/instructions/characteristics?

[John Schloendorn]

123, I have no idea how to begin answering your questions. Can you try to be more specific? In particular, can you define what you mean by "functions/instructions/characteristics" or give a few examples?

[jmmathieu]

1. Do each of the Deoxyribonucleic Acid bases (Adenine, Thymine, Guanine, Cytosine) have the ability to give instructions by themselves without pairing up with their counterpart/equal?

2. Regardless of the pairs ("Adenine and Thymine" or "Guanine and Cytosine"); A particular pair can be associated to one precise instruction or perhaps it, the pair, is responsible for more than one instructions?  Same question below, attempting to phrase better.  A pair of one Adenine molecule and one Thymine molecule located at any given point on the chromosome; does it have multiple functions/instructions/characteristics?

I'll try to answer your question as best I understand it. First of all it's important to realize that only one strand is transcribed into mRNA, this is called the template strand and it forms complementary base pairs with the mRNA. The mRNA itself is single stranded. Each base pair by itself, however, is meaningless. Three base pairs are actually needed to code for each amino acid. Three base pairs together is called a codon. So when you speak of instructions you must realize that they are only given in codons, or triplets. An easy answer to your first question however is that there are single stranded DNA viruses.

Regarding your second question, there are many genes that overlap, meaning that some of the base pairs in a gene also encode an adjacent gene. Do a search for overlapping genes and you'll get lots of info. Also there may be a gene on one strand and another gene on the other strand, both coding for different proteins but each serving as the non-template strand for the other. Hope this helps.

[John Schloendorn]

Why do senescent cells secrete factors that can promote tissue damage, including the malignant transformation of neighboring cells? (e.g. here)

[John Schloendorn]

I agree, killing them sounds like it might be explicable. But Campisi there did not report killing, but rather making them malignant.

Yes, selective advantage, selection of something else that causes it, or basically anything that could help with rationalizing the phenomenon...?

[John Schloendorn]

But this is at odds with a common interpretation of why senescence exists in the first place. The idea is that if cells would apoptose, rather than senesce, neighboring cells would need to proliferate to fill the empty space -- and this proliferation could push them towards the evolution of cancer. So senescence seems to exist precisely to *prevent* the transformation of neighboring cells, and it is completely unclear why they would actively compensate for this by doing what Campisi reports here.

So if you are right, and the old explanation of senescence is wrong, then the question would become why does senescence exist in the first place, and why don't the damaged cells just apoptose and let normal healing mechanisms take care of it?

[maestro949]

New Question:

It seems that looking for genes that affect aging from a bottom up approach is one method being pursued. Why not generate an assay for a various cell types on a periodic basis over the lifetime of different species and then evaluate the genes being expressed at the different ages? It seems that large samplings across species and within species would identify the guilty parties. From there work downstream on the proteomics to find the pathways that are being disrupted by the varied gene expression later in life and focus on drug therapies for those. Are there limiting factors to this approach?

[John Schloendorn]

Maestro, I believe much research effort is indeed similar to what you say. If you are having human interventions in mind, then, as always with interventions supposed to slow aging, an almost prohibitive problem is the time in combination with sample size required to run clinical trials.

[maestro949]

Agreed. I had done some more reading on this and it turns out that there is good data on th subject. For humans 2.8% of genes are expressed differently between young and old individuals(1). That may appear to be a small percentage but still a fairly large number of genes. Understanding these differences seems fairly important to our cause (and numerous others for that matter). Are the changes in gene expression a result of aging (i.e. damage), or is aging a result of altered gene expression or more likely, is it a combination of both.

As one ages the affects of this cycle increases exponentially which is fairly consistent with the data. Would restoring some level of an elderly person's gene expression to that of a young person have a significant impact on longevity? Regarless which of the various theories of aging are correct it would seem the research emphasis on fixing the physiological damage that is structurally inhibiting proper expression and then finding the genes that modulate aging gene expression and then finding ways to regulate them would be the highest priorities. I'm just thinking aloud here so I'm probably just coming to the same conclusions that others who have been studying this stuff for awhile.


1. GEIGL, J.B., S. LANGER, S. BARWISCH, et al. 2004. Analysis of gene expression
patterns and chromosomal changes associated with aging. Cancer Res. 64: 8550–
8557.

[caston]

What are the different types of DNA synthesizers?

Is there (existing or in development) virtual and or biological dna synthesizers?

[Karomesis]

what benefit will be derived from this therapy http://www.cytoritx.com/about/ once it comes to market?

I ask in reguards to possible life extension and systems repair, not cosmetic.

[John Schloendorn]

What are the different types of DNA synthesizers?

There is only one de-novo procedure in industrial use, which is the phosphoamitide chemistry. If you want to synthesize DNA, the way to go is most likely to outsource it. You get custom gene synthesis at about $1 per base pair. "Biological" synthesizers (pcr, cloning) are much cheaper, faster and better, but more or less confined to replicate pre-existing sequences. Not sure what you mean by virtual.

[caston]

thanks John,

I had almost forgot about this question. By virtual I meant like a virtual PC. Ie you get some idea of how a dna synthesizer would work by using a simulated one on your PC.

[John Schloendorn]

Yes, pcr and cloning simulators exist, but the accuracy of the predictions is sometimes doubtful. For chemical synthesis, prediction would not make much sense because it's totally linear.

[maestro949]

I know that sperm banks freeze eggs but is it possible to keep other various cell types frozen or near frozen such that they are in some sort of stasis? After reading an article about cells having some memory mechanisms I suspect that it may be be beneficial (though costly) for individuals to take a biopsy of the various cell types and preserve these young versions for potential medical/rejuvenation use later in life. e.g. replacement of aged and damaged tissues. Regrowing organs from a single cell seems like it's will be within most young peoples' time horizon. I know that stem cells are what we are banking on but why not archive off known working cell versions in case SCs don't pan out as holy grail?

Edited by maestro949, 25 August 2006 - 10:00 PM.