(I've gotten kind of technical, and I've tried to keep it short, so please do email me if you don't understand something, and I'll try to update the post to make it more readable.)
Updates posted on Oct 6 follow the original post.
Telomeres are what is known in the software design world as a "hack" - a quick and dirty fix to a bug or design flaw. To understand telomeres, you have to know a little about DNA and DNA replication. (I've attempted a terse explanation here, but there's always Wikipedia for a more thorough description.) A single strand of the DNA double helix consists of a string of nucleotides. These nucleotides contain the familiar A, C, G and T bases that are held by 5-carbon sugar rings, and the rings are connected by phosphate groups. These sugars are not symmetrical. They have an oxygen atom in one part of the ring, and a carbon atom sticking off the side. Biologists have labeled the carbons 1 - 5. The 3' carbon and the 5' carbon are the two that bond to the phosphate group, and to make a strand of DNA, you have to keep all the nucleotide lined up the same way: 3' - 5' - phosphate - 3' - 5' - phosphate and so on.
The problem is, the enzymes that assemble new DNA strands can only add nucleotides to the 3' end, not the 5' end. I'm not going to go into it here, but that causes an ugly little work-around called Okazaki fragments during the normal part of DNA replication. Where the real problem happens is at the ends of the DNA strand. You end up with a little bit that's too close to the end of the template to code on. If you could add to the 5' end, it wouldn't be a problem because you could work backwards from that end, but since you can only add to the 3' end, and you don't have the room to work there, you end up losing a little bit of your DNA every time it replicates.
The hideous hack we use to get around this is, whenever you make a gamete (sperm or egg) a special enzyme adds telomeres - non-coding nonsense DNA - to the ends of all of your chromosomes, so that as they fall off, it won't eat into your genes... until your cells have replicated for a bunch of years. When humans were only living into their 40s, this wasn't so much of a problem. Now, this might be one of the causes of aging. Your cells are losing their instruction manuals page by page, each time they divide.
There are two obvious fixes that an intelligent designer could have used. As previously mentioned, she could have engineered an enzyme that could add to the 5' end of the DNA. This would solve two problems and make your DNA replication much more efficient, both in time and energy consumption. The second fix is already used by bacteria. She could have stored the DNA in long rings, or just connected the ends during the final steps of replication. Bacteria store parts of their DNA in little rings, and those rings don't have the problem because they can build the last part of their DNA off the place where they started. I don't know how making a ring out of our DNA would affect chromosome storage, but you wouldn't have to keep it in a ring all the time. We have enzymes in our cells that cut DNA apart and paste it back together, so the rings could just be connected during the last parts of DNA replication. An intelligent designer would have been able to see these options and make the choice. Evolution blindly fumbled around for whatever worked, and we ended up with telomeres.
Update: Check out this short video of DNA replication:
On Oct 5, Nobel Prize for Physiology or Medicine was given to three scientists for their work finding telomeres and telomerase - the enzyme that creats them. From the press release
Elizabeth Blackburn and Jack Szostak discovered that a unique DNA sequence in the telomeres protects the chromosomes from degradation. Carol Greider and Elizabeth Blackburn identified telomerase, the enzyme that makes telomere DNA. These discoveries explained how the ends of the chromosomes are protected by the telomeres and that they are built by telomerase.And to complete this amazing coincidence of my writing this post and telomeres turning up in the international press, at least one prominent ID promoter has claimed telomeres as support for ID. In an article DLH posted on Uncommon Descent:
These telomeres can probably be shown to be essential to survival, and are likely to be irreducibly complex. If so, how can macro evolution explain the origin of this marvelous preservation feature that appears to be an Intelligent Design?Gonna do some research to show that they're irreducibly complex? Nope. Gonna do a little googling and find out that there are other, arguably better ways to solve the problem that telomeres fix? Nope. IDiot..
Go to Sandwalk for another explanation of what telomeres are, why we need them, etc. from a Professor of Biochemistry.