Biology Concepts – Apoptosis, synthaesthesia, mitochondria

Anthropomorphism is difficult thing to avoid. We are thinking beings, and we look at other organisms as if we were them – so we assign our thoughts to them. A typical example would be the belief that bacteria and viruses MEAN to do us harm, they have an evil intent when the infect us. It’s just not so……. except for athlete’s foot fungus. If you have had it before, you know that it means to make your life miserable.

It is especially difficult to avoid in biology, even scientists will say that an organism “decides” to do this or an enzyme interacts with a substrate “in order to” accomplish that – the enzyme doesn’t have an agenda, it is just chemistry and physics. Assigning feelings or motives to biological entities is often a way to help explain a concept. As long as everyone agrees that it is just a technique, I think it’s fine. The problem arises when not everyone understands that its just a verbal crutch and they start to internalize it.

In utero, your hands develop with individual fingers, but covered by tissue all over, then apoptosis divides them into individual fingers. The same thing happens with your toes…. Unless it doesn’t work as it should. If it doesn’t, you end up with syndactyly, or fused digits.

Then some of the skin cells between the digits began to die, and your fingers and toes started to become apparent. Sometimes the process doesn’t work completely, and people will have webs between their fingers or toes, or two digits will be fused together completely (syndactyly, syn = same and dactyl = digit). In the normal case, these skin cells are programmed to die. Why have the cell in the first place if it just going to die?

Necrosis is the cell death with inflammation and tissue destruction. This is what happens in frostbite. Can you imagine if you had this sort of reaction when undergoing apoptosis to make your individual fingers in utero?

Dying well means cell death without inflammation. In apoptosis, the mechanisms work to shrink the cell away from its neighbors but keeps the cell membrane intact for most of the time it is dying. This prevents the inflammatory response from being jump started.

This cartoon is a little detailed, but the take home message is that many insults can lead to mitochondrial damage (top arrows) and the damage can lead to several signals for cell suicide – apotposis (bottom arrows).

The extrinsic signals can cause the balance to shift toward mitochondrial leak of cytochrome c. This leads to apoptosome formation, and this activates caspases and other executioner protein enzymes that will start to destroy the cell from within. Some enzymes cut up the DNA into small pieces so that it is no longer functional. Others force the chromatin and nucleus to condense and shrink (become pyknotic) and stop making ribosomes. Some digest important proteins in the cytoplasm. The sum total of their actions is a non-functional cell, but one that is still intact. Over time, the shrunken and dying cell is recognized by macrophages or other cells that quietly break it up and digest it, all without causing any inflammation.

It is unfortunate that there aren’t very descriptive pictures that could show what it is like to have synthaesthesia – sure you can show a colored word or set  of letters, but you don’t get the idea of what it is to see it in your head when your hear a letter or word. This chart shows a little of how the senses can be combine, each combination has a name, but I like how Dr. Hugo Heyrman sums it up – Synesthesia is a love story between the senses.

But this is not the only use of apoptosis in the brain. You have heard the expression, “use it or lose it?” This applies to your brain as well. Neural connections in the brain that are stimulated by experiences or thoughts get reinforced, and are less likely to undergo programmed cell death. Those connections that are not used when young are not kept; it would be a waste of energy.

Cancer is a loss of cell cycle control, including the idea that cells are meant to die at an appropriate time. The problem is that there are many ways that a cell can circumvent the apoptosis signals, so you can’t induce apoptosis in all cancer cells by using just one medicine. Plus, how do you tell the cancer cells to undergo programmed cell death,  but tell the normal cells to stay alive?

So - too little apoptosis can be a bad thing. One other big example of this is cancer. Most cells have a life span, they should die at some point. But in some types of cancer, the mutations can tip the balance in the cell and mitochondria toward the survival end; they keep living and dividing and piling up; this is a tumor.