the creation of life, the end of vitalism and Dr Venter’s Frankenstein cell

Last year, biologist Craig Venter created the first artificial cell.  Or did he?  Apparently he was able to manufacture a genome and stick it in a bacterial cell which had its DNA neutralized or removed.  Many news outlets claimed that he created the first synthetic life form. 

The creation of a living cell from scratch would be no small feat considering the billions of atoms and thousands of proteins, and hundreds of lipids and carbohydrates that would have to be put in the correct place.  If we used a cooking analogy, it would be like constructing a single cookie one speck of flour and one speck of sugar at a time….that would be some cookie and it would take a long time to get every single speck of flour, sugar, baking soda, salt all in the right place.

However, that is not what Venter did.  So did he really create the first synthetic life form?

One of the nations leading bioethicists, Arthur Kaplan has inferred that this is the end of the idea that life has a spiritual dimension or a “vitalism"; an idea that has persisted in philosophical biology for hundreds if not thousands of years.

1 How did Venter make his genome and insert it into the bacterium?    How did he remove the original DNA?

2 Did he create a living cell?  Share your view.

3 Is this the end of vitalism?

"stretchy pants" and hemidesmosomes

In the movie Nacho Libre',  Nacho is a wrestler (luchador) and likes to wear the "stretchy" pants the luchadors wear.  Living things made out of cells can be very firm like plant structures, but in animals,  cells are very stretchy and can participate in making structures like human skin and other tissues which are very malleable.  In our next topic in class we will discuss how eukaryotic tissue cells communicate with the outside world. Certain outside stimuli involving the extracellular matrix can promote shape change in cells and it can cause them to stretch and contort in ways that seem extreme.  Some cells must be stretched and shaped in order to form the shape of internal organs and for wound healing.  How do you stretch a cell and not break it?  Answer:  very carefully.


In a recent paper in Nature, a mechanism for stretching cells is proposed.  The mechanism centers around fascinating membrane protein complexes called hemidesmosomes.  Hemidesmosomes have been known for quite some time to be attachment structures which attach cells to other cells or the extracellular matrix.  Hemidesmosomes also attach to cytoskeleton components inside cells.  But new studies suggest that hemidesmosomes are also mechanosensors able to detect outside forces which squeeze and stretch cells. Hemidesmosomes communicate with intracellular cell signaling components such as kinases and other proteins.  Here again we have another case where a protein is involved in multiple functions.  The end result of the squeezing and stretching is elongated cells that contribute to the final shape of an internal organ for example during embryogenesis.


1 Review hemidesmosome structure and suggest a mechanism for how they could be involved in cell stretching? 


2 What would be the overal mechanism that would drive the cells to take on shapes which would contribute to the final morphology of an internal organ?


3 How do cells know how much force they can take before they rip apart?

Life on Mixotricha paradoxa

No, this is not a newly discovered planet but a flagellated Trichomonad found in the gut of the termite (Mastotermes darwiniensis). Paradoxa helps digest wood fiber in the gut of the termite. It appears that paradoxa moves by using its flagellum. But a closer inspection shows that the flagellum is perhaps only a steering device and the entire structure moves by the locomotion of hundreds of bacteria on the surface of paradoxa.
 
Thus we can document yet another function for the flagellum.  There are several kinds of bacteria on the surface of paradoxa and some are held in what appears to be specialized brackets on the surface of paradoxa.  Some of these bacteria contain their own flagellum and some of the bacteria are spirochetes.  The spirochetes are thought to provide the locomotion on the surface of paradoxa.  It would seem that a most efficient way for this organism to move would be to communicate with its surface motors when it wants to stop or start or go faster.

And there is good reason to want to move fast because Mixotricha paradoxa is hunted and eaten by other creatures lurking in the shadows.  Maybe this is a good reason to live in a  nice safe place like a termite gut.

Questions:

1 Spirochetes move by rotating.  How can a rotating twisting bacterium promote locomotion of paradoxa and yet stay attached to its host if its entire cell body rotates?

2 If paradoxa communicates with its motor bacteria, what form of communication would this be?