Evolution of the first cells

evolution of the first cell in the prebiotic soup...why not???
 

Read this wiki about evolution of the first cells.  We have discussed the origin of the first cells.  We have seen that amino acids can be made from small molecules infused into a pre-biotic pond from an early reducing atmosphere.  We have noted that phospholipids can self assemble into certain kinds of membranes when they are place in water.  It may be possible for nucleotides to also self assemble given some kind of template.  A recent report shows that the smallest bacteria only requires 182 proteins. (In comparison how many proteins do animals and plants have?)

Given all of this what would the first cell look like? What are some of the most basic functions it would need?  Describe what you would think the first cell would look like in a purely evolution scenario.  Also what would it have to be protected from? Could a cell evolve given what we know about cells today? 

Due March 18

Membranes and the microbial cockatrice

We are discussing the four organic classes of molecules in class which play important roles in the structure and function of cells. We will soon be talking about membranes of cells and the phospholipids and proteins which are parts of cell membranes.


Phospholipids are amazing molecules. Place them in a watery environment and they self associate into a spherical ball and make membranes. Membranes made of phospholipids are fluid structures which are sticky to themselves, so that they make a barrier which typically defines, in part, the outer boundary of a cell and helps hold things in the cell, yet it remains a fluid. Life would not work without these fluid barriers. Who would of thought of that? What a perfect idea for a membrane, a fluid barrier! We would be very stiff creations indeed if our membranes were not made out of these soapy molecules.


So we see in membranes the same principle we discussed regarding the idea that all macro-organisms are made of smaller pieces or entities we call cells, i.e., membranes are made of lots of smaller parts (phospholipids). Relatedly, we also see modularity, i.e., the parts are somewhat interchangeable and pliable. And this modularity and pliability allows for a lot of things to be stuck in membranes.


But, if phospholipids are sticky (self associate because of hydrophobicity) why don't all cells near one another, stick together and form one big clump....for instance when we bump into each other why don't we form one big glumpy smear of phospholipid humanity on the earth. How do pond organisms swim around with these sticky membranes and not get stuck or fuse together?


In fact this is the secret involved in how some viruses work, they invade cells by fusing their outer lipid membrane envelope with the cell membrane, and they take advantage of this sticky/hydrophobic effect. Works like a charm; the virus fuses to the membrane and releases its contents ( at least some viruses work this way, not all do).


Membranes play important roles in prokaryotic cells also. One prokaryote, the microbial cockatrice has unusual membranes. A cockatrice was a wild dish served at medieval banquets. It was a cooked dish of a rooster fused to a suckling pig. Archaebacteria, as suggested by some microbiologists, are a microbial version of the cockatrice, since they appear to have genomes composed of both prokaryotes and eukaryotes. 
 
However, what is even more interesting is the different kinds of lipids and structures which make up the outer membrane and walls of the archaebacteria. Some archaebacteria have monolayers rather than bilayers in their membranes. They also have different lipids suggesting that the biochemistry involved in making archaebacteria lipids is very different from both eukaryotes and prokaryotes. Their cell wall also contains something called an S-layer which is an intriguing structure. Even more fascinating the flagellum they display is constructed differently from the flagellum of eubacteria.


Questions to answer:


1 Why and how do phospholipids self associate?
2 What prevents membranes from fusing with all other nearby membranes?
3 Could the self assembly of phospholipids be a possible explanation for how the first cell membranes evolved?
4 When phospholipids form membranes in a water based environment, do they make membranes similar to the cell membranes we find in cells today?
5 Explore the structure of the archaebacterial monolayers. How does this contribute to life in the extreme?
6 What is an S-layer and how does it contribute to cell function?
7 We discussed the problems inherent in trying to assemble a flagellum from pieces secreted from the eubacterial cell. How is this problem solved in the archaebacterial flagellum? Or is it solved?

 

DUE MARCH 2