p248 

Reconstitution of ribosomes

In the text, in vitro reconstitution was mentioned. As to  in vivo  reconstitution, a recent review is:

Keith Connolly and Gloria Culver, Deconstructing ribosome construction

Trends Bichem Sci.  34 256 (2009)

*The Nomura 30S subunit assembly map has survived nearly intact. 50S subunit assembly is not as well studied as its counterpart 30S.

*The in vitro analyses of subunit assembly suggest that rRNA falls victim to misfolding during assembly and that r-proteins might initially stabilize these conformations before rearrangement and appropriate folding. The isolation of cold-sensitive Escherichia coli strains suggests that improper folding of 16S rRNA can be detrimental to subunit biogenesis and cell growth.

*The maturation step is not understood well.

As to the 30S reconstitution in the test tube, the following review article is good:

Michael T. Sykes, James R. WilliamsonA Complex Assembly Landscape for the 30S Ribosomal Subunit

Ann Rev Biophys  38 197 (2009)

*Recent work using a combination of RNA footprinting and pulse-chase quantitative mass spectrometry paints a picture of small subunit assembly as a dynamic and varied landscape, with sequential and hierarchical RNA folding and protein binding events finally converging on complete subunits.

* The overall impression of 30S subunit assembly is that of a dynamic and fluid process. Proteins do not simply lock into place in a strict processive manner; they work their way into the network of RNA helices in a multiphasic manner. The 16S rRNA begins folding on its own but reacts and adapts to the influx of ribosomal proteins, adopting new local conformations around them and stabilizing others. There are many parallel folding and binding pathways, each of them proceeding simultaneously toward the final product of a complete 30S subunit.

Cell wall does not constitute itself spontaneity counterexample

The major classes of cellular membranes all grow by extension of an existing membrane.

 Polarity and membrane type are maintained during growth. Many membrane proteins are oriented wrt the membrane and catalyze vectorial reactions: this vector is not specified in the primary sequence, and is supplied by the cell [1]. Thus,  we may say that the membranes are a legacy as important as the genome that cells pass on to their offspring. These membranes, like DNA, appear to have been passed from one generation to the next since the dawn of cellular life. Even phospholipid bilayer membrane, which readily self-assemble in the test tube, rarely if ever do so in the living cell [2] .

[1]  That is, the inside and the outside of the cell is not in DNA. The sign of the curvature seems crucial. Cf. K S. Ramamurthi and R Losick, “Negative membrane curvature as a cue for subcellular localization of a bacterial protein,” Proc Natl Acad Sci  106 , 13541 (2009).

[2]  Eukaryotic phospholipid membrane formation : F. M. Harold, “Molecules into Cells: Specifying Spatial Architecture,”  Microbiol. Mol. Biol. Rev. 69 544 (2005): In the case of eubacteria, membrane phospholipids are produced by biosynthetic enzymes embedded in that membrane and incorporated  in situ . Eukaryotic cells generate phospholipids in the endoplasmic reticulum and initially incorporate them into those membranes. Membrane vesicles then bud off the endoplasmic reticulum, are processed in the Golgi apparatus and redistributed to other destinations such as the plasma membrane.

 Biology is so riddled with exceptions that a sweeping proclamation of the conservation of membranes naturally invites skepticism. Indeed, potential exceptions do crop up in the literature. The origin of yeast autophagosomes is not fully understood and may just possibly represent an instance of de novo membrane formation.

 It seems, however, that these are exceptions that probe the rule without overturning it:  the general rule is that membranes  grow by enlargement of an existing membrane.

Cell and self-organization

F. M. Harold, “Molecules into cells: specifying spatial architecture,” Mol. Microb. Rev.  69 , 544 (2005): “ Biological self-organization is real and important, but when it takes place in a living cell it is subject to constraint and control by the system as a whole. The only self that can truly be said to organize itself is the cell. ” (p547)