Living organisms do not just grow by synthesizing cellular components. As part of the necessary steps for existence, some components are degraded after synthesis. Even for bacteria in balanced, exponential growth some substances, under some conditions, are turned over. In other phases of growth turnover can be much more extensive, but it is still selective. This review covers studies with animals as a way to put the studies on microorganisms in perspective. The history, the mathematics, and experimental design of turnover experiments are reviewed. The important conclusion is that most of the proteins during balanced growth are very stable in bacteria, although ribosomal proteins are degraded under starvation conditions. Another generalization is that the process of wall enlargement in general is associated with obligatory turnover of the peptidoglycan.

Adenosine Triphosphate↗

PubMedDate not supplied

Primeval cells: possible energy-generating and cell-division mechanisms.

It is proposed that the first entity capable of adaptive Darwinian evolution consisted of a liposome vesicle formed of abiotically produced phospholipidlike molecules; a very few informational macromolecules; and some abiogenic, lipid-soluble, organic molecule serving as a symporter for phosphate and protons and as a means of high-energy-bond generation. The genetic material had functions that led to the production of phospholipidlike materials (leading to growth and division of the primitive cells) and of the carrier needed for energy transduction. It is suggested that the most primitive exploitable energy source was the donation of 2H+ + 2e- at the external face of the primitive cell. The electrons were transferred (by metal impurities) to internal sinks of organic material, thus creating, via a deficit, a protonmotive force that could drive both the active transport of phosphate and high-energy-bond formation. This model implies that proton translocation in a closed-membrane system preceded photochemical or electron transport mechanisms and that chemically transferable metabolic energy was needed at a much earlier stage in the development of life than has usually been assumed. It provides a plausible mechanism whereby cell division of the earliest protocells could have been a spontaneous process powered by the internal development of phospholipids. The stimulus for developing this evolutionary sequence was the realization that cellular life was essential if Darwinian "survival of the fittest" was to direct evolution toward adaptation to the external environment.

Adenosine Diphosphate↗

PubMedDate not supplied

Zonal turnover of cell poles of Bacillus subtilis.

Turnover of cell walls of Bacillus subtilis occurs in three distinct phases: a lag phase, a relatively rapid phase persisting for 2-3 generations and a much slower phase continuing for several additional generations. A lectin probe revealed that cell pole material was lost during the slow phase of turnover and that the loss of wall occurred in zones, beginning at the cylinder-pole junction and continuing to the cell tip. This is in contrast to cell wall turnover in cylinders where turnover occurs randomly at many surface sites.

Acetylglucosamine↗

PubMedDate not supplied

How does a Bacillus split its septum right down the middle?

This is a speculative paper which considers the possible ways that Gram-positive cells might employ to achieve an even thickness of the two daughter poles resulting from the fission of the cross-wall. The first is that the protonmotive force generated by the extrusion of protons at the cytoplasmic membrane acts to inhibit autolysins to a distance of about 25 nm. The second has to do with the stresses that develop as the poles form. On the tacit assumption that the autolysins will function faster when their substrates are under tension, it is shown how this, too, can lead to even bisection of the cross-wall. These possibilities are not alternative, both probably function.

Bacillus↗

PubMedDate not supplied

Orientation of the peptidoglycan chains in the sacculus of Escherichia coli.

The organization of chains of oligopeptidoglycan in the saccular wall is of critical importance in the study of the mechanism and physiology of prokaryotic wall growth. The electron microphotographs of De Pedro et al. present new findings and can be used to negate or at least raise questions about the previously accepted conclusion that the glycan chains are oriented transversely to the axis of rod-shaped Escherichia coli. This suggests caution in assuming that the glycan chains in the murein structure are parallel to each other and are perpendicular to the axis of the cell. These results should reopen the question of not only the orientation of the peptidoglycan chains, but the possibility of variability in orientation. Three classes of hypotheses about wall growth are reconsidered and problems with them are presented. The new results from De Pedro's laboratory and the experimental glycan chain length distribution argue against proposed systematic models. These include models that postulate belts or hoops stretched around the circumference of the cell and mechanisms that insert new chains of the length of presumptive "docking" strands in the stress-bearing wall. They are consistent, however, with the surface stress theory that proposes that random enzyme action together with physical forces are involved in the elongation of the rod-shaped Gram-negative wall.

Cell Wall↗

PubMedDate not supplied

The hospital-sponsored ambulatory dental services program, Part II: An evaluation of dental services.

This paper examines the appropriateness and continuity of dental care rendered by the 25 hospital facilities participating in the Hospital-Sponsored Ambulatory Dental Services Program, a $10 million effort established by the Robert Wood Johnson Foundation from 1979 to 1983. Record review data on 5,200 patients in 13 of the hospitals show that a substantially greater number of patients entered as episodic users of the system in the final phase of the evaluation than in the baseline visit; fewer of these episodic patients made the transition to initial care in the final phase. A followup study on baseline patients indicates that only 28% of the sample had a visit after the year of first contact. The trend toward episodic care is reflected in a reduced amount of preventive and operative services from baseline to final assessments. Compared with a study of private practices in California, the emphasis on surgery in the hospitals is dramatic: a dental patient accessing a hospital clinic will lose approximately one tooth as compared with a half tooth in private practice. Private practices also perform more crown and fixed partial denture services and more services across-the-board than the hospital clinics. Telephone interviews show that overall patient satisfaction with the hospital dental services remained high during the study (87% to 89%). Fewer patient in the final sample, however, planned to return to the hospital for all or part of their care. These findings reveal that continuity of care is a problem for hospital dental clinics. The preponderance of episodic care raises questions as to the breadth of experience offered by these hospitals to general practice residents.

Continuity of Patient Care↗