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Biomedical subjects

D J Clark

Publications and source records attributed to D J Clark.

104 records · Page 6Linked to original sources
PubMed1972

Cell division of Escherichia coli BUG-6: effect of varying the temperature used as the nonpermissive growth condition.

When Escherichia coli BUG-6 is shifted from 30 C to 36 or 38 C, division does not stop, but the rate of division of the cell population is initially decreased followed by a period of increased rate of division before the rates characteristic of growth at 36 and 38 C are obtained. After a shift from 30 to 40 C, the rate of cell division gradually decreases over a 10-min period and then stops. The inhibition continues for 25 min, and then the cells divide rapidly before the division rate characteristic of 40 C is obtained. If filaments produced by 45 min of growth at 42 C are temporarily replaced at 30 C and then returned to 42 C, division occurs at 42 C. The amount of division is dependent on the length of the period at 30 C and can be decreased by a 3-min pulse of chloramphenicol immediately before the 42 to 30 C shift.

Cell Division↗
PubMed1971

Nucleoside triphosphate pools in synchronous cultures of Escherichia coli.

Endogenous nucleoside triphosphate pools in synchronized cultures of Escherichia coli B/r/1 oscillate as a function of age. Purine nucleoside triphosphates show a gradual 50% increase from zero age to the time of subsequent division, immediately prior to division. In contrast, pyrimidine nucleoside triphosphates undergo a dramatic change of about 50% in the first half of the generation at a time coincident with the termination of a round of deoxyribonucleic acid replication. A 50 to 70% increase starts at the initiation of the next round of deoxyribonucleic acid replication and continues until cell division, in parallel with the purine nucleotides. The fluctuation of pyrimidines between zero age and the middle of the division cycle suggests a functional relationship for pyrimidine metabolism and the regulation of cell division.

Adenosine Triphosphate↗
PubMed1970

Regulation of Cell Division in Escherichia coli: Characterization of Temperature-Sensitive Division Mutants.

A temperature-sensitive division mutant of Escherichia coli was isolated by using differential filtration to select for filaments at 42 C and normal cells at 30 C. Cells shifted from 30 to 42 C stop dividing almost immediately, suggesting the temperature-sensitive element is required for cell division late in the cell cycle. Cells returned to 30 from 42 C divide abruptly, suggesting accumulation of division potential at 42 C. Inhibitors of protein, deoxyribonucleic acid, and ribonucleic acid synthesis do not block division during the recovery period at 30 C. Cycloserine does not stop cell division, vancomycin shows some effect on cell division, whereas penicillin completely stops cell division during this period. The addition of high concentrations of NaCl to filaments at 42 C results in a burst of cell division. The final cell number is equivalent to the control which is grown at 30 C if sufficient salt is added (11 g/liter, final concentration). After the original burst, cell division ceases at the nonpermissive temperature even at increased osmolality. Chloramphenicol, puromycin, vancomycin, and penicillin prevent division during the recovery in the presence of NaCl. Kinetic data indicate division potential decays to a reversible inactive intermediate which rapidly decays to an irreversible inactive form. Conversion of division potential to the inactive form is correlated with a 100- to 1,000-fold derepression of the synthesis of division potential. The mutation appears to involve a stage in cross-wall synthesis which is required during the terminal stages of division.

Journal Article↗
PubMed1968

Effects of ionizing radiation on synchronous cultures of Escherichia coli B-r.

The sensitivity of Escherichia coli B/r to X-irradiation is correlated with the replication cycle of deoxyribonucleic acid (DNA). The sensitivity to X-irradiation in the wild type can be attributed to the presence of nuclear targets plus DNA repair mechanisms. The effects of nuclear targets are observed in the recombination-deficient (rec-) mutant B/r, but the sensitivity reflected by changes in the slope of killing curves is absent. A study of different growth conditions indicates that maximal resistance to X rays occurs toward the middle of the division cycle. Evidence is offered that branched chromosomes respond as one-hit targets to X-irradiation. The killing effects of heavy-ion bombardment on E. coli are due primarily to ionizing radiation.

Cell Division↗
PubMed1968

Regulation of deoxyribonucleic acid replication and cell division in Escherichia coli B-r.

Synchronous cultures of Escherichia coli strain B/r were used to investigate the relationship between deoxyribonucleic acid (DNA) replication and cell division. We have determined that terminal steps in division can proceed in the absence of DNA synthesis. Inhibition of DNA replication with nalidixic acid prior to the start of a new round of replication does not stop cell division, which indicates that the start of the round is not essential in triggering cell division. Inhibition of DNA replication at any time prior to the termination of a round of replication completely blocks cell division, which suggests that there may be a link between the end of the replication cycle and the commitment of the cell to divide. Studies that use a temperature-sensitive mutant which is unable to synthesize DNA at the nonpermissive temperature are in complete agreement with those that use nalidixic acid to inhibit DNA synthesis. This adds support to the idea that the treatments employed limit their action to DNA synthesis. Investigation of minicell production indicates that the production of minicells is blocked when DNA synthesis is inhibited with nalidixic acid. Although nuclear segregation is not required for cell division, DNA synthesis is still required to trigger division. The evidence presented suggests strongly that (i) DNA synthesis is essential for cell division, (ii) the end of a round of replication triggers cell division, and (iii) there is considerable time lapse (one-half generation) between the completion of a round of DNA replication and physical separation of the cells.

Carbon Isotopes↗
PubMedDate not supplied

A little learning.

Explore the source record for details and available documents.

Clinical Competence↗
PubMedDate not supplied

Primary care groups: nurses on the board.

This article describes what happened in one region of England where 59 nurses who had put themselves forward were short-listed for appointment to 12 primary care groups. It identifies the leadership and motivational factors of those nurses and takes a retrospective view of the selection processes involved in appointing nurses to PCG boards in the region.

Attitude of Health Personnel↗
PubMedDate not supplied

Primary health care records: an integrated approach.

The extended primary health care team is expected to achieve the government's vision of an integrated service for patients. Key to this vision is an integrated record-keeping system, integrating GP and community nursing functions.

Community Health Nursing↗
PubMedDate not supplied

How nurses can participate in the development of an ICNP.

The goals set for an International Classification for Nursing Practice cannot be achieved by technical means alone, nor by the consultants or ICN alone. They require the collaboration and commitment of many people in many organizations and many countries. Developing an ICNP must be a truly participative process. The greater the contribution from nurses in all countries and in all fields of practice, the more confident we can be that an ICNP truly represents nursing practice and that it is a useful tool for its purposes.

Humans↗
PubMedDate not supplied

Course redesign. Incorporating an Internet web site into an existing nursing class.

The representation of nurses and the discipline of nursing on the Internet is a growing and important contribution to the profession. Nursing students must be prepared for the impact technology will have on their careers. Nursing faculties can assist in the preparation of students for the role technology plays by creatively introducing computers and the Internet into the curriculum. An Internet web site was incorporated into an existing sophomore nursing course entitled "Nursing Issues: A Compendium." The course content defined the scope of the web site. The purpose of the web site was to provide a resource for further study and research into the professional issues facing nurses today. A web site evaluation tool assisted students in thinking critically about nursing resources available on the Internet. The students evaluated each web site they located for usefulness to nurses and nursing students. The benefits described by the students included learning how to use a computer, e-mail, and the Internet to locate professional information. The nursing students obtained a broader perspective of the profession.

Computer Communication Networks↗