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Biomedical subjects

R Ramaswamy

Publications and source records attributed to R Ramaswamy.

42 records · Page 3Linked to original sources

Complex behaviour of the repressible operon.

The repressor-mediated repression process in bacteria is modelled using a gene-enzyme-endproduct control unit. A combined analytical-numerical study shows that the system, though stable normally, becomes unstable for super-repressing strains even at low values of the cooperativity of repression, provided demand for the endproduct saturates at large endproduct concentrations. In addition the system also shows bistability, i.e., the co-existence of a stable steady-state and a stable limit cycle. The tryptophan operon is used as a model system and the results are discussed in the light of differential regulation of gene expression in lower organisms, especially in mutant strains.

Gene Expression Regulation↗

On the dynamics of controlled metabolic network and cellular behaviour.

The existence of elaborate control mechanisms for the various biochemical processes inside and within living cells is responsible for the coherent behaviour observed in its spatio-temporal organisation. Stability and sensitivity are both necessary properties of living systems and these are achieved through negative and positive feedback loops as in other control systems. We have studied a three-step reaction scheme involving a negative and a positive feedback loop in the form of end-product inhibition and allosteric activation. The variety of behaviour exhibited by this system, under different conditions, includes steady state, simple limit cycle oscillations, complex oscillations and period bifurcations leading to random oscillations or chaos. The system also shows the existence of two distinct chaotic regimes under the variation of a single parameter. These results, in comparison with single biochemical control loops, show that new behaviours can be exhibited in a more complex network which are not seen in the single control loops. The results are discussed in the light of a diverse variety of cellular functions in normal and altered cells indicating the role of controlled metabolic network as the underlying basis for cellular behaviour.

Biological Evolution↗

Tuberculosis surveillance of community hospital employees. A recommended strategy.

OBJECTIVE AND METHODS: To suggest a cost-effective strategy with a high degree of surveillance for the transmission of tuberculosis infection to employees in community hospitals. We performed a cost-benefit analysis of tuberculin skin testing over a 4-year period. The setting was a community hospital in Bronx, NY. The subjects consisted of employees of the hospital who were categorized into high-risk employees defined as individuals who worked daily in patient care and low-risk employees defined as those not directly involved in patient care. All cases of tuberculin skin test conversion among employees were reviewed over a 4-year period. The departments involved, total number of employees, chest radiographic findings, and prophylaxis instituted were noted. RESULTS: The number of employees who were screened over the past 4 years consisted of 897 in 1990, 857 in 1991, 1357 in 1992, and 1316 in 1993. The mean annual conversion rate was 1%, 1.5%, 1.7%, and 1.4% for the 4 years, respectively. Skin test conversions according to job description revealed that of the total number of conversions 42% were from the nursing staff, 6.2% among the physicians and residents, and 52% among the ancillary staff. There was no difference in conversion between medical and nonmedical services such as the gynecology and surgical floors. CONCLUSION: Since tuberculin conversion rates of high-risk employees and those exposed to infectious tuberculosis cases have been low, we suggested a comprehensive strategy of 6-month tuberculin testing for high-risk employees and yearly testing for low-risk employees and eliminating boosting and repeated testing at 12 weeks in those exposed to infectious cases of tuberculosis.

Adult↗