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Biomedical subjects

C J Proctor

Publications and source records attributed to C J Proctor.

8 recordsLinked to original sources
PubMed2007

Modelling the checkpoint response to telomere uncapping in budding yeast.

One of the DNA damage-response mechanisms in budding yeast is temporary cell-cycle arrest while DNA repair takes place. The DNA damage response requires the coordinated interaction between DNA repair and checkpoint pathways. Telomeres of budding yeast are capped by the Cdc13 complex. In the temperature-sensitive cdc13-1 strain, telomeres are unprotected over a specific temperature range leading to activation of the DNA damage response and subsequently cell-cycle arrest. Inactivation of cdc13-1 results in the generation of long regions of single-stranded DNA (ssDNA) and is affected by the activity of various checkpoint proteins and nucleases. This paper describes a mathematical model of how uncapped telomeres in budding yeast initiate the checkpoint pathway leading to cell-cycle arrest. The model was encoded in the Systems Biology Markup Language (SBML) and simulated using the stochastic simulation system Biology of Ageing e-Science Integration and Simulation (BASIS). Each simulation follows the time course of one mother cell keeping track of the number of cell divisions, the level of activity of each of the checkpoint proteins, the activity of nucleases and the amount of ssDNA generated. The model can be used to carry out a variety of in silico experiments in which different genes are knocked out and the results of simulation are compared to experimental data. Possible extensions to the model are also discussed.

Cell Cycle↗
PubMed2001

Modelling antipredator vigilance and flight response in group foragers when warning signals are ambiguous.

The trade-off between feeding and vigilance in flocks of birds has been extensively studied and modelled. An assumption of many models is that if one bird spots the predator, it gives a signal and the rest of the flock takes flight. However, it has been observed that birds do not always respond to signals and in fact many signals turn out to be false alarms. Since taking flight is both costly in time and energy, it may be advantageous for birds not to respond to all alarm calls. A model is developed to show under what circumstances birds should respond to a signal. The model predicts that under most, but not all, circumstances, birds should respond to multiple detections but not to single detections. The model also predicts that if birds respond to all flights, they will have to compensate for the time lost to feeding and the greater energy requirement of spending more time in flight, by being less vigilant, and they have a lower probability of survival than birds which only respond to multiple detections.

Animals↗
PubMed2000

A spatial model of antipredator vigilance.

Many species of animals have to perform two contradictory tasks: feeding, and avoiding becoming food for others. A large number of theoretical and empirical studies have investigated the trade-off between feeding and antipredator vigilance, especially in birds. An important factor which has been neglected in these studies is that of the area occupied by the flock. If individuals feed close together, competition increases and feeding rates decrease. However, if individuals space themselves widely, then vigilance efficiency goes down and there is an increased predation risk. We develop a vigilance model which allows birds to control the area the flock occupies as well as their vigilance rate. The optimal strategy is found for the birds under a variety of environmental conditions. In particular the effect of each environmental parameter on this optimum is considered in turn. How the model can be adapted for different bird species is also investigated.

Animals↗
PubMed1991

Comparison of the measurement of serum cotinine levels by gas chromatography and radioimmunoassay.

Standard cotinine solutions, controls and human serum samples containing cotinine have been measured by both radioimmunoassay (RIA) and gas chromatographic (GC) techniques. Cross-checks on standards and controls showed good agreement. However, for samples containing greater than 50 ng ml-1 of cotinine, RIA gave results on average 60% higher than GC. Determinations by using RIA and GC on samples containing less than 7 ng ml-1 of cotinine gave no significant correlation. The importance of the age of the serum sample has been investigated, and it is suggested that the age may affect the determination when dealing with low levels of cotinine.

Chromatography, Gas↗
PubMed1989

Considerations of the chemical complexity of ETS with regard to inhalation studies.

Any inhalation study that investigates environmental tobacco smoke, ETS, is considering a very complex entity. ETS contains numerous chemicals that are continuously changing both in their absolute concentration, in the ratio of concentration between one and another, and even in their particulate to vapour phase distribution. Moreover, when considering ETS in real-life situations, many of the chemical components of ETS will be present as a result of sources other than tobacco smoking. This paper emphasises that the chemical and physical nature of ETS must be considered in the design and interpretation of any inhalation study on ETS, and illustrates the difficulty in defining precisely what constitutes ETS in such studies.

Administration, Inhalation↗