Botswana1 children's understanding of biological inheritance

This paper reports the findings of an investigation which probed Batswana students' understanding of inheritance. A sample of students (aged 12 to 16+) responded to a pencil and paper questionnaire, which presented them with a variety of situations which they were asked to explain. Half of the sample were presented with English questions, and the other half with questions in Setswana (the vernacular language of the students). In both cases, they were asked to respond in the same language as the questions. Analysis of the responses revealed a variety of ‘alternative frameworks’, including a widespread belief in the inheritance of acquired characteristics. These are reported and discussed and their implications for teaching are explored. The language of the questions and responses and the gender of the students appeared to have little effect on the nature of the ideas revealed.     

Chromosomes: the missing link — young people's understanding of mitosis,meiosis, and fertilisation

This paper considers school students' understanding of the processes of cell division and fertilisation towards the end of their compulsory science education. The difficulties which students have in understanding the purposes and products of these processes are discussed, and the origins of some of these problems are identified. In particular, it notes the widespread lack of understanding of the physical link between chromosomes and genetic material, and the relationship between the behaviour of chromosomes at cell division and the continuity of genetic information - both within and between organisms. Key words: Cell division, Chromosomes, Genetic information, Students' understandings.     

Comparison of the efficacy of slide/tape and cine-loop as teaching aids for a microbiological technique

The efficacy of slide/tape and cine-loop presentations in teaching a simple manipulative skill in micro-biology were compared in a population of first-year undergraduate students in Life Sciences. No difference could be found between the two techniques. Students whose first language was not English were at a disadvantage in comparison with others even when language did not appear to be a component of the teaching technique.     

The role of the IOB in the future of biological education

The Teacher Assessment Scheme (TAS) is a form of school-based assessment that has recently replaced the external practical examination in AL Biology of Hong Kong. This study aimed at understanding the problems encountered by teachers in implementing this innovation. Over 300 teachers expressed their concern about different aspects of the TAS in a questionnaire of 25 items and two open-ended questions. The responses showed that the teachers were deeply concerned about the lack of resource materials and training, as well as the heavy workload involved in designing and assessing practical activities for their students. Other key concerns included the impact of the scheme on student learning, the fairness of school-based assessment, and the need for a critical review on the implementation of the scheme. However, the teachers had a relatively low level of concern on their role in revising or improving the scheme. This paper also considers whether the levels of concern in different areas might change as the teachers gain experience in TAS.     

The science education of biology teachers

A report of a conference discussion at Nottingham on the need for augmenting the scientific knowledge of trainee biology teachers in University Departments of Education. Statistics were gathered from a sample of 64 students as a basis for the discussion. These indicate the extent to which the students lack training in relevant scientific subjects and in particular biological topics.     

ATP and AMP Mutually Influence Their Interaction with the ATP-binding Cassette (ABC) Adenylate Kinase Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) at Separate Binding Sites

Cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel in the ATP-binding cassette (ABC) transporter protein family. In the presence of ATP and physiologically relevant concentrations of AMP, CFTR exhibits adenylate kinase activity (ATP + AMP ⇆ 2 ADP). Previous studies suggested that the interaction of nucleotide triphosphate with CFTR at ATP-binding site 2 is required for this activity. Two other ABC proteins, Rad50 and a structural maintenance of chromosome protein, also have adenylate kinase activity. All three ABC adenylate kinases bind and hydrolyze ATP in the absence of other nucleotides. However, little is known about how an ABC adenylate kinase interacts with ATP and AMP when both are present. Based on data from non-ABC adenylate kinases, we hypothesized that ATP and AMP mutually influence their interaction with CFTR at separate binding sites. We further hypothesized that only one of the two CFTR ATP-binding sites is involved in the adenylate kinase reaction. We found that 8-azidoadenosine 5′-triphosphate (8-N₃-ATP) and 8-azidoadenosine 5′-monophosphate (8-N₃-AMP) photolabeled separate sites in CFTR. Labeling of the AMP-binding site with 8-N₃-AMP required the presence of ATP. Conversely, AMP enhanced photolabeling with 8-N₃-ATP at ATP-binding site 2. The adenylate kinase active center probe P¹,P⁵-di(adenosine-5′) pentaphosphate interacted simultaneously with an AMP-binding site and ATP-binding site 2. These results show that ATP and AMP interact with separate binding sites but mutually influence their interaction with the ABC adenylate kinase CFTR. They further indicate that the active center of the adenylate kinase comprises ATP-binding site 2.     

Induction of alkaline phosphatase in cultured human fibroblasts: Comparison of normal cells and those from patients with cystic fibrosis

The membrane glycoprotein enzyme, alkaline phosphatase was induced in cultured human fibroblasts by dibutyryl cyclic AMP, sodium butyrate, the serum glycoprotein fetuin, the Tamm-Horsfall urinary glycoprotein, and by a number of inhibitors of DNA synthesis. The uninduced basal enzyme activity increased at later stages of growth when the cells became confluent. Induction by dibutyryl cyclic AMP or fetuin was most effective when the agents were added after the cells had reached stationary phase and was maximal after at least two days of exposure. The levels of induction resulting from the addition of pairs of the agents, dibutyryl cyclic AMP, n-butyrate and fetuin were additive indicating that these have different modes of action. The inhibitors of DNA synthesis, cytosine arabinoside, hydroxyurea, and methothrexate were less effective inducers. Bromodeoxyuridine which also has non-DNA mediated effects induced to the same extent as dibutyryl cyclic AMP.Similar experiments with sex- and age-matched cell strains derived from patients with cystic fibrosis failed to detect differences in the levels of induction from those observed in normal cells. In addition, the combined inductive effects of Tamm-Horsfall glycoprotein, isoproterenol and theophylline, were similar with normal and cystic fibrosis cells.     

An Exact Confidence Interval for the Ratio of Two Related Proportions

I propose an exact confidence interval for the ratio of two proportions when the proportions are not independent. One application is to estimate the population prevalence using a screening test with perfect specificity but imperfect sensitivity. The population prevalence is the ratio of the observed prevalence divided by the test's sensitivity. I describe a method to calculate exact confidence intervals for this problem and compare these results with approximate confidence intervals given previously.     

Model of the cAMP activation of chloride transport by CFTR channel and the mechanism of potentiators

Mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis, a hereditary lethal disease. CFTR is a chloride channel expressed in the apical membrane of epithelia. It is activated by cAMP dependent phosphorylation and gated by the binding of ATP. The impaired chloride transport of some types of cystic fibrosis mutations could be pharmacologically solved by the use of chemical compounds called potentiators. Here it is undertaken the construction of a model of the CFTR activation pathways, and the possible modification produced by a potentiator application. The model yields a novel mechanism for the potentiator action, describing the activatory and inhibitory activities on two different positions in the CFTR activation pathway.     

Customizing lipases for biocatalysis: a survey of chemical, physical and molecular biological approaches

Lipases (triacylglycerol ester hydrolases, EC 3.1.1.3) are ubiquitous enzymes that catalyze the breakdown of fats and oils with subsequent release of free fatty acids, diacylglycerols, monoglycerols and glycerol. Besides this, they are also efficient in various reactions such as esterification, transesterification and aminolysis in organic solvents. Therefore, those enzymes are nowadays extensively studied for their potential industrial applications. Examples in the literature are numerous concerning their use in different fields such as resolution of racemic mixtures, synthesis of new surfactants and pharmaceuticals, oils and fats bioconversion and detergency applications. However, the drawbacks of the extensive use of lipases (and biocatalysts in general) compared to classical chemical catalysts can be found in the relatively low stability of enzyme in their native state as well as their prohibitive cost. Consequently, there is a great interest in methods trying to develop competitive biocatalysts for industrial applications by improvement of their catalytic properties such as activity, stability (pH or temperature range) or recycling capacity. Such improvement can be carried out by chemical, physical or genetical modifications of the native enzyme. The present review will survey the different procedures that have been developed to enhance the properties of lipases. It will first focus on the physical modifications of the biocatalysts by adsorption on a carrier material, entrapment or microencapsulation. Chemical modifications and methods such as modification of amino acids residues, covalent coupling to a water-insoluble material, or formation of cross-linked lipase matrix, will also be reviewed. Finally, new and promising methods of lipases modifications by genetic engineering will be discussed.     

The effects of an inhibitor of Na+-K+-active transport on the secretory activity of rat submaxillary gland cell cultures

Summary The role of electrolyte transport in the metabolism of mucosubstance has been investigated using cell cultures derived from rat submaxillary gland. When added to the culture medium at a concentration of 1 mM, ouabain, an inhibitor of active alkali metal ion transport through cell membranes, causes extensive cytoplasmic vesiculation suggestive of an accumulation of secretory materials within the cell; the rough ER and cytoplasmic polysomes are not affected. Isotopic experiments support these conclusions by demonstrating that ouabain inhibits the secretion of radioactive mucosubstances by the cells; comparative studies with ouabain and puromycin (2×10^–4M) indicate that the inhibitory effect of ouabain is not due to an inhibition of protein biosynthesis. A relationship between secretion and alkali metal ion movement is suggested which may be of significance in connection with the genetic disease, cystic fibrosis.The generous support of the Cystic Fibrosis Research Trust made this work possible; the skilful assistance of Peter Crosby, Jacqueline Gibson and Christine Johnson is gratefully acknowledged.     

Cellular localization of cystic fibrosis transmembrane regulator protein in piglet and mouse intestine

Antibodies raised against the cystic fibrosis transmembrane regulator protein (CFTR) were used to localize CFTR in intestinal tissues of piglets and mice. Positive staining for CFTR was detected in goblet cells of both species. A second population of epithelial cells of unknown phenotype was also labeled by anti-CFTR antibodies. The labeling pattern was abolished by preincubation of anti-CFTR antibodies with the immunogen or when non-immune IgG was used in place of anti-CFTR antibodies. These results support other studies that suggest that alterations in goblet cell function may be involved in the intestinal abnormalities associated with cystic fibrosis. Received: 4 May 1995 / Accepted: 6 September 1995     

Building an understanding of cystic fibrosis on the foundation of ABC transporter structures

Cystic fibrosis (CF) is a fatal disease affecting the lungs and digestive system by impairment of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). While over 1000 mutations in CFTR have been associated with CF, the majority of cases are linked to the deletion of phenylalanine 508 (ΔF508). F508 is located in the first nucleotide binding domain (NBD1) of CFTR. This mutation is sufficient to impair the trafficking of CFTR to the plasma membrane and, thus, its function. As an ABC transporter, recent structural data from the family provide a framework on which to consider the effect of the ΔF508 mutation on CFTR. There are fifty-seven known structures of ABC transporters and domains thereof. Only six of these structures are of the intact transporters. In addition, modern bioinformatic tools provide a wealth of sequence and structural information on the family. We will review the structural information from the RCSB structure repository and sequence databases of the ABC transporters. The available structural information was used to construct a model for CFTR based on the ABC transporter homologue, Sav1866, and provide a context for understanding the molecular pathology of Cystic Fibrosis.     

Auxotrophy of Pseudomonas aeruginosa in cystic fibrosis

Seventy-four of 403 (18.4%) sputum isolates of Pseudomonas aeruginosa from 49 of 136 (36.0%) adults with cystic fibrosis (CF) were auxotrophic mutants. Two of 11 (18.2%) isolates of P. aeruginosa taken from patients with non-CF bronchiectasis were also auxotrophic. All 99 strains taken from non-bronchiectatic sources were prototrophic. Forty-six of 55 (83.6%) CF auxotrophs required one or more of 36 growth factors tested; the requirements for the remaining 9 isolates were not identified. Methionine was the sole factor required by 17 of 22 (77.3%) isolated which depended on a single factor. We conclude that auxotrophy is a feature of P. aeruginosa infection in cystic fibrosis.     

Hydrogenases for biological hydrogen production

Biological H₂ production offers distinctive advantages for environmental protection over existing physico-chemical methods. This study focuses specifically on hydrogenases, a class of enzymes that serves to effectively catalyze H₂ formation from protons or oxidation to protons. It reviews the classification schemes (i.e. [NiFe]-, [FeFe]-, and [Fe]-hydrogenases) and properties of these enzymes, which are essential to understand the mechanisms for H₂ production, the control of cell metabolism, and subsequent increases in H₂ production. There are five kinds of biological hydrogen production methods, categorized based upon the light energy requirement, and feedstock sources. The genetic engineering work on hydrogenase to enhance H₂ production is reviewed here. Further discussions in this study include nitrogenase, an enzyme that normally catalyzes the reduction of N₂ to ammonia but is also able to produce H₂ under photo-heterotrophic conditions, as well as other applicable fields of hydrogenase other than H₂ production.     

The CLIC1 Chloride Channel Is Regulated by the Cystic Fibrosis Transmembrane Conductance Regulator when Expressed in Xenopus Oocytes

CLIC proteins comprise a family of chloride channels whose physiological roles are uncertain. To gain further insight into possible means of CLIC1 channel activity regulation, this protein was expressed in Xenopus oocytes alone or in combination with the cystic fibrosis transmembrane conductance regulator (CFTR). Whole-cell currents were determined using two-electrode voltage-clamp methods. Expression of CLIC1 alone did not increase whole-cell conductance either at rest or in response to increased intracellular cyclic adenosine monophosphate (cAMP). However, expression of CLIC1 with CFTR led to increased cAMP-activated whole-cell currents compared to expression from the same amount of CFTR mRNA alone. IAA-94 is a drug known to inhibit CLIC family channels but not CFTR. In oocytes expressing both CLIC1 and CFTR, a fraction of the cAMP-activated whole-cell current was sensitive to IAA-94, whereas in oocytes expressing CFTR alone, the cAMP-stimulated current was resistant to the drug. Cell fractionation studies revealed that the presence of CFTR conferred cAMP-stimulated redistribution of a fraction of CLIC1 from a soluble to a membrane-associated form. We conclude that when expressed in Xenopus oocytes CFTR confers cAMP regulation to CLIC1 activity in the plasma membrane and that at least part of this regulation is due to recruitment of CLIC1 from the cytoplasm to the membrane.     

Influence of nutrient media on the chemical composition of the exopolysaccharide from mucoid and non-mucoid Pseudomonas aeruginosa

Two mucoid Pseudomonas aeruginosa strains and their non-mucoid revertants isolated from two different clinical origins (cystic fibrosis and bronchiectasis) were grown in various chemically defined media. The extracted exopolysaccharide was characterized by gas-liquid chromatography and 1H-NMR spectroscopy. The exopolysaccharide was always heterogeneous, with an alginate fraction and a neutral fraction essentially composed of glucose, galactose, rhamnose and hexosamines. The alginate composition (mannuronate/guluronate ratio and O-acetylation degree) changed according to the carbon source in nutrient media and whether the strains tested were responding differently to these environmental stimuli. In all cases, the best carbon source for the alginate production was glycerol: the two cystic fibrosis strains produced a predominantly O-acetylated alginate whereas only the mucoid bronchiectasis strain produced a polymannuronate exopolysaccharide.