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Fluorescence probe data using 1,6-diphenyl-I ,3,5-hexatriene for various concentrations of intrinsic molecules (cholesterol, gramicidin A and cytochrome oxidase) within fluid lipid bilayers have been examined. The polarization value increases with increasing concentration of intrinsic molecule and then approaches a limiting value. Empirical curve-fitting of the experimental data, change of polarization with concentration, shows that each system can be fitted approximately by an exponential curve.A theory has been constructed based upon the assumption that only one intrinsic molecule need be adjacent to a fluorescent probe molecule to affect its motion drastically. The change in probe motion then depends upon the probability p of all positions next to a lipid chain being free of intrinsic molecules. The value of the probability p has been calculated and it is shown that p = (1 -x ) " where x = c or x = __ ~ depending on whether the intrinsic molecule spans the lipid bilayer or not. The approximation p = ePMx gives a good fit to the data for all x, thereby explaining the observed phenomenological fit.The fluorescent probe data is interpreted to show that protein-protein contacts increase as the intrinsic protein concentration increases within the lipid bilayer.An apparent dichotomy between the results from the fluorescence probe and from the deuterium magnetic resonance is explained in terms of a dominant affect on the probe being its hindrance to motion by interaction with the intrinsic molecule (protein) whilst individual C2Hz groups of the chain may exhibit greater disorder.The studies of protein-lipid interactions and cholesterollipid interactions are important for achieving a good basic understanding of biomembrane structure and function. The way in which the fluidity of the lipid bilayer matrix can be modulated by intrinsic molecules has been studied by variety of physical techniques including calorimetry and spectroscopic methods [l]. Some of these techniques involve the use of probe molecules and fluorescent probes have been developed for this purpose. Essentially, the probe molecule is considered to mimic a lipid molecular or lipid chain and then deductions are made concerning, for example, the change of lipid fluidity as the intrinsic protein (or cholesterol) concentration is increased. Some workers have interpreted probe data, particularly spin-probe studies of protein-lipid systems in terms of long-lived protein-lipid complexes where the lipid in the boundary region is rigid or ordered [2,3]. Recent deuterium magnetic resonance studies indicate that the intrinsic proteins (as distinct from cholesterol) disorder the lipid chains rather than increase their order and that rapid exchange of all lipids occurs [4,5]. There appears to be a dichotomy between the results obtained by some workers using spin-label data and the studies of deuterium magnetic resonance.In the present paper we discuss our studies of intrinsic molecules (cholesterol, gramicidin A and proteins) in fluid bilayers using the fluorescent p...

The resolution of minor amide components in the infrared spectra of membrane proteins has, in the past, been limited by the small differences in frequency compared to the large half-widths of the bands that are assigned to different secondary conformations. Here, second-derivative calculations are used to resolve the relatively weak bands that are associated with the beta-sheet conformation and the vibrations of some amino acid side chains in the infrared spectra of bacteriorhodopsin and Ca2+-activated adenosine-5'-triphosphatase (Ca2+-ATPase). The spectra presented indicate that bacteriorhodopsin in the purple membrane contains an appreciable amount of beta structure in addition to the predominant alpha II-helical structure. Both sarcoplasmic reticulum and purified Ca2+-ATPase in native lipids contain alpha-helical and random coil conformations together with a small amount of beta structure. In 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) Ca2+-ATPase adopts a secondary conformation similar to that in the sarcoplasmic reticulum, and this structure is unaffected by the phospholipid phase transition. A shift to a predominantly random coil conformation is associated with solubilization of both bacteriorhodopsin and Ca2+-ATPase in 20% Triton X-100. Second-derivative analysis of the carbonyl stretching vibrations of DMPC bilayers indicates that below the phase-transition temperature (Tm) both bacteriorhodopsin and Ca2+-ATPase perturb the interface region such that the sn-2 carbonyls adopt a conformation similar to the sn-1 carbonyls. Above Tm, these integral proteins have no effect on the static order of the interface region, and the conformational inequivalence of the sn-1 and sn-2 carbonyls is similar to that found in a pure lipid bilayer.

Multiple-choice question (MCQ) examinations are increasingly used as the assessment method of theoretical knowledge in large class-size modules in many life science degrees. MCQ-tests can be used to objectively measure factual knowledge, ability and high-level learning outcomes, but may also introduce gender bias in performance dependent on topic, instruction, scoring and difficulty. The ‘Single Answer’ (SA) test is often used in which students choose one correct answer, in which they are unable to demonstrate partial knowledge. Negatively marking eliminates the chance element of guessing but may be considered unfair. Elimination testing (ET) is an alternative form of MCQ, which discriminates between all levels of knowledge, while rewarding demonstration of partial knowledge. Comparisons of performance and gender bias in negatively marked SA and ET tests have not yet been performed in the life sciences. Our results show that life science students were significantly advantaged by answering the MCQ test in elimination format compared to single answer format under negative marking conditions by rewarding partial knowledge of topics. Importantly, we found no significant difference in performance between genders in either cohort for either MCQ test under negative marking conditions. Surveys showed that students generally preferred ET-style MCQ testing over SA-style testing. Students reported feeling more relaxed taking ET MCQ and more stressed when sitting SA tests, while disagreeing with being distracted by thinking about best tactics for scoring high. Students agreed ET testing improved their critical thinking skills. We conclude that appropriately-designed MCQ tests do not systematically discriminate between genders. We recommend careful consideration in choosing the type of MCQ test, and propose to apply negative scoring conditions to each test type to avoid the introduction of gender bias. The student experience could be improved through the incorporation of the elimination answering methods in MCQ tests via rewarding partial and full knowledge.