Since mid-1970s, the proton-centric proposal of ‘chemiosmosis’ became the acclaimed explanation for aerobic respiration. Recently, significant theoretical and experimental evidence were presented for ...an oxygen-centric ‘murburn’ mechanism of mitochondrial ATP-synthesis. Herein, we compare the predictive capabilities of the two models with respect to the available information on mitochondrial reaction chemistry and the membrane proteins' structure-function correlations. Next, fundamental queries are addressed on thermodynamics of mitochondrial oxidative phosphorylation (mOxPhos): (1) Can the energy of oxygen reduction be utilized for proton transport? (2) Is the trans-membrane proton differential harness-able as a potential energy capable of doing useful work? and (3) Whether the movement of miniscule amounts of mitochondrial protons could give rise to a potential of ~200 mV and if such an electrical energy could sponsor ATP-synthesis. Further, we explore critically if rotary ATPsynthase activity of Complex V can account for physiological ATP-turnovers. We also answer the question- “What is the role of protons in the oxygen-centric murburn scheme of aerobic respiration?” Finally, it is demonstrated that the murburn reaction model explains the fast kinetics, non-integral stoichiometry and high yield of mOxPhos. Strategies are charted to further demarcate the two explanations' relevance in the cellular physiology of aerobic respiration.
•Chemiosmotic & murburn explanations for aerobic respiration are compared.•Structure-function correlations of the two models are elucidated graphically.•Thermodynamics & reaction logic of both theories are critically assessed.•Kinetics & variable stoichiometry of aerobic respiration is tangibly explained.
Students’ attitudes towards science is a long-standing topic in science education. Among various sub-constructs of attitudes towards science, students’ motives for learning science and their ...self-efficacy in science learning may be the most frequently studied. Drawing from the expectancy-value theory (EVT), this study explored the extent to which the interaction between motives for learning science and self-efficacy in science learning can predict students’ behavioral tendency to learn science in the classroom. The subjects were 345 tenth graders in Hong Kong. The results of stepwise multiple regression analyses indicated that while there was a significant interaction effect between utilitarian motive for leaning science and self-efficacy in learning science in their impacts on students’ science learning, such effect was not found for intrinsic motive. Significant gender differences were revealed favoring boys in all four aspects covered in this study. The moderation of the levels of school on gender difference was found significant in students’ intrinsic motive and behavioral tendency to learn science in classroom. This study enriches both the theories about attitudes towards science and the EVT through revealing the value-specific feature of the expectancy × value interaction. It is necessary to consider the multiplicative effect emphasized in the EVT when teachers consider the strategies to influence students’ motives and self-efficacy so as to enhance students’ engagement into science learning.
F
1
F
o
ATP synthases produce most of the ATP in the cell. F-type ATP synthases have been investigated for more than 50 years, but a full understanding of their molecular mechanisms has become ...possible only with the recent structures of complete, functionally competent complexes determined by electron cryo-microscopy (cryo-EM). High-resolution cryo-EM structures offer a wealth of unexpected new insights. The catalytic F
1
head rotates with the central
γ
-subunit for the first part of each ATP-generating power stroke. Joint rotation is enabled by subunit
δ OSCP
acting as a flexible hinge between F
1
and the peripheral stalk. Subunit
a
conducts protons to and from the
c
-ring rotor through two conserved aqueous channels. The channels are separated by ∼6 Å in the hydrophobic core of F
o
, resulting in a strong local field that generates torque to drive rotary catalysis in F
1
. The structure of the chloroplast F
1
F
o
complex explains how ATPase activity is turned off at night by a redox switch. Structures of mitochondrial ATP synthase dimers indicate how they shape the inner membrane cristae. The new cryo-EM structures complete our picture of the ATP synthases and reveal the unique mechanism by which they transform an electrochemical membrane potential into biologically useful chemical energy.
Monoderm bacteria possess a cell envelope made of a cytoplasmic membrane and a cell wall, whereas diderm bacteria have and extra lipid layer, the outer membrane, covering the cell wall. Both cell ...types can also produce extracellular protective coats composed of polymeric substances like, for example, polysaccharidic capsules. Many of these structures form a tight physical barrier impenetrable by phage virus particles. Tailed phages evolved strategies/functions to overcome the different layers of the bacterial cell envelope, first to deliver the genetic material to the host cell cytoplasm for virus multiplication, and then to release the virion offspring at the end of the reproductive cycle. There is however a major difference between these two crucial steps of the phage infection cycle: virus entry cannot compromise cell viability, whereas effective virion progeny release requires host cell lysis. Here we present an overview of the viral structures, key protein players and mechanisms underlying phage DNA entry to bacteria, and then escape of the newly-formed virus particles from infected hosts. Understanding the biological context and mode of action of the phage-derived enzymes that compromise the bacterial cell envelope may provide valuable information for their application as antimicrobials.
The current review evaluates the status hypothesis, which states that that the desire for status is a fundamental motive. Status is defined as the respect, admiration, and voluntary deference ...individuals are afforded by others. It is distinct from related constructs such as power, financial success, and social belongingness. A review of diverse literatures lent support to the status hypothesis: People's subjective well-being, self-esteem, and mental and physical health appear to depend on the level of status they are accorded by others. People engage in a wide range of goal-directed activities to manage their status, aided by myriad cognitive, behavioral, and affective processes; for example, they vigilantly monitor the status dynamics in their social environment, strive to appear socially valuable, prefer and select social environments that offer them higher status, and react strongly when their status is threatened. The desire for status also does not appear to be a mere derivative of the need to belong, as some theorists have speculated. Finally, the importance of status was observed across individuals who differed in culture, gender, age, and personality, supporting the universality of the status motive. Therefore, taken as a whole, the relevant evidence suggests that the desire for status is indeed fundamental.
Respiratory complex I couples electron transfer between NADH and ubiquinone to proton translocation across an energy-transducing membrane to support the proton-motive force that drives ATP synthesis. ...The proton-pumping stoichiometry of complex I (i.e. the number of protons pumped for each two electrons transferred) underpins all mechanistic proposals. However, it remains controversial and has not been determined for any of the bacterial enzymes that are exploited as model systems for the mammalian enzyme. Here, we describe a simple method for determining the proton-pumping stoichiometry of complex I in inverted membrane vesicles under steady-state ADP-phosphorylating conditions. Our method exploits the rate of ATP synthesis, driven by oxidation of NADH or succinate with different sections of the respiratory chain engaged in catalysis as a proxy for the rate of proton translocation and determines the stoichiometry of complex I by reference to the known stoichiometries of complexes III and IV. Using vesicles prepared from mammalian mitochondria (from Bos taurus) and from the bacterium Paracoccus denitrificans, we show that four protons are pumped for every two electrons transferred in both cases. By confirming the four-proton stoichiometry for mammalian complex I and, for the first time, demonstrating the same value for a bacterial complex, we establish the utility of P. denitrificans complex I as a model system for the mammalian enzyme. P. denitrificans is the first system described in which mutagenesis in any complex I core subunit may be combined with quantitative proton-pumping measurements for mechanistic studies.
Implicit motive research has shown that implicit motives are important predictors of behavior and well-being. However, little is known about the interrelationship between the different implicit ...motives measures frequently applied. We aimed to shed light on the convergent validity of three implicit motive measures and wanted to test their assumed statistical independence from three explicit motive measures. Therefore, we administered the picture story exercise (PSE), the operant motive test (OMT), and the multi-motive grid in one and the same study. As explicit measures, we used the personality research form, the motive enactment test, and a goal questionnaire. We investigated the statistical overlaps between all these measures (sample: 202 undergraduate students) and found that the implicit motive measures showed either no or only little correlation with each other. Furthermore, they also partly correlated with explicit motive measures. Supplementary analyses showed that the lack of statistical overlap between PSE and OMT can partly be ascribed to their different scoring systems.
Given the prevalence of social media usage among consumers in China and the rise of social media endorsements, it is important to understand the effects of social media influencers and their product ...endorsements on consumers. The present study explores the effects of self-influencer congruence on brand attitude, brand engagement, and purchase intention in China's dynamic social media context. The perceived motive of social media influencer's endorsement behavior, parasocial identification with social media influencers, and their roles in the endorsement process were examined. The results of this study suggest that a high degree of congruence between the image of a social media influencer and the consumer's ideal self-image leads to effective endorsement outcomes. Parasocial identification was found to mediate the relationship between self-influencer congruence and endorsement outcomes while perceived endorser motive was found to moderate the effects of self-influencer congruence on such outcomes through parasocial identification.
As inhabitants of soda lakes,
are halo- and alkaliphilic bacteria that have previously been shown to respire with the first demonstrated Na
-translocating cytochrome-
oxidase (CO). The enzyme ...generates a sodium-motive force (Δ
) as high as -270 mV across the bacterial plasma membrane. However, in these bacteria, operation of the possible Δ
consumers has not been proven. We obtained motile cells and used them to study the supposed Na
energetic cycle in these bacteria. The resulting motility was activated in the presence of the protonophore 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), in line with the same effect on cell respiration, and was fully blocked by amiloride-an inhibitor of Na
-motive flagella. In immotile starving bacteria, ascorbate triggered CO-mediated respiration and motility, both showing the same dependence on sodium concentration. We concluded that, in
, Na
-translocating CO and Na
-motive flagella operate in the Na
energetic cycle mode. Our research may shed light on the energetic reason for how these bacteria are confined to a narrow chemocline zone and thrive in the extreme conditions of soda lakes.
PDF
