Vesicles are the primary modes of communication and transport in cell biology. Conventional wisdom based on thermodynamic equilibrium says that vesicles should have a certain minimum size and size distribution dictated by their thermal fluctuations. However, there is compelling experimental evidence that vesicles exhibit a vast variety of size distributions depending on their formation process and function which cannot be explained by equilibrium statistical mechanics alone. We investigate a non-equilibrium statistical mechanics-based model to understand the role of active membranes on the size distribution of vesicles. Active membranes contain proteins that use external energy sources, such as adenosine triphosphate hydrolysis, and are known to exert forces on the membrane during their activity to carry out different biological functions. The central idea behind our model is that activity, attributed to different sources, impacts vesicle fluctuations in two opposing ways — by active noise which enhances fluctuations, and membrane tension which decreases fluctuations. The interplay of active fluctuations and active tension endows the vesicles with the ability to achieve size distributions that are deemed improbable by equilibrium statistical mechanics. We show that our model for active vesicles, based on linearized curvature elasticity, can reproduce different experimental data for vesicle size distributions available in the literature by varying the activity. Elucidating how these vesicles achieve such diverse size distributions can open avenues for a deeper understanding of physiological and pathological processes and help design vesicles for diagnostics and drug delivery applications.

中文翻译：

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活性囊泡的统计力学和尺寸分布悖论


囊泡是细胞生物学中通讯和运输的主要模式。基于热力学平衡的传统观点认为，囊泡应该具有一定的最小尺寸和由其热波动决定的尺寸分布。然而，有令人信服的实验证据表明，囊泡根据其形成过程和功能而表现出各种各样的尺寸分布，而这不能仅用平衡统计力学来解释。我们研究了基于非平衡统计力学的模型，以了解活性膜对囊泡尺寸分布的作用。活性膜含有利用外部能源（例如三磷酸腺苷水解）的蛋白质，并且已知在其活动期间对膜施加力以执行不同的生物功能。我们模型背后的中心思想是，不同来源的活动以两种相反的方式影响囊泡波动——主动噪声增强波动，膜张力减少波动。主动波动和主动张力的相互作用使囊泡能够实现平衡统计力学认为不可能的尺寸分布。我们表明，基于线性曲率弹性的活性囊泡模型可以通过改变活性来重现文献中可用的囊泡大小分布的不同实验数据。阐明这些囊泡如何实现如此多样化的尺寸分布可以为更深入地了解生理和病理过程开辟途径，并有助于设计用于诊断和药物输送应用的囊泡。