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Structure and Function of Plasma Membranes

Structure and Function of Plasma Membranes

The ornate marble concourse of Grand Central Terminal, its tall arched windows and gilded moldings lit gold, a green ceiling painted with constellations overhead, and crowds of people moving across the floor below.
Despite its seeming hustle and bustle, Grand Central Station functions with a high level of organization: People and objects move from one location to another, they cross or are contained within certain boundaries, and they provide a constant flow as part of larger activity. Analogously, a plasma membrane’s functions involve movement within the cell and across boundaries' activities. (credit: modification of work by Randy Le’Moine)

The plasma membrane, the cell membrane, has many functions, but the most basic one is to define the cell’s borders and keep the cell functional. The plasma membrane is selectively permeable. This means that the membrane allows some materials to freely enter or leave the cell, while other materials cannot move freely, but require a specialized structure, and occasionally, even energy investment for crossing.

Sections

  • Components and Structure — the fluid mosaic model of the cell membrane, the roles of its phospholipids, proteins, and carbohydrates, and what makes a membrane fluid.
  • Passive Transport — why and how passive transport occurs, the processes of osmosis and diffusion, and tonicity’s role in passive transport.
  • Active Transport — how electrochemical gradients affect ions and the difference between primary and secondary active transport.
  • Bulk Transport — endocytosis — phagocytosis, pinocytosis, and receptor-mediated endocytosis — and the process of exocytosis.

This chapter is adapted from Biology 2e, Chapter 5: Structure and Function of Plasma Membranes by Mary Ann Clark, Jung Choi, Matthew Douglas, and OpenStax, © OpenStax, licensed under CC BY-NC-SA 4.0. Access the original for free at openstax.org. Each section page records its own changes from the source. Changes: the chapter-opening photograph is the source’s, re-encoded for the web with its credit kept in the caption and its alt text rewritten to describe the concourse rather than repeat the caption’s own description of its “hustle and bustle."

Connections between Cells and Cellular ActivitiesComponents and Structure