16: Plasma Membrane
- Page ID
- 38037
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Learning objectives
- Describe the structure and functions of cellular membranes.
- Describe the chemical components of cell membranes and review their chemical properties.
- Explain carbohydrate involvement in membrane structure, and their possible functions and location.
- Describe the types of proteins found in membranes and the roles they play in membrane function.
- Stress the importance of membrane fluidity to living cells and the mechanisms by which cells maintain an appropriate level of fluidity.
- Describe biological membrane asymmetry and the dynamic nature of membrane structure and function.
- Describe the different mechanisms employed by cells to transport materials across membranes: simple and facilitated diffusion, channel proteins, and active transport.
Plasma membranes must allow certain substances to enter and leave a cell, and prevent some harmful materials from entering and some essential materials from leaving. In other words, plasma membranes are selectively permeable — they allow some substances to pass through, but not others. If they were to lose this selectivity, the cell would no longer be able to sustain itself, and it would be destroyed. There are four major types of transport across the cell membrane:
- Diffusion,
- Diffusion through a channel,
- Facilitated diffusion (selective binding), and
- Active transport (requires ATP).
Thumbnail: Grey, Kindred, Chapter 16. 2021. CC BY-SA 3.0. Added Cell membrane detailed diagram blank by LadyofHats. Public domain. From Wikimedia Commons. Added ion channel by Léa Lortal. CC BY-SA 3.0. From Noun Project.