Fluid mosaic membranes
Introduced| English | Meaning |
|---|---|
| cell surface membrane/sel ˈsɜːfɪs ˈmembreɪn/ | The selectively permeable membrane surrounding a cell, separating its contents from the external environment. |
| fluid mosaic model/ˈfluːɪd məˈseɪɪk ˈmɒdl/ | The model of the cell membrane as a fluid phospholipid bilayer with proteins scattered through it like tiles. |
| partially permeable/ˈpɑːʃəli ˈpɜːməbl/ | partially permeable |
| channel protein/ˈtʃænl ˈprəʊtiːn/ | A membrane protein forming a passage through which particular ions or molecules can move down their electrochemical gradient. |
| carrier protein/ˈkærɪə ˈprəʊtiːn/ | A membrane protein that binds a specific substance and changes shape to move it across the membrane. |
| cholesterol/kəˈlestərɒl/ | A lipid molecule that stiffens or stabilises the membrane and regulates its fluidity. |
| antigen/ˈæntɪdʒen/ | A molecule or molecular feature recognised by the immune system that can trigger a specific immune response. |
| ligand/ˈlɪɡænd/ | An ion or molecule that binds to another species at a specific site, such as a metal centre or a receptor. |
| receptor/rɪˈseptə/ | A cell or molecule that detects a stimulus or binds a specific signalling molecule to initiate a response. |
The cell membrane
- Every cell is wrapped in a cell surface membrane 细胞膜.
- We describe it with the fluid mosaic model 流动镶嵌模型.
- It is partially permeable 半透 — it lets some things through and blocks others.
The phospholipid bilayer
- The membrane is built from phospholipids: each has a hydrophilic head and two hydrophobic tails.
- With water on both sides, they line up in two layers — a bilayer — heads facing the water, tails hidden inside.
- This forms by itself because of those water-loving and water-fearing parts.
The fluid mosaic model of the cell surface membrane
In the phospholipid bilayer, the molecules arrange so that:
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Heads are attracted to the water on both sides; the tails hide in the middle, away from water.
Fluid and mosaic
- Fluid: the phospholipids slide past each other, so the membrane bends and moves.
- Mosaic: many proteins are dotted through it, like tiles in a picture.
| Part | Role |
|---|---|
| channel proteins 通道蛋白 | water-filled pores for ions |
| carrier proteins 载体蛋白 | carry specific molecules across |
| cholesterol 胆固醇 | controls fluidity and adds strength |
| glycolipids / glycoproteins | cell recognition; some are antigens 抗原 |
Red blood cells under a scanning electron microscope, each wrapped in a cell surface membrane.
Explore the cell membrane
Tap each part of the fluid mosaic model — the bilayer plus the proteins and other molecules dotted through it.
Why is the model called "fluid mosaic"?
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"Fluid" = the phospholipids move; "mosaic" = proteins scattered through the bilayer like tiles.
In the fluid mosaic model the phospholipids are locked in place and cannot move.
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"Fluid" means the opposite — the phospholipids slide past one another, so the membrane can bend and move.
The molecule that sits between the phospholipid tails to control membrane fluidity is ______.
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Cholesterol controls fluidity and stabilises the membrane.
Match each membrane component to its role.
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Channel = ion pore; carrier = specific transport; glycoprotein = recognition (some act as antigens); cholesterol = fluidity.
Cell signalling
- Cells talk to each other by cell signalling:
- a cell secretes a signal chemical — a ligand 配体 (e.g. a hormone).
- it travels (often in blood) to a target cell.
- it binds a receptor 受体 whose shape matches that ligand only — triggering a response inside the cell.
In cell signalling, a ligand causes a response because it:
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The ligand binds a specific receptor (matching shape) on the target cell, triggering a response inside.
You've got it
- fluid mosaic model: a fluid phospholipid bilayer (heads out, tails in) with proteins as a mosaic
- channel/carrier proteins transport; cholesterol controls fluidity; glycoproteins = recognition/antigens
- the membrane is partially permeable
- cell signalling: ligand → target cell → matching receptor → response