4.1.24 · Cell Membranes and Transport
Components of Cell Surface Membranes — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
5 min read 9 parts Lesson 4 of 20 Unit quiz
Lesson summary
4.1.2 Components of Cell Surface Membranes — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe the molecules in cell membranes and state the function of each.Lipids — phospholipids, cholesterol and glycolipids.Proteins — glycoproteins and other proteins such as…
- Similar structure
- Signalling
- At low temperature
- At high temperature
- Other roles
- Cell markers
Part 1 of 7Molecules present
Molecules present
Lipids
- Lipids phospholipids, cholesterol and glycolipids.
Proteins
- Proteins glycoproteins and other proteins such as transport proteins.
Similar structure
- Similar structure cell membranes of all organisms have a similar structure.
Part 2 of 7Phospholipids
Bilayer
- Bilayer hydrophobic tails point inwards and hydrophilic heads point outwards.
Movement
- Movement individual phospholipids diffuse within their own monolayer.
Barrier
- Barrier the non-polar core stops polar molecules and ions crossing, so sugars, amino acids and proteins cannot leak out.
Signalling
- Signalling phospholipids can be modified to activate enzymes or hydrolysed to release small water-soluble messengers.
Part 3 of 7Cholesterol
Location
- Location fits between phospholipids with the head out and tail in; found only in eukaryotic membranes.
At low temperature
- At low temperature it prevents tight packing, so membranes do not freeze and fracture.
At high temperature
- At high temperature it binds the tails and stops the membrane becoming too fluid.
Other roles
- Other roles it reduces permeability to ions and increases mechanical strength.
Part 4 of 7Glycolipids and glycoproteins
Location
- Location carbohydrate chains on the outer surface.
Receptors
- Receptors for hormones and neurotransmitters, endocytosis, and cell adhesion.
Cell markers
- Cell markers act as antigens for cell recognition, e.g. ABO blood group antigens.
Part 5 of 7Proteins
Intrinsic (integral)
- Intrinsic (integral) embedded in the bilayer; most are transmembrane proteins.
Extrinsic (peripheral)
- Extrinsic (peripheral) on the inner or outer surface.
Transport proteins
- Transport proteins channel (pore) and carrier proteins create hydrophilic routes for ions and polar molecules.
Specificity
- Specificity each transport protein carries a particular ion or molecule.
Rate control
- Rate control the number of transport proteins controls the rate of transport.
Part 6 of 7Factors changing fluidity
Less fluid
- Less fluid more saturated fatty acids and lower temperatures.
More fluid
- More fluid more unsaturated fatty acids and higher temperatures.
Part 7 of 7More from the specification
More from the specification
Fluid Mosaic Membrane Architecture
- The fluid mosaic model describes the basic structure of plasma membranes in cells as a dynamic phospholipid bilayer formed with hydrophobic fatty acid tails sequestered inside and hydrophilic phosphate heads facing aqueous environments, studded with diverse protein types.
Cell Recognition Receptors and Ligands
- Cell surface membranes contain carbohydrate-bearing molecules called glycoproteins and glycolipids that act as specific receptors for extracellular signalling molecules (ligands), facilitating cell-to-cell recognition and hormonal communication.
Selective Permeability and Transport
- The lipid bilayer and embedded transport proteins regulate the movement of substances entering and leaving cells,
- allowing non-polar molecules to diffuse freely while controlling hydrophilic ions and polar solutes via channel and carrier proteins.
Fluid Mosaic Membrane Architecture
- The fluid mosaic model describes the basic structure of plasma membranes in cells as a dynamic phospholipid bilayer formed with hydrophobic fatty acid tails sequestered inside and hydrophilic phosphate heads facing aqueous environments, studded with diverse protein types.
Cell Recognition Receptors and Ligands
- Cell surface membranes contain carbohydrate-bearing molecules called glycoproteins and glycolipids that act as specific receptors for extracellular signalling molecules (ligands), facilitating cell-to-cell recognition and hormonal communication.
Selective Permeability and Transport
- The lipid bilayer and embedded transport proteins regulate the movement of substances entering and leaving cells,
- allowing non-polar molecules to diffuse freely while controlling hydrophilic ions and polar solutes via channel and carrier proteins.
Ligand
- A signalling molecule that binds a specific receptor.
Key terms
| Term | Meaning |
|---|---|
| Cholesterol | A lipid that regulates membrane fluidity and stability. |
| Glycolipid | A lipid with carbohydrate chains attached. |
| Glycoprotein | A protein with carbohydrate chains attached. |
| Channel protein | A transport protein forming a hydrophilic pore. |
| Carrier protein | A transport protein that changes shape to move a molecule. |
| Transmembrane protein | A protein spanning the whole membrane. |
| Antigen | A cell surface marker used for recognition. |
Avoid these mistakes
1
Saying cholesterol is in prokaryotic membranes — it is only in eukaryotes.
2
Saying carbohydrate chains face the cytoplasm — they project outwards.
3
Saying transport proteins are non-specific — each is specific to a particular molecule.
4
Saying saturated tails increase fluidity — they reduce it.
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