| Structure of cell-surface membrane | - Permeable layer
- Controls the entry and exit of materials
- Allows different conditions to be established inside + outside cell |
| Molecules that form the cell-surface membrane structure | - Phospholipids
- Glycolipids
- Proteins
- Glycoproteins
- Cholesterol |
| Phospholipids | - Hydrophilic heads, hydrophobic tails
- Arrange themselves into bilayer - heads face outwards to water
- Bilayer is hydrophobic - barrier against dissolved substances |
| Proteins | - Interspersed + imbedded in phospholipid bilayer |
| Function of protein in membranes | - Structural support
- Protein channels
- Active transport
- Form cell-receptors for identifying cells |
| Cholesterol | - Type of lipid
- In all cell membranes |
| How cholesterol maintains shape of animal cells | - Fit between phospholipids
- Bind to hydrophobic tails, packed more closely together
- Restricts movement of phospholipids, stabilizes membrane
- Especially in temperature fluctuations |
| Glycolipids | - Carbohydrate portion extends from the phospholipid bilayer
- Into watery environment outside cell |
| Function of glycolipids in membranes | - Acts as recognition sites
- Maintains stability
- Helps cells to attach to one another, form tissue |
| Glycoproteins | - Carbohydrate chains attach to many free proteins in cell membrane |
| Function of glycoproteins in membranes | - Acts as recognition sites
- Helps cells attach to one another, form tissues
- SELF ANTIGENS |
| Permeability of the cell-surface membrane | - Partially permeable, only some substances can pass through
- Substances move across membrane through diffusion, osmosis or AT
- There are membrane-bound organelles |
| Reasons some molecules cant diffuse across membrane | - Too large
- Not soluble in lipids, so cant pass phospholipid layer
- Charged molecules, difficult to pass through non-polar hydrophobic tails |
| Fluid-mosaic model of the cell-surface membrane | - Describe arrangement of molecules in the membrane |
| Fluid in model | - Individual phospholipid molecules can move relative to one another
- Flexible structure, constantly changing shape |
| Mosaic in model | - Proteins that are embedded in the phospholipid bilayer vary in shape, size and patterns
(like mosaics) |
