2a- Cell membrane structure Flashcards
Gateway to the Cell
* Acts as a boundary
* Controls what enters and leaves cell
* Regulates chemical composition
* Maintains homeostasis
Cell membrane
The cell membrane
is ____ and allows a
____ ____ to
move
- flexible
- unicellular organism
Biological membranes consist of
Lipid bilayers
Plasma membrane models
- Sandwich model
- Unit membrane
- Fluid Mosaic Model
Proposed sandwich model
Danielli + Davson
2 layers of globular proteins with phospholipid inside to make a layer and then join 2 layers together to make a channel for molecules to pass
Sandwich model
Outer layer of protein with phospholipid bilayer inside, -believed all cells same composition
Unit membrane model
Phospholipid bilayer with proteins partially or fully imbedded, electron micrographs of freeze fractured membran
Fluid Mosaic Model
The lipids in a membrane are organized into a
___ ___ ___
liquid crystalline lattice
The lattice becomes a ____ ____ gel at the transition temperature
frozen crystalline
Importance of two layers of lipids in plasma membrane?
at least a portion of
the membrane repels the water that constantly surrounds it. Too much water could burst the cell
plasma membrane has consistency of olive oil at body temperature, due to unsaturated phospholipids.
Fluid
proteins form a collage that differs on either side of membrane and from cell to cell (greater than 50 types of proteins)
Mosaic
Facing out
Hyrophilic portions
facing in
Hydrophobic portions
Low temperature
Gel phase, hydrocarbons are tightly packes
moves to fluid phase
At high temp., bilayer ‘melts’, movement is allowed
Types of phospholipids movement
- Flip-flop
- Lateral
- Flexion
- Rotation
