5 Flashcards
Gateway to the Cell
CELL MEMBRANE
- Acts as a boundary
- Controls what enters and leaves cell
- Regulates chemical composition
- Maintains homeostasis
CELL MEMBRANE
The ________
is flexible and
allows a
unicellular
organism to
move
cell membrane
Studies of the red blood cell plasma
membrane provided the ________ that
biological membranes consist of lipid
bilayers.
first evidence
Plasma Membrane Models
- Sandwich Model (Danielli + Davson)
- Unit Membrane Model (Robertson)
- Fluid Mosaic Model (Singer + Nicolson)
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 (Danielli + Davson)
-Outer layer of protein with phospholipid bilayer inside,
-believed all cells same composition,
-does not explain how some molecules pass through or the use of
proteins with nonpolar parts
-used transmission electron microscopy
Unit Membrane Model ( Robertson)
Phospholipid bilayer with proteins partially or fully imbedded, electron
micrographs of freeze-fractured membrane
Fluid Mosaic Model
(Singer + Nicolson)
Which membrane model is correct?
Fluid-Mosaic Model
Basic paradigm of biological membrane structure
Fluid-Mosaic Model
According to the electron micrograph which membrane model is
correct?
1) Rapidly freeze specimen
2) Use special knife to cut membrane in half
3) Apply a carbon + platinum coating to the surface
4) Use scanning electron microscope to see the surface
The lipids in a membrane are organized into a
__________.
liquid crystalline lattice
The lattice becomes a _______ at
the transition temperature.
frozen crystalline gel
The Plasma Membrane is composed of two layers of lipids
Why is this important?
Having lipids in the plasma membrane means that at least a portion of
the membrane repels the water that constantly surrounds it. Allowing
too much water inside the cell could cause the cell to burst.
- plasma membrane has consistency of olive oil at body temperature,
due to unsaturated phospholipids.
-phospholipids and proteins move around freely within the layer, like it’s a
liquid.
Fluid
– proteins form a collage that differs on either side of membrane
and from cell to cell (greater than 50 types of proteins)
-proteins span the membrane with hydrophilic portions facing out and
hydrophobic portions facing in.
-mosaic pattern produced by scattered protein molecules when membrane
is viewed from above.
Mosaic
gel phase–low temperatures
hydrocarbons are tightly packed
at higher temperature
it moves to fluid phase
at higher temperature –> it moves to fluid phase
bilayer “melts”, movement is allowed
Formation of sphere is ________
energetically favorable
planar phospholipid bilayer with edges exposed to water
energetically unfavorable
sealed compartment formed by phospholipid bilayer
energetically favorable
Planar Lipid Bilayers
Spontaneously Form
________
Vesicles
Small tears in
membranes are
_______ this way.
repaired
