2a - Cell Membrane Structure Flashcards
What is the primary function of the cell membrane?
The cell membrane acts as a boundary for the cell.
How does the cell membrane control the cell’s internal environment?
By controlling what enters and leaves the cell.
What role does the cell membrane play in chemical regulation?
regulates the chemical composition of the cell.
The cell membrane maintains homeostasis by ____ the internal conditions of the cell.
Regulating
is flexible and allows a unicellular organism to move
cell membrane
Studies of the ___ __ __ plasma
membrane provided the first evidence that biological membranes consist of lipid bilayers.
red blood cell
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
- protein -> phospholipid bilayer -> protein
Sandwich model
Phospholipid has ___ head while the tails that face the interior of the cell membrane are ___
Hydrophilic
Hydrophobic
What was the main flaw in the Sandwich Model?
The Sandwich Model did not account for the fluidity of the membrane and the presence of integral proteins that span the lipid bilayer, which led to its replacement by the Fluid Mosaic Model.
-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
Phospholipid bilayer with proteins partially or fully imbedded, electron
micrographs of freeze-fractured membrane
Fluid Mosaic model
describes the structure of cell membranes as a flexible layer made of phospholipid bilayer with proteins embedded in it.
Fluid Mosaic model
Why is the model called “Fluid”?
because the phospholipid bilayer is flexible, allowing lipids and proteins to move laterally within the membrane.
What does the “Mosaic” part of the Fluid Mosaic Model refer to?
patchwork of proteins that are embedded in or attached to the lipid bilayer, resembling a mosaic.
In fluid Mosaic model it span the entire lipid bilayer and are involved in various functions such as transport, signaling, and maintaining the cell’s structure.
Integral proteins
In the Fluid Mosaic Model, it is interspersed within the phospholipid bilayer and helps to maintain membrane fluidity and stability
Cholesterol
- technique used to study the structure of cell membranes by freezing a cell and then fracturing it to reveal the internal organization of the membrane.
- reveals the distribution of proteins within the phospholipid bilayer, showing that proteins are embedded in the membrane rather than just lying on the surface
Freeze-fracture membrane
Steps of freeze-fracture membrane technique
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
In a cell membrane, lipids are organized in a flexible, fluid-like layer called a ___ ___ ___.
liquid crystalline lattice
This means that while the lipids are arranged in a structured way, they can still move around, much like ice cubes floating in a drink.
liquid crystalline lattice
Each membrane has a specific temperature at which it changes from being flexible (liquid crystalline) to becoming more solid (frozen crystalline gel).
Transition temperature
Formed when the temperature drops below this transition temperature, the membrane lipids become less fluid and more rigid
solid-like structure (frozen crystalline gel).
at normal temperatures, the membrane is (1) ___ and __, but as it gets colder, it becomes more (2) ___ and less ___.
(1) Flexible and fluid
(2) Rigid and less flexible
