2.1 Cell Membrane Structure Flashcards
What are the primary functions of the cell membrane?
The cell membrane acts as a boundary and gateway to the cell, controlling what enters and leaves the cell. It regulates the chemical composition of the cell and maintains homeostasis.
acts as a boundary and gateway to the cell, controlling what enters and leaves the cell. It regulates the chemical composition of the cell and maintains homeostasis.
cell membrane
Why is the lipid bilayer important for the function of the plasma membrane?
The lipid bilayer is important because it creates a semi-permeable barrier that separates the cell’s internal environment from the external environment, enabling selective transport of materials and maintaining the cell’s internal conditions.
What was a significant discovery from studies of the red blood cell plasma membrane?
first evidence that biological membranes consist of lipid bilayers.
creates a semi-permeable barrier that separates the cell’s internal environment from the external environment, enabling selective transport of materials and maintaining the cell’s internal conditions.
lipid bilayer
What role does the plasma membrane play in cellular communication?
The plasma membrane plays a crucial role in cellular communication by containing receptors that bind to signaling molecules, allowing cells to respond to changes in their environment and communicate with other cells.
What are the three models of plasma membrane?
- Sandwich Model (Danielli-Davson Model)
- Unit Membrane Model (Robertson Model)
- Fluid Mosaic Model (Singer-Nicolson)
What is the Sandwich Model of the plasma membrane, and who proposed it?
- proposed by Danielli and Davson
- describes the plasma membrane as consisting of two layers of globular proteins sandwiching a phospholipid layer in between, creating a channel for molecules to pass.
The plasma membrane model proposed by Danielli and Davson, describes the plasma membrane as consisting of two layers of globular proteins sandwiching a phospholipid layer in between, creating a channel for molecules to pass.
Sandwich model (Danielli-Davson model)
What are the main features of the Unit Membrane Model, and who developed it?
- developed by Robertson
- proposes that the plasma membrane has an outer layer of protein with a phospholipid bilayer in between. It suggested that all cell membranes had the same composition but did not explain how some molecules pass through or the role of proteins with nonpolar parts. This model was developed using transmission electron microscopy.
The plasma membrane model developed by Robertson, proposes that the plasma membrane has an outer layer of protein with a phospholipid bilayer in between. It suggested that all cell membranes had the same composition but did not explain how some molecules pass through or the role of proteins with nonpolar parts. This model was developed using transmission electron microscopy.
Unit membrane model (Roberston model)
What does the Fluid Mosaic Model propose about the structure of the plasma membrane, and who are the scientists behind it?
- proposed by Singer and Nicolson
- describes the plasma membrane as a phospholipid bilayer with proteins partially or fully embedded within it. This model is supported by electron micrographs of freeze-fractured membranes.
The plasma membrane model proposed by Singer and Nicolson, describes the plasma membrane as a phospholipid bilayer with proteins partially or fully embedded within it. This model is supported by electron micrographs of freeze-fractured membranes.
Fluid-Mosaic Model (Singer-Nicolson Model)
What limitation did the Unit Membrane Model have that was addressed by the Fluid Mosaic Model?
The Unit Membrane Model did not explain how some molecules passed through the membrane or the role of proteins with nonpolar regions. The Fluid Mosaic Model addressed these limitations by showing that proteins are embedded in a fluid bilayer and can move laterally within it, facilitating selective permeability.
What is the process used to observe the plasma membrane in detail? Enumerate the processes.
Freeze-Fraction Technique
1. Rapidly freeze the specimen.
2. Use a special knife to cut the membrane in half.
3. Apply a carbon + platinum coating to the surface.
4. Use a scanning electron microscope to view the surface.
(A carbon layer is first applied to ensure conductivity and prevent charging. The platinum layer is then deposited to enhance surface detail and contrast.)
Which membrane model is supported by electron micrographs?
Fluid-Mosaic Model
Why is the lipid composition of the plasma membrane important?
The lipid composition creates a barrier that repels water, preventing excessive water from entering the cell and causing it to burst.
What is the “Fluid” aspect of the Fluid-Mosaic Model?
The plasma membrane has the consistency of olive oil at body temperature due to unsaturated phospholipids. This allows phospholipids and proteins to move freely within the layer, like a liquid.
What does the “Mosaic” aspect of the Fluid-Mosaic Model refer to?
The “Mosaic” refers to the collage of proteins that form a varied pattern on the membrane. Proteins span the membrane with hydrophilic portions facing outward and hydrophobic portions facing inward, creating a mosaic pattern when viewed from above.
How do proteins arrange themselves in the Fluid-Mosaic Model?
Proteins span the plasma membrane with their hydrophilic portions facing the aqueous environments outside and inside the cell, while the hydrophobic portions face the interior of the membrane.
What happens to the plasma membrane in the gel phase at low temperatures?
In the gel phase, at low temperatures, hydrocarbons in the plasma membrane are tightly packed, making the membrane more rigid and less fluid.
How does the plasma membrane change at higher temperatures?
At higher temperatures, the plasma membrane transitions to a fluid state, where the bilayer “melts,” allowing increased movement of lipids and proteins within the membrane.
Why is the formation of a sphere energetically favorable for lipid bilayers?
- The formation of a sphere minimizes the exposure of hydrophobic regions to water and reduces the surface area of the bilayer, which is energetically favorable.
- This reduction in surface area lowers the system’s free energy, making the spherical shape more stable and energetically favorable.
What do planar lipid bilayers spontaneously form?
Planar lipid bilayers spontaneously form vesicles, which are spherical structures with a lipid bilayer surrounding an aqueous interior.
How are small tears in membranes repaired?
Small tears in membranes are repaired by the spontaneous formation of vesicles from planar lipid bilayers, which helps seal and restore the membrane’s integrity.
a gentler non-ionic detergent used as a solubilizing agent.
Triton X-100
it does not denature proteins as aggressively and is often used to solubilize membrane proteins while preserving their functional state.
Triton X-100
What is the first step in the scheme to study membrane proteins?
Solubilization: Membrane proteins are solubilized using detergents (Triton X-100 or SDS) that disrupt the lipid bilayer of the membrane, allowing the proteins to be extracted.
What is the purpose of using detergents in the study of membrane proteins?
Detergents disrupt the lipid bilayer of the membrane, which helps to solubilize the membrane proteins by breaking up the hydrophobic interactions that hold the membrane together.
What is the next step after solubilization of membrane proteins?
Purification: After solubilization, the proteins are purified to isolate the specific membrane protein of interest from other components.
What is the final step in the study of membrane proteins after purification?
Reconstitution in Liposomes: The purified membrane proteins are reconstituted into liposomes to study their function and interactions in a controlled lipid environment.
What type of movement is most frequent in membrane lipids and proteins?
Lateral Movement: Most lipids and some proteins drift laterally within their layer.
What type of movement in membranes is rare?
Flip-Flop Movement: Phospholipids rarely switch from one layer to the other.
What type of movement refers to the bending of hydrocarbon tails within the lipid bilayer?
Flexion: Refers to the bending of hydrocarbon tails within the lipid bilayer.
