2.1 Cell Membrane Structure Flashcards
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
The lipid bilayer is important because it creates a __ barrier that separates the cell’s internal environment from the external environment, enabling __ transport of materials and __ the cell’s internal conditions.
- semi-permeable
- selective
- maintaining
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 are the three models of plasma membrane? (3)
- Sandwich Model (Danielli-Davson Model)
- Unit Membrane Model (Robertson Model)
- Fluid Mosaic Model (Singer-Nicolson)
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)
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)
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 shows 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 (4)
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
“fluid” in the fluid-mosaic model: The plasma membrane has the consistency of __ at body temperature due to __. This allows phospholipids and proteins to move freely within the layer, like a liquid.
- olive oil
- unsaturated phospholipids
The “Mosaic” in the fluid-mosaic model refers to the collage of __ that form a varied pattern on the membrane. __ span the membrane with hydrophilic portions facing __ and hydrophobic portions facing __, creating a mosaic pattern when viewed from above.
- proteins
- Proteins
- outward
- inward
In the gel phase, at low temperatures, hydrocarbons in the plasma membrane are __, making the membrane more __ and less __.
- tightly packed
- rigid
- fluid
At higher temperatures, the plasma membrane transitions to a __, where the bilayer “__,” allowing __ movement of lipids and proteins within the membrane.
- fluid state
- melts
- increased
- The formation of a sphere minimizes the ________ and _________, which is energetically favorable.
- This reduction in surface area __ the system’s free energy, making the spherical shape more stable and energetically favorable.
- exposure of hydrophobic regions to water
- reduces the surface area of the bilayer
- lowers
What do planar lipid bilayers spontaneously form?
vesicles, which are spherical structures with a lipid bilayer surrounding an aqueous interior.
Small tears in membranes are repaired by the spontaneous formation of __ from __, which helps seal and restore the membrane’s integrity.
- vesicles
- planar lipid bilayers
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
Steps in the scheme to study membrane proteins (4)
1) Membrane fraction - isolate membranes from cells; contain protein of interest
2) solubilization - extract membrane protein from lipid bilayer using detergents
3) purification - purify membrane protein
4) reconstitution to liposomes - reinsert the purified protein to a liposome to study their function and interactions in a controlled lipid environment.
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.
Detergents
What type of movement is most frequent in membrane lipids and proteins?
Lateral Movement
What type of movement in membranes is rare?
Flip-Flop Movement: Phospholipids rarely switch from one layer to the other.
