Membranes Structure Flashcards
What is a cell membrane?
A lipid bilayer in which protein are embedded found in all cells that separates the interior of the cells from the outside environment.
What does it mean for a membrane to be selective?
A membrane that allows specific, small molecules and ions to be imported and exported.
What is the role of the cellular membrane?
- Receiving information from the environment.
- Import and export of small molecules
- Capacity for movement and expansion
How does the membrane receive information from the environment?
The cellular membrane have receptor proteins in the plasma membrane that enable the cells to receive signals from the environment.
What does the cellular membrane have that enable the importing and exporting of small molecules?
Channels and Transporter
Why is it important that the cellular membrane have the capacity for movement?
It allow the cell to grow, change shape, and move.
What are the main components that make up the cell membrane?
Protein and Lipids
What components of lipids make up the cellular membrane?
Phospholipid, Glycolipids (lipid with a carb), sterol
What components of protein makes up the cellular membrane
Integral and Peripheral proteins
How does the lipid bilayer being amphipathic important if the bilayer were to be in an aqueous environment?
It helps the bilayer assemble in water. The hydrophilic heads face water on both surfaces of the bilayer, while the hydrophobic tails are shielded from the water within the bilayer interior. This is also the most energetically favorable way to assemble.
Why would a phospholipid bilayer want to eliminate its free edge, forming into a spherical vesicle?
The bilayer wants to eliminate its free edge to minimize water contact. This is more energetically favorable because it minimizes bonding with the water.
What is a liposome?
A liposome is a closed, spherical lipid bilayer, which forms an internal cavity capable of carrying aqueous solutions.
How can a phospholipid move within a lipid bilayer?
The phospholipid may flex, rotate, or laterally diffuse (move to another location laterally). However, phospholipids do not spontaneously from one monolayer to the other.
What is membrane fluidity?
Freedom of movement of protein and lipids within the cell membrane.
Why is membrane fluidity important?
- Enables protein to diffuse rapidly in the plane of the bilayer to interact with one another.
- Enable lipids and protein to diffuse from place of insertion to cite of function
- It ensures that membrane molecules are distributed evenly between daughter cells when a cell divides. (lipids are distributed equally)
- Adaptation to temperature change
What are the factors that affect membrane fluidity?
- Phospholipid composition
- inverse relationship between chain length and fluidity
- inverse relationship between saturation and fluidity - Sterol
- inverse relationship between the concentration of cholesterol and fluidity
cholesterol can increase fluidity if most fatty acids are saturated.
How does cholesterol make the bilayer more rigid?
With its short and rigid steroid ring structure, cholesterol can fill the spaces between neighboring phospholipid molecules left by the kinks in their unsaturated hydrocarbon tails. This makes the bilayer more rigid and less permeable.
Where does membrane synthesis begin?
Endoplasmic reticulum.
How does the newly made membrane get transported to the bilayer?
There are enzymes that deposit the newly made phospholipids exclusively in the cytosolic half of the bilayer.
If the newly made phospholipids are added only to the cytosolic side of the bilayer, would that make the bilayer unbalance? How do the bilayer deal with the unbalance?
Scramblase is a protein that removes randomly selected phospholipids from one half of the bilayer and insert them in the other.
Most cell membranes are asymmetric. But if membranes emerge from the ER with an evenly assorted set of phospholipids, where does this asymmetry arise?
It begins in the golgi apparatus. The golgi apparatus contains a protein called flippase. Flippase remove specific phospholipids from the side of the bilayer facing the exterior space and flip them into the monolayer that face the cytosol.
What does it mean for a cell membrane to be asymmetric?
One side of bilayer can be different from the other bilayer
How does the endoplasmic reticulum and the golgi apparatus work together?
The endoplasmic reticulum gives the golgi apparatus lipids and protein. The golgi apparatus used the lipids and protein to form vesicle to transport the membrane it also receives from the endoplasmic reticulum.
How does the membrane retain its orientation when transported to the cellular membrane?
It is transported in vesicles produced by the golgi apparatus.
