Lecture 8: The Plasma Membrane Flashcards
What are characteristics of the plasma membrane?
- Boundary of the cell.
- 10 nm width.
- Flexible, repairable, and expandable. (but will break if expended too much)
What are functions of the plasma membrane?
A. Provides compartment different from outside
B. Regulation of internal environment
C. Cell communication
D. Cell joining
How are these two arrangement of phospholipids called?
What is important that phospholipid bilayers can form?
water-filled compartments in water.
- The phospholipid bilayer can be punctured (separated) by a small needle and will reform.
- This is microinjection, a technique to inject a substance (e.g., DNA) into a single cell.
Injection micropipette
What is the other component as much present as phospholipids in plasma membrane?
membrane proteins
What are the classes of membrane proteins?
1) integral proteins: have domains embedded in the membrane
2) Peripheral proteins: associated with one surface of the membrane. Often interact with integral proteins.
What is a Transmembrane protein?
Specific type of integral protein that completely span a membrane, with segments facing out into both its interior and exterior surfaces.
True or false: proteins can be amphipathic. How come?
What are the four functions Types) of membrane proteins?
- Transport Proteins
- Cell Communication Proteins
- Enzymes
- Attachment proteins
What do transport proteins do?
Transport chemicals across the membrane
What do cell communication proteins do?
A. Act as cell identity markers.
B. Receive a signal and relay the message.
What do enzymes do?
Catalyze chemical reactions of a metabolic pathway.
What do attachment proteins do?
Attach cells to other cells or to the extracellular matrix (ECM) in tissues.
What does the fluid-mosaic model suggest?
that components of the membrane are free to move within the membrane and that some proteins are inserted into the phospholipid bilayer.
What does it mean when we say that the phospholipid bilayer is “fluid”?
- Individual phospholipids can rotate, move laterally throughout the lipid bilayer, and flip between layers.
- How quickly phospholipid molecules move within and across the bilayer is a measure of its fluidity.
The ________ of the phospholipid bilayer is directly proportional to its fluidity.
permeability
By tagging individual phospholipids and following their movement, researchers have clocked average speeds of how much?
2 μm / second.
What is the other model suggesting how membrane proteins are associated with the lipid layer other than fluid-mosaic model?
Sandwich model
How did we discover that the fluid-mosaic model is correct? (that proteins are embedded in the membrane). What would we have expect if the sandwich model was correct?
Freeze-fracture studies of the plasma membrane support the fluid mosaic model.
The “interior part” of the bilayer would be smooth rather than have complementary bumps and holes (proteins)
Do membrane proteins also move within the lipid bilayer?
if two cells with different membrane proteins are fused:
A. What would you expect if membrane proteins move?
B. Don’t move?
yes
A. hybrid with mixed proteins
B. Proteins would be locked in their domains and hybrid would look like half-half f the two types of proteins.
What is permeability of a structure?
its tendency to allow a given substance to pass across it.
What type of permeability do membranes have?
selective permeability.
* Allows a cell (or internal compartment) to have an internal environment different from the external environment.
What two components determine the permeability of a membrane?
membrane proteins and the lipid bilayer
