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
How does membrane proteins play a role in permeability of the membrane? For which type of molecules is it the most important?
they can specifically transport substances in and out of the cell
Important for larger, polar
molecules and ions.
How does the lipid bilayer play a role in permeability of the membrane?
What two characteristics of the molecule will determine its ability to cross a phospholipid bilayer?
size and polarity
Predict whether amino acids and nucleotides will cross a phospholipid bilayer readily.
Generally polar and charged, so they don’t cross
How does glucose cross the cell’s plasma membrane?
Through facilitated diffusion, a type of passive transport with the help of transport proteins
Which uncharged polar molecule is the baseline to know if another one goes through the bilayer?
*if built in the same format
ex: steroids are bigger but pass through
What factors influence the fluidity of the lipid bilayer?
- Temperature
- Type of fatty acids in the phospholipids
A. chain length
B. degree of saturation - Cholesterol
What are two structural properties in fatty acids that give rise to different types of fatty acids?
A. chain length
B. degree of saturation
A membrane’s ____________ (directly through the phospholipid bilayer) is directly proportional to its fluidity.
permeability
What is the trend between the membrane temperature and fluidity?
What is the trend between the fatty acids saturation and fluidity? How come?
- Double bonds in the unsaturated fatty acids cause a “kink” (bend) in the chain.
- The kinks prevent the close packing of hydrocarbon tail and reducing hydrophobic interactions between phospholipids.
- The lipid bilayer is more fluid when these unsaturated fatty acids are present.
What is the trend between the fatty acids hydrocarbons tail length and fluidity?
Why is cholesterol considered as a fluidity buffer when it comes to rigidity?
- Overall, as cholesterol concentration in the membrane increases, membrane fluidity decreases.
Cholesterol increases hydrophobic interactions within the membrane and favors a more rigid structure.
Why is cholesterol considered as a fluidity buffer when it comes to changes in temperature?
keeps fluidity in range to support the structure and activities of the cell.
- Behaves differently at each temperature extreme:
A. Warmer -> Decreases fluidity and prevents membranes from
falling apart.
B. Colder -> Increases fluidity to prevent membranes from solidifying.
Which organisms contain cholesterol in their cell membranes?
eukaryotes, especially animals
What is ECM?
Extra cellular matrix
What does the amount and composition of the ECM depend on?
the cell and tissue type
What are the functions of the ECM?
A. Support and protection of
cells.
B. Makes strong structures for the body (e.g., bones)
C. Joins cells and organizes cells into tissues.
D. Communication between cells.
ECM connects to cells via ___________ and so connects indirectly to the cell’s ___________ .
membrane proteins
cytoskeleton
What are the components of the ECM structure?
In green: sugars
In purple: proteins
What are the most common components of ECM?
Fibers:
Gel:
How is this extracellular structure similar to the cell wall of a plant cell?
How do cells connect to make certain tissues in multicellular organisms?
- Neighboring cells can directly connect to each other to form certain tissues
*Specific connections made between specific membrane proteins (and the cytoskeleton).
What are the two specific types of junctions that form epithelial tissues?
A. Tight junctions (Occlusion junctions)
B. Desmosomes (Anchoring junctions)
What are epithelial tissues? What are the functions?
Epithelial tissues are characterized by tightly packed cells that form continuous sheets, covering the body surfaces, lining internal organs, and composing glands.
These tissues serve various functions, including protection, absorption, secretion, and sensation.
What is the difference between tight junctions and desmosomes?
In what type of tissues desmosomes the most important?
epithelia and muscle tissues
How do plant cells attach to each other?
via their cell walls
What are the three layers deposited by plants cells to attach together?
A. Primary cell wall
B. Secondary cell wall
C. Middle lamella
* Secondary cell wall mature in specialized cells and varies in composition.
Øe.g., lignin in wood
What are gap junctions versus plasmodesmata?
both are: junctions connecting the cytoplasms of cells and allow them to exchange substances and to communicate and coordinate processes in organs.
- Gap junctions: are channels (formed by proteins) that connect animal cells.
- Plasmodesmata: are channels (formed by breaks in the cell wall) that connect
plant cells.
What are leaflets?
the inside and outside faces of membranes
What are the inside leaflets of membranes called?
cytoplasmic leaflets
What are the outside leaflets of membranes called?
extracellular leaflets
By what is the plasma membrane built in eukaryotic cells?
endomembrane system
When is the asymmetrical distribution of lipids and proteins (and associated carbohydrates) in the plasma membrane determined?
when the membrane is built by the ER and Golgi apparatus.
How can membranes of many species adapt to specific environmental conditions?
*Variations in the lipid composition of the cell membranes
*Ability to change (acclimation) the lipid composition of the cell membranes in response to temperature changes has evolved as adaptations in organisms that live where temperatures vary in their habitat.
What does acclimation mean?
ability to change depending on climat
What membrane characteristics might you expect to see in the in the cells of fish that live in very cold water? In terms of: fatty acid saturation and fatty acid tail length?
Since unsaturated fats are more fluid but colder temperature decrease fluidity, they tend to have more unsaturated fatty acids
Shorter fatty acid tails are also more fluid and prevent the membranes to become overly rigid in cold temperatures (and stay functional and flexible)
Complete this table
