List 6 functions of the cell membrane
Define
Segregate (seems the same as define)
Connect
Protect
Identify
Control passageway
Explain how and why the composition of a cells membrane changes between organisms / cell type
Each plasma membrane has a specific set of lipids and other molecules that are associated with it. Each one of those molecules has a specific function somehow related to the cell or to the organism. Compositionally, bacteria have 75% protein v. 25% phosph
What types of molecules are able to cross lipid bilayers, polar or non-polar? Why?
Nonpolar. Because of the bilayer. They have hydrophilic heads which can interact with charged/polar molecules, but because of the hydrophobic nature of the middle of the bilayer, they are unable to cross.
Fluid Mosaic Model - Give 4 properties of the fluid mosaic model
Membrane is a bilayer
Contains proteins (different for inside v outside the cell)
Structural and functional asymmetry
Fluidity
Describe why proteins within a cell membrane may have different functions based on their location
Proteins that are more extracellular, or are located on the outside of the membrane will have functions specific for that area, which is a different environment than inside the cell. Internal proteins will be specific for internal functions. Etc.
Why is fluidity important for the cell membrane?
Fluidity means that the cell membrane can adapt to the molecules that are going in and out. If it were more rigid it would be unable to bring large molecules across and would break instead.
What makes the cell membrane fluid?
The types of interactions that occur between the lipids in the bilayer. Because the interactions across the membrane are NOT exceptionally strong interactions (like covalent linkages) there is "give", meaning that the van der waals interactions / hydropho
Why do different organisms have different membrane compositions?
Because each membrane has a unique function to play for that organism/cell. It's job is not simply to be a "fence", it has other roles to play which rely on specific molecular compositions in order to function properly.
Explain what drives a system to form mycells, or clumping of oils together in water. How?
Entropy drives the system. Increasing the surface area (dispursing the lipids) would be "favorable" in the sense that it increases the order of the system, however, that decreases entropy, which we know nature really doesn't do. Instead, what occurs is th
What 3 things to amphipatic lipids in water form?
How can you use this property as a tool?
Micelles, bilayers, vesicles.
A delivery tool
Is lipid distribution in a cell membrane symmetric or asymmetric?
asymetric
What is the role of phospatidylionsitols?
Role in signal transferring from a receptor to inner cellular components.
What is the the role of Phosphatidylserine?
When in the outer layer, plays a role in blood clotting of platelets. In other cells it marks the cell for destruction. (normally inside, moves outside)
true or false:
Cell membranes have a very strictly regulated function controlling the composition of the membrane
True.
One mistake could mark the cell for destruction or bring in an unwanted substance or send an improper signal etc.
What type of lipid category is mostly found in the outer layer?
Sphingolipids (although they are still 50/50 inside to outside ratio, they are the dominant outside)
What is an integral protein?
A covalently associated protein that spans the membrane
How would you remove an integral protein?
Detergents / organic solvents
What is a peripheral protein?
A non-covalently associated protein.
How would you remove a peripheral protein?
Change the pH / use a chelating agent
What is a chelating agent? What are two examples of them that could be used to remove a peripheral protein?
A molecule that can form multiple bonds to a single metal ion. Urea / carbonate
What is an Amphitropic protein?
A protein in cytosol that is associated with the membrane. Their localization is typically regulated.
True or false:
The localization of amphitropic proteins is not typically regulated.
False.
How can you use detergents / proteases to determine the localization of a protein?
I'm not sure on this answer
Based on what the proteases binding site / active site is, it would give you information about the protein if it is able to bind it. If it is able, then you know that somewhere on the native comforation there is something that
How do detergents remove integral proteins?
The hydrophobic domain of the protein becomes coated /surrounded by the detergent, enabling it to be removed from the bilayer.
True or false:
Integral membrane proteins are helixes
True
What kind of amino acid residues are typically found within the trans-membrane region of a protein? What are some of those AA's?
Hydrophobic amino acids:
Leu, Thr, Lle, Ala, Gly, Met, Val, ser, etc.
What would you use to remove an integral protein?
a. Detergent
b. Chelating agents / pH change
c. Biological regulation
A.
What would you use to remove a peripheral protein?
a. Detergent
b. Chelating agents / pH change
c. Biological regulation
B.
What would you use to remove a amphitropic protein?
a. Detergent
b. Chelating agents / pH change
c. Biological regulation
C.
What defines a type I integral membrane protein?
The protein begins on the outside of the cell (N terminus is outside)
What defines a type II integral membrane protein?
The protein beings inside the cell (N terminus inside)
What defines a type III integral membrane protein?
It is serpentine, crosses back and forth many times
What defines a type IV integral membrane protein?
Separate chains form a channel (usually) and/or is a receptor (usually)
What defines a type V integral membrane protein?
Lipid anchor
What defines a type VI integral membrane protein?
Lipid anchor + transmembrane region
A sequence of how many hydrophobic residues typically signify that the segment of the protein spans the membrane?
20
What percentage of all proteins are integral?
20-30%
What does a hydrophathy index tell you?
It shows the hydrophobicity of amino acids
What does a positive value on the hydrophobicity index tell you?
That those residues are hydrophobic, and therefore more likely to be transmembrane regions.
how many residues long is a beta barrel?
7-9 to span the membrane
Every 2nd residue for beta barrels and porins in hydrophobic. Why?
It is to form a channel, you want the hydrophobic portions to line up, and the hydrophobic portions to line up in the secondary structure to form a favorable channel for certain charged molecules. Hydrophobic for bilayer, hydrophilic for the molecules pas
Beta barrels are typically
A. Antiparallel
B. Parallel
A.
What would the hydropathy plot look like for a beta-barrel?
Rapid ups and downs. Every other molecule would be up
Alpha and beta structures are for what type of membrane protein?
Integral proteins
What are anchored proteins?
Covalently attached proteins with the help of a lipid anchor.
What are some examples of anchored proteins?
Sterols, long chain fatty acids, isoprenoids, GPI's
Where are fatty acid anchors usually located, on the outside or the inside of the membrane?
Inside
Where are GPI anchors usually located, outside or inside?
on the outer layer of the membrane.
What has the stronger association, integral proteins or anchored proteins?
Integral
What are the differences between integral and peripheral proteins?>
Integral = covalently attached; span membrane.
Peripheral = non-covalent
What two types of membrane proteins are covalently associated? Which two are not?
Cov = Integral + anchor
Non-Cov = Amphitropic, peripheral