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51 Cards in this Set

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  • Back
Define plasma membrane:
The membrane separating cytoplasmic contents from the ECF
How thick is the lipid bilayer?
5 nm
Membrane-embedded proteins constitute how much of the membrane mass?
Most abundant type of lipid in PM:
e.g. phosphatidylethanolamine
What happens to lipids in an aqueous environment:
-in low concentration
-in high concentration
Low: lipids form monolayer w/ hydrophobic tails sticking up into the air.
High: lipids form bilayer w/ hydrophobic tails facing each other.
Important consequence of the forces that form the bilayer:
self healing
What determines the PM physical and biochemical properties?
Chemical structures of
How do phospholipid compositions of opposing bilayer leaflets compare?
What is the bilayer impermeable to?
-small and large, H2O-soluble CHARGED MOLECULES
-charged ATOMS
What are some H2O-soluble CHARGED MOLECULES?
-Nucleic acids
What are some charged atoms?
So what is the plasma membrane permeable to?
Water, gases (O2/CO2) and NH3
What does membrane fluidity depend on?
What types of movement can occur within the membrane?
1) Lateral
2) Rotational
3) FA tail flexion
Between the bilayer leaflets:
-What can flip easily?
-What can't flip easily?
Phospholipids stay on their leaflet.
Cholesterols flip easily
What is the function of having cholesterol in the PM?
It aids in stiffening the membrane.
What is the function of membrane fluidity?
For passage of lipophilic solute molecules through it.
What can pass through the lipid bilayer?
-Respiratory gases
-Neutral molecules
What is the 'TRANSITION TEMP'?
The minimum temperature for lateral diffusion within the leaflet.
What does "Transition" refer to?
Transion from the GEL to SOL state.
What factors determine the transition temp?
-FA chain length (directly)
-FA double bonds (inversely)
How will a high concentration of cholesterol in the membrane affect mobility?
It will decrease mobility b/c it stiffens the membrane.
2 main categories of membrane-associated proteins:
1. Peripherally associated
2. Integral
How are peripheral proteins associated with the PM?
Via noncovalent bonds to integral proteins in it.
How can peripheral proteins be removed from the PM?
Depends on how the protein is bound to the membrane:
-Ionic bonds: use high salt
-Hydrogen bonds: use low salt
What must be done to remove integral proteins from the bilayer?
Completely dissolve it with a detergent
In what ways can integral proteins be incorporated into the PM?
1. One transmembrane span
2. Multiple spans
3. Not completely span
4. Attach to FA or phospholipid
What is an important linkage between integral proteins and a phosphlipid?
GPI - glycosylphosphotidyl inositol linkage; breaking it with PLC produces IP3 and DAG which are important in calcium increase in muscles.
What are the important Structural Properties of MEMBRANE-SPANNING portions of transmembrane proteins?
1. Contains 20 sequential AA that are hydrophobic
2. That makes a 6-turn a-helix which across membrane.
Why can these 20 lipophilic, uncharged amino acids span the membrane so uniformly?
Because they are at their MOST STABLE ENERGY level when situated beside the nonpolar lipid tails of the bilayer.
When a transmembrane protein has multiple spans, how are they connected to each other?
Via hydroPHILIC chains looping out into ECF and ICF
Are membrane-spanning proteins capable of diffusion within the bilayer leaflet?
Yes - like lipids; but neither flip back and forth between leaflets.
3 Functions of Integral membrane proteins:
1. Ligand-binding receptors
2. Adhesion molecules
3. Pores/pumps/channels
What are classic examples of ligand-binding receptors?
-Hormone receptors
-NT receptors
-Pharmacologic receptors
What is the mechanism employed by ligand-binding receptors?
Transmembrane signal transduction
Sequence of steps in Transmemb signal transduction:
1. Ligand binds extracell domain of receptor
2. Conformational change in transmembrane domain
3. Conformational change in intracellular domain
What is the result of transmembrane signal transduction?
-Intracell domain becomes enzymatically active OR
-2nd msgr cascade activated
2 Types of integral proteins that are Adhesion molecules:
1. Cell-matrix adhesion molec.
2. Cell-cell adhesion molecule
What are cell matrix adhesion proteins called?
Integrins - form adhesion plaques
How do extracellular matrix signals make Integrins function? (sequence)
1. Conformation of integrin changes
2. Conformation of cytoplasmc tails changes
3. Intracell structure activated and signals stuff
4. Cell's internal environment changes
Give a functional example of Cell-matrix adhesion signalling:
Endothelial cells in arterioles - stimulate vasodilation to change blood pressure and flow.
Give a functional example of a Cell-Cell adhesion molecule:
-Guidance of axons in nervous system development
What is loss of cell-cell and cell-matrix adhesion a HALLMARK of?
Tumor cell metasthesis
Conduits for PASSIVE passage of H2O, ions, or proteins DOWN CONCENTRATION GRADIENT
Difference between Pores vs Channels:
Pores = always open, not gated

Channels = gated
Function of Carrier proteins:
Facilitated membrane transprt of specific molecules at a rate faster than simple diffusion
Definition of a Pump:
Protein that uses chemical energy to drive transport against an electrochemical gradient.
Structural design of transmembrane transporters:
-Transmembrane a-helices are amphipathic
-Hydrophilic faces together make lumen
Functional advantage of transport protein structures:
-Selectivity (by hydrophilic amino acids lining lumen)
Are all transport integral proteins just one protein?
NO - pores/channels can be composed of several contributing proteins/domains.
What is the structure of a potassium channel like?
4 subunits, each made up of 6 a-helices spanning the membrane.