Week2 Plasma Membrane Module Flashcards
What are the four functions of the plasma membrane
- compartmentalize the cell 2. receives information 3. import/exports molecules 4. Enables movement and expansion of the cell
How does the lipid bilayer appear under an electron microsocpe?
Tri-laminar apearance (three layers)
What is the general structure of phospholipids?
2 hydrophobic FA tails connected to a glycerol molecule. The glycerol has an attached phosphate. The phosphate is attached to a variable group (choline, ehtanolamine, serine…)
What are the four major types of phospholipids found in the plasma membrane? What is the minor one (by mass)?
Posphatidyl-ethanolamine, phosphatidylserine, phosphatidylcholine, sphingomyelin (FAs connected to sphingosine instead of glycerol) Minor one is phosphatidylinositol
Phosphatidylserine, where is it found? Charge?
Negative charge found in inner monolayer of membrane
Where is phosphatidylcholine primarily found?
major lipid of outer monolayer of plasma membrane
where is Phosphatidylinositol found? charge? role?
inner leaflet, negative charge, important in cell signaling
Where is cholesterol found in the plasma membrane? Role?
Cholesterol is found evenly distributed throughout the plasma membrane especially between gaps created by cis-bonds in FA tails. Cholesterol is also a major component of lipid rafts. Role: stiffens membrane and makes it less permeable.
Glycolipids: what are they? where are they found in the PM? Fxn?
Lipids that contain sugar molecules. Found ONLY in the outer monolayer of the PM. play a role in recognition sites (responsible for A, B and O blood type)
How does the charge of the inner leaflet of the membrane compare to the charge of the outer leaflet of the PM membrane?
the inner leaflet is more negative due to the presence of net negative phospholipids (PI, PS)
What can diffuse through the PM? why?
Small hydrophobic molecules and small uncharged polar molecules can diffuse. This is because the PM is a hydrophobic barrier where only small non-charged molecules can pass.
Categorize the following molecules as diffusable through the PM or not diffusable: H+, Na+, amino acids, glucose, water, glycerol, CO2, O2
Diffusable: CO2, O2, water and glycerol (small uncharged polar) Not: H+, Na+ (ions), amino acids, glucose (large polar)
What are lipid rafts? Composition?
microdomains within the PM with specialized function. contain cholesterol and glycopsphingolipids
What are the four types (functional categories) of proteins within the PM?
Transporters, anchors, receptors, enzymes
What are the four types of associations proteins can have with the PM?
transmembrane, membrane associated, lipid-linked, protein attached
What are integral membrane proteins? what three types of association classify as integral? how do you isolate integral membrane proteins?
proteins that span or are covalently attached to the PM. Includes transmembrane proteins, membrane associated proteins, and lipid-linked proteins. Can only be isolated by disrupting membrane with a strong detergent.
What are peripheral membrane proteins? what type association classifies as peripheral? How can they be isolated
Proteins not directly attached to the PM (non-covalent association). Includes protein attached proteins.
Describe transmembrane proteins. what class of proteins do they belong to? what can be said about their phobicity?
type of integral membrane protein that spans the entire length of the membrane. amphipathic: hydrophobic residues reside in the membrane and hydrophilic residues reside outside the membrane.
Transmembrane proteins typically adopt what structure in the transmembrane region? why?
alpha-helix. this ensures that hydrophobic residues are facing the lipids and the hydrophilic polypeptide backbone is on the interior of the helix
What is a hydrophilic pore? how is it formed?
a hydrophilic channel through the PM. formed by multiple amphipathic alpha helices. Less commonly beta sheets can coil into cylinders (see in mitochondria)
Lipid-linked proteins: how are they attached to PM? Function? (3)
covalently bound to lipids in the membrane. This secures hydrophilic proteins to the PM. Functions in cell growth, differentiation, and morphology
What are 4 ways in which lateral diffusion within a membrane can be restricted?
- binding of membrane proteins to other proteins within the cell 2. binding of membrane proteins to ECM 3. binding of membrane proteins to another cell 4. barriers within the PM that prevent diffusion
What is the cell cortex? What are the major players in RBCs?
the meshwork of fibrous proteins on the inside of a cell that stabilize the PM. Spectrin and Ankyrin are major players of RBCs.
Glycoproteins? Abundance? Where are sugars attached (extracellular domain or intracellular domain)
Proteins with sugars attached. most proteins are glycosylated. sugars attached to extracellular domain of proteins.
Glycocalyx: waht is it? role? (3)
the outer later of PM made by sugars. cell-cell recognition, lubrication (helps cells move through capillary), protection from mechanical damage.
What type of protein is this?
Transmembrane Protein
What type of protein is this?
Membrane associated
what type of membrane protein is this?
Lipid linked
what type of membrane protein is this?
Protein attached
