Chapter 11 Flashcards
Describe the evolution of the plasma membrane model from the beginning to a lipid bilayer (3 models)
Permeable to nonpolar molecules → Made of lipids
Pure phospholipids in vitro form monolayers → Monolayer of lipids
Measurements of lipid number vs surface area → Bilayer of lipids
Describe the evolution of the plasma membrane model from a lipid bilayer to the current model (2 models)
Properties cannot be explained by only lipids → Lipid bilayer coated in proteins
Current Model → Cell membranes are a fluid bilayer of lipids with a mosaic of associated proteins
Describe FRAP
Fluorescent Recovery After Photobleaching
Attach dye to component of interest → destroy fluorescence with laser → look at % and rate of recovery
Describe the movements of lipids in membranes
Lipids can diffuse laterally, or flex and rotate in place
Can flip-flop with the aid of flippases
Describe lipid synthesis (made by X, goes to X, ends at X)
New lipids are made with enzymes on the outer/cytosolic side of the ER membrane
Scramblases in Golgi place lipids on the correct side and in the correct composition (ex: glycolipids are only found on extracellular side)
Describe how lipid asymmetry is maintained from creation to insertion in membranes
Membrane asymmetry (two sided) continues to Golgi to vesicles to plasma membrane
Side facing the cytosol will remain facing the cytosol
Name the most common phospholipid and describe its structure
Phosphatidylcholine
Hydrophobic head → choline linked to a phosphate group
Two fatty acid tails → one saturated, on with a double bond in the middle
Glycerol → links head to tail
Name and describe the three lipid components of the plasma membrane
Phospholipids: hydrophilic head (made of a polar group, a phosphate, and a glyceroal) and two fatty acid tails
Glycolipid: hydrophilic head with two fatty acid tails, one or more sugars in polar region in head
Steroid: Multiple ring structure with hydrophobic head
Define Tm
TM is the temperature above which the membrane is fluid and functional (want to be low)
What are the two main factors that affect membrane fluidity and what are their effects?
It depends on saturation levels and the length of phospholipid tails
More double bonds → Lower TM
Fewer double bonds → Higher TM
Longer → Higher TM
Shorter → Lower TM
What is the role of cholesterol in the plasma membrane?
Cholesterol (and other sterols) stiffens membranes
Very rigid, decreases fluidity above TM and increases fluidity below TM (buffer)
Also makes membrane less permeable
Define cell cortex
Meshwork of fibrous proteins that stabilizes the plasma membrane and is attached to the underside of the membrane
Name the four ways proteins can associate with the plasma membrane
transmembrane, monolayer, lipid-linked, protein-attached
Describe a general transmembrane protein
one or more alpha helices that pass through the plasma membrane
(may also be beta sheets → rare)
Describe a general monolayer protein
rarer, amphipathic
Describe a lipid-linked protein
covalently attached to a lipid inserted in the membrane, lipid can be attached to C or N terminus and proteins can be on either side
Describe a protein attached protein
also called peripheral membrane proteins, protein-protein interaction with noncovalent bonds, most loosely attached
Describe alpha helices and beta sheets in the plasma membrane
Have hydrophobic and hydrophilic regions to pass through membrane or form channels
What are four ways proteins can be anchored?
Attached to actin cytoskeleton
Attached to extracellular matrix (ex: collagen)
Forming cell-cell interactions
Tight junctions between cells
Describe the experiment that proves some proteins are nonmotile
Studies using protein molecules tagged with antibody-coated gold nanoparticles have shown that proteins display a range of movement from random diffusion to complete immobility.
Describe the structure and role of detergents in protein study
Mild detergents with hydrophobic tails and hydrophilic tails can be used to separate out membrane proteins when followed with purification with antibodies
Can be used to study proteins in isolation when also followed with removal of detergent and addition of phospholipids
Describe the four main functions of proteins in the plasma membrane
Transporters/channels
Anchors
Receptors
Enzymes
Define lectin. Give an example of its role in the cell.
A protein that binds to a particular oligosaccharide chain
Cells lining blood vessels bind to neutrophil sugars on white blood cells to allow them to migrate to the infected tissue
Describe the use of x-ray crystallography in determining protein structure
Can be done, super hard because of hydrophobic regions
Describe the use of hydropathy analysis in determining protein structure
Find delta G of transforming amino acid from hydrophobic → hydrophilic environment
Hydrophobic amino acids have positive values
Hydrophobic stretches of 20+ amino acids are likely transmembrane alpha helices
Define glycoprotein and proteoglycan
Some proteins also have short chains of sugars, and are called glycoproteins, or have long polysaccharide chains, and are called proteoglycans
Define glycocalyx
a protective layer of sugar residues, including the polysaccharides to protein or lipid molecules, on the outer surface of a cell
Describe the role and location of sugars in the plasma membrane
All of the sugars on the outside of the cell membrane help form the glycocalyx.
Some also are involved in cell-cell recognition and adhesion.
What are the two main roles of the glycocalyx?
It protects the cell from mechanical damage by giving it a slimy surface, helping it squeeze through narrow spaces and also prevents blood cells from sticking to one another or to the walls of blood vessels.
Describe the use of lectin in sugar study
Staining with particular lectin-fluorescent dyes can selectively show sugars
