How would each phospholipid be oriented in a membrane?
- sphingolipids
- glycolipids
- steroids
- cardiolipin
- sphingolipids: heads out (hydrophilic); tail in
- glycolipids: tail in; sugar outside
- steroids: nestles up against the bottom of the hydrophobic tails
- cardiolipin: has to fold (U-shaped) (R1 and R2 are hydrophobic)
What are the advantages (consequences, importance) to a cell of the presence of lipid in the membrane?
selective permeability (allows access to some; polar molecular ions need help)
allows buildup of concentration of cells
structure (if hydrophilic, they'd dissolve)
energy saving
Explain the energy saving advantage of lipids?
because of their chemical nature, if you put them in a particular environmnt, they will spontaneously form a bilayer with no energy needed (preferred arrangement)
Working outside of cells and not in them: __
Working inside of cells and with them: __
in vitro
in vivo
True or False. Explain
Membranes in cells never have a free end.
True
because it will cause exposure of hydrophilic regions
- allows for cell division, splitting, etc.
Arrangements of Membrane: first model?
Davson-Danielli Model (1935)
What was the Davson-Danielli Model
sugar proteins on outside (globular)
lipids inside (sandwich model)
What was the Davson-Danielli revision made?
there may be some hydrophilic pores
Second model
Robertson Unit Membrane Model (1960)
What is the difference of the Robertson Unit Membrane Model?
shape of protein; he stated theywere extended, not globular
Why did the RUM model state what it stated?
said this because he looked at cells with better EM
also, new fixative was introduced
Explain the fixatives Robertson used?
the old was osmium tetroxide: you would see it as a solid black line
the new one: potassium permanganate allows you to see two solid black lines with a line in between (you can even measure the space and black lines)
Evidence supporting the RUM theory:
one
a densely packed lipid bilayer can account for high percentages of lipid found in membranes
Evidence supporting the RUM theory:
two
lipids are poor electron conductors
- if you have alot= you have high resistance
Evidence supporting the RUM theory:
three
increased permeability to non-polar molecules
- allows it to get through easily
- polar molecules do not
Evidence supporting the RUM theory:
four
phospholipid will spontaneously form bilayers in water
Evidence supporting the RUM theory:
five
accounts for electron micrograph he was seeing
The first four points of evidence deal with __.
What don't the five points talk about?
lipid
proteins
Third model
Singer and Nicholson's Fluid Mosaic Model
The fluid mosaic model has been around for about __.
forty years
Similarities of fluid mosaic, DD, and RUM.
phospholipid bilayer
there are proteins
Differences between fluid mosaic, DD, and RUM.
arrangement of proteins
Two basic categories of proteins
peripheral
integral
The proteins that were in the same position as the DD and RUM models were __.
How prominent are they?
peripheral (extrinsic) proteins
in the minority
The majority of proteins are __. They are embedded in the __ and are __ present.
integral (intrinsic)
membranes
70-80% (majority)
is the lipid composition the same in every membrane?
no, it varies
Is the chemical composition the same of various cell membranes?
no, it varies
What does phosphatidyl indicate?
that the lipid is a phospholipd
__ comprise another category of lipids found in membranes. Here again, there is a great variety of complex compounds. The structure common to all of the compounds is a __ on which two other __ are substituted.
sphingolipids
sphingosine residue
residues
R1 on a sphingolipid may be __ while R2 can __.
a variety of fatty acids
vary widely
In a sphingomyelin, there are __ and __ regions. There are two __ and a __. The latter is called is __ because it carries both a negatively charged group.
polar
nonpolar
hydrophobic tails
strongly hydrophilic head
zwitterion
What is the hydrophilic portion of a steroid?
hydrophobic portion?
hydrophilic: the -OH group
hydrophobic: the rest of hte structure
What is the hydrophilic portion of a glycolipd?
hydrophobic portion?
hydrophilic: the sugar residue (such as galactose)
hydrophobic: the rest of hte structure
Like phospholipids, glycolipids are composed of a __ and a __.
hydrophic region containing two long hydrocarbon tails
polar region (one or more sugar residues and no phosphate)
A cardiolipin has to have what occur?
it has to fold inward so that its hydrophobic R groups are away from aqueous solution
Who came up with the term unit membrane?
Robertson
WHat were the masurements Robertson made of his model?
20 angstroms protein each side
35 angstrons phospholipid
= 75 angstroms
What are the requirements for dissociation from the membrane of :
peripheral proteins
mild treatment sufficient; high ionic strength, metal ion chelating agents will cause them to easily come off
What are chelating agents?
molecuels that hold onto something tightly (hold peripheral proteins)
Examples of peripheral proteins
cytochrome C
protein kinases
What are the requirements for dissociation from the membrane of :
integral proteins
really have to beat the membrane up and take it apart
Association with lipids when solubilized:
peripheral proteins
usually soluble free of lipids; if you can get proteins out of the membrane, the lipids don't usually come with these proteins
Association with lipids when solubilized:
integral
usually associated with lipids when solubilized
Solubility after dissociation from membrane:
peripheral proteins
soluble and moleculary dispersed in neutral aqueous buffers
Solubility after dissociation from membrane:
integral proteins
usually insoluble or aggregated in neutral aqueous buffers
How many classes of integral proteins?
four
two are partially embedded
transmembrane
complex of proteins
How are membrane proteins classified?
according to their mode of attachment to the membrane
Integral membrane proteins contain one or more __ that are embedded within the __.
hydrophobic regions
lipid bilayer
A few integral proteins appear to be embedded in the membrane on only one side of the bilayer (__)
integral monotopic proteins
However, most integral proteins are __ that span the lipid bilayer either once (__) or multiple times (__).
singlepass proteins
multipass proteins
__ can consist of either a __ or several __ (__).
multipass proteins
single polypeptide
several associated polypeptides (multisubunit proteins)
Peripheral membrane proteins are __ but are attached to the membrane by __ and __ that link them to adjacent membrane proteins or to __.
too hydrophilic to penetrate into the membrane
electrostatic
hydrogen bonds
phospholipid head groups
__ are hydrophilic and do not penetrate into the membrane; they are __ to lipid molecules that are embedded in the lipid bilayer.
lipid anchored proteins
covaletly
Proteins on the inner surface fo the membrane are usually anchored by either a __ or a __ group. On the outer membrane surace, the most common lipid anchor is __,
