Chapter 11 Flashcards
Membranes act as
Permeability barriers
All cells have a
Plasma membrane
have internal membranes that enclose intracellular compartments (e.g., organelles and vesicles)
Eukaryotes
Membrane functions are
Receive info from environment, selective import and export, enable cells to change shape, expand
The membrane is a
thin bilayer + proteins
Carbohydrates are located on the
ECF surface of membrane
Membrane proteins float in a
sea of lipids
how thick is the plasma membrane
5 nm thick
Membrane lipids __ form bilayers in water
spontaneously
The lipid bilayer is a __ dimensional fluid
2
The fluidity of a lipid bilayer depends on its
composition
The lipid bilayer is asymmetrical or symmetrical
asymmetrical
Lipid asymmetry is preserved during
membrane transport
Membrane lipids have __ head group and __ hydrocarbon tails
polar, one or two (hydrophobic)
Membrane lipids form a bilayer in
water
Geometry of membrane lipids favors
bilayer formation
Phospholipid bilayers __ form sealed compartments
spontaneously
Holes in membranes are __ to minimize interactions of hydrophobic molecules with water
rapidly resealed
Membrane lipids move rapidly within one
monolayer
The most abundant lipids in cell membranes are
phospholipids
have a phosphate-containing polar head group
phospholipid
the most abundant phospholipid
Phosphatidylcholine
what determines membrane fluidity
length and saturation of hydrocarbon tails
__ tails promote membrane fluidity
short
Double bonds introduce kinks and __ membrane fluidity
increase
Special membrane lipid
cholesterol
Cholesterol characteristics
Rigid sterol ring with a polar head group & one
short hydrocarbon tail
can fill the spaces between neighboring phospholipid
molecules produced by the kinks in their tails
cholesterol
Tends to stiffen membranes with unsaturated tails
cholesterol
phospholipids have what charge
negative
Increasing the number of double bonds in lipid tails does what to fluidity
increases
Shortening the length of lipid hydrocarbon tails does what to fluidity
increases
saturated fats have long or short tails
short
Moving veggie oil from room temp to fridge does what to the fluidity
decreases
Glycolipids have
carbs on their heads
T or F the two monolayers have the same lipids
false, different
Lipids are __ arranged between two monolayers
asymmetrically
New phospholipids are synthesized
by
enzymes bound to cytosolic surface of the ER
Enzymes that synthesize phospholipids insert the new lipids into the
cytosolic monolayer of the ER membrane
randomly transfer lipids to the lumenal (or extracellular) monolayer
Scramblases in the ER
Membrane bilayers move from
ER to Golgi
selectively transfer some lipids from the monolayer that faces the lumen to the cytosolic monolayer
flippases in golgi
flippases in golgi generate an
asymmetric distribution of membrane lipdis
Asymmetry is maintained during
transport and after
becomes the
extracellular surface of the
plasma membrane
lumenal surface
Enables membranes to
maintain the asymmetric
distribution of lipids, proteins,
and carbohydrates
lumenal surface
The cytosolic surface is
outside
The c terminal end is always in the
cytosolic surface
provides the barrier function,
membrane proteins provide other functions
lipid bilayer
Proteins (membrane spanning polypeptide chains) usually cross membranes as an
alpha helix
Membrane proteins can be purified using
detergents
The plasma membrane is often reinforced by the
cell cortex
proteins that are directly attached to the membrane
Integral membrane
Transmembrane, monolayer-associated, lipid-linked
integral membrane proteins
Can only be removed from the membrane using detergents
integral membrane proteins
Non-covalent association with other membrane proteins
peripheral membrane proteins
Can be released from the membrane with gentle procedures (e.g. salt)
peripheral membrane proteins
what protein is easier to seperate
peripheral membrane proteins
__ amino acids
form an alpha-helix
20 hydrophobic
Polar atoms of the polypeptide
backbone are
hydrogen bonded
inside the alpha-helix
Hydrophobic amino acid side
chains on the surface of the
helix interact with
lipid tails
Multiple a-helices can pack together to form an
aqueous pore
Several __
alpha-helices cross
the lipid bilayer
amphipathic
_ surfaces (green) contact the
bilayer
hydrophobic
_ surfaces (red) form an aqueous pore
hydrophilic
Some transmembrane proteins use several
__ to cross the membrane
beta sheets
e “beta barrels” form
large pores
detergents contain
hydrophobic regions that solubilize lipid bilayer and hydrophilic regions
SDS will __ proteins
denature
Detergents have __ hydrophobic tail, so they
form __ rather than bilayers
1, micelles
How to measure membrane protein movement?
Fluorescence Recovery After Photobleaching (FRAP)
Look at the behavior of many molecules; Time for recovery reflects the mobility of the molecules
FRAP
Look at the behavior of only a few labeled molecules; Distance traveled reflects mobility of molecule
SPT
The cells can restrict membrane protein mobility by tethering to
cytoskeleton, extracellular matrix, membrane proteins in another cell, and form junctions to create domains
Distinct membrane domains are common in
epithelial cells
mediates transport of nutrients from the gut into the cell
Protein A (apical side)
mediates transport of solutes from the cell into the bloodstream
Protein B (basal side)
form a belt that keeps A and B from mixing
tight junctions
The plasma membrane is reinforced by
interactions with the
cell cortex
good model for studying membrane cortex interactions
red blood cells
Major fibrous protein is
spectrin
spectrin is attached to
transmembrane proteins
Forms a mesh that protects RBC from mechanical damage
spectrin
recognize specific
oligosaccharides on a neutrophil
lectins on endothelial cells
lectins facilitate
attachment to blood vessel wall
