Module 2 : Internal Organization of the Cell Membrane Structure Flashcards
encloses the cell, defines its boundaries, and maintains the essential differences between the cytosol and the extracellular environment
Plasma membrane
provides the basic structure for all cell membranes
The Lipid Bilayer
50% of the mass of the most animal cell membranes
Lipids
most abundant membrane lipids
Phospholipids
Parts of Lipids
Head : Phosphate group, hydrophilic
Tail : 2 hydrocarbon tail, hydrophobic
The bonds that create links in the tail
cis-double bonds (unsaturated)
Major Classes of Lipids in Cell membranes
- Phosphoglycerides
- Glycolipids
- Cholesterol
main phospholipids
Phosphoglycerides
Two subclasses of phospholipids
- gylcerophospholipids
- sphingolipids
from sphingosine (long acyl chain with an amino group (NH2) & two hydroxyl groups (OH)
Sphingolipids
most common sphingolipid
spingomyelin
a fatty acid tail is attached to the amino group, and a phosphocholine group is attached to the terminal hydroxyl group
Sphingomyelin
resemble sphingolipids;
sugars
Glycolipids
sterol; contains a rigid ring structure, to which attached a single polar hydroxyl group and a short nonpolar hydrocarbon chain
Cholesterol
Major Phospholipids in Mammalian cells
phosphatidylethanolamine, phosphatidylserine, and phosphatidylcholine
tails inward
Spherical micelles
hydrophobic tails sandwiched
Bilayers
What does unpaired electron spin create?
Paramagnetic signal
can be detected by electron spin resonance (ESR) spectrum
Paramagnetic signal
phospholipid molecules in synthetic bilayers very rarely migrate from the monolayer on one side to that on the other
Flip-flop
lipid molecules rapidly exchange places with their neighbors within a monolayer
Rapid lateral diffusion
the lipid component of a biological membrane is a ___ ____
two-dimensional liquid
catalyzes the rapid flip
flop of phospholipids from one
monolayer to the other
Phospholipid translocators (flippases)
a change from a liquid state to a two dimensional rigid crystalline state at a characteristic temperature
Phase transition
How does cholesterol modulates the properties of lipid bilayers
- Enhances the permeability-barrier properties
- Decretase motility of the few CH2 groups
- Prevents the hydrocarbon chains from coming together and crystallizing
Has 20–25-carbon long prenyl chains
Archea
specialized membrane microdomains that serve as to organizing centers for assembly of signaling molecules
Lipid rafts
in which specific lipids come together in separate domains
Phase segregation
storage of lipids
Lipid droplets
- specialized for lipid storage
- contain a giant liquid droplet
Fat cells or adipocytes
neutral lipids; exclusively hydrophobic molecules, and therefore aggregate into 3 dimensional droplets
triacylglycerols and cholesterol esters
contains a large variety of proteins
Single monolayer of phospholipids
by definition, the two monolayers have different composition
Lipid asymmetry
Mainly found in the outer layer of RBC
phosphotidylcholine and sphingomyelin
translocate from the inner monolayer to the outer monolayer when cells undergo apoptosis
Phosphotidylserine
Mainly found in the outer layer of RBC
are used in yet another way to convert extracellular signals into intracellular ones
Phospholipids in the plasma membrane
cleaves an inositol phospholipid in the cytosolic monolayer of the plasma membrane to generate to fragments
Phospholipase C
- sugar-containing molecules
- most extreme asymmetry in their membrane distribution
Glycolipids
results from the addition of sugar groups to the lipid molecules in the lumen of the Golgi apparatus
Asymmetric distribution of glycolipids in the bilayer
- exposed apical surface;
- may help to protect the membrane against the harsh conditions
Epithelial cells
charged glycolipids; important because of their electric effects
Gangliosides
Functions of glycolipids
- Come from their localization
- Provide entry points for certain bacterial toxins and viruses
- Cell-to-cell recognition
Types of integral proteins
- polytopic
- bitopic
- monotopic
extends through the lipid bilayer
Transmembrane proteins
do not extend into the hydrophobic interior of the lipid bilayer; bound to either face of the membrane by noncovalent interactions
Peripheral proteins
control the Membrane Localization of Some Signaling Proteins
Lipid anchors
– small amphiphilic molecules; more soluble in water than lipids
Detergents
Three commonly used detergents to disrupt lipid bilayer
- Sodium dodecyl sulfate
- Triton X-100
- β-octylglucoside
Detergent that is anionic
SDS (Sodium dodecyl sulfate)
Two nonionic detergents
- Triton X-100 and β-octylglucoside
– surfactant concentration at which micelle formation is first seen in the solution
critical micelle concentration
small, uniformly sized patches of membrane that are surrounded by a belt of protein,
which covers the exposed edge of the bilayer to keep the patch in solution
Nanodiscs
Movements of membrane proteins
- Flip-flop
- Lateral diffusion
- Rotation
measures lateral diffusion rates of membrane proteins
FRAP (Flourescence recovery after photobleaching)
labeling individual membrane molecules and track their movement by video microscopy
Single-particle tracking
Gives Membranes Mechanical Strength and Restricts Membrane Protein Diffusion
Cortical cytoskeleton
long, thin, flexible rod;
it maintains the structural integrity and shape of the plasma membrane
Spectrin
