Module 2A Membrane Structure Flashcards
encloses the cell, defines its boundaries, maintains essential differences between the cytosol and the extracellular environment, and supports ion gradients, protein sensors/receptors, and membrane proteins.
plasma membrane
What is the basic structural component of all cell membranes?
lipid bilayer
How much of the mass of animal cell membranes is made up of lipids?
50%
What property makes lipid molecules suitable for membrane formation?
amphiphilic - contain both hydrophobic and hydrophilic regions.
the most abundant membrane lipids, with a hydrophilic head and two hydrophobic hydrocarbon tails, forming the core of the lipid bilayer.
phospholipids
create kinks in the hydrophobic tail, which increases fluidity and prevents tight packing in the lipid bilayer.
cis-double bonds
- It is the main phospholipids.
- They have a three-carbon glycerol backbone, two long-chain fatty acids, and 3rd carbon is attached to a phosphate group linked to a head group.
phosphoglycerides
What is the main structure of phosphoglycerides? (3)
- three-carbon glycerol backbone
- two long-chain fatty acids
- 3rd carbon is attached to phosphate group linked to a head group.
Name three major types/classes of phosphoglycerides (most abundant ones in mammalian cell membranes and derived from glycerol)
- Phosphatidylethanolamine
- phosphatidylserine
- phosphatidylcholine
- Another important class of phospholipids derived from sphingosine rather than glycerol.
- derived from sphingosine, which includes a long acyl chain, an amino group, and two hydroxyl groups.
sphingolipids
Sphingolipids are derived from __, which includes a __, an __, and two __.
- sphingosine
- long acyl chain
- amino group
- hydroxyl groups
What is the most common type of sphingolipid?
sphingomyelin
Sphingomyelin has a __ attached to the amino group and a __ attached to the terminal hydroxyl group.
- fatty acid tail
- phosphocholine group (a simple molecule containing a choline group bonded to a phosphate group)
resemble sphingolipids but have sugars attached, often contributing to cell recognition and protection.
glycolipids
a sterol with a rigid ring structure, a single polar hydroxyl group, and a short nonpolar hydrocarbon chain. It helps modulate membrane fluidity and stability.
cholesterol
Phospholipids spontaneously form bilayers in aqueous environments due to their __ nature. Phospholipid molecules spontaneously __ to bury their __ tails, forming bilayers where tails are shielded inside, away from water.
- amphiphilic
- aggregate
- hydrophobic
structures with hydrophobic tails inward, formed when amphiphilic molecules aggregate in water at certain concentrations or conditions.
spherical micelles
Lipid bilayers have a __ where any small tear causes lipids to rearrange spontaneously to eliminate the free edge, often closing to form a sealed compartment.
self-sealing property
synthetic (artificial) lipid bilayers, which can be made in the form of spherical vesicles.
liposomes
How can the motion of individual lipid molecules in a bilayer be measured?
Fluorescence Recovery after Photobleaching (FRAP)
By constructing a lipid molecule with a fluorescent dye or small gold particle attached to its polar group, allowing observation of its diffusion.
like =N-O, is a modified lipid head group containing an unpaired electron. It produces a paramagnetic signal detected by electron spin resonance (ESR) to study lipid motion.
spin label
A spin label, like =N-O, is a modified lipid head group containing an unpaired electron. It produces a paramagnetic signal detected by __ (__) to study lipid motion.
electron spin resonance (ESR)
the rare migration of phospholipid molecules from one monolayer of a bilayer to the other.
flip-flop
It’s the quick exchange of places among lipid molecules within the same monolayer of a bilayer, allowing for membrane fluidity.
rapid lateral diffusion
What gives lipid molecules flexibility and rapid movement in the bilayer? (2)
- flexibility of hydrocarbon chains
- the rapid rotation of lipid molecules around their long axis
enzymes that catalyze the rapid flip-flop of phospholipids between monolayers in the lipid bilayer.
phospholipid translocators (flippases)
How does the composition of a lipid bilayer influence its fluidity? (2)
- lipid composition
- temperature
a change from a liquid state to a two-dimensional rigid crystalline state at a characteristic temperature
phase transition
enhances the permeability barrier, decreases deformability, and prevents hydrocarbon chains from crystallizing, modulating bilayer properties.
cholesterol
Archaeal bilayers are built from ______, differing in molecular design from those in most prokaryotes and eukaryotes.
20–25-carbon-long prenyl chains
Eukaryotic plasma membranes are highly varied, containing __ different lipid species, more diverse than those of prokaryotes and archaea.
500-200
specialized membrane microdomains that organize signaling molecules, influence membrane fluidity and protein trafficking, and regulate processes like neurotransmission and receptor trafficking.
- highly ordered and tightly packed lipid molecules
- contain high levels of sphingolipids, including gangliosides and cholesterol.
Lipid rafts
What process causes certain lipids to come together in separate membrane domains?
phase segregation
- store lipids within the cell
- surrounded by a single phospholipid monolayer that contains a variety of proteins.
lipid droplets
What types of cells are specialized for lipid storage?
fat cells/adipocytes
What kind of lipids form the contents of lipid droplets? (2)
Triacylglycerols and cholesterol esters, which are neutral and hydrophobic
What structure surrounds lipid droplets?
a single phospholipid monolayer that contains a variety of proteins.
Under what condition do lipid droplets form rapidly in cells?
when cells are exposed to high concentrations of fatty acids.
- refers to the difference in composition between the two monolayers of a lipid bilayer.
- important for converting extracellular signals into intracellular responses.
lipid asymmetry
What lipids are primarily found in the outer monolayer of red blood cells (RBCs)? (2)
- phosphatidylcholine
- sphingomyelin
What lipids are primarily found in the inner monolayer of red blood cells (RBCs)? (2)
- phosphatidylethanolamine
- phosphatidylserine.
Which proteins bind to specific lipid head groups in the cytosolic monolayer? (An example)
protein kinase C (PKC)
serves as a lipid kinase for signaling pathways, specifically involving phosphoinositide 3-kinase (PI 3-kinase).
Phosphatidylinositol (PI)
cleave an inositol phospholipid to generate two fragments, one that activates protein kinase C and another that stimulates the release of Ca²⁺ from the endoplasmic reticulum.
Phospholipases C
Phospholipases C cleave an __ to generate two fragments, one that activates __ and another that stimulates the release of __ from the endoplasmic reticulum.
- inositol phospholipid (or phosphatidylinositol)
- protein kinase C
- Ca²⁺
Animals use phospholipid asymmetry to distinguish between live and dead cells. Animals exploit phospholipid asymmetry by detecting the translocation of __ from the inner to the outer monolayer during apoptosis.
phosphatidylserine
- sugar-containing molecules found in cell membranes.
- exclusively found in the outer monolayer of the lipid membrane.
- most extreme asymmetry in their membrane distribution
glycolipids
The asymmetric distribution of glycolipids results from the __ of __ groups to __ molecules in the __ of the Golgi apparatus.
- addition
- sugar
- lipid
- lumen
Glycolipids are present in all __ plasma membranes and some __ membranes, making up about __ of the membrane composition.
- eukaryotic
- intracellular
- 5%
The function of glycolipids is influenced by their __, providing specific roles in cell recognition and protection.
localization
In __ cells, glycolipids on the exposed apical surface may help protect the membrane against harsh conditions.
epithelial
are charged glycolipids that have significant electric effects and are important for cell-to-cell recognition.
gangliosides
provide entry points for certain bacterial toxins and viruses, aiding in their ability to infect cells.
glycolipids
perform most of the membrane’s specific tasks, giving each type of cell membrane its characteristic functional properties.
membrane proteins
The amounts and types of proteins in a membrane are __.
highly variable
- can function on both sides of the bilayer or transport molecules across the membrane.
- have a unique orientation, with different functions in their cytosolic and noncytosolic domains.
transmembrane proteins
Lipid anchors: Proteins that function on only one side of the lipid bilayer are often associated exclusively with either the __ or a __ on that side.
- lipid monolayer
- protein domain
control the membrane localization of some signaling proteins, helping to keep them attached to specific membrane regions.
lipid anchors
The __ of a polypeptide chain is formed into an α helix, contacting the hydrophobic area of the lipid bilayer.
membrane-spanning segment
Proteins that have a polypeptide chain that crosses the membrane only once.
single-pass transmembrane proteins
have multiple transmembrane strands of a polypeptide chain arranged as a β sheet rolled up into a cylinder.
Multipass transmembrane proteins
are used to localize potential α-helical membrane-spanning segments in a polypeptide chain.
hydropathy plots
What is estimated about the proportion of transmembrane proteins in an organism?
about 30%
Where are oligosaccharide chains located in relation to membrane proteins?
noncytosolic side of the membrane.
bonds that form on the noncytosolic side to help stabilize the folded structure of the polypeptide chain or its association with other polypeptides.
Disulfide bonds
extensively coat the surface of all eukaryotic cells.
carbohydrates
are small amphiphilic molecules that are more soluble in water than lipids, with a polar side that can be ionic (like sodium dodecyl sulfate) or nonionic (like octylglucoside and Triton).
detergents
What is necessary to solubilize and purify membrane proteins?
detergents
Give examples of ionic (1) and nonionic detergents (2)
ionic
- SDS (sodium dodecyl sulfate)
nonionic
- Octylglucoside
- Triton
the surfactant concentration at which micelle formation is first seen in the solution.
Critical micelle concentration (CMC)
When mixed with membranes, the __ ends of detergents bind to the __ regions of membrane proteins, displacing __ molecules with a __ of detergent molecules.
- hydrophobic
- hydrophobic
- lipid
- collar
allow for the reconstitution of functionally active membrane protein systems from purified components, enabling the analysis of activities of membrane transporters, ion channels, signaling receptors, etc.
Mild detergents
are small, uniformly sized patches of membrane surrounded by a belt of protein that covers the exposed edge of the bilayer to keep the patch in solution.
nanodiscs
How can nanodiscs be analyzed structurally?
by single particle electron microscopy techniques
Membrane proteins often function as part of __.
multicomponent complexes
captures light energy and uses it to pump H+ across the membrane.
photosynthetic reaction center
Do membrane proteins flip across the lipid bilayer?
No
Membrane proteins can __ about an axis perpendicular to the plane of the bilayer and move laterally within the membrane (__).
- rotate
- lateral diffusion
What technique measures the lateral diffusion rates of membrane proteins?
Fluorescence recovery after photobleaching (FRAP)
involves labeling individual membrane molecules and tracking their movement by video microscopy.
single-particle tracking
Most cells confine membrane proteins to specific regions within the membrane. In epithelial cells, certain plasma membrane enzymes and transport proteins are confined to the __, while others are confined to the __ and __. (ex. lipid rafts)
- apical surface
- basal; and
- lateral surfaces
The __ distribution of membrane proteins is often essential for the function of the epithelium.
asymmetric
What creates barriers that confine proteins in epithelial cells?
Barriers set up by specific types of intercellular junctions
- interactions in that membranes create nanoscale raft domains that function in signaling and membrane trafficking.
- Within lipid rafts, this interaction promotes signal transduction and cellular responses.
Protein-protein interactions
Cells that create lipid rafts enriched in cholesterol and proteins, facilitating efficient signaling and membrane trafficking, which enhance motility and the acrosome reaction for fertilization.
Sperm cells or mammalian spermatozoon
- gives membranes mechanical strength and restricts membrane protein diffusion
- It forms mechanical barriers that obstruct the free diffusion of proteins within the membrane.
cortical cytoskeleton
What is the primary component of the cytoskeleton that gives red blood cells their characteristic biconcave shape?
Spectrin
- long, thin, flexible rod
- a filamentous protein, forms a meshwork that maintains the structural integrity and shape of the plasma membrane.
Spectrin
- It provides mechanical strength, allowing red blood cells to withstand stress and deform as they pass through narrow capillaries.
- It is a deformable, netlike meshwork that covers the entire cytosolic surface of the red cell membrane.
spectrin-based cytoskeleton
What happens to red blood cells with genetic abnormalities in spectrin? (3)
cells become:
- anemic;
- spherical; and
- fragile
due to the lack of structural integrity.
What processes are influenced by membrane-bending proteins that deform bilayers? (3)
- Vesicle budding
- cell movement
- cell division
The shape is controlled dynamically by the __ and __ forces exerted by __ or __ structures.
- pushing
- pulling
- cytoskeletal
- extracellular
They facilitate the deformation of lipid bilayers, which is essential for various cellular processes like vesicle formation and cell motility.
membrane-bending proteins
