Term
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Definition
Protects inner contents fo the cell from environment
Thin fragile structure 5-10nm
cant see w/ Light Microscope
seen as 3layers structure dark outside/ light inside
Same structure in all membranes (plant, animal, plasma membrane |
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Term
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Definition
1.Compartmentalization
2. Scaffold for biochemical activities
3. Selectively permeable barrier
4. Transporting solutes |
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Term
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Definition
| Allows specialized activities to proceed w/o external interference & indpt of each other |
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Term
| Scaffold for biochemical activities |
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Definition
| Not dependent on random collisions in cytoplasm in cytoplasm |
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Term
| Selectively permeable barrier |
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Definition
| Prevent unrestricted exchange of molecules |
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Term
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Definition
Allows cell to accumulate substances neccessary for building blocks & metabolism
- Esp impt in nerve, muscle that establish gradients |
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Term
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Definition
Response to external stimuli
Intracellular interaction
Energy transduction |
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Term
| Response to external stimuli |
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Definition
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Term
| Intracellular interaction |
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Definition
mediates interactions btw cells and its neighbors
Allows cell recognition, adherence, material & info exchange |
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Term
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Definition
photosynthesis
ATP synthesis from carbs fats |
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Term
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Definition
Gorter & Grendel extracted RBC lipid & measured surface area when spread of over water
Found 2:1 ratio, concluded must be bilayer of lipids
Polar grpups facing out
nonpolar groups facing in
thermodynamic favored arrangement |
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Term
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Definition
Surface Tensions lower than what a pure lipid structure
made by SInger & Nicolson
mobel component can come together for interactions |
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Term
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Definition
Varies depending on the type of membrane, organism, etc
Inner mitochondrial membrane > RBC membrane > myelin sheath around nerve cell ( electrical insulation) |
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Term
Membrane LIpids;
Amphipathic: Can be have what type of regions
Types of membrane lipids include |
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Definition
Hydrophobic and hydrophilic regions
Phosphoglycerides (phospholipids)
Shingolipids
cholestrol |
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Term
Phospholipids
What are the R groups |
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Definition
2 fatty acid chains, one glycerol, one phosphate group, one "R" group
Groups include choline, ethanolamine, serine and inositol
Phosphate + R group = head of phospholipid (hydrophilic)
-Saturated- no DBL bonds
monounsaturated- one DBL bond
POlYunsaturated: many DBL Bonds |
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Term
Sphingolipids
Derivatives of sphingosine
Sphingosine can link to? |
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Definition
Amino Acid + hydrocarbon chain
fatty acid (ceramide)
choline (shingomyelin)
Carbohydrate (glycolipid)
simple sugar (cerebroside)
small sugar cluster (ganglioside)
Hydrophobic on 1 side, philic on the other
impt roles in the nervous system, microbe entry |
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Term
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Definition
Canbe up to 50% of the lipid in animal membranes
Absent in most plants and all bacterial membranes
Hydrophilic group twd surface, remaider in lipid bilayer |
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Term
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Definition
Every membrane is different, from different lipid types, head groups, fatty acid chains
Affect Biological properties of membrane
-change physical state
activity of membranous proteins
precursors for chemical messengers
Membranes form interconnected networks throughout cell.
Extensively deformable
cell fusion
locomotion
cell division |
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Term
| Asymmetry of Membrane Lipids |
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Definition
Bilayer has two leaflets:
lipases on RBC's degrade 80% of PC but only 20% of PE and 10% of PS
High conc of PC in outer leaflet,
low conc of PE & PS
PS on outer leaflets is cellular marker for destruction
PI on inner leaflets impt for transfer of stimuli from PM to cytoplasm
All glycolipids are in outer leaflet serves as receptors for extracellular ligands
Different roles depending on location |
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Term
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Definition
Membranes can self-assemble in liposomes
simpler structures used for membrane research
Used as vehicles to deliver drugs or DNA molecules |
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Term
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Definition
Ranges from 2-10% by weight
-90% is linked to proteins to form glycoproteins
<10% to lipids to form glycolipids
Protein + Carb= GLYCOSYLATION
Impt in enviromental interactions & sorting of membrance proteins (Nlinked & O LInked
Blood groups |
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Term
BLood Groups
What determines Blood group |
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Definition
Glycolipid
Two enzymes responsible for adding GAINaC or GAl to end of chain |
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Term
Structure/ Function of Membrane Proteins
Each membrane protein has sidedness:
What is slidedness?
the 3 types are? |
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Definition
The defined orientation relative to cytoplasm
3 types are intregal proteins, peripheral proteins, lipid-anchor proteins |
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Term
| Integral Membrane Proteins: |
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Definition
Transmembrane Proteins
Pass entirely thru bilayer and have protruding domains on each side
May have one or many membrane-spanning
20 to 30% of all proteins
Functions include
Receptors for chemicals at cell surface
Channels or transporters for ions/solutes across membrane
transfer electrons during photosynthesis and respiration
identified use freeze-fracture analysis
Tissue frozen fractured in half
Look for bump in one half and corresponding pit in other
Can be labeled for specific groups |
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Term
| Peripheral Membrane Proteins |
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Definition
Located entirely outside of lipid bilayer
Either extracellular or cytoplasmic ( NOT BOTH)
Associated w/ Surface by noncovalents |
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Term
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Definition
Located outside bilayer on either side
Covalently linked to lipid molecules in bilayer |
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Term
| Detergent for Solubilization |
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Definition
Difficult to isolate in soluble form because of hydrophobic transmembrane regions
Detergent is solution
Nonpolar ends associate with nonpolar transmembrane regions
Polar ends interact with surrounding water to keep protein in solution
Nonionic detergent keeps protein natured |
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Term
Hydrophobicity Plot
Used to determine location of transmembrane segments.
Every AA is assessed for nonpolar properties |
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Definition
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Term
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Definition
measures distances nitroxides-produce an unusual spectrum when monitored with EPR spectroscopy
Attaced to cysteine groups
Closed PH at 6.5 open at 3.5 |
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Term
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Definition
Associated with membrane by weak bonds, not always attach membrane
can solubilized with high concentrations salt solutions
Best studied are located on the cytoplasmic side;
form network, acts as membrane skeleton
provide mechanical support for membrane
function as anchor for integral membrane proteins |
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Term
| Lipid-Anchored Membrane Proteins |
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Definition
GPI-anchored proteins
outer leaflet of bilayer
bound by small oligosaccharide linked to PI in membrane
Example: normal non-prion brain protein, receptors, enzymes cell adhesion proteins
Proteins linked to hydrocarbon chains
inner leaflet of bilayer
anchored by long hydrocarbon chains
examples: Src and Ras, resp for malignant cells |
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Term
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Definition
Physical state of membrane
at warm temps lipid is very fluid
-parallel arrangment
-ind phospholipids can rotate round their axis
Transition temp
as temp decreases, point where bilayer changes
lipid turns into frozen gel
movement of phospholipids is greatly restricted |
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Term
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Definition
Depends on the ability of the lipid molecules to be packed together which depends itself on the particular lipids
Saturated:straight, flexible rod
Unsaturated: crooks
So saturated pack more tightly
the greater the unsaturation (more crooks) the lower the temperature b4 the bilayer gels
Cholesterol decreases the temp by disrupting the close packing of bilayer, create fluidity |
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Term
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Definition
Allows for interactions in the membrane
-example: intercellular junctions, photosythetic complexes, synapses
Membrane assembly
growth accomplished by insertion of lipids/proteins into membraneous sheet |
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Term
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Definition
Internal temperature of most organisms (ex: for warm-blooded animals) fluctuates w/ external temp
Cells adapt to cold by changing membrane fluidity
changing phospholipid chains to ones with two unsaturated fatty acids
Seen in hibernating animals, fish, cold-resistant plants bacteria in hot springs |
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Term
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Definition
Cholestrol & sphingolipids:
self-assemble into microdomains on membranes
GPI- anchored proteins usually found here
Thought to be floating platforms to concentrate particular proteins |
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Term
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Definition
Mobility depends on end location
laterally from one end of bacteria to other in 2sec
Flip-flop to other side in hrs to days (most difficult bec head group must go thru hydrophobic middle |
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Term
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Definition
Segregated in own hemisphere
As time increase, moved laterally into other hemisphere
At lower temp, mobility decreased |
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Term
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Definition
To follow protein movement using fluorescence and photobleaching
Rate of discovery varies depending on the protein being following |
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Term
| Movement of Integral Membrane Proteins |
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Definition
A. Move randomly throughout membrane
B. Immobilized
C. Highly directed movement
D. Random movement, but restricted by neighbors
E. Random movement, but restricted by cytoskeletal "fences"
F. Restricted by extracellular materials |
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Term
| Movement of Membrane Lipids |
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Definition
Much smaller, would expect greater movement than proteins
-studies show equal confinement as proteins
Tagged lipids show temporary confinement, then hop from one confined area to another
-confinement is partly due to cytoskeletal "fences" & integral membrane protein attached to them |
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Term
| Differentiated Functions of Membranes |
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Definition
Most membrane studies are done w/ homogeneous plasma membrane
differentiated w/ different lipid & protein composition & even differences bet, top & bottom |
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Term
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Definition
Most highly differentiated structure
Divided into head, midpiece & tail but continous plasma membrane |
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Term
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Definition
Protein solubilized
PAGE
Approx 12 major proteins |
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Term
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Definition
Most abundant are Band 3& glycophorin A
BAnd 3:
Homodimer
spans membrane > 12x
channel for passive exchange of anions membrane (bicarbonate & chloride |
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Term
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Definition
Glycophorin A
homodimer
spans membrane once
huge carb cover 60% of molecule's weight)
large "-" charge from carbs
receptor for malaria pathogen |
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Term
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Definition
Spectin is major component
attached to internal surface by ankyrin
Ankyrin is attached to cytoplasmic domain of Band 3
Organized in hexagonalor pentagonal arrays
Many genetic diseases w/ abnormally shaped RBCs are due to defects in spectrin or ankyrin |
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Term
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Definition
Membrane integrity tied into spectrin/ ankyrin network
-removal of peripheral proteins to fragmentation of membrane into small vesicles
RBC must be both durable & deformable to squeeze thru capillaries while under pressure
spectrin/ankyrin network gives cell strength & elasticity
Pther cells have similiar type of membrane skeletons
Dystropjin is in spectrin family, found in muscle cells
Mutations lead to muscular dystrophy (cells destroyed due to mechanical stress exerted on them as muscle contracts |
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Term
Chap 4B
Movement across Cell Membranes |
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Definition
Dual function of plasma membrane
retain dissolved material of cell
allow material exchange
influx vs effux
Types of movement |
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Term
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Definition
2 qualifications
Substrance must be higher must be higher concentration on one side vs another
Membrane must be permeable to subtrance
Rate based on size
Membranes are highly permeable to O2 CO2, NO2 and H20
Larger polar molecules not so permeable but PM prevents the PM from diffusing out |
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Term
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Definition
2 qualifications
Substrance must be higher must be higher concentration on one side vs another
Membrane must be permeable to subtrance
Rate based on size
Membranes are highly permeable to O2 CO2, NO2 and H20
Larger polar molecules not so permeable but PM prevents the PM from diffusing out |
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Term
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Definition
| Osmosis is movement of water from region of low solute concentration to high solute concentration |
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Term
| Osmosis in Living Organisms |
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Definition
Digestive tract secretes liters of fluid daily which is reabsorbed by intestinal cells
-lack of reabsorption results in diarrhea
Plants are usually in a hypotonic environment
turgor pressure pushes against cell wall
provides support
Plasmolysis occurs in hypertonic environment |
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Term
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Definition
Agre found the water channel on RBC membrane
-put protein int frog oocyte, placed in hypotonic medium, and oocytes swelled up
Called pore aquaporin
allow passive movement of only water across membrane
Prominent in kidney tubule, plant root |
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Term
| Diffusion of Ions thru Membranes |
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Definition
Movement of ions is critical to many cellular activities
formation & propagation of nerve impulses
extracellular secretion
muscle contraction
regulation of cell volume
opening of stromatal pores on plant leaves
Sakmann and Neher established that membranes have ions channels |
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Term
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Definition
Highly selective
Most are gated- exist in open or closed configuration
-Voltage-gated channel- depends on ionic charge difference on both sides of membrane
Ligand-gated channel- depends on binding of ligand (not solute to membrane
Mechano-gated channel: depends on mechanical forces applied to membrane |
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Term
| Structure/Function of KcsA channel |
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Definition
Bacterial voltage- gated K+ ion channel M1 & M2 membrane- spanning helices
Pore where ions pass thru selectivity filter
which contains O at 3A
2.7 K ion binds
Entry of 3rd K+ ejects the ion at end
Na+ is too small ( 1.9 and isnt stabilized by O |
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Term
| Hinge-bending model for KcsA |
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Definition
M2 helices are straight and cross over
Channel opens when M2 helices bend at specific glycine |
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Term
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Definition
Contain 6 membrane assoc helices (S1-S6)
-Voltage-sensing domain S1-S4 that senses voltage across plasma membrane
Pore domain- S5- S6 same basic structure as bacterial, contains selectivity filter |
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Term
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Definition
Negative potential across membrane keeps gate closed
depolarization to more positive value exerts electric force on S4
residues shift from cytoplasmically exposed to extracellularly exposed
opens gate |
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Term
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Definition
Once opened, 10M K+ ions pass thru channel per second
So much goes thru that they are stopped by a small peptide into pore (inactivation)
Afterwards, the peptide is removed and gate is closed
So potassium channel can exist in 3 states: open, inactivated, closed |
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Term
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Definition
Diffusion of substances from high to low concentration by binding to membrane-spanning protein- facilitate transporter
Binding of solute on one side of membrane triggers conformational change in protein
Passive operation: no energy
Can mediate movement of solutes equally well in both directions
-depends on relative concentration of substance of both sides of membrane
similar to enzyme-catalyzed reaction:
transporters are specific for molecule they transport
exhibit saturation-type kinetics |
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Term
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Definition
Most mammalian cells contain glucose transporter
Human have 5 isoforms
Gradient maintained by phosphorylating sugar after it enters cytoplasm
Increase in blood glucose triggers insulin release which stimulates uptake of glucose
-low insulin, cells contain few PM transporters
increasing insulin stimulates fusion of vesicles of PM |
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Term
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Definition
Generates steep concentration gradients across PM
K+,Na, Ca2+
depends on integral membrane proteins
Requires energy since movement is against gradient
ATP, light, electron transport |
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Term
| Active Transport + ATP hydrolysis |
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Definition
Skou discovered an ATP- hydrolyzing enzyme in crab nerve cells that was only active w/ Na+ and K+ ions present
-responsible for transporting two ions
consumes 1/3rd of the energy produced by most animal cells 2/3rd by nerve cells
Found only in animal cells
Plant cells have a H+ pump
transport of solutes, control of ph, and control of cell growth |
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Term
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Definition
Found in epithelial lining stomach for maintaining high ph of stomach
While resting, pumps are in cytoplasmic membranes & are nonfunctional
When food enters stomach, hormone activates cells to move protein to apical cell surface & become functional
Prilosec prevents heartburn by inhibiting this protein
Zantac, Pepcid, tagamet block receptor from being activated by hormone |
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Term
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Definition
Use ATP w/o transfer of P to pump
occur in lysosomes, secretory granules, plant cell vacuoles |
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