LIPID MEMBRANES AND TRANSPORT Flashcards
1
Q
Describe the kind of membrane that all cells have. What makes it so unique and important for the cell? What additional membrane does the eukaryotic cell have that prokaryotic does not have?
A
All cells have plasma membrane
It is a barrier that prevents intracellular molecules from leaking cell and blocks harmful molecules form entering cell.
Eukaryotic cells have internal membranes that limit intracellular mem compartments and organelles.
2
Q
what other functions besides barriers do cell membranes do? What specific structures are included?
A
sense changes in environment, control the passage of solutes across membrane, allow cells to move and acquire certain shapes.
They have membrane proteins and a bilayer.
3
Q
describe the bilayer structure that all membranes have? What structures are present? what is the unique characteristic?
A
double layer made of lipids, specifically phospholipids. bilayer has mosaic structure, with membrane proteins embedded in in it. They have amphiphilic nature (both hydrophilic and hydrophobic).
4
Q
Describe the structure of phospholipids? How do phospholipids differ?
A
phospholipids have hydrophilic head that have phosphate groups, hydrophobic tail that have fatty acids. They differ by their size of hydrophobic tails and chemical structure of POLAR HEAD specific groups (form ester bond with phosphate)
5
Q
What are fatty acids? Provide examples of fatty acids?
A
simple lipids that have hydrophobic carboxylic acid head and long hydrophobic, aliphatic radical (R) tails.
Ex: fats, oils, cholesterol, steroid
6
Q
Describe the structure of triacylglycerol. What are some examples? What makes them different from phospholipids?
A
Triacylglycerol- 3 fatty acids attached glycerol atom by ester linkages. examples include FATS (animal flat, plant oils).
makes them different- they are completely HYDROPHOBIC(lack of groups, so no H-bonds). Phospholipids are amphiphilic.
7
Q
Distinguish between the energy use of carbohydrates vs. triacylglycerol in the cell. where are triacyclglycerols stored?
A
energy from carbohydrates (glycogen, starch) are stored for immediate use. While triacyclglycerols are for long- term storage of energy.
stored in adipocytes (as free intracellular droplets)
8
Q
What are the most abundant lipids in the cell membrane? What defines the class of lipids?
A
phospholipids. polar head.
9
Q
How do the four major membrane phospholipids differ? What structural feature define phospholipids?
A
They differ in size of hydrophobic tails, shape and charge.
Polar heads defines phospholipid
Ex: phosphatidyl- choline, serine, ethanolamine
10
Q
What is another major component of membrane and has similar amphiphilic nature like phospholipids?
A
Cholesterol (form of sterol)
11
Q
What feature distinguishes lipids from carbs (polysaccharide) and nucleic acids?
A
lipids are chemically diverse and characterized by their ability to be extracted into organic solvents, when cells are homogenized.
12
Q
list all functions of lipids.
A
lipids serve as membrane building blocks, store energy, and SIGNALING (membrane receptors, endocrine), TRANSPORT .
13
Q
What lipid structure is responsible for transporting water insoluble molecules in blood? list examples of insoluble molecules.
A
serum albumin
examples include: fatty acids, triacylglycerols, steroid hormones
14
Q
Describe the other types of membrane lipids (besides phospholipids) that are amphiphilic. What are their chemical structures?
A
polyisoprenoids (made form isoprene units)
steroids- multiple ring structure, polar head that has OH group, 1 hydrocarbon tail(also made of isoprene units)
Glycolipids (2 long hydrophobic tails, polar region of OH and sugar (galactose)
15
Q
Describe the behavior of phospholipids when in water.
A
polar heads are exposed to water, while hydrophobic, nonpolar tails minimize interaction with water and hide inside, by forming micelles
16
Q
What are two ways of hiding polar tails? what are the two different structures?
A
in water, spontaneously form micelle or lipid bilayers (allowing tails to hide inside structure) and facing polar heads out to aqueous environment.
17
Q
Why do lipid bilayers spontaneously close? what happens if bilayer had open edges or was in a planar form?
A
spontaneously close to form sealed compartments and prevent hydrophobic tails from being exposed to aqueous environment. if the bilayers have open edges, hydrophobic interior will be exposed to outside, water environment and be unstable
18
Q
What are liposomes? what is the function?
A
closed bilayer compartments (sphere shape) that are artificially made by mixing pure lipids in water.
Used for drug delivery
19
Q
What three chemical forces keep phospholipids together in the right orientation and stabilize plasma membrane in water? Describe how each force does this.
A
Hydrophobic interactions-major force that keeps lipids together, form bilayer
VDW- strengthen interactions between tails when tails are close to each other
hydrophilic- position polar heads outward in each layer
20
Q
What defines the elasticity of plasma membrane? describes the different types of examples of this feature?
A
mobility of phospholipids
ex of movement: flexion (side to side), rotation, flip flop of leaflet (rarely occurs unless assisted by enzymes)
21
Q
How can carboxyl groups of fatty acids be connected to other organic molecules?
A
Carboxy group can form esters or amides
22
Q
What role do triacyclglycerols play in the cell?
A
major energy deposits the cell, structural component of cell, store energy.
23
Q
How do fatty acids vary in phospholipids?
A
vary by length and saturation (max number of hydrogens). Some fatty acids are unsaturated (have double bonds)
24
Q
provide an example of each type of lipid
A
Phospholipid- ex: phosphatidyl-choline, sphingomyelin
Steroid- ex: cholesterol, testosterone
Glycolipid- ex: galactocerebroside
Polyisoprenoid- (made from isoprene units)
ex: Dolichol phosphate that carries activated sugars in membrane associated synthesis of glycoproteins.
25
Which two enzymes help overcome and support bilayer leaflet's asymmetric composition? List specific function of each.
Flippases and Scramblases.
Flippase- support and maintain asymmetric lipid in Golgi. They catalyze transfer of SPECIFIC phospholipids from exterior space, flip and move them into cytosolic monolayer.
Scramblases- newly synthesized phospholipids added to cytosolic half of bilayer (ER) . enzyme catalyzes transfer of random lipids from one monolayer to another, allowing for symmetric growth, even distribution.
26
How are newly synthesized lipid membranes and lipids delivered through plasma membrane and organelles?
lipids are synthesized in the smooth ER, passes golgi complex, and delivered to PM through TRANSPORT VESICLES
27
What adds to the asymmetry of cell membrane bilayers?
Functional phospholipid modification
28
Differentiate between saturated and unsaturated fatty acids? what feature makes them different. Provide examples of each.
saturated-fatty acids with no double bonds
ex: stearic acid, palmitic acid
unsaturated- fatty acids with 1 or more double bonds ex: oleic acid, maleic acid and fumaric acid (trans db)
29
What does the presence of double bond indicate in fatty acid chain
Indicates fatty acid is unsaturated, double bond creates a kink in the chain, does not allow free rotation about that specific C-C bond.
30
what differentiates oleic acid from stearic acid? how are they similar?
Oleic acid has double bond (unsaturated); similarities- both have 18 carbon long fatty acid chain.
31
What 3 factors fluidity of plasma membrane depend on? Describe the relationship between temperature and fluidity.
composition of PM and temperature and length of fatty acid.
| The HIGHER the TEMPERATURE, the HIGHER the FLUIDITY
32
what happens to fluidity, with saturated fatty acids? Why does this occur?
when saturated fatty acids increases, the fluidity decreases. occurs because van der Waals interaction increases between lipids (strong attraction to keep tails together)
33
How does the Length of fatty acids affect membrane fluidity?
The longer the fatty acid, the less fluid a fatty it is. (due to more VDW interactions formed, making it stiff)
34
How do fatty acid residues vary in length? Which fatty acids are extremely long? How many carbon atoms?
They vary from 14 to 20 carbon atoms long. phospholipids are very long like SPHINGOMYELIN with 24 carbon atoms.
35
Do fats with unsaturated triacylglycerols have a Higher or Lower melting point?
Lower melting point (due to db)
36
Distinguish between the two types of triacyclglycerols in terms of saturation.
Plant oils have unsaturated fatty acids. Animal fats have large portion of saturated fatty acid residues.
37
How can cell membranes maintain fluidity at low temperatures? What occurs if the temperature is too high?
INCREASE UNSATURATED FAs. Membranes rich in unsaturated hydrocarbon tails remain fluid at lower temps.
temp too high, you will add extra fluidity and make membrane too loose and porous (not good).
Hence maintain fluidity without losing integrity in broad rang of temps.
38
What other major component of cell membrane is important and determines fluidity of membranes?
```
Cholesterol!
They help create a constant rate of fluidity under broad range of temperatures.
function as FLUIDITIY BUFFER
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39
Elaborate on Cholesterol's fluidity buffer role in cell membranes. How does it maintain it with high temps? Lower temps? what percentage of cholesterol composes membrane lipids?
cholesterol keeps fatty acid fluidity in intermediate range, regardless of temperature shifts. In high temps, it keeps membrane more solid.
lower temps- keeps membrane more liquid.
30%
40
Describe the interaction of cholesterol in the lipid bilayer.
```
Cholesterol forms nonpolar and polar interactions with membrane lipids.
polar group (OH) of cholesterol are in contact with polar head of phospholipids.
short nonpolar tail of cholesterol interact with hydrophobic tail of phospholipids
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41
Describe the structure of cholesterol and how it helps maintain fluidity. Compare it to phospholipids.
Cholesterol has rigid, flat steroid ring structure that does not change conformation during temperatures shifts, which helps to maintain fluidity.
However, phospholipids can be densely packed (less fluid) or too loose based on temp
42
distinguish the effect of cholesterol at low temps vs its effect at high temps.in terms of mechanism
Low temps- steroid rings help break down compactness of lipids (create more space), allowing more liquidity, fluidity.
High temps- inserts vertically to preserve fluidity, keep lipids together and prevent them from spreading.
43
What would happen to phospholipid molecules without cholesterol?
The phospholipid membranes would change their physical properties in narrow range of temps, greatly affecting cellular functions (make them fluid and disordered)
Cholesterol- helps keep membranes fluid (elastic) and non-porous.
44
What are lipid rafts? What are their components? Function and structure?
viscous lipid membrane in leaflet of PM spontaneously made from combining CHOLESTEROL and SPHINGOMYELIN.
they help regulate receptor trafficking and signaling molecules, hold together proteins.
structure- tightly packed and ordered with lipids, but can float within bilayer.
45
Describe Cardiolipin in terms of structure and function
Cardiolipin- major component of inner mitochondrial membrane (20% of lipids)
structure- 2 phospholipids connected to glycerol; 3D tetrapod structure. (cone shaped, curve)
Function- stabilizes intermembrane folds like cristae in mitochondria, immunogenic and antibodies against them are indicators of autoimmune diseases.
46
what happens to membranes when temperature decreases?
it solidifies.
47
What is the normal structural features of membranes? How does saturation affect viscosity?
fluid like, low viscosity, which defines its elasticity.
| higher portion of saturated chains are very viscous (lower fluidity)
48
what happens if there is too much cholesterol?
it will stiffen the membrane.
49
Describe the two membrane permeability is based on, as well as specific permeability of different compounds.
based on size and charge of molecules
small, nonpolar- (O2, CO2, steroid hormone) can easily cross membrane (simple diffusion)
small, uncharged polar molecules (water, ethanol)- capable of crossing lipid bilayer because of their small size and high concentration.
Larger, uncharged polar molecules (amino acids, glucose)- low capability of crossing membrane (almost non-exist)
IONS- (H+, K+ Ca, Na) CANNOT CROSS MEMBRANE at all. needs channels and transporters.
50
Why is cell membrane a good dielectric? Why is this important.
they are insulators of electric charges (separates opposing charges inside from outside cell)
Important b/c it generates membrane potential and propagates action potential
51
What is osmosis and how does it affect solute concentration?
| How does solute concentration affect osmotic pressure?
Osmosis- flow of solvent (water) across semi-permeable membrane that occurs due to differences in [ ] of solute (which cannot pass membrane)
difference in solute concentration also creates difference in solvent concentration as the solvent moves toward reaching thermodynamic equilibrium and establishing osmotic pressure.
52
Why is one ion osmotically active as one large molecule or protein?
they (ions, large protein) are both impermeable to cell membrane, cannot cross?
53
Define tonicity, and provide 3 main examples of osmotic changes in volume
Tonicity- movement of water in and out of cell, creating membrane tone.
1. Isotonic- equal concentration of ions in solution
2. Hypertonic- higher concentration of ions in solution than in cell
3. Hypotonic- lower concentration of ions in solution than in cell.
54
What causes cells to have constant buildup of osmotic pressure? List the intracellular molecules that do this.
High concentration of intracellular molecules.
The intracellular molecules that cannot cross membrane:
1. small inorganic (cation and anions)
2. polar and charged organic metabolites (aa, sugars)
3. Charged macromolecules (proteins, DNA, RNA)
55
Describe the Donnan effect and how it affects osmotic pressure.
Donnan effect- about how large macromolecules that are constantly synthesized cannot cross the membrane, and thus attract a lot of osmotically active particles inside the cell (generating excessive osmotic pressure in cell).
56
what cell structure allows the fast passage of water through membrane?
Aquaporins (high permeability)
57
Describe how protozoans, plant and animal cells create solutions for osmolarity.
Protozoans- have centralized vacuoles that extrude water
plant cells- rigid cell walls, prevent swelling of cell (tolerate osmotic diff)
animal cells- Na+/K+ ATPase actively pump out ions.
58
Describe the biochemical composition of plasma membrane, including their features, function and examples.
composition varies from cell-cell.
PM composed of:
1. Lipids (phospholipids, steroid lipids- cholesterol)
-Amphipathic (amphiphilic) and Hydrophobic interior serves as barrier
2. Carbohydrates (normally attached to lipids or proteins)
-important in recognition of cell types
-intracellular signaling (during tissue growth, cells do not trespass boundaries of other tissues)
-signaling
3. Proteins- have specialized functions
ex: myelin sheath - insulate axons; made of mainly lipids, some proteins
RBC Plasma membrane- majority proteins, lipids
Mitochondria inner membrane- ATP production
59
what percentage of genome are made of membrane proteins? Describe which structures make membrane proteins and where they are located on membranes. Also distinguish between integral and peripheral proteins. Provide example of membrane proteins.
30% membrane proteins
-made in SARCOPLASMIC RETICULUM (modified ER, few different proteins) of skeletal muscle and PLASMA MEMBRANE (> 100 different proteins)
-located on both intracellular and extracellular sides of membrane
-Integral- protrude membrane fully or partly (ion channels)
-Peripheral- attached to integral proteins (subunit of receptors/ion channels)
Ex: transmembrane protein (one alpha helix), protein of multiple alpha helixes, Beta barrel, leaflets (protein attach to cytosol and alpha helix), covalently attached to lipids, noncovalent with transmembrane protein.
60
Describe the types of membrane proteins and their functions
-Transporters (like Na+ pump)- that actively pumps Na+ out and K+ in
- Ion channels (like K+ leak channel)- allow K+ oions to leave cells, influence cel excitability.
Anchors- link intracellular actin filaments to extracellular matrix ex: integrins
Receptors- bind to a molecule to generate signals that direct cell growth and division. Ex- platelet-derived growth factor receptor
Enzymes- catalyze reactions; like production of small intracellular signaling molecule cyclic ATP in response to extracellular signals.
Ex: adenylyl cyclase
61
How are aqueous channels in membrane formed?
from amphiphilic alpha- helices help form the channels. (4 helices surrounded by aqueous pore)
also GFP has similar structure to beta barrel.
62
what are the structural membrane proteins? provide examples.
proteins that help strengthen and support the plasma membrane. Ex: spectrin is found in cortex of red blood cells that support PM and provides RBC's biconcave shape.
Spectrin- dimeric protein that forms a lattice and is linked to Pm by intracellular cells attached to transmembrane proteins form meshwork (tetramers linked to actin filaments).
63
Describe the structure and mechanism of potassium leak channels.
K+ leak channel- tetramer structure with 4 identical protein subunits wrap around central ion pore; also have selectivity filters and loops ( alpha helix has negative charge that attracts positive ion in pore)
Mechanism- K+ leak channels allow K+ ions to move freely across membrane. When cell is resting, these channels are open making membrane permeable to K+ more than other ions. This makes K+ ions flow outside cell down its concentration gradient. Loss of positive charge inside cell, causes voltage difference or membrane potential. Charge imbalance will prevent any further K+ ions from leaving cell and establishing equilibrium.
64
What are Bacteriorhodopsins? what is their purpose? Describe the retinal cycle
light driven proton pumps. It captures light energy and uses it move protons (H+) out of cell.
65
What parameters does rate of diffusion depend on ?
depends on MAGNITUDE (steepness) of gradient, PERMEABIILITY of membrane to substance (lipid solubility of compound, density of membrane openings, pores or channels allow for cross specific solutes) and SURFACE AREA to membrane (ex: small intestine, ability to absorb nutrients)
66
List the different types of membrane transport
Passive transport -channel mediated and transporter mediated; does not require energy and goes down concentration gradient.
Active transport- pump; requires energy (ATP) and driven against concentration gradient
67
what structures allow PM to ensure selective permeability of cell and its organelles to molecules that normally cannot cross membrane? how do steroid hormones differ
```
Transporter proteins.
STEROID HORMONES (estrogen, cholesterol) can cross membrane on their own.
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68
Describe the lipid solubility of drugs.
comparing different drugs, to highlight that drugs that are more hydrophobic are more addictive, however more difficult to be administered or hydrolyzed.
Ex: Heroin (diacetylmorphine) is more addictive and reaches brain faster than morphine because it is more hydrophobic.
Crack cocaine (free base) is more hydrophobic than powder cocaine (salt), hence it is more addictive and reaches nerve very quickly
69
Describe the permeability of ion channels. How are ions transported?
the permeability of channels is controlled (GATED). ions are transported through CHANNEL TUNNELING (do not form complexes with transported molecules)
the channels are activated based on whether they are closed or open.
Channels are selective towards substances allowed through.
K+ leak channels- are always open
other channels open and close at certain conditions- hence gated
70
What is GLUT-4? Explain what kind of transporter it is and how it's used.
glucose transporter in skeletal muscles.
its a uniporter that facilitates passive transport of glucose down its concentration gradient
the concentration of glucose is always smaller inside skeletal muscle than outside (blood plasma) because muscles consume lots of energy, using glucose for ATP production (excess of glucose rapidly converted into glycogen)
71
What is Active transport? How does it differ from Passive transport? What is an example of membrane transporter that uses active transport?
Active transport- always occurs against concentration gradient, moves farther from equilibrium. requires external source of energy.
Passive transport- goes down [ } gradient.
ex: Na+ K+ ATPase (pump)
72
What are the two major types of active transporters and how do they differ? provide examples.
primary transport- energy directly from biochemical reaction (ATP Hydrolysis) or other external source (light)
secondary transport- use energy of existing electrochemical gradient generated by active transporters (gradient driven) (dissipation of one gradient coupled with building another) Ex: antiport or symport
These transporters differ by source of energy
73
Describe the composition of ion concentrations inside and outside.
More Na+ Ca and Cl- ions outside (extracellular) and K+, inside (intracellular)
74
What kind of transporter is Na+-glucose? what is it's function? Describe the connection between the two molecules.
symport active transporter (transport of 2 compounds coupled)
uses energy of sodium gradient to accumulate glucose inside the cell (1 Na+ out, 1 glucose in). Na+ ion moves into cell down its [ } gradient, bringing glucose into cell as well (binding of one of ions, enhances binding of other; gut lumen)
difference in Na concentration results in different probability of forming Na glucose complex inside and outside cell, inside cell, even if glucose [} higher in cell, since Na is lower concentration probability of forming complex lower.
75
What is a common example of primary active transport? What products does it produce?
Na+ K+ ATPase. it pumps 3 Na+ outside cell, and 2 K+ ions inside the cell.
uses primary source of chemical energy (hydrolysis of ATP).
76
Name the three major functions for Na+/K+ ATPase.
1. electrogenic- (pumps 3 Na out for every 2 K+ pumped in, increasing negative charge inside cell; cells normally negatively charged.
2. supports osmotic balance-by pumping ions(Na) out to prevent a net movement of water into cell
(ATPase is inhibited by the drug ouabain, causing cells to burst)
3. harnesses Na+ gradient that can be used as a source of energy for other transport.
77
How does drug ouabain affect the cell? What happens?
it causes the cell to burst since ouabain inhibits Na+ ATPase
78
What is the purpose of Ca^2+ ATPase? where does this process occur in the cell? What kind of transport is it? How is it similar to Na+ ATPase?
SERCA (Sarco endoplasmic reticulum, Calcium ATPASE) - transports 2 Ca^2+ per ATP from the cytosol to lumen of sarcoplasmic reticulum
process occurs in sarcoplasmic reticulum
primary active transport
Both SERCA and Na+ K+ ATPase use chemical energy of ATP hydrolysis to convert into mechanical energy allowing ions to move through DIRECT PHOSPOHORYLATION OF PROTEIN DOMAINS.
79
Distinguish between uniport, symport and antiport transporters. list examples of each/
They distinguish between number of transported molecules that carrier may support
Uniport- transports a single substrate across membrane (down [ } gradient)
ex: GLUT4 in skeletal muscle.
Symport - carries two different ions or molecules in the same direction
Na+ Glucose cotransporter in intestinal cells
Antiport - carries two different ions in opposite directions.
ex: Na+ Ca+ exchanger in heart cells
symport and antiport are coupled transport by gradient-driven pumps (co-transporters, allow carriers to use energy of existing transmembrane gradient to create new gradient).
80
How do eukaryotic cells use primary and secondary active transporters to couple in system? distinguish between transporters used in animal vs plant cells.
in animal cells, Na+ gradient that is generated by Na+ pump is used for other transporters.
Plant cells- use proton gradient that is generated by H+ pump that will be used for importing solutes through transporters.
Similarly, animal cell lysosomes and plant cells vacuoles, have additional proton pumps that pump H+ into those structures to keep environment acidic.
81
Describe how Na+/glucose symport is coupled with other transports in intestinal cells? Which ones are involved?
2 glucose transporters at opposite ends of cell
apical domain of PM that has the Na+ glucose symport (use Na+ gradient to bring in glucose) for high [ } of sugar in cytosol (take up glucose from gut)
Basal domain- cells have passive glucose uniport that releases glucose down its [ } gradient for use by other tissues.
82
Describe the different pharmalogical applications that relate to use of transporters. list examples.
Some drugs may inhibit Na+/K+ pump that will create weakened heart muscle since:
less Na/K pump activity- causing more sodium inside cell and less activity of Na/Ca exchanger (antiporter clears out Ca form cardiomyocytes upon contraction), creating more Ca left inside the cell leading to stronger contraction (inotropy increases) of heart; while relaxation is affected and heart becomes stiffer.
Examples of drugs that inhibit Na/K pump are DIGITALIS, OUABAIN)
Treatment for weakened heart- CARDIAC GLYCOSIDES
CHOLERA TREATMENT- drinking solution of glucose with NaCl (oral hydrogenation therapy)-
cholera toxin inverts Cl- channels in intestinal epithelial cells; pumping Cl- outside epithelial cells into intestine. This causes osmotic active Cl- to drive lots of fluid away from cells, causing life-threatening dehydration.
Treatment- drink glucose with NaCl as sodium and glucose will co -transport back into blood and blood osmotic pressure rises, osmotic flow drives water back to blood (saving 95% victims).
83
what is the special type of passive transport that requires energy? How do they work? why do they require energy and what form of energy is used?
Translocases- special membrane proteins that allow passage of long biopolymers across membrane.
require energy because there is no effective thermodynamic force that would favor movement of molecule in either direction,( equal concentrations of monomers in and out of cell)
use energy in form of ATP hydrolysis.
84
Explain the three effective ways translocases acquire energy for effective unidirectional translocation.
1. hydrolyzing ATP
2. using chaperone proteins to unfold protein
3. use ribosomes to add extra aa, make chain longer.
85
What is the resting (equilibrium) membrane potential?
the "normal" negative potential when the cell is at rest (not stimulated).
86
What is Electric potential? what is another name for it? How does it work?
electric potential- the separation of electric charges that can be concerted in to electric current (movement of e- charges)
aka as Potential
potential can be stored and remain constant, until it is released to create current (reduces potential)
No potential when order of charges are uniformly neutral (+ - + -)
87
Why are all cells negatively charged inside the cell? Why is this negative membrane potential important? What about cells whose membrane potential cells change ? (give examples)
negatively charged in cell due to FIXED ANIONS (protiens, nucleic acids, phosphate attached to macromolecules) that cannot cross the plasma memrbane.
important to for proper cell homeostasis. all cells have membrane potential that is normally stable.
Some cells have evolved to change their membrane activity due to their normal activity (ex: neurons, muscle fibrils, cardiomyocytes, pacemaker cells).
88
How can negative membrane potential be measured? List the range of membrane potential for cells and provide resting potential for neurons. Also explain what the negative sign means for on voltage values.
by magnitude and direction
membrane potential of cells vary from -50 -120 mV depending on cell type. (neurons have resting potential around -70 mV.
Negative sign means cell is negatively charged inside relative to outside.
89
what are the two major contributors to cell membrane potential?
Potassium Leak Channels and fixed anions that cannot cross cell membrane.
90
How is potassium equilibrium potential established? what kind of transmembrane protein used? what happens if this transporter is closed?
established through cells at rest (not stimulated) that have potassium leak channels open.
when k+ leak channels open, they stabilize resting membrane potential by allowing K+ ions to leak out or enter cell any time, counteracting small changes in membrane potential (no net movement of K+ in or out cell)
if K+ leak channel close, plasma membrane potential = 0, since + and - charges are balanced.
91
List the different types of changes in membrane potential.
Resting potential, repolarization, hyperpolarization, rising phase, falling phase
92
Distinguish between upward deflection and downward deflection in terms of potential.
upward deflection- decrease in potential (becomes more positive)
Downward deflection- increase in potential (more negative)
93
What occurs in resting potential compared to depolarization and hyperpolarization? what transporters are involved in these processes? Also explain how action potential is involved.
repolarization- K leak channels allow free passage of K+ ions, establishing K equilibrium. cells are negatively charged inside relative to outside (due to negative polymers inside)
Depolarization - in response to neurotransmitter or change in membrane potential allows, channels to create influx of Na+ ions; since their is more Na+ outside cell than inside, Na+ leaks inside, bringing + charges in cells and DECREASING membrane potential (decreasing negative charge inside cell)
Hyperpolarization- channel receptors that allow the flow of Cl- ions become open in response to neurotransmitter. since more Cl- ions outside cell than inside, Cl- leak in, bringing more negative charge inside cell. due to already negatively charged cell inside, entry of Cl- INCREASES membrane potential (increases difference in charges across PM)
94
What is action potential? Which transporters initiate action potentials?
the local change in membrane potential that unidirectionally propagates along an axon and delivers electrochemical signal from one cell to another
Na+ voltage gated channels that are located at AXON HILLOCK (high density) initiate AP. They are also located along axon
95
What occurs during the rising phase of an action potential? Describe how depolarization affects voltage gated channels.
Rising phase- depolarization occurs, where Na+ voltage gated channels open and allow Na+ ions to rush inside cell, making a more positive membrane potential.
small depolarization of neuronal membrane triggers the action potential.
-depolarization too small, only small number of Na+ voltage-gated channels will open, will not result in strong membrane depolarization
-if initial depolarization stronger than or equal to certain threshold potential, the number of Na channels are strong enough to allow Na ions to escape and cause rising phase of AP. (-20mV)
96
What occurs during overshoot in an action potential?
Overshoot- at end of rising phase, Na+ voltage gated channels close and influx of Na+ ions stops. Positive membrane potential causes inactivation of voltage-gated Na+ channels. (20 mV)
97
Describe what occurs during falling phase and after- hyperpolarization. Why do these specific ions rush out of cell? What transporter helps restore balance?
Falling phase- voltage-gated K+ channels open, allowing efflux of K+ ions and it carries away previous positive charge in cell; Restores cell's negative membrane potential. (-20 mV)
After-hyperpolarization- although potential has been restored at this point, concentration of ions inside cell is off balance (lots of Na outside cell and little K inside). To restore proper ion balance, Na+/K+ ATPase pumps sodium out and potassium in will work constantly during all phases.
98
Which transporter does neuronal cell spend 60% of it energy on?
Na+/K+ ATPase
99
Describe the process of unidirectional propagation of the action potential?
Action potential propagate unidirectionally because Na+ channels have an absolute refractory period where the channels are inactivated and cannot generate an AP back to back (Right after one just occurred)
100
What stimulates exocytosis in chemical synapses? Describe the process.
depolarization stimulates exocytosis. Steps:
1. Action potential depolarizes axon terminal
2. depolarization occurs that opens voltage gated Ca+ gated channels
3. Ca+ ions rush inside cell, that triggers exocytosis of synaptic vesicle (vesicle fuse w/ PM and expel out neurotransmitters)
4. Neurotransmitters go to synaptic cleft and bind to receptor on pos-synaptic cell.
101
how does each neuron establish many contacts in the brain?
through synapses- contact point where one neuron communicates with another. 10,000 total synapses on spinal motor neuron (2,000- cell body; 8000 on dendrites)
in cortical neuron in brain there are 15,000 inputs.
102
What does osmolarity and tonicity of solutions depend on?
they depend on number of solubilized particles. (do not depend on chemical nature of solute or size of particles)
103
Explain the mechanism of action for K+ channels in terms of selectivity filter and repulsion
Selectivity filter- to pass through filter in channel, K+ ions must shed and break through water molecules. only allows K+ ions to pass and not other ions since K+ is larger and longer than Na+ and has a perfect fit binding with backbone carbonyls. On the other hand, Na is too small and cannot fit to K+ binding site as it would be thermodynamically favorable. Carbonyl Oxygen atoms (interacting with K+ atoms) mimic hydration by water molecules and replace them.
Repulsion- 4 levels of K channels- since K+ ions interact with each other in single file line, they repel one another and result in bouncing from the first level to the second level and to the next, towards lower concentration.
104
What factors ensure K+ ions to move and change position within 10-100 ns?
combined effect of K+ binding to carbonyl atoms that mimic hydration and mutual repulsion between K+ ions.
105
What defines the rate of diffusion?
the amount of molecules cross a certain area of membrane over a given period of time.
106
Explain the purpose of the Na+Ca+ exchanger, including what kind of transporter it is and the mechanism behind it.
uses the electrochemical gradient (energy)of sodium to pump Calcium outside of the cell. 3 Na+ ions are being being imported in the cell (goes down [ ]), while one Ca^2+ is being exported out. Process occurs in PM, Mitochondria and ER.
form of secondary active transporter (antiporter)
107
What transmembrane protein helps restore ion balances during action potential process?
Na+/K+ ATPase
108
What is the absolute refractory period?
period of time where a cell cannot repeat an AP after one just occurred; as Na channel are inactivated (time for membrane to respond to another stimulus after returning to resting state).
