Basic Cell Membrane & Potentials (PREMATRIC)
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| show | 1. Physical isolation
2. Regulation of exchange with environment
3. Sensitivity
4. Structural support
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| Membrane Function: Physical isolation | show 🗑
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| show | Transporting nutrients in and metabolic wastes out
"Compartmentalization with communication"
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| Membrane Function: Sensitivity | show 🗑
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| Membrane Function: Structural support | show 🗑
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| show | 1. Lipids
2. Proteins
3. Carbohydrates
*composition of lipids & proteins varies from cell to cell
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| Membrane composition and structure: Lipids | show 🗑
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| Membrane composition and structure: Proteins | show 🗑
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| show | Important in recognition of cell types:
-immunity (outside of the cell)
-intercellular signaling - during tissue growth, cells will not trespass past boundaries of other tissues
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| show | - Not static/solid sheets of molecules locked rigidly
- Membrane held together primarily by HYDROPHOBIC ATTRACTIONS (mutual exclusion of water)
- When molecules are close together, VAN DER WAALS ATTRACTIONS (+ and -) reinforce hydrophobic interactions
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| show | Main lipid constituent of most membranes
-similar to triglyceride fats, but have only 2 fatty acid tails rather than 3
-Amphipathic
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| show | -3rd hydroxy group of glycerol is joined to a phosphate group, which is negative in electrical charge
-add'l small molecules (usually charged or polar) can be linked to the phosphate group.
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| show | -Hydrophilic molecules (polar head) dissolve in H2O b/c contain charged groups -> interact with H2O
-Hydrophobic molecules (hydrocarbon tails) insoluble in H2O b/c all/most of their atoms are uncharged & nonpolar (no energetically favorable interactions)
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| Phospholipid conformation | show 🗑
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| show | 30% of proteins encoded in a cell's genome are membrane proteins.
for example:
-Sarcoplasmic Reticulum of skeletal muscle have only a few different proteins while plasma membranes have > 100 different proteins.
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| Membrane Protein Orientation | show 🗑
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| show | Compact 3-D structures are are either
1. Integral: all or part penetrates the phospholipid bilayer
2. Peripheral: do not interact with hydrophobic core of bilayer
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| show | 1. Transport
2. Enzymes
3. Receptor sites
4. Cell Adhesion
5. Attachment to the cytoskeleton
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| show | a hydrophilic channel (mostly for ions) or a carrier/pump
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| show | built into the membrane with active sites exposed to aqueous medium
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| show | binding domain is exposed to ECF; may induce signal transduction through membrane
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| Membrane Protein Functions: Cell adhesion | show 🗑
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| show | important in maintaining cell shape and fixing the location of certain membrane proteins
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| Properties of Membranes (REVIEW) | show 🗑
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| show | 1. External Membranes (cell membrane)
2. Internal membranes (nucleus, organelles)
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| show | 1. Chemical gradient
2. Electrical gradient
3. Electrochemical gradient
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| Chemical Gradient | show 🗑
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| Electrical gradient | show 🗑
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| Electrochemical gradient | show 🗑
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| show | net flux of molecules from one region to another via random thermal motion
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| Net rate of diffusion (J) | show 🗑
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| show | takes into account:
1. Partition coefficient (solubility in lipid (more perm) vs. H2O (less perm)
2. diffusion coefficient (mol wt & viscosity)
3. membrane thickness (ex: when sick, mucous layer on membrane makes thicker, harder to diffuse thru)
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| show | Water flows across a semipermeable membrane b/c of differences in SOLUTE [ ].
-The [ ] of impermeable solutes establish osmotic PRESSURE differences.
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| show | Burst
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| A cell in a hypertonic solution will... | show 🗑
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| show | Stay the same
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| Facilitated diffusion: Channels | show 🗑
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| 2 distinctions between ion channels and aqueous pores | show 🗑
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| Membrane Permeability | show 🗑
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| Hypotonic Solution | show 🗑
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| Isotonic Solution | show 🗑
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| Hypertonic Solution | show 🗑
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| Osmolarity | show 🗑
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| show | 1. [ ] of solute
2. # of particles the solute dissociates into in solution (ex. CaCl2 = 3 particles)
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| show | (mOsm/L) = g x C
where g is the # of particles per mole in solution (Osm/mol)
and C is the concentration (mmol/L)
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| Types of Carrier-Mediated Transport | show 🗑
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| show | -Mediated by carrier proteins
-moves molecules against [ ] gradient
-requires direct input of energy
ex: Na+/K+ ATPase Pump
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| Secondary Active Transport | show 🗑
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| Membrane Potential | show 🗑
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| show | Difference in ionic [ ] & selective permeability of channels
-RMP is maintained by Na+/K+ pump (pumps 3 Na+ ions out/2 K+ ions in per cycle. utilizes 1 ATP per cycle.)
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| Intracellular [ ] of certain ions | show 🗑
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| Extracellular [ ] of certain ions | show 🗑
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| show | I = mV/R
where:
I = current
mV = voltage
R = resistance
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| Conductance | show 🗑
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| Magnitude of potential | show 🗑
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| show | 1. Unequal transport of cations generates a membrane potential.
2. maintains [ ] gradient.
(ion [ ] difference & selective permeability determines the resting membrane potential of -70.
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| show | The ion with the largest resting conductance will have the greatest influence on RMP. (in this case, K+ = -90 b/c channels are more open than Na+ channels = +60)
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| Nerst equation | show 🗑
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| show | Ek = 61 x log { [5mM] / [150mM] } = -90 mV
(5mM outside cell; 150mM inside cell)
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| Membrane Potential (bottom line) | show 🗑
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| Changes in membrane potential as signals (two types) | show 🗑
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| show | 1. threshold
2. Depolarization
3. Repolarization phase
4. Hyperpolarization afterpotential
(upward deflection = decrease in potential; downward deflection = increase in potential)
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| show | the value of the MP which, if surpassed, leads to the all-or-nothing initiation of an AP.
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| show | the rising phase of the AP (a large # of Na+ channels start to open once threshold is reached. - net movement of Na+ into the cell starts)
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| show | the return of the MP to the resting potential (voltage gated Na+ channels start to close and voltage gated K+ channels start to open; net movement of Na+ into cell stops; net movement of K+ into cell starts (delayed rectifying response))
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| show | time at which the MP is actually more negative than the RMP (voltage gated K+ channels remain open for a relatively long time before eventually closing - net movement of K+ into the cell continues for a while before stopping)
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| Action Potential Features | show 🗑
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| Action Potential Features (cont.) | show 🗑
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| show | 1. Highly selective pores that open and close (only appropriate size/charge may pass)
2. 10^5 times greater transport from channel than carrier protein (but usually not coupled to energy source (down gradient process)
3. gated, not continuously open
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| Voltage-gated Channels | show 🗑
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| show | 1. Rest: Na+ channel is in closed conformation (low energy, high stability)
2. Depolarized: channel is open (exists only transiently) (high E, low S).
-inactivated is lower E still, so after a period spent in open position, channel becomes inactivated.
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| show | 1. shape & size of AP usually invariant, the FREQUENCY of AP can be used in the code for info transmission. (higher the freq, more important the message.)
2. Max freq is limited by duration of absolute refractory period (1 msec) to ~1000 impulses/sec
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| Graded Potentials | show 🗑
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| show | 1. names differ according to location
2. small, local changes
3. may be depolarizing or hyperpolarizing
4. direction and magnitude of response is proportional to direction and mag of stimulus.
5. decay rapidly with distance. (short-lived)
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| show | 1. in muscles: endplate potential
2. in neurons: postsynaptic potential
3. sensory organs: receptor potential
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| Ligand gated channels | show 🗑
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| show | the chemical and electrical forces of a particular ion are balanced so that there is no net movement of molecules
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| Absolute Refractory Period | show 🗑
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| show | time after one AP is initiated when can have a 2nd AP (due to hyperpolarization), but only with a greater stimulus (depolarization) than necessary to initiate the 1st.
-Na+ channels are starting to reset, but inward K current is still greater than at RMP
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Created by:
Kanarema
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