physio: struc/func of biological membrane & solute transport

lipid

• predominant species on membrane

• phospholipids

• cholesterol

what are 3 types of phosphatidyl?

• phosphatidylcholine (PC)

• phosphatidylethanolamine (PE)

• phosphatidylserine (PS)

  • phosphatidylinositol (PI)

what does cholesterol do to membrane fluidity

increase fluidity

• makes membrane more flexible & dynamic

• mem can’t be dull

phosphatidylcholine (PC)

phosphatidylethanolamine (PE)

phosphatidylserine (PS)

what do phospholipids do in water

• form lipid bilayers w/ polar heads outside w/ np inside

  • creating order

• do not permit polar moc to get acx bilayer

what lipids are key signaling lipids?

phosphatidyllinositol (PI)

• participate in communication, signal process

• PLC splits PIP2 > DAG & IP3

• PI3 kinase adds Pi on PIP2 → PIP3

what does PIP3 do?

lipid 2nd messenger

• triggers cell growth, survival, movement

• huge cancer target

• growth promoting signal

IP3

• 2nd chemical messenger

• triggers rel of in ER Ca2+

membrane proteins

make up most part of membrane

• allows things to move in/out

fluid-mosaic model

• mix of protein & lipids

• accommodate motion, neurons are very active

what are 2 types of membrane protein

intergal & peripheral

peripheral mem protein

• water soluble

• inner / outter of membrane or on top of a integral protein

• not embedded in np core

• regulate mem struc & fuction

integral mem protein

• integrated in the bilayer

• help transport solute

• continuously undergo shape change

• major drug target receptors, transporters, ion channels

selective permeability of mem

• cells controls what gets in& out via integral proteins

• channels, pumps, carrier/exchangers

what are 2 types of solute transport

• diffusion

  • ion channels

  • no energy, travel down conc gradient, fast

• active transport

  • pumps, exchangers

  • need energy, move solute against conc gradient, atp hydrolysis, slow

Na+/ K+ ATPase/ pump

• maintain high [Na+] out & [K+] in

• stabilize potential

• enable neurons to fire action potential

steps of Na/K pump

for 1 ATP —> 3 NA+ out & 2K+ in

• ATP binds pump —> promotes 3 Na+ binds to pump

• ATP → ADP & Pi, Pi binds to pump and changes shape

• shape change allows pump to rel Na+ out & 2K+ binds to pump

• Pi gets released → back to normal shape → 2k+ gets rel

what contributes to resting membrane potential

• an unequal distribution of charged ions inside and outside the cell & the selective permeability of the cell membrane

• ion conc gradeint

• K+ leak channel

• Na/K pump

Na+

• higher conc outside the cell → want to go back in the cell

K+

more inside cell → favors the leaving of K+

Ca2+

• very very large conc outside

• strong driving force to enter cell when channel opens

• a rush of calcium inside the cell can cause cell death

Leak Channels

• Passive transport: Ions move down their concentration gradient

• Always open: non-gated pathways

• Creates the charge: Potassium leak channels let K⁺ flow out of the cell faster than Na⁺ leaks in —> inside more (-)

ex: 1 using ion gradient to transport solute

• na+ gradient

• secondary active transport

• MAT uses Na+ gradient energy to bring NT back inside cell

• 1. NT gets rel to synaptic cleft to signal postsynaptic neuron

• 2. once done, NT needs to be removed → needs MAT (transporter)

  • high sodium outside bc of pump → tendency to go back in side cell

• MAT: binds to both, Na+ movement provides energy to help NT move in against its conc gradient

ex: 2 using ion gradient to transport solute

• VAT & VMAT uses H+ gradient to bring NT into vesicle

• proton pump uses ATP

• brings H+ into vesicle → more proton in vesicle, wanna leave

• transporter uses H+ gradient energy to bring H+ out and NT in

drug targeting key solute transporter

• blocking serotonin (5-HT) transporter increases serotonin signaling

• usually, SERT brings back serotonin into presynaptic neuron via Na+

• inhibition: blocks movement, more serotonin stays in synaptic cleft, can bind to receptors on postsyn terminal

• more serotonergic signaling

what establishes the resting mem Potential?

• high selective permeability of K+ ion

electrical & chemical forces

• 2 factors of electrochemical gradient that drive movement of charged ions acx cell

resting membrane potential

• electrical potential: -70 mV

• K+ flow in & out are balance bc chemical gradient

• electrical force = chemical force

restoring resting mem after stimulation

• depolarization: more positive (-60), process not isolated point

• inside became more positive —> smaller electrical force inside

• cause

  • stimulus trigger voltage gated Na+ channels to open

  • Na+ rush in cell down conc grad → more (+) inside

  • Na+ gated channels close & K+ volatge gated channels open

  • repolarizes → restore membrane to resting

• 
  

restoring resting mem after inhibition

hyperpolarization: more negative (-80)

• larger electrical force

• cause

  • too much k+ leaving via gated channels (until close)

  • passive leak channels bring K+ back in

  • K+ influx → depolarize membrane to resting