Diffusion and osmosis

channels, diffusion

diffusion

random movement of particles (in chemical)

when there is a concentration gradient diffusion goes

DOWN the gradient

simple diffusion

no barrier or the ion/molecule is fully permeable

semipermeable membrane

permeable to some ions/molecules (selective), but not other ions/molecules

facilitated diffusion

• ex) glucose

either channel or carrier to move ion/molecule thru membrane

• still down the gradient

• carriers have specificity and saturation

glucose: 135 → 5 mM

• carriers are amino acids

channels:

what they have, function, what for

have specificity for size, shape, and charge

• can saturate opening

• change location of ion molecule, cant change chem bonds

• flow is down gradient

• h2o and ions

water channels are called

aqua pores, always open

channel between outside and inside cell thru cell membrane

• are unregulated except kidney collecting duct

isotonic

same osmolarity/concentration/tension

hypotonic

high solute inside cell, less water inside cell

outside water flows in because there is less concentration of solute outside cell

hypertonic

more concentration of solute inside cell

low solute inside cell, more water inside cell

water moves out

describe (basic) diffusion of O2, CO2, and Na+ in cell

through the phospholipid bilayer O2 has simple diffusion into cell, CO2 diffuses out of cell, Na+ is facilitated through channels into the cell

what is concentration gradient

energy source (not ATP), like a water wheel

channels for ions are either (3)

1. open (rare)

2. leak channels (small amounts go thru)

3. gated channels (regulated like enzymes)

   1. allosteric

   2. covalent

osmisis

spontaneous net movement of solvent molecules, typically water, through a selectively permeable membrane from a region of higher water potential (lower solute concentration) to a region of lower water potential (higher solute concentration)

• to equalize concentrations to achieve equilibrium

• restricts the movement of solute particles

what do all channels have (3)

1. specificity

2. allosteric regulation

3. covalent regulation

what is allosteric regulation

mechanism by which the function of a protein, such as an enzyme or receptor, is modulated by the binding of a regulatory molecule (an allosteric effector or modulator) at a site distinct from the protein's active site

when the saturation channels are full

channels move ions (change location)

• down concentration gradient

gated channels

they open/close

• some always open (rare)

• leak channels

what are the 4 mechanisms of gating

1. ligand-allosteric

2. voltage gating

3. mechanical gating (sensory)

4. covalent/enzyme

describe ligand gated channels

• charged in/out the cell

• ions and concentrations

• enzyme

  • activation

motor, allosteric regulation

• in cell negative, out cell positive

• 150mM Na outside, 15mM inside

• Acetylcholinesterase (AChE)

  • deactivation when reached enzyme

Acetylcholinesterase (AChE)

an enzyme that catalyzes the breakdown of the neurotransmitter acetylcholine into choline and acetic acid

ligand gated channels examples and function

for sensory (smell, pain, taste, itch)

• NT

• hormones

  • paracrines

describe voltage gated channels

• charged in/out the cell

  • open/closed channel

• ions and concentrations

• mV charge

neurons and muscles

• K+ ion, 5mM outside, 160mM inside

• closed channel: positive outside, negative inside

• open channel: negative outside, positive inside

  • opens with electrical charge

• -70mV inside

describe enzyme gated channels (?)

• ions and concentrations

• 1mM Ca2+ outside, 0.001mM inside

• kinase and Pi alone channel

• slow channel, is rare

what is kinase

enzyme that catalyzes the transfer of phosphate groups from high-energy phosphate-donating molecules, such as ATP, to specific substratesd

describe mechanical gating

• neuron type

• ion

• function

• unipolar neuron

• Na+ channel, squishes neuron?

  • for touch, hearing, proprioception, blood pressure

describe regulation of myelin

• insulation and receptor allows ion to go in

• vesicle has carriers

• ion goes to inserted vesicles to have glucose carriers

Describe up the gradient (short version) of primary 1 active transport

• in the cell

• out the cell

• pump

• 150mM Na+ out, 5mM K+ out

• 15mM Na+ in, 160 2K+ in

• 1 primary ATPase pump (directly uses ATP)

Describe up the gradient (long version) of primary 1 active transport (3 steps)

• in the cell

• out the cell

• pump

1. 3Na+ out the cell, goes into cell thru membrane, ATP turns into ADP and Pi

   1. Na+ is the active enzyme

2. There is 2K+ in the membrane, with ADP and Pi

3. 2K+ goes out the membrane into the cell, with Pi

• Na+/K+ ATPase pump

what is kind of substrate ATP

active substrate

moving any ions up the gradient with ___

ATP 1 primary pump

uses ATP hydrolysis

K+, H+, Ca+

Secondary 2 primary active transport uses what

uses the movement of 1 ion DOWN its gradient to move another molecule/ion UP its gradient

An ion would move up its electrochemical gradient only when? why?

energy is supplied to overcome the natural tendency of the ion to move down the gradient

• essential for maintaining the resting membrane potential and cellular ion homeostasis

• Without an external energy source, ions cannot spontaneously move up their electrochemical gradient

Primary 1 vs secondary transport

Primary active transport directly uses metabolic energy from the hydrolysis of ATP to pump molecules or ions across a membrane.

secondary active transport does not use ATP directly. Instead, it relies on the electrochemical gradient of one ion—typically Na⁺ or H⁺—established by primary active transport to drive the movement of a second molecule against its own gradient

while primary active transport generates ion gradients using ATP, secondary active transport exploits these pre-existing gradients to move other substances, making it indirectly dependent on ATP

describe 3 changes of glucose concentrations from apical to basal

1. up glucose 10

2. 150 glucose

3. 100 glucose out

what is co-transport

same direction (one goes up one goes down)

has transporter

glucose and amino acids w Na+

from lumen to basal

counter transport

opposite direction, one goes out other goes in

Na+ and H+

from lumen to basal

sodium and potassium are always

primary, 1 primary pump use ATP

2nd prime co-transport

H2O follows sodium

diffusion down gradient

from lumen to basal