Lecture 9: Membrane Transport, Part II Flashcards
Ion channels
- Form pores across lipid bilayer and allow passage of charged molecules through cell membrane
- Do not change shapes to transport individual solutes across membrane
- Only passive transport
Ion channels can be open or closed which allow
effienency as when open channels, polar molecules can flow 1000 times faster than transporters
Ion channels have specificity with
selective filter that are protein structures of narrow region of ion channel on one end that determines what ions can pass through pore
regulates size and charge of each ion to pass through
Other end of ion channel forms gates that can be opened or closed which helps
not changing shape for every individual solute traveling through
Big advantage is efffiency to ion channels, but trade off is
only passive transport
Opening of ion channel is regulated by
different gating mechanisms
Voltage gated
Opening controlled by voltage inside cell
protein structures can detect charge on inside cell and shape change depending on negative and positive charge
positive charge opens channels
Ligand gated
opening controlled by binding of a molecule (ligand) to the channel
channels have binding sites not for solute traveling, but for signaling molecules
Signaling molecule bind to binding site on ion channel to cause conformational change of ion channel t open
Mechanically gated
opening controlled by mechanical stress
Concentration of ions is tightly regulated in cells by ___ and ___ to provide _____
transporters and channels
equilibrium
Concentration outside cell and inside cell
outside: high concentration of sodium (Na+) and chloride ions to neutralize positive charge
inside: high concentration of potassium (K+) and DNA to neutralize positive charge
Membrane potential
voltage difference (charge) between inside and outside of cell
Resting membrane potential
ensures Na+-K+ pump is working to maintain negative charge inside cell
animal cell is -20 to -200 mV
K+ leak channels
Doing minor adjustments to maintain resting membrane potential in animal cells
Usually open and allow passive transport of K+ to travel outside cell down concentration gradient
K+ push out to make cell more negative
When electrochemical gradient for K+ is zero and has no movement, cell is at
resting membrane potential
Slight negative charge inside cell is governed by:
- Na+-K+ pump
- K+ leak channels:
if too + on inside, start to push K+ out
if too - on inside, start to pull K+ in
Na+K+ pump is ___ while K+ leak channels go
consistent
back and forth
Neurons function to
receive and transport signals
Cell body of Neuron
contain nucleus and most organelles
Dendrites of Neuron
short extensions from cell body that receive signals from other cells
Axon of Neutron
long extension that branches at end to send electrical signals away from cell body and to target cells
Signaling initiates in
cell body (acts as headquarters) to make decision whether to fire or not to change membrane potential
Nerve terminal of Neutron
end of axon that send signals (neurotransmitters) to target cell
Cell body receives signals to change _____ and shoot down _____
membrane potential
axon terminal