BIO 360 - Exam 1 - Chapter 5 Membrane Dynamics Diffusion SP 2023 PowerPoint Flashcards
What are ion channels?
Membrane proteins that form aqueous pores between intra and extracellular fluids.
- Some ion channels are usually open (“leaky”)
- Most are actively “gated” between open and closed conformations
What causes channels to open or close?
*
*
*
- change in voltage across plasma membrane
- binding of neurotransmitter
- mechanical stretch
Facilitated diffusion only works down a concentration
gradient. Can we transport molecules against a gradient?
Yes
* we can “pump” solutes against a concentration gradient but it requires energy.
Types of mediated transport:
* ______ ______: uptake of glucose from interstitial fluid
* ______ transport:
primary active transport
secondary active transport
facilitated diffusion / active
Facilitated diffusion only works down a ______ ______ - driving force.
does ___ require additional energy (no ATP needed)
Substrate ______ ___ ______ causing conformational change
in transporter leading to release of substrate on the other side
of the membrane
concentration gradient / NOT / binds to transporter
What is a primary and secondary active transport?
Primary active transport
* energy released from hydrolysis of ATP to ADP + Pi by transporter
used to drive activity of transporter
* Example: Na+/K+ ATPase pump
Secondary active transport
* primary active transport generates and maintains gradient (Na+ usually)
* as Na+ moves down its gradient into cell, another solute can be cotransported against its gradient into or out of cell
* glucose transport and amino acid reabsorption in kidney - later
What kind of molecule is Na+ / K+ ATPase?
*Name ends in “ase” so it’s ADP an enzyme.
* Present in plasma membranes of all cells.
What is the mechanism of the Na+-K+-ATPase?
Primary Active Transport
What is the 2-State Model of Na+ / K+ ATPase?
State 1:
* ATP bound
* can bind 3 molecules of intracellular Na+ with high ______.
* ______: measure of how tightly two molecules bind to each other
* binding of Na+ turns on ______ activity; ATP is hydrolyzed.
* phosphorylates transporter leading to conformational change.
State 2:
* exposes Na+ to extracellular fluid and _____ ___ ___ _____ affinity of transporter for Na+; Na+ “pumped” out of cell.
* high affinity of transporter for K+ and up to 2 K+ bind to transporter
* Binding of K+ causes transporter to be ______ and it returns to State 1.
(1) affinity / affinity / ATPase / phosphorylates
(2) leads to a decrease / dephosphorylated
Why are Na+ / K+ ATPases important?
Most ions are ____ in chemical equilibrium among body
compartments
* cell membranes are barriers to free diffusion of many
molecules and …
* ____ expended to maintain chemical ______ of Na+,
K+, Cl¯, HCO3¯, Ca2+, etc
Intracellular Extracellular Na+ mM mM Cl- mM mM K+ mM mM
NOT / ATP / disequilibrium
Intracellular Extracellular Na+ 15 150 Cl- 7 110 K+ 150 5
Polarized epithelia have different transport proteins on
apical and basolateral membranes
* Allows for selective directional transport
* ______ – from lumen to ECF
* ______ – from ECF to lumen
Absorption / Secretion
A general rule in physiology:
H2O follows Na+
H2O is enormously important because it is the ______ ______ ______. 2/3 of H2O is ______.
universal physiological solvent / intracellular
Chemical disequilibrium
* Ions are ______ ______ ______ across the cell membrane.
* Cells ______ ___ ____ ___ ______ (ATP) to keep it that way.
not equally distributed / expend a lot of energy
What happens when 2 compartments with different
osmolarities are separated by a membrane that is freely
permeable to solutes and H2O?
Membrane freely permeable to solutes and H2O
