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
What happens when 2 compartments with different
osmolarities are separated by semi-permeable
membrane (impermeable to solutes)?
Membrane freely permeable to H2O
NOT permeable to solutes
What is osmotic pressure?
The amount of pressure it would take to prevent net
flux of H2O across a semi-permeable membrane from a
compartment with pure H2O to one with higher osmolarity.
What is tonicity?
If a cell swells in solution, the solution was ______.
* If a cell shrinks in solution, the solution was ______.
* If there is no change in cell volume the solution was ______.
* Depends upon osmolarity but also whether the membrane is permeable to solutes in solution.
Describes how a cell reacts to a given solution.
hypotonic / hypertonic / isotonic
How does H2O move between compartments?
- H2O moves passively down its concentration gradient
across plasma membranes through H2O channels:
aquaporins. - H2O is polar – does not move readily through lipid bilayer. However, H2O moves freely into or out of most cells.
What is osmosis?
Net movement of H2O down its concentration gradient.
The key to treating cholera and similar diseases is to replace the water and salts that have been lost.
Oral rehydration therapy (ORT) consists in giving the patient solutions to drink which have both Na and glucose.
