Membrane Transport Flashcards
What are the three types of transporters?
- Uniporters - allow diffusion or passive transport of a single type of solute from higher to lower concentration
- Symporters (cotransporters) - allow simultaneous transport of two different solutes in same direction
- Antiporters - allow net transport of two different solutes simultaneously in opposite direction
What are the two types of solute movement? What transporters are involved in each?
- Passive
• Uniporters - Active
• Symporters and anitporters
What is secondary active transport?
Type of transport that powers one’s solute movement by coupling its transport with another solute
What happens during facilitated transport (facilitated diffusion)?
Molecules travel across membrane via channel and carrier proteins without requirement of ATP
Describe channel proteins.
Form a hydrophilic pore (where charged molecules pass and avoid hydrophobic layer of membrane)
Either always open or gated
Describe carrier proteins.
Binds to specific solute that changes conformation
Rate of transport is not dependent on concentration gradient, but rather…
Number of carrier proteins available
Compare the rate of channel proteins vs carrier proteins.
Channel proteins - 10 million molecules/second
Carrier proteins - 1,000 to 1 million molecules/second
What is primary active transport?
Transport that utilizes energy from ATP hydrolysis to transport ions against their electrochemical gradients
Describe the sodium-potassium pump.
Extracellular side closed
Intracellular side open and associated with ATP
High affinity for sodium ions in cytoplasm
3 Na+ ions enter from cytosolic side and bind to pump
Intracellular side closes
Extracellular side opens
Decreases pump’s affinity for sodium ions but increases affinity for potassium ions
Two potassium ions bind to pump
New molecule of ATP associates with intracellular side (allows potassium ions to exit into cell)
What is an example of secondary active transport?
Sodium glucose linked transporter-1 (SGLT-1)
Describe the sodium glucose linked transporter-1 (SGLT-1). How does its structure contribute to its function in secondary active transport?
Cytosol facing side is closed
Extracellular end is open
Exposes two negatively charged sodium-binding sites to environment
Bound by positively charged sodium ions
High affinity for glucose
Glucose attaches to transporter against its concentration gradient
Extracellular region closes and cytoplasm facing side opens
Na+ ions detach and enter cytoplasm
Affinity for glucose decreased –> released into cytoplasme
Transporter returns to its original orientation
More sodium ions populate the ____________ than the ________.
Extracellular space; cytoplasm
Glucose is present at a ___ concentration outside the cell and a ______ concentration inside the cell.
Low; high
What are ion channels?
Transmembrane proteins that allow passive movement of ions
What are the two categories of ion channels?
- Gated:
* Require a stimulus (e.g., ligand, voltage change, mechanical stress) - Non-gated (leak/passive channels)
* Don’t need a stimulus
* Open and close at random
What are potassium leak channels? What are they an example of?
Example of non-gated channels
Allow excess potassium ions to diffuse out of cell (down concentration gradient)
Plays a role in maintaining negative charge on cytoplasmic side and positive charge on exoplasmic side of membrane
What is the structure of a ligand-gated ion channel?
- Receptor domain - where ligand binds
- Transmembrane pore - where ions pass through
How do ligands affect gated ion channels?
Channel remains closed when receptor is not bound by a ligand
Channels undergoes a conformational change when ligand binds to receptor (opens channel pore)
What are two categories of ligands? Give examples for each category.
- Extracellular (e..g, acetylcholine, glutamate)
- Intracellular (e.g., cAMP, ions (calcium))
What are chemical synpases
Sites where electrical signals from a presynaptic neuron are relayed by neurotransmitters to postsynaptic neuron to propagate an electrical impulse
What are the key structures at a chemical synapse?
- Axon terminal of presynaptic cell - synaptic vesicles (filled with neurotransmitters)
- Postsynaptic neuron - neurotransmitter receptors
- Synaptic cleft - fluid-filled space between presynaptic and postsynaptic neuron
Explain the events that occur at chemical synapses.
- Action potential at axon terminal of presynaptic neuron (causes membrane depolarization)
- Membrane depolarization triggers voltage-gated calcium channels to open (allows calcium ions to rush in)
- Neurotransmitters bind to ion channels on postsynaptic membrane
–> opens specific ion channels
–> Allows ions to enter postsynaptic cell
