Week 8 - Membrane Proteins and Transport (Part II) Flashcards
What do multi-pass transmembrane proteins create and for what function?
They create a protein-lined path across the cell membrane; to transport polar and uncharged particles
Are transport proteins selective?
Yes; they transport a specific class of molecules.
What is passive transport?
Movement down the concentration gradient; does NOT require energy; uses channel proteins.
What is active transport?
Movement against the concentration gradient by transporter proteins; requires energy.
What are the 2 types of transport proteins?
- Channel proteins
2. Transporter proteins
What are channel proteins?
A type of transport protein; do NOT interact much or bind strongly to the transported molecule. Passive Transport only.
Do channel proteins change conformation?
They do not change conformation a lot.
What are transporter (a.k.a. carrier) proteins?
A type of transport protein; interact a lot with and bind to the transported molecule. Passive and Active transport.
Do carrier/transporter proteins change conformation?
Yes, they change to transport the solute across the membrane.
What is resting membrane potential?
Membrane potential is an electrical gradient aiding in transport.
What makes up the electrochemical gradient?
Concentration gradient + Membrane potential = Electrochemical gradient
The two gradient must be consider as they work against each other.
Are channel proteins hydrophilic or hydrophobic?
They are hydrophilic pores across a membrane.
Are channels or transporters faster at passive transport?
Channels are faster than transporters at passive transport as several molecules can pass through at once when open.
What are the two types of ion-channels?
- Non-gated ion channels
2. Gated ion channels
Example of a non-gated ion channel?
Always open; K+ leak channels that play a major role in resting membrane potential in animal cells.
What do gated-ion channels require to open?
Gated ion channels require signal to open; i.e. a chemical or electrical signal
What do larger and small fonts represent on membrane diagrams?
Large font = higher concentration
Small font = lower concentration
What are 4 kinds of GATED ion channels?
- Voltage-gated
- Mechanically-gated
- Extracellular Ligand-gated
- Intracellular Ligand-gated
What do voltage-gated ion channels require?
A change in voltage across the membrane; a.k.a. membrane polarization and depolarization
What do mechanically-gated ion channels require?
Mechanical stress; i.e. opening if the plasma membrane is stretched.
Extracellular v.s. Intracellular ligands examples?
Extracellular ligand: neurotransmitters
Intracellular ligand: ions, nucleotides
Do Uniporters do passive or active transport?
Passive transport by a transporter via facilitated diffusion; transport is reversible
What is an example of a uniporter and how does it function?
GLUT uniporter; transports glucose down the electrochemical gradient. Can work in both directions.
What are 3 types of active transport?
- Co-transporters
- ATP-driven pumps (a.k.a. Pumps or ATPases)
- Light-driven pumps (i.e. bacteria)
How do co-transporters move molecules?
They move one molecule down the gradient and one against the gradient.
What is a symporter and what does it move?
An active transporter that move 2 molecules in the same direction.
What is an antiporter and what does it move?
An active transporter that move 2 molecules in opposing directions.
The free energy created from the co-transported ion moving down the electrochemical gradient does what?
Use the energy to transport the second molecule.
In a Na+/Glucose symporter, what does moving Na+ down the electrochemical gradient do?
It provides energy to move glucose against the concentration gradient.
What does cooperative binding of Na+ and glucose to a symporter lead to?
Leads to a conformational change in the protein.
How is cytosolic pH (neutral) regulate?
Excess protons leak into the cell, produced by acid forming reactions; Na+ driven antiporters maintain pH.
How does a Na+/H+ exchanger (antiporter) maintain cytosolic pH?
It responds to pH drops by increasing transporter activity; gets better at removing protons.
How does a Na+/H+ exchanger (antiporter) move H+ out of the cell?
It uses the free energy stored in the Na+ electrochemical gradient to move the H+ out of the cell.
As symporters and antiporters both use the sodium gradient to move molecules, what happens when the Na+ eventually gets equalized on both sides?
Na+/K+ pump (a transport ATPase) keeps the concentration different.
What are P-type transport ATPases and what so they do?
P-type transport ATPases are ATP driven pumps that phosphorylate themselves to move molecules against the gradient.
What does the Na+ gradient do?
- transports nutrients into cells
- maintenance of pH and cell volume
What are the 8 steps of the pumping cycle of the Na+/K+ pump?
- ATP bound to pump, 3 Na+ bind an open cytosolic pocket.
- Pocket closes preventing Na+ escape.
- ATP hydrolysis; pump phosphorylated, ADP released due to change in E1 conformation to E2 (phosphorylation).
- E2 binding pocket exposed on the extracellular side; 3 Na+ exit.
- 2K+ bind to E2.
- Pocket closes preventing K+ escape.
- Pump is de-phosphorylated.
- ATP bind to pump to return to E1 state and K+ is released into cytosol.
What happens when ATP binds to an E2 conformation of Na/K pump?
It changes back to E1 conformation and K+ is released.
During ATP hydrolysis, what happens when the Na/K pump is phosphorylated?
ADP is released and E1 conformation changes to E2.
Which conformation of the Na/K pump has ATP bound to it?
The E1 conformation has bound ATP. Change to E2 requires the phosphorylation of this ATP to occur.
