Membrane Proteins Flashcards
What type of molecules can pass directly through the membrane?
Non-polar molecules
What are the two types of channels?
Gated and Ungated
Give an example of an ungated channel
Aquaporin
Describe Aquaporin and it’s function
Ungated channel that allows water to pass through the membrane
Describe the structure of Aquaporin
Surface has some hydrophobic R groups(to allow it to be embedded in the membrane) but also some hydrophyllic R groups to help water molecules pass through the narrow parts of the pore
What are the two types of gated channels?
Ligand and Voltage Gated
What is required for a ligand gated channel?
Binding of a ligand
Give an example of a ligand gated channel
A channel in the synpase, where a neurotransmitter binds to allow Na+ ions through
What do voltage gated channels rely on to open?
A large enough change in the ion concentration across the membrane
Describe how transporter proteins work
Change conformation to transport molecules across the membrane
What are the two mechanisms that transporter proteins work with?
Facilitated
Active
What is facilitated transport?
Passive process that does not require energy (but does require a conformational change if by a transporter)
Give an example of a facilitated transporter protein and what it is used for
GLUT4 transporter in fat and muscle cells
Provides the route for facilitated diffusion of glucose across the cells
What is coupled transport? Give an example
Coupled transport is where two substances are moved together
Glucose Symport
What is the difference between a symport and an antiport?
Symport - both molecules move in the same direction
Antiport- both molecules move in opposite directions
What does the glucose symport move?
Glucose and Na+
Where can the glucose symport be found?
Cells lining the small intestine
What is Signal Transduction?
A process triggered by the binding of a chemical signal to a receptor leading to a cellular response
Where do hydrophobic signal bind?
Receptor proteins inside the cell
What does the binding of a hydrophobic signal cause?
Activates/Inhibits the transcription of certain genes
Give examples of responses that signal transduction can trigger
Changing the cell metabolism
Altering the uptake/secretion of molecules
Rearranging the cytoskeleton
Altering gene expression
How are G proteins involved in signal transduction?
Involved in transmitting signals from outside the cell
Invovled in cascades, activated by binding GTP
How many sodium ions are moved by the sodium potassium pump?
3 Na+ ions
In what direction does the pump move sodium ions?
Out of the cell
How many potassium ions are moved by the Na/K ATPase?
2 K+ ions
In what direction does the pump move potassium ions?
Into the cell
Describe the first conformation of the Sodium Potassium Pump
Binding sites exposed to the cytoplasm
High affinity for sodium ions
No ATP binded
Describe the steps in the sodium potassium pump
Stage 1:
Ion binding sites exposed to cytoplasm
Protein has high affinity for sodium ions
3 Na+ ions bind
Stage 2:
ATP is hydrolysed by the protein forming ADP and Pi.
Pi binds to the protein, causing a confirmational change
Stage 3: In second confirmation, pump no longer has affinity for sodium so releases them. High affinity for potassium ions. 2 potassium ions bind
Stage 4: Dephosphorylation occurs and the pump loses the Pi
This causes another confirmational change, binding sites facing cytoplasm
Loses the K+ ions
Back to original confirmation
Give three reasons why the movement of sodium and potassium ions is so important
Maintains an osmotic balance in animal cells
Generation of sodium ion gradient for glucose symport
Generation of sodium ion gradient in kidney tubules
Generation and Maintenance of ion gradients for resting potential in neurons
How does the sodium potassium pump help maintain an osmotic balance in animal cells?
Moves three Na ions out and 2 K ions into the cell, lowers the overall ion concentration
increases the new water concentration
How does the sodium potassium pump help the glucose symport?
Creates a sodium ion gradient from intenstine to lining cell
Enables the action of glucose symport to absorb sodium ions and glucose from the intestine
What is the resting potential?
Imbalance in the electrical charge across a neuron membrane
Where does the neurotransmitter bind?
Ligand gated Sodium Channel
How is a nerve impulse generated?
Neurotransmitter binds to a receptor protein on a ligand gated sodium channel
Binding allows Na ions to diffuse into cell
If sufficent ion movement, voltage changes across the membrane
Causes neighbouring voltage gated Na+ channels to open
Triggers the next voltage gated channel and a wave of depolarization
How is the resting potential restored?
When voltage reaches a critically high level, voltage gated Na+ channels close
Voltage K+ Channells open, so K+ ions diffuse out of neuron
Restoring the resting potential
K+ channels close when the resting potential is reached
