Unit 1 - section 3 Flashcards
Name 2 small molecules that can diffuse directly across the phospholipid bilayer
Oxygen
Carbon dioxide
How does the bilayer act as a barrier to most other ions and molecules?
Molecules that are too large or too polar cannot diffuse directly across the phospholipid bilayer so require to be transported
What is the function of channel proteins?
Allow passive transport down concentration gradients
What is the function of transporter proteins?
Actively moves molecules across the membrane against concentration gradient
What is the function of receptor proteins?
Receive signals and bring about responses
Describe the role of membrane proteins in specialisation
Cell specialisation allows cells to perform specialised functions as different cell types and compartments must contain different channel and transporter proteins
What is the membrane protein involved in the passive transport of water?
Aquaporin 2
Name 2 types of gated channels
Ligand-gated channels
Voltage-gated channels
Describe the operation of ligand-gated channels
Open and close following the binding of a ligand
Describe the function of voltage-gated channels
Respond to changes in ion concentration
Describe facilitated transport stating the energy requirement
Passive process so does not require energy. Unlike passive transport it involves a conformational change in the protein
Describe active transport stating the energy requirement
Requires energy to bring about the necessary conformational change. Energy required comes from hydrolysis of ATP
What is an example of an active transport protein?
Sodium potassium pump
Define intracellular and extracellular
Intracellular means inside the cell
Extracellular means outside the cell
What is the type of membrane proteins that bind to signal molecules?
Receptor proteins
What is the type of pathway that is activated when a signal molecule is received?
A signal transduction pathway
What are 4 potential responses of a cell to a signal molecule?
Activation of special enzymes or G-proteins
Changes in molecule uptake or release
Rearrangement of cytoskeleton
Activation of proteins that regulate gene expression
What is the sodium-potassium pump also know as?
Na/KATPase
Which way do ions go through the sodium-potassium pump?
Pumped against a steep concentration gradient
Is energy required for the sodium-potassium pump?
Significant energy is required
Describe the sodium-potassium pump’s affinity for sodium and potassium
Has a high affinity for the sodium ions inside the cell. Three sodium ions would bind to the pump. This would allow an ATP to bind to the pump changing its shape, causing it to release the sodium ions outside the cell. This causes a conformational change to the pump allowing two potassium ions to bind. This causes a conformational change to the pump releasing the potassium ions inside the cell. This process then repeats.
When do phosphorylation and dephosphorylation occur in the sodium-potassium pump?
Phosphorylation - phosphate group binds to pump
Dephosphorylation - phosphate group is released
What causes conformational changes to the sodium-potassium pump?
When the ligand binds to the pump
This allows the sodium be potassium ions to be pumped across the membrane
What are 4 functions of the sodium potassium pump?
Maintenance of osmotic balance in animal cells
Generation of the ion gradient for glucose symport in the small intestine
Generation and long term maintenance of ion gradient for resting potential in neurons
Generation of ion gradient in kidney tube
Why is the sodium-potassium pump so important in mammalian metabolism?
The generation of ion gradients by the pump accounts to a significant part of basal metabolic rate in mammals (25% in humans)
What does depolarisation mean?
When a neuron becomes more positive and less negative
What is nerve transmission?
The passing of a signal from one neuron to the next caused be a wave of depolarisation along a neuron
What is resting potential?
The difference in voltage across the membrane when there is no signal
What are the stages in the transmission of a nerve impulse?
Resting potential of the membrane is stable and slightly negative inside the neuron
Neurotransmitter binds to ligand gated channel
Ligand gated channels open and sodium ions enter the neuron
Neuron becomes less negative
If threshold is reached the voltage changes and the voltage gated ion channels open
Sodium ions flood into the neuron
Increase in sodium ions cause a wave of depolarisation through the neuron
Describe phosphorylation of the sodium potassium pump?
Pump has high affinity for sodium ions inside the cell before binding
Phosphorylation by ATP causes conformational change to pump reducing affinity for sodium ions and releasing them outside the cell. Now high affinity for potassium ions outside the cell
Dephosphorylation occurs causing conformational change and releasing potassium ions inside the cell
