Unit 1 Membrane Proteins
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| What is a transmembrane protein | one that spans the membrane
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| What is the function of transmembrane proteins | to transport molecules across the membrane
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| What are the two types of transmembrane proteins | 1. channels 2. transporters
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| How do channel proteins move molecules across membrane | passive transport/diffusion
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| What name is given to all channel proteins that involve a conformational change | gated channels
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| What are the two types of gated channels | 1. ligand 2. Voltage
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| What type of gated channel responds to hyperpolarisation/depolarisation | voltage gated channels
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| What type of channel transports water across the membrane | aquaporin
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| what are the two ways to transport water across the membrane and contrast their efficiency | 1. aquaporin (most efficient) 2. phospholipid spaces (less efficient)
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| How do small uncharged molecules cross the plasma membrane | through gaps in phospholipids
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| Name a small uncharged molecule | oxygen/carbon dioxide
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| True or false different cell types/ compartments have different channel and transporter proteins. | true
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| What triggers conformational change in voltage gated channels | change in ion concentration across membrane e.g. K or Na move across membrane causing hyper/depolarisation
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| What causes a ligand gated channel to open | specific ligand (signal molecule)
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| Give an example of a ligand or voltage gated channel | K or Na channel (do not confuse with Na/K ATPase
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| Name two transporters | 1. glucose symport 2. Na/K ATPase
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| By what process is glucose moved across cell | facilitated diffusion i.e. Na needed to provide energy for glucose to move
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| By what process does Na/K ATPase move ions across membrane | active transport
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| What provides energy for Active transport of Na or K | energy from hydrolysis of ATP
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| In the unphosphorylated state the Na/K pump has a high affinity for | Sodium
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| How many Na leave the cell in the Na/K pump | 3
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| How many K enter the cell via the Na/K pump | 2
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| In what direction does Na move via the Na/K pump | from intracellular (cytoplasm) to extracellular (outside) cell
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| In what direction does K move via the Na/K pump | from extracellular (outside) to intraceullar (cytoplasm)
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| In the phosphorylated state the Na/K pump has high affinity for | Potassium
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| What feature defines a molecules as a transporter | They must change CONFORMATION to work
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| What happens first Na leaves cell OR pi binds to Na/K ATPase | pi binds to Na/K ATPase
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| What causes the Na/K pump to change conformation | Pi binding or becoming unbound
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| Describe the key stages of the Na/K ATPase | unphosphorylated 3 Na binds inside the cell;
phosphorylation by ATP causes conformational
changes releasing 3 Na outside
High affinity for K outside in phosphorylated state,
Dephosphorylation & conformational change
2 K released inside cell
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| Name 2 roles of Na/K ATPase | 1. maintaining osmotic balance in animal cells;
2. generation of the ion gradient for glucose symport in
small intestine;
3. generation and maintenance of ion gradient for resting
potential in neurons
4.generation of iongradient in kidney tubule
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| Name 3 responses to a cell following signal transduction | 1. activation of an enzyme or G protein (photoreceptor eye)
2. change in uptake or secretion of molecule (nerve impulse)
3. rearrangement of cytoskeleton (cell cycle)
4. activation of proteins that regulate gene transcription.(hydrophilic signalling)
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| resting membrane potential is approx | -70 mv
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| What term means the cell is getting more positive | depolarisation
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| what term means the cell is getting more negative | hyperpolarisation
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| What is the first step in a nerve impulse | Signal molecule ieneurotransmitter, triggers the opening of
ligand-gated ion channels at a synapse
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| . If sufficient ion movement occurs changing the voltage the ion concentrations either side of membrane | voltage-gated ion channels will open and
the effect travels along the length of the
nerve
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| Once the wave of depolarisation has passed what happens next? | hyperpolarisation
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| Describe how hyperpolarisation (becoming more negative) occurs | the channel proteins that were open now close and others open in the opposite direction to restore the
resting potential.
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