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18 Cards in this Set
- Front
- Back
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How are membrane proteins involved in transmitting signals across the plasma membrane? |
They take an extracellular signal, which causes a signal transduction pathway, resulting in an intracellular response. |
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What are the three stages of signal transduction? |
1. Reception (A signal molecule binds to a receptor in the membrane). 2. Transduction (Signal transduction pathway). 3. Responce (Activation of cellular response) |
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Describe the process of a change in secretion or uptake of substances. |
Signalling molecule binds to a ligand gated ion channel. Channel opens, allowing a passive movement of ions. Channel closes when ligand dissociates from the protein. |
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What is a G protein? |
Proteins that act as molecular switches inside cells, and are involved in transmitting signals across the membrane. |
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What activates a G-protein? |
G-Protein Coupled Receptors (GPCRs) |
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What happens when there is no signalling molecule bound to the GPCR? |
The G protein is bound to GDP, and is inactive. |
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What makes the G protein activated? |
When a signalling molecule is bound to the receptor, and GTP replaces the GDP bound to the G protein. |
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What occurs once the G protein is activated? |
The G protein activated an associated enzyme, generating an intracellular response. |
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Once activated, what happens to the GTP bound to the G protein? |
It is hydrolysed to GDP+Pi. The phosphate is then released and the GDP remains bound to the G protein, restoring its inactive state. |
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Describe the type of receptor which is involved in the activation of enzymes. |
It is composed of two separate subunits with extracellular binding sites and regions with many tyrosine amino acids. |
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What happens when a signalling molecule binds to the receptor involved in the activation of enzymes? |
This causes the two subunits to associate in the membrane. The subunits use phosphate from ATP to phosphorylate tyrosine R groups on the other subunit, meaning that it is activated. |
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What happens when the receptor involved in the activation of enzymes becomes activated? |
It may now bind and activate other intracellular proteins. |
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Define the term "membrane potential". |
The voltage measured across the membrane, caused by differences in ion concentration. |
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What does nerve transmission rely on? |
The generation of an electrical impulse within a neuron. Movement along the neuron. Transmission across the synapse to another neuron. |
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What is a nerve impulse? |
A wave of depolarisation. |
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What is step one in nerve transmission following stimulation? |
A signal molecule triggers the opening of ligand gated ion channels, allowing sodium ions to flow in. This changes the membrane potential and is depolarisation. |
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What is step two in nerve transmission following stimulation? |
If sufficient ion movement occurs, then voltage gated ion channels open, generating an action potential. |
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What is step three in nerve transmission following stimulation? |
Depolarisation travels along the length of the neuron. Then, the resting potential must be restored (repolarisation). This means that gated sodium channels close, while gated potassium channels open, restoring the membrane potential. |
