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Bio U1, KA4
| Question | Answer |
|---|---|
| What happens when a signal molecule binds to a receptor | changes the conformation of the receptor, which initiates a response within the cell |
| Feature of a multicellular organism | different cell types may show a tissue-specific response to the same signal |
| Hydrophobic signalling molecules | diffuse directly through the phospholipid bilayers of membranes, and so bind to intracellular receptors |
| Receptors for hydrophobic signalling molecules | transcription factors |
| Examples of hydrophobic signalling molecules | steroid hormones- oestrogen, testosterone |
| Where do steroid hormones bind | specific receptors in the cytosol or the nucleus |
| Where does the hormone-receptor complex go | it goes to the nucleus where it binds to specific sites on DNA and affects gene expression |
| Hydrophilic signalling molecules | bind to transmembrane receptors and do not enter the cytosol |
| What happens when a hydrophilic signalling molecule binds | transmembrane receptors change conformation when the ligand binds, and the signal is transduced across the plasma membrane |
| How do transmembrane receptors act as signal transducers | by converting the extracellular ligand-binding event into intracellular signals |
| What do transduced hydrophilic signals often involve | g-proteins or cascades of phosphorylation |
| What do phosphorylation cascades allow | more than one intracellular signalling pathway to be activated |
| What does binding of insulin to its receptor result in | results in an intracellular signalling cascade that triggers recruitment of GLUT4 to the cell membrane of fat and muscle cells |
| Resting membrane potential | a state where there is no net flow of ions across the membrane |
| What does transmission of a nerve impulse require | changes in the membrane potential of the neuron's plasma membrane |
| Action potential | a wave of electrical excitation along a neuron's plasma membrane |
| How do neurotransmitters initiate a response | by binding to their receptors at a synapse |
| How are voltage gated sodium channels opened | Depolarisation of the plasma membrane as a result of the entry of positive ions |
| How is resting membrane potential restored | Inactivation of sodium channels and opening of potassium channels |
| What causes adjacent cells to also become polarised | once action potential reaches the end of the neuron, vesicles containing neurotransmitter fuse with the membrane, releasing neurotransmitter and stimulating a response |
| What is the retina | area within the eye that detects light and contains two types of photoreceptor cells: rods and cones |
| How are the photoreceptors of the eye formed | retinal combined with opsin (rhodopsin) |
| What happens when a retinal absorbs a photon of light | rhodopsin changes conformation to photoexcited rhodopsin |
| What does photoexcited rhodopsin activate | a g-protein which activates PDE |
| What does PDE do | catalyses hydrolysis of cGMP |
| What does absorption of a photon result in | closure of ion channels in membrane of rod cells, triggering nerve impulses in neurons in the retina |
| How can rod cells respond to low light intensities | Very high degree of amplification |
| Cone cells | different forms of opsin combine with retinal to give different photoreceptor proteins, with different wavelength sensitivities |
Created by:
LCRV