Communication and Signalling Flashcards
How do multicellular organisms signal between cells?
Using extracellular signalling molecules.
What are examples of extracellular signaling molecules?
Steroid hormones, peptide hormones and neurotransmitters.
What are receptor molecules of target cells?
Proteins with a binding site for a specific signal molecule.
What does the conformational change that occurs when a receptor binds result in?
A response within the cell.
Why may signalling molecules have different effects on different target cell types?
Because of differences in the intracellular signalling molecules and pathways that are involved.
What does hydrophobic signalling molecules being able to diffuse directly through the phospholipid bilayer allow?
The signalling molecule being able to bind to intracellular receptors.
What are transcription factors?
Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
What are the receptors for hydrophobic signalling molecules?
Transcription factors.
Where do steroid hormones bind?
To specific receptors in the cytosol or the nucleus.
Where does the hormone-receptor complex move to?
The nucleus where it binds to the specific sites on DNA and affects gene expression.
What does the hormone-receptor complex bind to?
Specific DNA sequences called Hormone Response Elements (HRE).
What does binding at different HRE’s influence?
The rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
What do hydrophilic signalling molecules bind to?
Transmembrane receptors.
Do hydrophilic signalling molecules enter the cytosol?
No.
What are examples of hydrophilic extracellular signalling molecules?
Peptide hormones and neurotransmitters.
How do transmembrane receptors act as signal transducers?
By converting the extracellular ligand-binding event into the intracellular signals, which alters the behaviour of the cells.
What do transduced hydrophilic signals often involve?
G-proteins or cascades of phosphorylation by kinase enzymes.
What allows more than one intracellular signalling pathway to be activated?
Phosphorylation cascades.
What is the role of G-proteins?
To relay signals from activated receptors to target proteins such as enzymes and ion channels.
What are phosphorylation cascades?
They involve a series of events with one kinase activating the next in the sequence and so on. Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.
What does the binding of the peptide hormone insulin to its receptor result in?
An intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.
What does exercise trigger?
Recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in people with type 2.
What is resting membrane potential?
A state where there is no net flow of ions across the membrane.
What does the transmission of a nerve impulse require?
Changes in the membrane potential of the neuron’s plasma membrane.
What is an 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.
What are neurotransmitter receptors?
Ligand-gated ion channels.
What is depolarisation?
A change in the membrane potential to a less negative value inside.
What happens when an action potential reaches the end of a neuron?
Vesicles containing neurotransmitters fuse with the membrane which causes the release of the neurotransmitter.
What is the retina?
The area within the eye that detects light and contains two types of photoreceptor cells: rods and cones.
What is combined to form the photoreceptor of the eye?
The light sensitive molecule retinal and the membrane protein opsin.
What is the retinal-opsin complex called in rod cells?
Rhodopsin
What are rod cells responsible for?
Vision in dim light.
What are cone cells responsible for?
Colour vision.
Where is photopsin found?
Cone cells
In cone cells, why do different forms of opsin combine with retinal?
To give different receptor proteins which each have a maximal sensitivity to a specific wavelength: red; green; blue or UV.
