Cell Signalling 1 Cell Signalling

Question Answer
Explain the difference between ‘sensitivity’ in terms of hormones binding to receptors. Sensitivity: high affinity receptor/low Kd values/co-operative nature of ligand binding/amplification via cascade mechanism. Overall, small amount of hormone causes ‘large’ intracellular effect.
Explain ‘specificity’ in terms of hormones binding to receptors. Specificity: cell distribution of receptors/complementary nature of ligand binding to receptor. Only one type (class) of ligand should bind to a given receptor.
In general terms, describe the key differences between GPCR and ion channel-coupled receptors. GPCR: serpentine and effect of receptor occupancy is transduced via G-protein on cytoplasmic face of membrane.Ion-channel coupled receptors: transmembrane proteins too, but transduces own effect within the cell by acting as a pore.
Describe the role of alpha subunits within a heterotrimeric G-protein. GDP-b is inactive/GTP-b is active. GTP a dissociates from partners b &y and from receptor. > interact with effector. GTPase hydrolyses GTP to GDP plus Pi. a reassociates with b y dimer.
Explain the roles of the second messengers IP3 and DAG. IP3 causes release of calcium ions from endoplasmic reticulum in cell.Ca2+ and DAG combine to activate protein kinase C.
Describe the role of a phosphodiesterase in cellular signalling. PDEs are a family of enzymes which hydrolyse the phosphoester bond in cyclic nucleotides such as cAMP and cGMP.cAMP ——> 5’AMPThis terminates the role of these molecules as second messengers.
Amplification of the signal from receptor to intracellular effect. Cascade mechanism
Loss of receptor from the cell surface following chronic stimulation. Desensitisation
Describe the mode of action of nitric oxide as a signalling molecule. Gaseous molecule which passes through cell membrane and binds directly to guanylyl cyclase (intracellular isoform) causing increase in levels of cGMP.
Other than via a PDE, state two ways in which cellular signalling pathways can be terminated. Phosphatase removing phosphate modifications.Reuptake of second messenger (eg calcium ions)
List the three broad classes of biomolecules used by multicellular organisms as chemical signals. Protein/peptides, Lipids and Amines
Specificity and cell signalling Complementary binding between the ligand and the receptor; the binding site on the receptor is specific to the ligand. Not all cells contain receptors to a specific ligand, only those who require to illicit a response
Sensitivity and cell signalling The high affinity of receptors for their ligand. Binding of a small amount of ligand promotes the subsequent binding of more ligand. Binding of a ligand to a receptor leads to a cascade of events which further amplify the response.
What is a receptor? Proteins that are responsible for binding specific molecules.
On cell-surface receptors, where does ligand binding occur; intracellular or extracellular? Extracellular
Name the three main categories of receptors. G-protein coupled receptors, ion channels and Tyrosine kinase receptors
Name an example of a hormone which works through a GPCR. Adrenaline, Prostaglandin E1 or Vasopressin
Name some of the ions you would expect to pass through an ion channel. Na+, K+, Cl-, Ca2+
Name an example of a Tyrosine Kinase Receptor. Insulin Receptor

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