Cell Signalling Pathways - BIOL111 Lecture 36 PDF

Biol111: Cellular Biology and Biochemistry Lecture 36 Cell Signalling Pathways  Signal transduction pathways Themes 1. Signal reception Receptor changes Receptors: usually...

Biol111: Cellular Biology and Biochemistry Lecture 36 Cell Signalling Pathways  Signal transduction pathways Themes 1. Signal reception Receptor changes Receptors: usually shape when ligand found in the plasma binds membrane Receptor is switched off by ligand dissociation 2. Signal Protein switches: GTP/GDP and transduction phosphorylation/ Second messengers or desphosphorylation signalling proteins Small molecules (second messengers) activate other proteins 3. Signal response Effectors Transduction - Amplification  Transduction - Amplification Amplification allows a small initial signal to be massively increased. Example: * 1 molecule of epinephrine binds a G protein-coupled receptor. * 100 or more activated G proteins. * 1000 molecules of cAMP. * 1 million activated molecules of glycogen phosphorylase. * 100 million molecules of glucose-1-phosphate. Reece et al. (2011) Campbell Biology, 9th ed, Fig. 11.16 Common theme: Turning on and off the signal Receptors are turned on (ligand binding) and off (ligand release) Second messengers can be turned on and off Enzymes can be turned on and off (by kinases and phosphatases) 6. Response 1. Signal reception Receptors: usually found in the plasma membrane 2. Signal transduction Second messengers 3. Signal response Effectors  Response Signal transduction pathways can have various outcomes: I. Altered metabolism Reece et al. (2011) Campbell Biology, 9th ed, Fig. 11.16  Response Signal transduction pathways can have various outcomes: II. Altered gene expression  Growth factors  Steroid receptors Reece et al. (2011) Campbell Biology, 9th ed, Fig. 11.15  Response Signal transduction pathways can have various outcomes: III. Altered cell movement or shape For example, activation of actin-binding proteins and changes to the cytoskeleton. Involved in: Muscle contraction Wound healing Embryo development Phagocytosis Alberts et al (2004) Essential Cell Biology, 2nd ed.  Response Signal transduction pathways can have various outcomes: III. Altered cell movement or shape For example, activation of actin-binding proteins and changes to the cytoskeleton. Involved in: Muscle contraction Wound healing Embryo development Phagocytosis Alberts et al (2004) Essential Cell Biology, 2nd ed. 6. Response Signal transduction pathways can have various outcomes: i. Altered metabolism ii. Altered gene expression iii. Altered cell movement or shape Extracellular signals can act slowly or rapidly.  Response - Timing Extracellular signals can act slowly or rapidly. Example: Example: adrenaline growth factors Alberts et al (2004) Essential Cell Biology. Fig. 16.23  Today’s Key Messages Cells can detect and respond to a wide variety of signals, most of which are chemical signals Signalling can be direct, local, or long-distance Signalling molecules are diverse in structure and solubility Signalling consists of three steps Signal reception Signal transduction Signal response Ligand-ion channels and GPCRs are examples of membrane- bound receptors Steroid receptors are an example of an intracellular receptor Key Points Signal reception - Signal transduction - Signal response Receptors include G protein-coupled receptors, ion channel receptors and steroid receptors. Second messengers include cAMP and calcium Amplification pathways exist for signalling through phosphorylation cascades. Responses include modification of gene expression and protein production, modification of enzyme activation, and modifications in protein activity.