My AP Biology Thoughts Unit 4 Cell Communication and Cell CycleWelcome to My AP Biology Thoughts podcast, my name is Victoria Villagran and I am your host for episode #90 called Unit 4 Cell Communication and Cell Cycle: Cellular Responses in Signaling Pathways. Today we will be discussing general cellular responses in signaling pathways. Segment 1: Introduction to Cellular Responses in Signaling Pathways Signaling pathway: Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein in a target cell The ligand-binding domain of a receptor recognizes a specific chemical messenger, which can be a peptide, a small chemical, or protein, in a specific one-to-one relationship Signal reception, which is when the target cell receives a signaling molecule; transduction, which is a series of events that converts the signal to something the target cell can respond to; and cellular response, which is when the target cell responds to the signal. They are many varieties of ligands and receptors, and them binding can lead to many different responses May involved 2nd messengers or phosphorylation, and protein phosphorylation They all produce some kind of cellular response The same signal or ligand can lead to different responses Signal Pathways may influence how the cell responds to its environment Responses can be short or long term We can see changes such as an increase in the transcription of certain genes or the activity of particular enzymes. We may be able to see changes in the outward behavior or appearance of the cell, such as cell growth or cell death, that are caused by the molecular changes Three Response Types 1. Metabolism/Growth/Enzyme Activation/Open Ion Channel Altering the activity of specific enzymes, metabolic enzymes in the cell become more or less active Activated G Protein binds to a molecule that starts the transduction pathway, we will go into more detail later Some signals bind to ligand-gated ion channels which either open or close in response to binding 2. Gene Expression The process where information from a gene is used by the cell to produce a functional product, a protein. It involves two steps, transcription and translation. Signaling pathways can target either or both steps to alter the amount of a particular protein produced in a cell. Intracellular receptor: ligands are small or non-polar and can diffuse into the membrane. They are an activated hormone-receptor that can act as a transcription factor and affect gene expression Controlling which genes are expressed or not through a number control mechanisms 3. Apoptosis: programmed cell death in cell cycle (also T cell Recognition) Internal signals (such as those triggered by damaged DNA) can lead to apoptosis, but so can signals from outside the cell. Segment 2: More About Specific Cellular Responses Metabolism: Epinephrine When epinephrine binds to its receptor on a muscle cell (G protein-coupled receptor), it triggers a signal transduction cascade involving production of the second messenger molecule cyclic AMP (cAMP). This cascade leads to phosphorylation of two metabolic enzymes, causing a change in the enzymes' behavior. The first enzyme is glycogen phosphorylase (GP) which breaks down glycogen into glucose. Phosphorylation activates glycogen phosphorylase, causing lots of glucose to be released. The second enzyme that gets phosphorylated is glycogen synthase (GS) and it is involved in building up glycogen, and phosphorylation inhibits its activity. Through regulation of these enzymes, a muscle cell rapidly gets a large, ready pool of glucose molecules. The glucose is available for use by the muscle cell in response to a sudden surge of adrenaline aka the “fight or flight” response. Apoptosis: External Signaling Most animal cells have receptors that interact with the extracellular matrix, a structural