Lecture 8 - Cell Communication PDF

Lecture 8 - Cell communication Chapter 11 External signals are converted to responses within the cell unicellular organisms identify their sexual mates by chemical signalling. In yeast, there are two sexes, or mating types, called a and ɑ. Each type secretes a specific fac...

Lecture 8 - Cell communication Chapter 11 External signals are converted to responses within the cell unicellular organisms identify their sexual mates by chemical signalling. In yeast, there are two sexes, or mating types, called a and ɑ. Each type secretes a specific factor that binds to receptors only on the other type of cell. When exposed to each other’s mating factors, a pair of cells of opposite type change shape, grow toward each other, and fuse (mate). Bacterial cells secrete molecules that can be detected by other bacterial cells. Sensing the concentration of such signalling molecules allows bacteria to monitor the local density of cells, a phenomenon called quorum sensing. low density high density cells in a multicellular organism usually communicate via signalling molecules targeted for cells that may or may not be immediately adjacent Communication by direct contact between cells is a type of local signalling Communication by direct contact between cells is a type of local signalling the orientation of hairs is an example of direct contact signaling Paracrine signalling is another type of local signalling, in which molecules are secreted by the signalling cell and these molecules travel only short distances. This is an example of paracrine signaling A more specialized type of local signalling called synaptic signalling occurs in the animal nervous system. muscle contractions involve synaptic signaling between a neuron and a muscle Acetylcholine A ligand-gated ion channel is a type of membrane channel receptor containing a region that can act as a “gate,” opening or closing the channel when the receptor changes shape  axon terminals, synaptic boutons are small swellings that are found at the terminal ends of axons. They are typically the sites where synapses with other neurons are found, and neurotransmitters are stored Both animals and plants use chemicals called hormones for long-distance signalling Give me examples of signaling happening in the impala’s body cell signalling can be divided into three stages: signal reception, signal transduction, and cellular response. Reception: A signalling molecule binds to a receptor protein, causing it to change shape Most water-soluble signalling molecules bind to specific sites on transmembrane receptor proteins that transmit information from the extracellular environment to the inside of the cell. A G protein-coupled receptor (GPCR) works with the help of a G protein, a protein that binds the energy-rich molecule GTP GTP is like ATP but with guanine instead of adenine. It mostly is used for signaling Guanosine triphosphate Adenosine triphosphate Receptor tyrosine kinases (RTKs) belong to a major class of plasma membrane receptors characterized by having enzymatic activity. A kinase is any enzyme that catalyzes the transfer of phosphate groups. phosphorylation is a widespread mechanism for regulating protein activity Phosphorylation can activate or inactivate proteins Intracellular receptor proteins are found in either the cytoplasm or nucleus of target cells. Steroid hormones have intracellular receptors. Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell In a phosphorylation cascade, a series of different proteins in a pathway are phosphorylated in turn, each protein adding a phosphate group to the next one in line Small Molecules and Ions can also act as Second Messengers cAMP = Cyclic adenosine monophosphate Calcium ions (Ca2 + ) and inositol trisphosphate (IP3) are other examples of second messengers enzyme cascades amplify the cell’s response to a signal. Response: Cell signalling leads to regulation of transcription or cytoplasmic activities Many signalling pathways ultimately regulate protein synthesis, usually by turning specific genes on or off in the nucleus. Example: expression of antimicrobial peptides a signalling pathway may regulate the activity of proteins discuss the relationship between the signalling model with the mutant cells lacking Fus3 or formin. more info on next slide green=membrane red=newly made membrane yellow=green+red Thank you for attending the cell biology unit