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## Cell Signalling ### Types of Signalling - Autocrine: a cell targets itself - Paracrine: affects nearby cells - Endocrine: long-distance signalling through the bloodstream (e.g. hormones) ### Cell Signalling Process - **Reception:** A ligand binds to a receptor on the cell surface. Think of it...

## Cell Signalling ### Types of Signalling - Autocrine: a cell targets itself - Paracrine: affects nearby cells - Endocrine: long-distance signalling through the bloodstream (e.g. hormones) ### Cell Signalling Process - **Reception:** A ligand binds to a receptor on the cell surface. Think of it like a lock and key. - **Transduction:** Signal is relayed through intracellular pathways (e.g., phosphorylation, second messengers.) - **Response:** Cellular response such as changes in gene expression or ion flow. ### Key Components - **Ligand:** Binds to receptors to initiate signalling. - **Receptor Tyrosine Kinase (RTK):** Activated by ligands to promote signalling pathways. - **G-Protein-Coupled Receptor (GPCR):** Regulates signalling by activating G-proteins. - **Mitogen-activated Protein Kinase (MAPK):** Part of the process that amplifies signals to the cellular response. - **Second Messenger (e.g., cAMP):** Amplifies the signal inside the cell. - **Phosphorylation:** Addition of a phosphate group, often activating or deactivating proteins. Helps pass messages from outside the cell to the inside. ### Proteins and Receptors - Proteins are involved at all levels. - Receptors on the cell surface are often proteins. ### Second Messengers - Think text messages that spread the word inside the cell. After the receptor receives a signal, second messengers (like cAMP) carry the signal to different parts of the cell, leading to a response. ### Enzymes and Phosphorylation - Enzymes (like kinase) add a phosphate group to other proteins. This often "turns on" the proteins to do their job. This is part of the signal transduction process. ### Amplification - This is where one signal molecule can cause a huge response inside the cell. Imagine a microphone amplifying a voice -- one molecule binding to a receptor can trigger a chain reaction, activating multiple proteins and amplifying effects. ### Ribosomes - Ribosomes are the cell's protein builders. They read instructions from mRNA (which comes from DNA) and makes proteins, including the ones involved in signalling pathways like GPCR. ### End of Signalling Process - At the end of signalling process, the signal reaches the nucleus, affecting gene expression. Proteins like transcription factors bind to DNA, causing the cell to produce specific proteins for the response, such as for growth or repair. ### Signal Reception - **Signalling Molecule:** Ligand binds to a receptor on the cell surface. - **Example:** Adrenaline binds to GPCR. ### Signal Transduction - The receptor changes shape, activating internal proteins (e.g. G-proteins). - G-proteins trigger enzymes like adenylate cyclase. ### Second Messenger Activation - Enzymes produce second messengers (e.g. cAMP) which amplify signal inside the cell. ### Cellular Response - Kinases are activated, leading to specific responses (e.g. activating genes).