Cell Communication Flashcards
Four main processes essential for cells to communicate.
1) synthesis, release, and transport of signaling molecules; 2) reception of information by target cells; 3) signal transduction, the process by which a receptor converts an extracellular signal into an intracellular signal and relays the signal, leading to a cellular response; and 4) response by the cell, e.g., some metabolic process may be altered.
Neurotransmitters
Most neuron signal one another by releasing chemical compounds called neurotransmitters.
Hormones
Are chemichal messengers in plants and animals. In animals they are secreted by endocrine glands, glands that have no ducts. Most hormones diffuse into capillaries and are transported by the blood to target cells.
Local regulators
They diffuse through the interstitial fluid and act on nearby cells. This process is called paracrine regulation. E.g. growth factors, protaglandins and nitric oxide.
Reception as a highly specific process
Each type of receptor has a specific shape, and only the signaling molecule that fits the specific receptor can affect the cell.
Ion channel-linked receptor
When a signaling molecule binds to and ion channel, this one opens or closes. They convert chemical signals into electrical signals.
G protein-linked receptors
They are transmembrane proteins that extend into the cytosol or outside the cell. These receptors couple specific signaling molecules to signal transduction pathways inside the cell. The tail of the receptor that extends into the cytosol has a binding sito for a specific G protein, a regulatory protein that binds to GTP.
Enzyme-linked receptors
They are transmembrane proteins with a binding site for a signaling molecule outside the cell and a binding site for an enzyme inside the cell. Many of them are tysorine kinases. In a protein kinase cascade, each molecule in the signaling pathway is phosphorylated bu the preceding protein kinase in the chain. The last protein kinase in the cascade activates the target protein by phosphorylation.
Intracellular receptors
They are located in the cytosol or in the nucleus. Their ligands are small, hydrophobic molecules that diffuse across the plasma membrane. These receptors are transcription factors that activate or repress the expression of specific genes.
Responses that cells make to signaling molecules
Ion channels open or close, enzyme activity changes, leading to metabolic changes and other effects, ans specific genes are activated or repressed.
Signal amplification
It is the process of enhancing the cell’s response to a signal as the signal is relayed through a signal transduction pathway. Before it becomes inactive, each enzyme can catalyze the production of numerous product molecules.
Signal termination
It is the process of inactivating the receptor and each component of the signal transduction pathway once they have done their jobs. Signal termination allows molecules in the system to respond to new signals.
Evolution of Cell Communication
Molecules importan in cell signaling first evolved in prokaryotes. G proteins, protein kinases, and phosphatases have been highly conserved and are part of most signaling pathways.
