Cell Signalling
Biology: Cambridge International A Level, topic 4.1.2
Signal Recognition
Cell signaling pathways begin when the ligand binds to a receptor, a protein that is embedded in the plasma membrane of the target cell or found in the cell cytoplasm.
Secretion & transport
- Signals can be transmitted over longer distances by using chemical signaling.
- Chemicals (ligands) are secreted from cells and travel in the blood to their target cells.
- For example, signals from distant cells are called endocrine signals. They originate from endocrine cells.
- Endocrine cells are located in endocrine glands, such as the thyroid gland, the hypothalamus, and the pituitary gland.
Reception
- Cell signaling pathways begin when a ligand binds to a receptor, a protein that is embedded in the plasma membrane of the target cell or found in the cell cytoplasm.
- The receptors are very specific, and each ligand is recognized by a different one.
- This stage of the pathway is called reception.
- Ligands can be peptides, small chemicals, drugs, and others.
Non-polar compounds
- Molecules that are nonpolar, such as steroids, diffuse across the cell membrane and bind to internal receptors.
- In turn, the receptor-ligand complex moves to the nucleus and interacts with cellular DNA.
- This changes how a gene is expressed.
Polar ligands
- Polar ligands, on the other hand, interact with membrane receptor protein.
- Some membrane receptors work by changing conformation so that certain ions, such as Na+ and K+, can pass through the plasma membrane.
- Other membrane receptors interact with a G-protein on the cytoplasmic side of the plasma membrane, which causes a series of reactions inside the cell.
- Receptors coupled to G-proteins are a good example of a receptor-type found in eukaryotic cells.
Multiple receptors
- It is important to keep in mind that each cell has a variety of receptors, allowing it to respond to a variety of stimuli.
- Some receptors can bind several different ligands; for example, odorant molecules/receptors associated with the sense of smell in animals.
- Once the signaling molecule and receptor interact, a cascade of events called signal transduction usually amplifies the signal inside the cell.
Test yourself on Cell Signalling
Which of the following would be most likely to a membrane-bound receptor?
Which of the following is a non-polar ligand?