4.1.2

Cell Signalling

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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.

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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.
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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.
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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.
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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.
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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.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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