AH Biology - Unit 1 - KA4(a) - Coordination

How do multicellular organisms signal between cells?

Multicellular organisms signal between cells using extracellular signalling molecules.

What are the examples of extracellular signalling molecules?

The examples of extracellular signalling molecules are:

• Steroid hormones

• Peptide hormones and neurotransmitters

What are steroid hormones?

Steroid hormones, such as testosterone, oestrogen, thyroxine, and cortisol, are extracellular hydrophobic signalling molecules. They can pass through the plasma membrane.

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What are peptide hormones and neurotransmitters?

Peptide hormones and neurotransmitters, such as insulin and acetylcholine, are hydrophilic and cannot pass through the plasma membrane.

What do target cells for the signalling molecules have?

Target cells for the signalling molecules have specific receptor molecules (proteins) with binding sites for their specific signal molecule.

What does the binding of the signalling molecule to the receptor molecule cause?

The binding of the signalling molecule to the receptor molecule causes a conformational change of the receptor molecule and this initiates a response within the cell.

What do different types of cell produce in regards to communication and signalling?

Different types of cells produce specific signals that can only be detected by and responded to by the target cells with the specific receptor. However, the same signalling molecules may have different effects on different types of target cells due to the different intracellular signalling molecules and pathways involved. This allows a tissue specific response to be produced by the same signalling molecule.