Communication Within Multicellular Organisms Flashcards
How do multicellular organisms achieve coordination of communication?
They use extracellular signalling molecules and complementary receptor proteins. The two main forms are hormonal and nervous.
Describe how an extracellular signal produces an intracellular response.
One cell releases an extracellular signal molecule that another cell (target cell) detects and responds to. The target cell has receptor proteins with a binding site for the specific signal molecule. When binding occurs, the protein changes conformation which then changes the behaviour of the cell which is called an intracellular response.
How do hormones work as signalling molecules?
Hormones are extracellular signalling molceules secreted by one tissue into the blood. The hormone is carried in the bloodstream until it reaches its receptor protein on its target cell or is broken down. Hormones can either be hydrophobic (thyroxine etc) or hydrophilic (e.g. insulin).
How do neurotransmitters work as signalling molecules?
Neurotransmitters create a very specific and rapid effect due to the intimite association between the signalling and target cell.
Where are hydrophobic signalling molecules receptor proteins likely to be found and why?
Inside the cell as they are able to pass straight through the membrane.
Describe the action of steroid hormones acting as signalling molecules.
- The receptor proteins for steroid hormones are transcription factors (a protein that binds to DNA and controls the rate of transcription). Transcription factors can enhance or block the binding of RNA polymerase to specific genes so they control whether a gene is transcribed or not. When the steroid hormone binds to the receptor protein, it changes conformation and is able to bind to gene sites of DNA to allow transcription to take place.
Describe the action of thyroxine acting as a signal molecule.
- Thyroxine is a hormone produced by the thyroid gland which controls the rate of metabolism.
- When thyroxine reaches its target cell, it is converted to thyroid hormone and stimulates the transcription of certain genes such as those for the sodium-potassium pump.
- In the absence of thyroid hormone, its receptor protein binds to DNA, inhibiting transcription.
- When thyroid hormone binds, the receptor changes conformation and can no longer bind to DNA, allowing transcription for the sodium-potassium pump gene.
- An increased production of sodium-potassium pump results in an increased metabolic rate.
Where are hydrophilic signalling molecules receptors likely to be found and why?
On the surface of the protein as hydrophilic molecules are unable to pass through the hydrophobic centre.
How are hydrophilic signals often transducted?
Transducted hydrophilic signals often involve cascades activated by G-proteins or phosphorylation by kinase enzymes. When GPD is bound to a G-protien it is inactive, but when a signal binds to the receptor, GTP replaces GDP and the G-protein becomes active and is able to stimulate an enzyme, creating a response.
