Communication & Cell Signalling

Living organisms can sense what is present in environment & respond appropriately to changes

AMOEBA

Detect nutrient molecules in surrounding water, move towards them & take them in.                        If they are unable to do this, they cannot survive

MULTICELLULAR ORGANISMS

Survive by each cell playing a part

• Cells detect internal & external signals to carry out processes (e.g. growth, movement)
• Must be able to carry out functions in response = extremely complex

                                                                                                                                                                    To detect signals, cells have receptors on their surface to recieve them (often proteins / modified proteins)

In multicellular organisms, communication between cells is often mediated by hormones.

Hormones = Chemical messengers produced in certain tissues and then released into the organism.                                                                                                                                       Any cell with a receptor for the hormone = target cell

The insulin receptor

• Insulin released from beta-cells in the pancreas, in response to increased blood sugar levels
• Insulin = Protein molecule that attatches to receptors on cell surface membrane
• Triggers internal response (more glucose channels present in membrane)
• Allows cell to take up more glucose from blood = reducing blood sugar levels

Medicinal drugs- interfering with receptors

• Medicinal drugs have been developed = complimentary to receptor molecule
• They are intended to block receptors. Beta-blockers used to prevent heart muscle from increasing heart rate
• Some drugs mimic natural neurotransmitter that can't be produced (Schizophrenia)

Hijacking receptors

• Viruses enter cells by binding with receptors
• HIV infects humans as it can enter cells of immune system. It has a shape which fits a receptor on the cell surface
• Once HIV enters, after a period of inactivity it may reproduce inside the cell and eventually destroy it

• Poisons also bind with receptors
• Toxin extracted from bacterium Clostridium botulinum binds with receptors on muscle fibres & prevents them from working properly = paralysis
• Toxin = lethal, but is used in small amounts in BOTOX to paralyse muscles in the face, reducing wrinkling of the skin

Cells communicate with one another by signals. Many molecules act as signals- some signal during processes taking place inside cells; others signal from one cell to another.                          Cytokines are an example of cell signals.