Cell Signalling | Bright Minds Mentori

Cell Signalling

Cells in multicellular organisms communicate

using extracellular signal molecules.

Types of Signal Molecules

Non polar: pass through membrane Polar: can't pass through membrane

Nuclear/cytosol receptor Surface membrane receptor

Hydrophobic Signalling

Stages of Hydrophobic signalling

1. Non polar signal molecules (oestrogen/testosterone steroid

hormones) can pass through the cell membrane.

2. They bind to specific intracellular receptors in cytosol/nucleus that

are transcription factor forming the hormone receptor complex.

3. The hormone receptor complex moves to the nucleus & binds to

HRE (Hormone response elements), specific regions of DNA.

4. This influences the rate of transcription which affects synthesis of

specific proteins.

Hydrophilic Signalling

1. Extracellular signals binds to the extracellular face of

transmembrane surface receptors changing its conformation.

2. The receptor acts as a signal transducer by converting the

extracellular signal binding into an intracellular response.

3. Two types of intracellular response induced by receptor conformation change.

G protein relay mechanism Phosphorylation kinase cascade.

1 kinase transfers & phosphorylates

the next kinase in the series.

4. This alters the behaviour of the cell

- ion channel opens/close - enzyme activation/deactivation

Tissue Specific Response

A signals can only be detected if a cell has the specific receptor

-cell surface (hydrophilic signalling)

-cytosol/nucleus (hydrophobic signalling)

The same signal may have different effects on different target cell

types due to different intracellular signalling molecules/pathways.