Cell Signalling Flashcards
What is cell signalling?
The ability to communicate between cells
In unicellular organisms: -respond to chemical signals from neighbouring cells
-quorum sensing (bacteria react to cell density through chemical molecules)
In multicellular organisms: -Integrate signals from neighbouring and distant cells
- need to respond to changes in the environment
- co-ordinate growth and development
What are the four forms of intracellular signalling?
1) Contact dependent
2) Paracrine
3) Synaptic
4) Endocrine
What are the features of each form of intracellular signalling?
Contact dependent - Important during development and the immune system via gap junctions using small molecules
Paracrine - signals released into extracellular space and act locally on neighbouring cells eg growth factors
Synaptic - neurotransmitters, long range signalling secreted into synapse and bind to receptors on target cells
Endocrine - hormones released from endocrine cell eg insulin in the pancreas enter the blood stream and act on many target cells
What is a ligand?
a molecule that binds to another molecule
What is an agonist?
The molecule that binds to the receptor
What is a first messenger?
The molecule that is the ligand/agonist/hormone
What is a secondary messenger?
Intracellular molecule produced in response to first messenger (cAMP is most common example)
What is signal transduction?
Process by which signal is transmitted into cell and then to produce final response
What are the steps to the simple signalling pathway?
1) Signal molecule binds to the receptor protein
2) The receptor activates intracellular signalling proteins that initiate a signalling cascade
3) This signalling cascade influences a target protein, altering this target protein and thus altering the behaviour of the cell
4) This whole process if often called signal transduction
What are the different types of effector proteins that can be stimulated by cell signalling?
- metabolic enzyme
- gene regulatory protein
- cytoskeletal protein
How is the cell signal amplified?
One hormone binds to one receptor, but that receptor can bind to a huge amount of second messenger so the signal is largely amplified in a cascade
How can the time of the extracellular signals vary?
When a signal has to enter and act within the nucleus the response is more likley to be Minutes or hours
When a signal only travels in the cytosol it can occur in seconds to minutes as the protein synthesis doesn’t have to be altered
What is cross talk?
Different signal transduction pathways from different first messengers may converge on a common target
Why does cross talk occur?
- To enhance the response
- To attenuate the response
What are the characteristics of first receptors?
-Ligands that bind to specific receptors two different types: Hydrophobic ligands (estrogen, testosterone) are steroid hormones and vitamin D. They are lipid soluble and membrane permeable they bind to intracellular receptors to directly alter gene expression
Hydrophilic ligands eg proteins are water soluble and membrane impermeable. They bind to cell surface receptors and reuire signal transduction mechanisms
