Cell Signalling Flashcards
What are the three cycles of cell signalling?
- Ligand-receptor interaction
- Signal transduction
- Cellular response
What is ligand-receptor interaction ?
A process by which a specific receptor protein on or in target cell detects the signal
This occurs during complementary binding of the ligand (signalling molecule) to the specific site on receptor
What is a ligand ?
Molecules that specifically bind to another molecule
What are the characteristics of ligands that bind to cell surface receptors ?
Water soluble
Generally too large to pass freely through plasma membrane
What are some examples of cell surface receptors ?
G-protein linked receptor
Receptor tyrosine kinase
Ion channel receptor
What are the two effects of ligand-receptor interaction ?
- Ligand binding generally causes receptor protein to undergo conformational change, which in many receptors would directly activates the receptor, enabling it to bind with other cellular molecules
- For other kinds of receptors, the immediate effect of ligand binding is to cause the aggregation of two or more receptor molecules, which leads to further molecular events inside the cell
What is signal transduction ?
A process by which extra cellular signals are converted into intracellular signals to generate specific cellular responses
Usually a multi step pathway, involving a series of interactions between relay molecules that operate in sequence
How is signal transduced ?
- Phosphorylation (and dephosphorylation) of relay proteins which changes conformation of these proteins and thus results in their activation (and deactivation)
- Production of small non-protein molecules and ions known as second messengers to relay the signal inside of the cell
What does upstream and downstream mean, relative to a particular molecule of interest ?
Upstream - molecules and events that come earlier in the relay chain
Downstream - molecules and events that come later
What is a kinase ?
An enzyme which catalyses the addition of phosphate groups from ATP to protein
What are phosphatases ?
Enzymes that can catalyse removal of phosphate groups from the proteins, making them inactive which ends signal transduction thus making proteins in the pathway available for reuse
What is a phosphorylation cascade ?
Where a series of different protein kinases arranged in a pathway are phosphorylated sequentially
What are second messengers ?
Small, non-protein, water-soluble molecules or ions
Able to spread throughout the cell by diffusion
What do second messengers do?
Molecules that relay signals received at receptors on the cell surface to target molecules in the cytoplasm and/or nucleus
They also serve to greatly amplify the strength of the signal
What are the widely used second messengers?
cAMP
Calcium ions
What is the significance of the multistep pathway in cell signalling ?
Amplification of signal
What is a phosphorylation cascade ?
An active kinase catalysing the phosphorylation of many kinases, thus activating them. Each of these active kinases go on to phosphorylate and activate many kinases in subsequent steps
At which point in the signal transduction pathway does the cell’s specific response occur ?
The end of the signal transduction pathway
What are the two types of cellular responses ?
Cytoplasmic responses
Nuclear responses
What is involved in cytoplasmic responses ?
Mainly changes in activity of enzyme and proteins in cytoplasm leading to changes in cell metabolism
What are nuclear responses ?
When specific genes coding for synthesis of enzymes or other proteins are switched on or off ( in nucleus )
Why can two cells respond differently to the same signal ?
Due to difference in one or more of the proteins that handle and respond to the signal
What does the response of a particular cell to a signal depend on ?
On the specific collection of signal receptor proteins, relays proteins and functional proteins need to carry out the response
What are scaffolding proteins ?
Large relay proteins to which several other relay proteins are simultaneously attached
