Cell Signalling Flashcards
How does a signal cause a change in a cell?
Signal - receptor - (amplification) transduction - responses
What are the 5 types of signals that can be involved in signal transduction?
- Endocrine signals - released from a gland and travel through the bloodstream to act on a distant target organ e.g insulin
- Paracrine signals - released from cells to act on adjacent cells
- Autocrine signals - act on the same cell that they are released from -gh
- Cell-cell signalling - where the secretory cell is directly attached to the target cell by the signal e.g T cell activation.
- Ligand - the signals that bind to receptors
Describe the lock and key analogy for receptors:
This describes how each hormone has its own specific receptor. Only when the hormones or ligand engages with the correct receptor can it activate the receptor and trigger intracellular signalling leading to a response
How do drugs inhibit the receptor?
They can either partially block the receptor by not properly fitting into it or they can mimic its effect to inhibit intracellular signalling
Why does the receptor undergoes a conformational change when a hormone/ligand binds to it:
This is done so that signalling can occur without a hormone passing through the membrane allowing the receptor to act as a gate keeper or activity so that activity can be controlled at the cell surface
Describe the process of transduction:
The arrival of the signal then needs to be relayed through the cell - transduced. Cascades of molecular interactions relay signals from the receptors to target molecules in the cell. It usually involves multiple steps which can amplify a signal. It provides more opportuities for coordination and and regulation of cellular responses.
What are the 2 most common methods of signal transduction?
- Second messengers
2. Phosphorylation
Describe how second messengers work:
They are chemical signals that are not embedded in the membrane that can diffuse in and out of the cell to pass on the message. They change in concentration to convey info to the cell. And example of this is cAMP which can occur in many tissues and cells because other aspects are tissue specific
How does the same signal have different effects in different cells?
Because different types of cells have different collections of proteins which allow cells to detect and respond to different signals. Each cell has different proteins and pathways. Pathway branching and cross-talking further helps the cell to coordinate incoming signals
How does phosphorylation occur and what is it?
Phosphorylation and dephosphorylation act as a molecular switch that can turn protein activity up/down or on/off as required by the cell. Protein kinases transfer phosphates from ATP to protein. Many relay molecules in signal transduction pathways are protein kinases creating a cascade. Protein phosphotases do dephosphorylation
Describe signal amplification:
At each step the number of activated products is much greater than the preceding step. This means that only a very small amount of the initial hormone is required and a few receptors need to be activated to produce a response i.e each receptor may produce many second messenger molecules to amplify the signal
Describe the cellular response
The changes in chemicals result in the activation or inhibition of proteins e.g pumps enzymes etc
Describe the termination step of signal transduction:
After the cell has completed its response to a signal the process must be terminated so that the cell can respond to new signals. Signalling processes that fail to terminate can have highly undesirable consquences
Name and describe the 3 receptor classes:
- G protein coupled receptors GPCR’s - receptors that work with the help of a G protein
- Receptor tyrosine kinases RTK - receptors that attach phosphates to tyrosines to signal
- Ligand gated ion channel receptors - a signal molecule binds as a ligand to the receptor, opening the receptor gate and allowing specific ions to pass through a channel in the receptor into the cell
Describe the structural features of a GPCR:
7 transmembrane regions (serpintine) - with an extracellular N-terminus and intracellular C-terminus. There are 3 intracellular loops and 3 extracellular loops