Cell Signalling Flashcards
How are chemical signals transmitted?
First messenger binds the ligand to a specific receptor. The second messenger is a substance that relays the ligand from the receptor to the cytoplasm to trigger a response
Where is the receptor for a hydrophobic molecule found?
The receptor is found inside the cell as hydrophobic molecules can diffuse through the cell membrane
Where is the receptor for a hydrophilic molecule found?
The receptor is found on the cell surface membrane. All cell surface receptors require a second messenger to relay the signal
What are the ways a signal can be stoppped?
Spontaneous breakdown, enzymatic breakdown, reuptake and receptor/ligand internalisation
How does spontaneous breakdown work?
A NO molecule reacts with O2 to produce NO3-
How does enzymatic breakdown work?
An enzyme is used to break down a signal, eg the break down of choline using the enzyme acetyl-cholinesterase.
Another example is the use of proteases that cleave the peptide chain at low concentrations and have a long-term effect
How does reuptake work?
This is when neurotransmitters are taken up again by the same cell
How does receptor/ligand internalisation work?
The receptor/ligand complex is endocytosisd
What is the purpose of eNOS and how is it used to control blood pressure?
eNOS is an enzyme found in the epithelial cells of blood vessels. The endothelium cells in the smooth muscle of the vessels are stimulated by the binding of acetylcholine/histidine. NO diffuses into the cells to relax them, causing blood pressure to drop. The target for NO is guanylate cyclase. GTP is converted to cGMP as the second messenger
How is cGMP converted into GMP?
Phosphodiesterase breaks the phosphodiester bonds at the 3’OH ribose
How does steroid signalling work?
Steroids are hydrophobic so they cannot be stored in the celland therefore carried by a protein to the target cell. They are lipophilic so they diffuse into all cells but only activate cells when they bind to the correct receptor. The receptor then undergoes a conformational change and unmasks a DNA binding site
How do ligand-gated ion channels work?
Allows the transport of ions, however the change in ion conce on each side of the membrane happens rapidly. Some ions bind and cause a conformational change which allows the transport of the ions.
How do G-linked protein receptors work?
Transmembrane protein, crosses the membrane 7 times. MAde of alpha, beta, gamma subunits, the aplha subunit has the GTP/GDP binding site that uses GTPase to convert GTP to GDP. Binding of a ligand at the extracellular surface of the GPCR results in a conformational change in the receptor that is transmitted to the bound Gα subunit
What are the targets of the actived Galpha unit?
Adenylate Cyclase converts ATP to the
second messenger cyclic AMP (cAMP).
* cAMP activates a protein kinase called
Protein Kinase A (PKA).
* cAMP binds to the regulatory subunits of
protein kinase A releasing the active catalytic
subunits.
