Cell signaling Flashcards
What sorts of activities can signalling trigger a cell to do?
Metabolism, protein production, physiological functions, survival, division, apoptosis, growth
What is signal transduction?
The process by which an extracellular signal is turned into an intracellular response
What is the general series of steps?
- A signal binds to a receptor
- The pathway gets activated and the effector proteins get activated
- Cellular response
- Deactivation of all the components of the pathway
What are 5 characteristics of signaling pathways?
- Has a programmed series of steps
- One signal can trigger many different responses depending on the cell type, what receptors are present, and the pathways in the cell
- Amplification occurs, each step can activate many copies of the next one
- signals and pathways integrate and converge
- Fast on and fast off process
What is signal integration?
Cross talk between pathways. One signal can activate many pathways, two separate receptors can activate a pathway, messengers within a pathway can affect another pathway
What are the 4 common components of pathways?
- A ligand interacting with a receptor
- GTP binding proteins (G proteins)
- Kinases and phosphatases
- Secondary messenger molecules
What is a ligand?
The signalling molecule that binds to a receptor to change its shape and turn on the pathway
How is ligand binding reversible?
Weak, non-covalent interactions hold the ligand to the receptor
What changes a G protein between its off conformation and its on conformation?
If it is binding to GTP, it’s on. If its binding to GDP, it’s off
What proteins switch a G protein between its on and off conformation?
GEF: guanine exchange factor removes the GDP and replaces it with a GTP
GAP: GTPase accelerating protein speeds up GTP hydrolysis
How do G proteins automatically turn themselves off?
They have an intrinsic GTPase activity and will eventually break down the GTP to GDP and turn off the protein
What is the difference between monomeric and heteromeric G proteins?
Monomeric is one protein chain and is used in other activities besides signalling. Heteromeric is made of 3 different protein chains in alpha, beta, and gamma subunits that are only involved in signalling
What are kinases?
Enzymes that phosphorylate stuff
What are phosphatases?
Enzymes that dephosphorylate stuff
What are intracellular secondary messengers? How are they different from all other common components of pathways?
Amplified molecules that bring messages and activate other stuff. They are created every time the pathway is turned on, which is different from everything else that is already expressed when the pathway is turned on
What are long term responses to cellular signalling? How does the cell respond to these signals?
They don’t occur very frequently, and take longer to do (such as cell division). Long term responses are related to gene expression
What are the 3 components of the Ras/MAPK pathway?
- formation of a receptor complex
- activation of kinases
- activation and movement of transcription factors
What is the structure of tyrosine kinase receptors?
A single transmembrane domain, with a ligand binding domain on the extracellular side and a tyrosine kinase domain on the intracellular side
What happens first in the Ras/MAPK pathway?
EGF binds to EGFR
What happens after EGF binds in the Ras/MAPK pathway?
EGFR dimerizes with another EGFR and they cross phosphorylate each other
What happens after EGFR is cross phosphorylated in the Ras/MAPK pathway?
It recruits GRB2 and it binds to EGFR with the SH2 domain
What happens after GRB2 binds to EGFR in the Ras/MAPK pathway?
GRB2 recruits Sos
What kind of protein is Sos?
GEF
What happens after Sos is recruited in the Ras/MAPK pathway?
Sos exchanges the GDP on Ras, which is now right beside it, for a GTP and activates Ras
