Lecture 12 - Cell Signaling Flashcards
What 3 stimuli can cells receive signals from? (name, example, response)
- Mechanical Stimulus = opening K+ and Ca+ channels which will create a change in membrane potential. (ex: bending stereocillia in the cochlea)
- Chemical Stimulus = can cause influx of Na+ ions which will cause the opening of Ca channels, allowing for contraction (ex: release of acetocholine in the neuromuscular junction)
- Photo Stimulus = absorbtion of light by a pigment molecule (ex: photosynthesis)
What are gap junctions and what are they made up of?
Animal cells utilize gap junctions to connect with neighboring cells that are touching to allow for a faster way of diffusion of molecules. Gap junctions are made up of 2 connexons which is made up of 6 connexins, the integral protein.
What are plasmadesmata?
Unlike animal cells, plant cells have a cell wall so they don’t have junctions, instead they have whats called plasmadesmata which connects neighboring plant cells together. Plasmadesmata are bigger than gap junctions and are typically used for a faster way of transportation of water.
What are the 4 kinds of chemical signals?
- Autocrine Signals: when the cell signal affects itself
- Juxtacrine Signal: when the cell signal affects neighboring cells that are touching or very close proximity
- Paracrine Signal: when the cell signal affects neighboring cells that are a bit farther away
- Endocrine Signal: when the cell signal affects cells that are much farther away and need to transport through blood to get there.
The signal transduction pathway involves three steps, what are they? Provide a short summary how it works.
The three steps are: signal -> receptor -> response
How it works (simplified): A signal molecule will bind to a receptor imbedded in the cell membrane which will then activate a signal transduction molecule which can cause short term or long term changes. Short term includes enzyme activation or cell movement. Long term includes alterned DNA transcription.
What are the two kinds of receptors? (what do they receive, examples, and simplified breakdown)
- Intracellular receptor: in the cell and recieve small or nonpolar ligands (ex: steroid hormones)
Steroid hormone is brought by carrier protein where it diffuses in the cell and attaches to a receptor in the cytosol. That hormone-receptor complex than moves into the nucleus where it attaches to DNA and alters transcription/expression.
- Membrane receptor: on the cell membrane and recieves large or polar ligands (ex: acetylcholine)
Signal attaches to receptor protein in the membrane, where intracellular signaling molecules are activated and can be amplified if needed. It can lead to changes in protein activity in the cytoplasm or it can enter the nucleus and effect the DNA.
What are protein kinase receptors and how do they work?
Protein kinase receptors catalyze phosphorylation of themselves or other proteins. An example of how they work is :
a signal like insulin will bind to the insulin receptor which is in the membrane because insulin is a large ligand. Insulin will bind the to the alpha subunits which will cause a change of shape to the beta subunits. The change in the beta subunits will activate the receptors protein kinase domain which is located in the cell. The protein kinase receptor will phosphorylate an insulin-response substrate, triggering various of chemical responses in the cell.
What are g-coupled protein receptors? How do they work?
G-coupled protein receptors are ones that are embedded in the membrane and when a ligand is binded it will activate a G-protein inside the cell. That g-protein once activated, will interact and activate a channel, enzyme, or protein.
What is cortisol and what are the effects of it?
Cortisol is a stress hormone and some effects include:
- Suppressing your immune system
- increase glucose in the blood, raising BP, and raising your chance of blood clots
- Helps us start functioning in the morning
How does a steroid hormone like cortisol get into the nucleus to send a signal?
Cortisol will enter the cell and bind to an intracellular receptor. Before cortisol binds, the intracellular receptor is inactive and bimded to a chaperone protein. Once binded to the cortisol, the intraceullular receptors changes shape and dettaches from chaperone protein. The receptor and cortisol ligand complex enter the nucleus and attach to DNA.
What would the signal transduction pathway look for an intracellular response to an extracllular signal (ex: damage in the cell)
A growth factor will bind to a receptor, in this case thid ligand is bigger so the receptor will be embedded in the membrane. Once binded it will cause the protein kinase domain to phosphorylate itself. This allows ras (a g-protein) to bind with GTP and become activated. One ras is activated it will bind to rat (a protein kinase). rat will activate MEK, another protein kinase, which will then bind to MAP kinase. MAP kinase will enter the nucleus once activated. This process is an example of a protein kinase cascade.
How does ras function differ in a normal cell and a cancer cell?
In a normal cell, ras will be inactivated while its binded to GDP. Once a receptor is activated, GTP will be activated and bind to ras which will then activate it. The activated ras will provide a brief stimulation of cell divison. After a brief time, ras will return to its inactive state.
In a cancer cell, the same process wil occur, however since ras will be modified or mutated, it wont be able to be deactivated after being activated. This would lead to a constant stimulation of cell division.
What is CAMP and what does it do?
CAMP is a secondary messanger used to amplify signals between receptors and target molecules. It does this by activating protein kinases, which will phsophorylate proteins, and by activating Glycogen phosphorylates, this will allow Glycogen to go around and activate g-proteins that will release more CAMP.
What is the difference between first messenger and second messenger? What are some examples?
First messenger are extraceullar signals (ex: chemical, mechanical, photo signal)
Second messenger are intracellular signals (ex: cAMP, cGMP, PIP2, Calcium ions, nitric oxide)
Where can secondary messengers be derived from?
lipids
