Flashcards in Chapter 11 - Cell Communication Deck (22):
What is cellular messaging?
External signals are converted to responses within the cell.
Cell junctions allow molecules to pass between adjacent cells
Two cells may communicate with molecules protruding from their surfaces.
What are the two types of cell signaling?
Local and long distance
What are implied within local signaling?
Paracrine signaling - secretory cells release signaling molecule to near by cells
Synaptic signaling - Nerve cell releases neurotransmitter into synapse to propagate a nerve impulse
What is Long-Distance signaling?
The signal will come from cells that are at a further distance away from the target cell; in our bodies it is often found in the form of a hormone and will travel through the blood.
What are the three stages of cell signaling?
What is Reception?
The target cell will detect signaling molecule from outside the cell.
- the signaling molecule will behave as a ligand
What is a Ligand?
A molecule that binds to another, often larger.
What is a receptor?
It usually is a transmembrane protein.
- G protein-coupled receptors
- Receptor tyrosine kinase
- Ion channel receptors
How does the G protein-coupled receptor work?
a signaling molecule will tell the G protein-coupled receptor to start a cellular response by sending GTP to an inactive enzyme on the cell membrane. This will trigger a cellular response.
How does the Receptor tyrosine kinase work?
A ligand (signaling molecule) will bind to the binding sites found on top of the Receptor tyrosine kinase proteins (pillar like structures with 6 tyrosine molecules). After ligand binds to the two proteins they will combine to make a dimer 6 ATP will then bind to add phosphates to each tyrosine. Inactive proteins will then bind to the phosphorylated tyrosine and trigger a cellular response.
How does the Ion channel receptor work?
A signaling molecule will attach to the ligand-gated ion channel receptor. The signaling molecule with open the gate which will let the ions in to the cell and then the cellular response can happen.
What are Intracellular Receptors?
They are receptor proteins found in either the cytoplasm of nucleus of target cells. To reach such a receptor, a signaling molecule passes through the target cell's plasma membrane.
How does the Intracellular Receptor work?
1. The steroid hormone aldosterone passes through the plasma membrane. (they can pass through the membrane because they are hydrophobic enough or small enough to pass through the membrane)
2. Aldosterone binds to a receptor protein in the cytoplasm, activating it.
3. The hormone receptor complex enters the nucleus and binds to specific genes.
4. The bound protein acts as a transcription factor, stimulating the transcription of the gene into mRNA.
5. The mRNA is translated into a specific protein.
What is Transduction?
They are cascades of molecular interactions that relay signals from receptors to target molecules in the cell.
What molecules/enzymes can be found in a Transduction stage?
Protein Kinase - enzymes that transfer a phosphate group from ATP
Protein phosphatase - rapidly removes phosphate groups from proteins
First messenger - Signaling molecule or ligand (i.e. a hormone)
Second Messenger - A small, non-protein, water soluble molecule or ion which is used in the cascade to propagate signal.
What is Phosphorylation Cascade?
The "cascading" of different types of protein kinase to get an specific active protein.
What happens in a Phosphorylation Cascade?
A signaling molecule will activate a relay molecule.
1. A relay molecule activates protein kinase 1.
2. Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase.
3. Active protein kinase 2 then catalyzes the phosphorylation (and activation) of protein kinase 3.
4. Finally, active protein kinase 3 phosphorylates a protein that brings about the cell's response to the signal.
5. Enzymes called protein phosphatases catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse.
What are cyclic AMP (cAMP)?
They are second messenger molecules that aid in activating proteins to start a cellular response. Example: Epinephrine without passing through the plasma membrane of a cell causes glycogen breakdown. This is done because second messengers will transmit the signal from the plasma membrane to the metabolic machinery in the cytoplasm.
What are calcium ions?
Ions that also aid in cellular response by acting as a second messenger.
How can Calcium ions act as a second messenger?
PIP2 is split into diacyglycerol and IP3 which is a second messenger. Because of the Ca2 gradient (lower concentration of calcium in the cytosol) When the IP3 molecule binds with an IP3 gated channel, it will open and move Ca2 out of the ER and will then become a 2nd messenger.
What is Response?
A response is the regulation of one or more cellular activities after a signal transduction occurs.
- The response may occur in the nucleus or in the cytoplasm.
- Many signaling pathways lead to the regulation of protein synthesis.
- Activation of a transcription factor will turn on a gene.