Chapter 11 Flashcards
Cell Communication
External Signals
External signals are converted to responses within the cell.
External signals: Signals coming from other cells.
Signal Transduction Pathway
Signal reception, signal transduction, cellular response. 3 major steps. Exist in the cells of both unicellular and multicellular organisms.
Local vs. Long distance signaling
Contact between cells: Cell junctions and Cell-surface molecules.
Local distance (few cells distance): Paracrine signaling or synaptic signaling.
Long distance (up to body-length distance): Endocrine (hormonal) signaling.
Paracrine Signaling
A signaling cell acts on nearby target cells by secreting molecule of a local regulator.
Just to neighboring cells. Fast (just into ECF (extracellular fluid)). Handful of target cells.
Synaptic Signaling
A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell, such as a muscle or another nerve cell.
(Sort of a subset of paracrine) Very targeted. Superfast. From 1 to 1 target cell across the synaptic cleft.
Endocrine (hormonal) Signaling
Specialized cells release hormones, which travel through the circulatory system to other parts of the body, where they reach target cells that can recognize and respond to them.
Always involves blood. Slowish. Long distance. Lots of possible target cells.
Autocrine Signaling
(Sort of a subset of paracrine). Cell secretes signal (primary messenger). Cell has receptors for its own signal. Can talk to itself.
Cell/cell via cytosol connection
Cell Junctions/Plasmodesmata allow molecules, including signaling molecules, to pass readily between adjacent cells without crossing plasma membranes.
Cell/cell via surface molecule connections
Cell-surface molecules on adjacent cells interact with each other, resulting in a signal passing between the cells.
Three stages of Cell signaling
- Reception: Reception is the target cell’s detection of a signaling molecule coming from outside the cell. Detected when the signaling molecule binds to a receptor protein located at the cell’s surface (or inside the cell, discussed later).
- Transduction: The binding of the signaling molecule changes the receptor protein in some way, initiating transduction. Converts the signal to a form that can bring about a specific cellular response. Can sometimes occur in a single step, but more often requires a sequence of changes in a series of different molecules, a SIGNAL TRANSDUCTION PATHWAY.
- Response: The transduced signal finally triggers a specific cellular response. The response may be almost any imaginable cellular activity, such as catalysis by an enzyme, rearrangement of the cytoskeleton, or activation of a specific genes in the nucleus.
Ligand
Signaling molecule. Any molecule that binds to another molecule.
Signal Reception
Happens in the plasma membrane, cytosol and nucleus.
Plasma Membrane receptors: required by
Proteins, glycoproteins, amino acids and dipeptides
Cytoplasmic/nuclear receptors
Required by Steroid molecules, CO and NO.
Examples of plasma membrane receptors
G-protein coupled receptor, ligand-gated ion channels, and Receptor Tyrosine Kinases (RTKs)
G-protein coupled receptors (GPCRs)
A signaling molecule in the receptor activates the G protein, which in turn will activate an enzyme, which in turn will activate a cellular response.
7 crosses over PM.
Receptor tyrosine kinases
2 inactive receptor tyrosine kinase proteins that bind together with 2 signaling molecules. Requires 6 ATP. Bind to activated relay proteins, begins cellular response.
Ion-channel receptors
Closed ion channel receptor. Signaling molecule binds to it and opens it. Ions flow into cell, stimulating a cellular response.
Examples of intracellular (cytoplasmic OR nuclear) receptors
Hormones (i.e. aldosterone) go through PM and bind to receptor protein.
Steroid hormone receptors
Transport hormone into nucleus and binds to specific genes.
Examples of Steroid hormones
Lipid-soluble molecules that act as hormones. Androgens, estrogen, testosterone and progestagens are all sex steroids. Aldosterone is a steroid hormone.
Signaling gases
NO (nitric oxide) and CO (carbon monoxide)
Signal Transduction
Chain of molecular interactions that leads to a particular response within the cell.
Protein phosphorylation & dephosphorylation
Protein Kinases: An enzyme that transfers phosphate groups from ATP to a protein
Protein Phosphatases: Enzymes that can rapidly remove phosphate groups from proteins, a process called dephosphorylation.
Second messengers
Small, nonprotein, water-soluble molecules or ions.
1. Cyclic AMP (cAMP): Small molecule produced from ATP. Adenylyl cyclase converts ATP to cAMP in response to an extracellular signal. Phosphodiesterase turns it back to AMP.
- Calcium ions: Low calcium ions within cytosol. Protein pumps in the plasma membrane and ER membrane, driven by ATP, move calcium ions from the cytosol into the ECF and into the lumen of the ER.
The pathways leading to calcium release involve two other second messengers.
3. Inositol Triphosphate: IP_3. Comes from PIP_2, which is separated via phospholipase C. Is water soluble. Goes to a ligand ion gated channel on the ER for calcium ions.
- Diacylglycerol: DAG. Comes from PIP_2, which is separated via phospholipase C. Is not water soluble (a neutral lipid). Involved in other metabolic pathways.
Both produced by cleavage of a certain kind of phospholipid in the PM.
Cellular response to signals
- Gene regulation via activated transcription factor controlling
- Gene regulation via regulating activity of proteins
- Termination of the Signal
Nuclear responses to a signal
Protein receptor enters the nucleus, and can copy a section of DNA to make more proteins using transcription.
Cytoplasmic response to a signal
The stimulation of a glycogen breakdown by epinephrine (adrenaline) is an example of what can happen in the cytoplasm.
Apoptosis
A process of programmed cell death that occurs in multicellular organisms and some eukaryotic, single-celled microorganisms such as yeast.
Useful for developing digits and the such. Instead of webbed feet.
During apoptosis, a cell turns itself into membrane-bound cell fragments, known as
Lobes (blebs).
Signal Molecules
-Steroid molecule (hormones), cytosol/nucleus
-Proteins/glycoproteins, pm
-Dipeptides, pm
-Amino Acid, pm
-CO, NO, cytosol/nucleus
