Chapter 11 Packet
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What is a signal transduction pathway?
a series of steps linking a mechanical or chemical stimulus to a specific cellular response
numerous cells can simultaneously receive and respond to the molecules of growth factors produced by a single cell in their vicinity
a secretory cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid
an electrical signal along a nerve cell triggers the secretion of a chemical signal carried by neurotransmitter molecules. These diffuse across the synapse (narrow space between the nerve cell and its target cell) (often another nerve cell). The neurotransmitter stimulates the target cell
a nerve cell releases neurotransmitter molecules into a synapse stimulating the target cell
How does a hormone qualify as a long-distance signaling example?
- -they use chemicals for long-distance signaling
- - specialized cells release hormone molecules, which travel via the circulatory system to target cells in other parts of the body
- - secrete hormones into body fluids and may virtually reach all body cells
the target's cell detection of a signal molecule coming from outside the cell
the conversion of the signal to a form that can bring about a specific cellular response
the specific cellular __ to the signal molecule after it goes through the signal transduction pathway
Explain the term ligand.
a molecule that binds specifically to another molecule, usually a larger one
What activates a G protein?
- receptor is activated and changes shape, causing it to bind a G protein
- -when it binds to the G protein- coupled receptor
- -this causes a GTP to displace the GDP
- This activates the G protein
A G-protein is also a GTPase enzyme. Why is this important?
Now inactive again, the G protein leaves the enzyme, which returns to its original state, allowing the G protein to be reused.
- It causes the change in the enzyme and G protein to be temporary. It then hydrolyzes its ound GTP to GDP.
- --> It allows the pathway to shut down rapidly when the signaling molecule is no longer present
- - activates ?
Explain the function of transcription factors in the cell.
They function in turning genes on and off, controling which genes are turned on- that is, which genes are transcribed into mRNA
What is the difference between a first messenger and a second messenger?
- First messenger--> extracellular signaling molecule that binds to the membrane receptor (receptor stage)
- Second messenger--> small, nonprotein water-soluble molecule or ion, such as a calcium ion or cyclic AMP that relays a signal to the cell's interior in response to a signaling molecule bound by a signal receptor protein
What specifically happens to a cell during the process of apoptosis?
Cellular agents chop up DNA and fragment the organelles and other cytoplasmic components. The cell shrinks and becomes lobed and the cell's parts are packaged up in vesicles that are engulfed and digested by specialized scavenger cells, leaving no trace
Give one example when the signal comes from outside the cell and two examples of cellular occurrences that would prompt an apoptosis signal from inside the cell.
- 1) death-signaling ligand occupies a cell-surface receptor, leading to activation of caspases and otehr enzymes that carry out apoptosis
- 2) Nucleus when DNA has suffered irreparable damage
- 3) ER when excessive protein misfolding occurs
What is the first step in the G protein-coupled receptors?
1) Loosely attached to the cytoplasmic side of the memrane, the G protein functions as a molecular switch that is either on or off, depending on which of two Guanine nucleotides is attached, GDP or GTP. When GDP is bound to the G protein, as shown abouve, the G protein is inactive. The receptor and G protein work together with another protein, usually an enzyme.
What is the second step in G protein-coupled receptors?
2) When the appropriate signal molecule binds to the extracellular side of the receptor, the receptor is activated and changes shape. Its cytoplasmic side then binds an inactive G protein, causing a GTP to displace the GDP. This activates the G protein.
Explain the third step of the G protein-coupled receptors.
3)The activated G protein dissociates from the receptor, diffuses along the membrane, and then binds to an enzyme , altering the enzymes shape and activity. When the enzyme is activated, it can trigger the next step in a pathwa leading to a cell response
What is the fourth step in the G protein-coupled receptors?
- The GTPase function of the G protein allows the pathway to shut down rapidly when the signaling molecule is no longer present.
4) The changes in the enzyme and G protein are only temp. because the G protein also functions as a GTPase enzyme. Now inactive again, the G protein leaves the enzyme, which returns to its original state. The G proteine is now available for reuse.
Explain the first step of the ion-gated channel.
The gate remains cloesd until a ligand binds to the receptor
What is the second step in the ion gated channel?
2) When the ligand binds to the recepotr and the gate opens, specific ions can flow through the channel and rapidly change the concentration of ions inside the cell. THis change may directly affect the activity of the cell in some way.
What is the last step of the ion channel?
3) When the ligand dissociates from this receptor, the gate closes and ions no longer enter the cell
Explain Sutherland's experiment.
What is the benefit of a second messenger?
- 1. amplify the signal
- 2. contribute to specificity of the response
- --> makes response even more specific
- --> can activate another pathway that may inhibit a response
Explain Sutherland's experiment.
Sutherland was investigating how epinephrine stimulates glycogen breakdown within liver cells and skeletal muscle cells. Glcogen breakdown releases glucose-1-phosphate, which the cell converts to glucose-6-phosphate. The cell then uses this for energy prodcution. They also discovered that removing a phosphate group from this compound can cause it to be released from the liver cell into the blood as glucose. Epinephrine is the mobilization of fuel reserves.
What did Sutherland discover in his experiment?
- Epinephrine stimulates glycogen breakdown by somehow activating a cytosolic enzyme, glycogen phosphorylase. However, gylcogen can not be broken down in a test tube. It must be broken down in an intact cell. This told Sutherland that
- 1- epinephrine does not interact directly with the enzyme responsible for glycogen breakdown; an intermediate step and group of steps must be occurring inside the cell
- 2- the plasma membrane is somehow involved in transmitting the epinephrine signal
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