Week 5 Study Problems Flashcards
- How can two different cell types exposed to the same signal respond differently?
-The two cell types can differ in either what intracellular signaling proteins the receptor binds to, or differ in what effector proteins are present to carry out the response.
Also, different genes may encode receptors that share the same binding selectivity (they bind the same signal), but differ in their cytosolic domain, or are even a different class of receptor.
What are four general functions of intracellular signaling pathways?
- Relay/transduce
- Amplify
- Integrate and distribute
Primary transduction is also a general function.
Primary transduction is the general function of the receptor.
For each way of sending a signal, state whether the signal acts locally or in a distant tissue.
-Paracrine
Paracrine
The signal acts locally. It is secreted by one cell and acts on other cells in the
same tissue or organ.
An examples of Paracrine?
Examples are growth factors such as epidermal growth factor, and signals, such as cytokines, that regulate inflammation at the site of an infection.
For each way of sending a signal, state whether the signal acts locally or in a distant tissue.
-Endocrine
Endocrine
The signal is secreted into the circulatory system and distributed through out the body so that it acts on cells in distant tissues and organs.
Examples of Endocrine.
Examples are insulin and glucagon, secreted from the pancreas into the blood stream.
For each way of sending a signal, state whether the signal acts locally or in a distant tissue.
-Neuronal
Neuronal
This type of signaling is specific to neurons. The signal acts very locally. The signal is a neurotransmitter and is released into a gap between the axon terminus and the target cell. The neurotransmitter signal, however, is the end result of another signal that was initiated far away (at the dendrites) that then traveled as an electrical impulse to the axon’s terminus.
Example of Neuronal
An example is a neuron regulating the contraction of a muscle fiber.
For each way of sending a signal, state whether the signal acts locally or in a distant tissue.
Contact-Dependent
Contact-Dependent This signal is very local as it involves a transmembrane protein, or other cell surface component, on one cell binding to a transmembrane protein on an adjacent cell. This signal is not secreted from a cell, but remains part of the cell’s surface.
Example of Contact-Dependent
An example is during development where adjacent cells use contact-dependent signaling to prevent each other from differentiating into the same cell type.
What is a molecular switch?
A molecular switch is a signaling protein that switches between an ‘on’ active conformation and an ‘off’ inactive conformation. An incoming signal turns the signaling protein ‘on’, in which state the signaling protein relays the signal, and does so until turned ‘off’.
Draw and label a molecular switch that involves a protein kinase and protein phosphatase.
See study guide
Draw and label a molecular switch that involves a G-protein.
See study guide
What are the three main classes of cell-surface receptors?
- Ligand-gated ion channels
- G-protein-coupled
- Receptors enzyme-coupled receptors (Receptor Tyrosine Kinases being the most common).
Describe how ligand binding to a G-protein-coupled receptor activates an intracellular signal.
Ligand binding to a G-protein-coupled receptor (GPCR) causes the receptor to change conformation.
GPCR’s have 7-transmembrane helices that can move relative to each other so can couple ligand binding to a change in the conformation of the GPCR’s cytosolic domain.
The cytosolic domain then has complementarity to the alpha-subunit of trimeric G-proteins.
Binding of the trimeric G-protein to the receptor causes the alpha- subunit to change conformation so that GDP is released and the alpha-subunit disassociates from the beta/gamma unit.
The alpha-subunit rapidly binds to GTP, which causes change in shape so that the alpha-subunit will then bind other proteins to relay/transduce the signal.
What are three small, second messengers?
Three common second messengers are Ca2+, inositol trisphosphate (IP3) and cAMP.
Describe how the Ca2+ second messenger is generated?
Ca2+ is in low amounts in the cytosol, but higher amounts outside the cell or in the endoplasmic reticulum (ER). The electrochemical gradient of Ca2+ favors flow into the cytosol. There are IP3-ligand-gated Ca2+ channels in the ER’s membrane. When IP3 binds to the channel, the channel opens and lots of Ca2+ flows into the cytosol.
Describe how the IP3 second messenger is generated?
IP3 is a head group of phospholipids in the cytosolic monolayer of the plasma membrane. The enzyme phospholipase C catalyzes breaking of the covalent bond between IP3 and the glycerol of the phospholipid. The result is free IP3, which diffuses through the cytosol, and diacylglycerol (glycerol plus the two fatty acid tails), which remains in the cytosolic monolayer of the plasma membrane.
Describe how the cAMP second messenger is generated?
cAMP is generated by the enzyme adenylyl cyclase, which binds ATP and catalyzes the chemical transformation of ATP into cAMP.
State how the second messenger inositol trisphosphate (IP3) can amplify a signal?
For each active phospholipase C enzymes, many IP3 molecules can be released into the cytosol.
State how the second messenger cAMP can amplify a signal?
For each active adenylyl cyclase enzymes, many cAMPs can be generated from ATPs.
State how the second messenger Ca2+ can amplify a signal?
For each Ca2+ channel that opens, thousands of Ca2+ ions flow into the cytosol.
Give an example of a signaling protein that is activated by the Ca2+ messenger.
There are numerous proteins that can bind Ca2+, change conformation and relay the signal. One example is the protein Calmodulin.
Give an example of a signaling protein that is activated by the IP3 messenger.
There are numerous proteins that can bind IP3, change conformation and relay the signal. One example is the Ca2+-channel.