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Chapter 11 - Cell Communication Study Guide
1.What is a signal transduction pathway? Give an example
A receptor protein receives a signal, changes shape and triggers a chain of molecular interactions that eventually lead to a cellular response.
Epinephrine is a signaling molecule that binds to a G protein-coupled receptor. The G-protein activates the enzyme adenylyl cyclase, which in turn catalyzes the reaction that turns ATP into cyclic AMP, a secondary messenger. Cyclic AMP goes on to activate protein kinase A, which activates other proteins/enzymes that break down glycogen into its monomer glucose. The glucose is now available for use in respiration in muscle and liver cells.
2. How does yeast mating serve as an example of a signal transduction pathway?
Yeast of two types a and α secrete signaling molecules called mating factors that bind to receptors on surface of the cells. Once the mating factor is received by the yeast cell it triggers a transduction pathway that causes changes in cytoskeletal filaments and cause the two types of yeast to grow toward eachother.
3. How do intercellular connections function in cell to cell communication?
Plasmodesmata in plant cells and gap junctions in animal cells allow cell signaling molecues to be travel directly between adjacent cells. Cell to cell recognition through receptor proteins and glycolipids/glycoproteins initiate cellular response through direct interaction.
4. Explain the difference between paracrine and synaptic signaling.
Synaptic signaling is similar to paracrine signaling but here is a special structure called the synapse between the cell originating and the cell receiving the signal. Synaptic signaling only occurs between cells with the synapse; for example between and neuron (nerve cell) and the muscle that is controlled by neural activity.
5. How are long distance signals sent? Give an example in the body
Long distance signaling molecules are usually secreted into the blood stream by originating cells. The pancreas secretes insulin which signals cells all over the body to take up glucose from the blood.
6. How do nerve cells provide example of both local and long distance signaling?
Between an individual neuron and another neuron or muscle cell the signaling is local because the signaling molecule (neurotransmitter) is traveling only a short distance across the synapse. However, as a nerve impulse is continually transmitted along a series of neurons the distance traveled could be far, like from the brain to your big toe.
7. A signal transduction pathway has three stages. Use Figure 11.6 to label the missing parts of
the preview figure below, and then explain each step.
Reception:The signal (ligand) is received usually by a receptor protein located on the membrane or in the cytoplasm.
Transduction: Once the signal is received a conformational (shape) change occurs in the receptor protein, the receptor then activates a relay molecule starts a signal transduction pathway like a phosphorylation cascade.
Response: Eventually a protein that acts as a transcription factor or enzyme is activated by the transduction pathway and the cellular response is elicited. Examples of response include protein/enzyme manufacture, cytoskeletal modifications, cell division, programmed cell death (apoptosis), etc.
8. Explain the term ligand. Give an example of how a ligand is used.
Ligand = a signaling molecule. Ligands bind to receptor molecules and elicit a cellular response. Epinephrine, acetylcholine, testosterone, estrogen, mating factors, growth hormone etc. are all ligands.
9. Fill-in the chart below regarding the 3 types of membrane receptors:
Receptor / How it functions as a receptor / ExampleG-Protein / Signal received on the cell membrane and activates a G-protein. This activated G-protein (with GTP) moves along the membrane and activates an enzyme. This enzyme produces relay molecules or secondary messengers that elicits a signal transduction pathway. / Yeast mating factors, epinephrine, hormones, neurotransmitters all use different G proteins
Tyrosine Kinase / Signal is received on the cell membrane and the protein changes shape. ATP’s phosphorylate tyrosine on the tyrosine kinas. Later the phosphates are used to phosphorylate relay proteins that initiate transduction pathways (many different pathways could be activated). / Primarily growth factors, cell division and cell survival, some are overexpressed in many breast cancers
Ion Channel / A ligand joins with the ion channel on the membrane and either opens or closes the gated ion channel. Ions rush in or rush out initiating a cellular response. / Neurotransmitters act as the ligand and these gated ion channels exist on the membrane of muscle cells. The change in ion concentration causes muscles to contract.
10. What does conformation mean?
The spatial arrangement of atoms in a molecule. Shape changes usually associated with ligand binding or phosphorylation with regard to our discussion of signal reception or transduction pathways.
11. In what body system are ligand-gated ion channels and voltage-gated ion channels of
particular importance?
The nervous system.
12. How are intracellular receptors unique? Give an example.
Instead of the signal being received on the membrane these receptors receive signals in the cytoplasm because the signaling molecule is non-polar/lipid soluble and meets with the receptor intracellularly. These receptor complexes then often directly participate in transcription as transcription factors.
13. Where would you expect most water soluble messengers to bind and why?
On the membrane because they cannot pass through the phospholipid bilayer given their polar, water soluble nature.
14. How are phosphorylation cascades similar to a row of dominoes falling down?
One activated molecule activates another, then the one just activated activates another and on and on until a cellular response is achieved.
15. Explain the role of these enzymes in transduction:
a.proteinkinase -transfers phosphate groups from ATP to other proteins (turns protein “on”).
b. protein phosphatases – removes phosphate from active proteins (essentially turning them “off”)
16. What is the difference between a first messenger and a second messenger?
The first messenger is the signaling molecule typically received on the membrane by the receptor protein. The secondary messenger is generated by an enzyme (in the case of cyclic AMP) after the signaling molecule had initially been received.
17. Explain the role of the second messenger cAMP.
cAMP amplifies a cellular response by activating many proteins (typically protein kinase A), which in turn amplifies the cellular response.
18. When cell signaling causes a response in the nucleus, what normally happens?
Proteins activated by the transduction pathway usually serves as transcription factors initiating production of mRNA and eventually protein in the cytoplasm.
19. When cell signaling causes a response in the cytoplasm, what normally happens?
The cell shape can be altered by protein building that affects the cytoskeleton, and signaling causes regulation of enzymes that affect many cell functions (division, programmed cell death, etc.)
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