Biosignaling Exercise Key |
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1.
Table 1: Protein Binding |
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type of protein |
enzyme |
transport protein |
receptor |
What type of molecule does it bind? |
substrate |
solute |
ligand/hormone |
Name the part of the protein that binds the molecule. |
active site |
binding site |
binding site |
What happens to the molecule it binds? |
converted to product |
moved across the membrane |
nothing; eventually released |
How does the protein change, if at all? |
no change |
conformation changes during transport |
conformation changes → change in the cell |
2.
a. ACh binds the receptor → ion channel opens → Na+ and Ca2+ enter the cell.
b. ACh dissociates from the receptor and is hydrolyzed by acetylcholinesterase;
the ion channel closes; Na+ is removed from the cell by the Na+-K+ ATPase, and
Ca2+ is removed from the cell by the Ca2+ ATPase.
3.
Table 2: G-protein Pathway |
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protein |
activated by |
inactivated by |
(a) β-adrenergic receptor |
epinephrine binding |
epinephrine dissociation |
Gsα protein |
activated receptor, causing release of GDP and Gβγ | converting GTP → GDP |
AC (adenylyl cyclase) |
associated with activated Gsα | no association with a G protein |
PKA (protein kinase A) |
cAMP binding to the R subunits | removal of cAMP; R subunits bind C subunits |
phosphorylase kinase, an enzyme activated by PKA |
phosphorylation by PKA | removal of phosphoryl group by phosphatase |
4. Classify each molecule in the sequence below by indicating whether it is an enzyme (E), a non-enzyme protein (P), or a non-protein molecule (M).
Table 3: G-Protein Pathway Molecules |
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molecule |
β-adrenergic receptor |
Gs protein |
AC (adenylyl cyclase) |
type of molecule |
P |
E |
E |
molecule |
cAMP |
PKA |
phosphorylase kinase |
type of molecule |
M |
E |
E |
5. a.
Gα : GTP + H2O → GDP + Pi ; AC: ATP → cAMP + PPi;
PKA: protein-OH + ATP → protein-phosphate + ADP
b. GDP inactivates Gα; cAMP activates PKA;
protein-phosphate has changed activity and causes a change in cell behavior.
6. a. hormone + receptor → activation of Gi → inhibition of AC
b. hormone + receptor → activation of Gq → activation of phospholipase C →
cleavage of phosphatidyl inositol into
a. PIP3 → increased [Ca2+] in the cytosol → Ca2+–CaM complex → protein activation
b. DAG → activation of PKC (assisted by Ca2+).
Another version is shown below.
a. Write a similar sequence for the Gi pathway.
b. Write a similar sequence for the Gq pathway. You will have a branch point for this pathway.
7.
a. Amplification occurs when the receptor activates Gsα, when AC makes c-AMP, and when PKA modifies enzymes.
b. Amplification occurs when the receptor activates Gqα, when phospholipase C converts phosphatidyl inositol into IP3 and DAG, when IP3 causes release of many Ca2+, when PKC modifies enzymes, and when the activated, modified proteins have effects on the cell.
8. a. PKA recognizes X-R-(R/K)-X-(S/T)-B-;
PKC recognizes -(R/K)-(R/K-X-(S/T)-B-(R/K)-(R/K)-.
b. Exterior (mostly charged or polar)
c. The activity is changed (increased for some enzymes, decreased for others).
d. A phosphatase hydrolyzes the phosphoryl-S/T bond, and phosphate is released.