Download Chapter 11. Review Notes [10-2

Just a Quick Mnemonic Overview
for Southern/Western Blots
SNoWDRoP
Southern: DNA
Northern: RNA
Western: Protein
Essential Amino Acids:
Any Help In Learning These Little Molecules Proves Truly Valuable
Arginine, Histidine, Isoleucine, Leucine, Threonine Lysine, Methionine, Phenylalanine,
Tryptophan, Valine
Chapter 11. Cell Signaling By Chemical Messengers

A quick note: Never focus on the wording of things as with Biochem its always A to D
(i.e. If A, then also B and C but most important the last effect D), not what does this what
does that. Most medical questions will be cause and effect, so knowing how things are
accomplished (the cell produces more IFN-B when exposed to dsRNA) is more important
than knowing details. Don’t get lost in them (Akt di-phorylates TNF-a which then…
there isn’t room in your brain to remember all this)
Three characteristics of Chemical Messengers:
1.
2.
3.
4.
5.
Secreted upon a specific stimulus
Diffuses or is transported through blood or extracellular fluid to target
Target cell has receptor specific for messenger
Binding of messenger elicits a specific response
Signal ceases and is terminated
Nicotinic Acetylcholine Receptor: (N-Ach-R
Ach is sequestered in vesicles near pre-synaptic membrane
5 subunits
1.
2.
3.
4.
Ach released by Ca++
Binds alpha unit of Ach-R
N+ In/K+ Out
Action terminated by ACE in post-synaptic mb.l
Endocrine: Extremities
Paracrine: Parallel Cell
Autocrine: Aint goin no where
TYPES OF CHEMICAL MESSENGERS
Nervous System (smallest, also most potent)
-
Small molecule NT (Ach)
Neuropeptides, 4-35 AA
Endocrine System (All have extremity targets)
-
Hormones
o Polypeptide (Insulin)
o Catecholamine (epinephrine)
o Steroids (from cholesterol)
o Thyroid (from Tyrosine)
Immune System (usually function to either increase cell metabolism or kill cells)
-
Cytokines (20kDa)
ILs, TNFs, IFN, CSFs
Eicosanoids: all derived from the precursor arachadonic acid
-
This is the only detail that is important to remember here
Prostaglandins, leukotriene’s
o Pain from gout is associated with production of a leukotriene due to
inflammation from the crystals
Growth Factors: Pretty Self Explanatory.. these influence cell metabolism.
-
Might be important to know that PDGF is a platelet factor required for plaque
formation, could be important for heart attack patients
Intracellular-R: Bind to lipophilic messengers (steroids etc)
Steroid/Thyroid Hormones:
-
Water insoluble, piggyback on Serum Albumin or Thyroid-binding globulin
Most receptors reside in the nucleus
o Glucocorticoid-R in cytoplasm connected to a HSP
o Cortisol binds Glco-R, exposes a Nuc. Localization Tag
o Glco-R dimerizes and goes to Nuc. And serves as a TF
Cortisol:
-
Synthesized and released from adrenal cortex
Production stimulated by ACTH
o This is synthd in the anterior pituitary gland
o In response to stress (pain, hypoglycemia, hemorrhage exercise)
 Hypothal to ant. Pit
 Basically ramps up the fight/flight response of cells
 Use of glucose etc
Plasma Mb Receptors: Respond to Lipophobic messengers, have extracellular binding and
intracellular activity domain
-
-
Contain an anchor that consists of an alpha-helix
o Can be rapid (ion channel etc)
o Can be slow (transcription factor cascade
 Sometimes they converge
3 types
o Ion Channel:
o Receptor-Kinases: intracellular domain binds kinase or product
o Heptahelical
 Transmb receptors with 7 “loops” tha weave in and out of mb.
 Usually work through cAMP and are G-Protein Coupled
1. Tyrosine-Kinase-R:
-
Ras and Map Kinase
1. Receptor binds GF and dimerizes
2. Receptor autophosphorylates itself
3. Binds GRB2/GEF
4. GEF is guanine exchange factor, binds Ras
5. GEF displaces GDP for GTP on Ras
6. Activated Ras-GTP binds RAF
7. MAP Kinase pathway activated
-
Phosphatidylinositol(PI) Phosphates
Tyrosine kinase or heptahelical receptors
1. PI4,5bisP (PI45) has 3 PO4 groups cleaves to:
DAG  PKC
IP3  - Sarcoplasmic and Endoplasmic Reticulum binding
site: Stimulates release of Ca2+
2. PI3,4,5trisP (PI345) can serves as a docking site for signal
transduction proteins
Activity:
1. PI is on inner mb, phosphorylated to PI45
a. Phosphorylation is on inositol ring @ 4/5C’
2. PI45 is cleaved by phospholipaseC (PLC)
a. Generates DAG and IP3
3. PI45 can be phospho’d by PI3Kinase (PI3K)
a. PI345
-
Insulin Receptor
o PROVIDES DIVERGENCE EXAMPLE
o Exists as a preformed dimer (1 α, 1 β in each subunit)
 Activity
1. Β units phosphorylate eachother 3X
2. Binds to IRS (Insulin Recep Substrate)
3. IRS is Phospho’d 3X, can bind proteins w/ SH2 domain
a. Binds to PLC
b. Binds to PI3K
c. Binds to GRB2 (Ras/Map)
4. PLC gives DAG and IP3
a. PI3K gives PI345
i. PI345 along with PDK1 activates Protein
Kinase B (Akt)
ii. PKB(Akt) gives you the glucose response
1. Phospho of proteins by Akt gives
promotion of cell survival
2. JAK-STAT-R:
Cell Mb, Receptor
No Kinetic Activity:
Activity Series is:
1.
2.
3.
4.
5.
6.
7.
R binds CYTOKINE  Dimerize
Each R binds 1 JAK
JAK P JAK’
JAK p R
R binds STAT
JAK p STAT
STAT dissociates and dimerizes, acts as a transcription factor to regulate gene
expression
3. Ser-Threonine –R:
Two receptor types, R-I and R-II
Type II binds TGF-B or Smad Family of CYTOKINES
Function as Hetero-dimers: Type-I and Type-II Receptors form a I-II dimer for activity
Activity:
1. Type I R binds TGF/I-R complex
2. II -R p I-R at a Serine
3.
4.
5.
6.
I-R recruits R-Smad (Receptor-Binding Smad (1)
I-R p R-Smad 2X
R-Smad-PP dissociates binds with Co-Smad (4) to form active transcription factor
Inhibits Transcription
HeptaHelical Receptors: 7 TMB domains of α-helices, specific extracellular domain
-
No natural kinetic activity, intiate signaling through G-proteins
G-proteins have 3 subunits, α β γ
-
Heterotrimeric G-Proteins
1. Until binding of hormone, all 3 subunits are bound, with α associated with
GDP
2. Upon activation α leaves β/γ by exchangings GDP for GTP
3. GTP- α binds target enzyme in Mb. (adenyl cyclase)
a. Over time Gα inactivates self by hydrolyzing GTP to GDP+Pi
b. Action is unrelated to # of cAMP formed
c. Reforms trimeric G-protein complex
d. This activity is why prolonged levels of hormone are necessary for
effect
e. Good area for loss of control (cancer)
4. G-protein complexes are extremely variable
Adenyl Cyclase and Phosphodiesterase
-
Form and cleave cAMP
Concentration of cAMP and other 2nd messengers is kept low
o Think of the 2nd messenger as the apex of the cascade triangle, 1
cAMP  2000 responses
cAMP is an allosteric activator of PKA
PKA
o rapid: response to glucagon and epinephrine
-
o slow: phosphorylate a TF for CREB
cAMP can also activate ligand gated channels directly
PI Signaling by Heptahelical Receptors
-
Certain HH-R bind the q isoform of Gα
o Activates PLC
o Gives DAG and IP3
Dynamic Response
-
Receptors can be downregulated
Can have internal phosphorylation sites to inhibit activity
Signal Termination:
CLINICAL COMMENTS:
Myasthenia Gravis:
B/T Cell Ab production against Ach-R
-
Causes bunching and lysosomal degradation of multi-mer complexes of AchR
No problem in levels of Acetylcholine production, just limited effect due to #
of R
Dx: history, physical, electromyogram (partial blockade of ion flux across muscular mb
Anorexia nervosa:
-
Compulsive exercise, distorted self image
-
While patietns may gain weight, they are low on stored fuel for extended
exercise
Prolonged starvation can cause release of cortisol and glucagon
o Decrease in insulin
 Cortisol activates gluconeogenesis
 Glucagon binds liver/adipose HH-R, works with PKA and
cAMP to use fast metabolism fuel
 Insulin promotes fuel storage
Cholera Toxin
-
Absorbed in intestine
Complexed with Arf (helps with vesicular transport)
Cleaves NAD and transfers ADP to other proteins
o ADP ribosylates the GDPs  always ON G-proteins
cAMP goes UP, channels for secretion of Cl- and Na+, results in
hyperosmotic lumeninflux of water to intestine  watery diarrhea
rehydration is most important, use glucose electrolytes to help with reuptake
of Na+