Cell Signaling. Exam 1 Flashcards
Ligand activated ion channels can be on the ______ or within an ________.
plasma membrane
organelle
How can drugs affect ligand activated ion channels?
by influencing synaptic transmission at different loci
Liberation of which ion will have a profound effect on cells?
Ca ++
What are four important mechanisms/receptors of cell signaling?
- Ligand activated ion channels
- G-protein coupled receptors
- Tyrosine-Kinase receptors
- Ligand Activated Nuclear/Transcription receptors
What are the two mechanisms of action for Ligand Activated Nuclear receptors?
Class One Nuclear Receptors
Class Two Nuclear Receptors
Earl Sutherland determined that hormonal activation of liver phosphorylase is mediated by ______ and he deemed this a __________.
cAMP
Second Messenger
What kind of enzymes were determined by Krebs and Fischer to be important in the phosphorylation cascade?
Kinase enzymes
What type of receptor is responsible for signalling in excitable cells and is commonly within the plasma membrane?
Ligand-Activated Ion Channels
Ligand-Activated Ion Channels are ______ proteins that produce _______ (with local effect).
multisubunit
graded potentials
Signaling in excitable cells is done via Ligand-Activated Ion Channels that either _____ or _____ the cell.
Depolarize
Hyperpolarize
Which ion is commonly associated with depolarization of the plasma membrane?
Sodium (Na+)
Which ion is commonly associated with hyperpolarization of the plasma membrane?
Chloride (Cl-)
Activating and inhibiting ____________ channels is the basis of synaptic transmission of nerve impulses (lots of drugs are targeted here).
Ligand Activated Plasma Membrane Ion
What are four ways in which drugs might affect Ligand Activated Ion channels at the plasma membrane?
Affect synaptic transmission: 1. Mimic or Block actions of neurotransmitters 2. Block the channel Affect at the synaptic cleft: 3. Influence transmitter reuptake 4. Transmitter metabolism
Which organelle is commonly associated with Ligand Activated Ion Channels?
Endoplasmic Reticulum (Calcium)
What second messenger is responsible for mediated calcium release from the internal stores of the ER?
IP3 (inositol triphosphate)
Which complex is associated with most of the cell signalling that involves calcium?
Calcium-Calmodulin
The increase in calcium in the cytoplasm, due to signaling by _____, will thus increase binding of calcium to _______.
IP3
calmodulin
What happens after cytoplasmic calcium increases and then binds with calmodulin?
The Ca++-Calmodulin Complex is able to interact and ACTIVATE numerous EFFECTOR PROTEINS
How many calcium must bind to calmodulin in order to form the complex?
4 calcium
What are two important examples of protein activation by Ca++-Calmodulin? (remember there are about 300 proteins that bind to this complex, this is just two discussed).
- Calcium-Calmodulin dependent protein kinase
2. Nitric Oxide Synthase
Nitric Oxide Synthase acts in endothelial and neuronal cells to activate ________ from Nitric Oxide precursors.
Guanylate Cyclase
G-protein coupled receptors consist of a single polypeptide and seven ________.
transmembrane alpha helices
Approximately how many drugs target G-Protein Coupled Receptors?
40%
How do agonists activate G-Protein Coupled Receptors?
They bind to the receptor and alter the protein’s conformation which leads to the activation of a trimeric G protein
What are the four steps in the G Protein Cycle?
- Ligand binds and stimulates GDP-GTP exchange
- G Protein complex breaks into two pieces: G-alpha and G-BetaG-gamma
- G-alpha is involved in GTP hydrolysis (beta-gamma has downstream effects)
- The complex reassembles
The GTPase activity is intrinsic to which part of the G-protein?
G-alpha
Hydrolyzation of GTP to GDP and Pi is accelerated by which proteins?
RGS proteins
Both pieces of the G-Protein complex will participate in ________ but the piece with the major activity is ____.
signalling events (activation of other proteins in the cell) G-alpha
How many classes of G-alpha proteins are there?
Five
How are the five classes of G-alpha proteins distinguished?
classes are based on what they activate
What is the major effector of G-alpha?
Adenylate Cyclase
How is ATP converted to cAMP?
Adenylate Cyclase
cAMP will activate _________ which will phosphorylate a large number of proteins and produce a large number of biological effects.
Protein Kinase A
An increase in G-alphas will stimulate _______ to break ______ into cAMP which activates _______ and leads to the phosphorylation of a large number of proteins.
Adenylate Cyclase
ATP
PKA
What important enzyme does cAMP activate?
Protein Kinase A
What does PKA do?
alters the activity of many target proteins via phosphorylation
How can PKA and other protein kinases lead to changes in gene expression in cells?
by phosphorylating transcription factors (causing dimerization)
How can PKA affect glucose in the liver?
PKA mobilizes glucose in the liver by starting a phosphorylation cascade that activates glycogenolysis
How do G-Protein coupled receptors influence signaling molecules in the plasma membrane?
Signaling molecules are embedded within phospholipids in the membrane, the GPCRs activate PHOSPHLIPASEs and liberate the molecules
G-alpha will activate phosphlipases in the membrane wihich will then liberate signaling molecules. What is the importance in activating Phospholipase A2?
PLA2 will activate arachidonic acid… which is the source of eicosinoid signaling molecules
What are eicosinoid signaling molecules? Where do they come from?
Molecules involved in inflammation and immunity: Prostaglandins, leukotrienes, thromboxanes
They come from arachidonic acid
What two important signaling molecules are derived from PLC-beta mediated hydrolysis?
DAG
IP3
What is PIP2?
a minor phospholipid component of cell membranes that is a substrate for important signaling molecules.
PIP functions as an intermediate in the IP3/DAG pathway
PIP2 is the phospholipid that serves as the substrate for ______.
Phospholipase C
Cleavage of PIP2 by PLC yields ______ and _____ via hydrolysis.
DAG
IP3
What is a main difference between DAG and IP3?
DAG binds and remains on the cell membrane to activate PKC.
IP3 enters into the cytoplasm and activates receptors on the ER which mobilizes calcium.
True or False: DAG mobilizes calcium from the smooth ER.
False. Those are actions of IP3
DAG activates ________.
Protein Kinase C
The PKC gene family is _______ dependent.
calcium
How does DAG regulate PKC binding of calcium?
DAG allows the PKC to bind calcium more tightly which allows the enzyme to function at lower calcium concentrations.
Which part of the G-protein complex plays a critical role in turning off the GPCRs?
G-betaG-gamma
G-betaG-gamma helps to ________ the trimeric G protein to the membrane.
localize
True or False: The trimeric G protein gets turned on, but it turns itself off.
True. signalling molecules turn the G protein on, GbetaGgamma turns it off.
Because the G protein turns itself off, the agonist is free to activate other G proteins. However, the signal does not last forever. Why?
The receptor eventually gets turned off by a process known as desensitization.
Describe the steps in G-Protein receptor desensitization.
- Phosphorylation by a GRK prepares a receptor for arrestin binding
- Binding by a beta-arrestin stops further signaling
- Formation of a clathrin-coated pit
- Endocytosis
What is arrestin?
a family of proteins important for regulating cell signaling: binding blocks further G protein-mediated signaling, targets receptors for internalization, and redirects signaling to alternate pathways
After endocytosis, what are the possible fates of the GPCR?
- Recycling
2. Degradation
The G Protein receptor is desensitized within an ______ by dephosphorylation.
endosome
If the receptor is sent for recylcing, it is ______ within the endosome.
resensitized
If the receptor is sent for degradation, it is does this within a ______.
lysozome
What is the importance of receptor desensitization?
Sometimes drugs are administered chronically which can lead to loss of responsiveness to the drug
Cell signaling that involves receptor tyrosine kinases (RYKs) will either contain a ______ or ______ tyrosine kinase enzyme.
Intrinsic
Extrinsic
What occurs to RYKs after a ligand binds?
ligand binding leads to dimerization of the receptor
Name three examples of possible ligands that would bind to RYK.
Growth Factors
Differentiation Factors
Cytokines
Receptor dimerization of RYKs will be of what forms?
Homodimers
Heterodimers
a combination of both
Dimerization (whether homo or hetero) will lead to ________ of the receptors.
transphosphorylation
What will occur after phosphorylation of tyrosine receptors?
signaling molecules will dock on the outer side of the membrane and will pass that signal to a protein on the inside of the membrane
After a signaling molecule binds to the RYK in the membrane, how are different signaling cascades initiated?
The position of proteins near the inside of the membrane will determine which cascade is begun
______-domains on proteins will bind to receptors and allow activation of many signaling pathways
SH2
True or False: The MapKinase pathway begins with binding to Grb2 through the FH1-demain
False: Grb2 is activated through the SH2 domain (a common activator of many signaling proteins)
In the Map Kinase Pathway, signaling molecules bind and activate the membrane receptor which will bind to Grb2. Grb2 will then bind with _______ in order to activate _____.
SOS
Ras
After Ras is activated by Grb2-SOS, the protein kinase activity of _____ will be turned on and it will phosphorylate ______ to start the cascade.
Raf
MEK
What is the end result of the Map Kinase Pathway?
Transcriptional regulation through the phosphorylated transcription factors
In the MapK Pathway: Raf, Mek1/2, and ERK1/2 are all _____.
Protein kinases
Phosphorylation of transcription factors by PKA and other protein kinases can lead to ________ in cells.
changes in gene expression
Which protein in the Map Kinase pathway is commonly associated with mutations and cancer?
Ras
because it requires other protein modifications to work
The Akt signaling cascade is a ______ mediated pathway that pushes the cell toward ______.
YKR (tyrosine kinase receptor)
growth and proliferation
The JAK-STAT pathway uses which type of receptor?
Tyrosine Kinase (YKR)
Which signaling pathway is commonly used by cytokines?
JAK-STAT
Binding of cytokine will initiate phosphorylation of the YKR by ______ kinase which will lead to binding of ______ protein.
JAK
STAT
JAK Kinase binding to STAT protein will enable phosphorylation and ________ of the STAT protein.
dimerization
After STAT has dimerized, it is translocated to the nucleus where it activates _______.
transcriptional panels of genes
STAT monomers contain both a _______ and a _______ that can be phosphorylated.
SH2-domain
Tyrosine
True or False: STAT is slow.
False. it is fast.
How does an inactive STAT differ from an active STAT?
Inactive: monomers of SH2 and tyrosine
Active: dimers, SH2-Y-Phosphate
(“Y” = tyrosine)
STAT proteins mediate the profound biological responses to _______.
Cytokines
Looking at one signaling pathway may not be a good predictor of what is actually happening in the cell because there is _______ among pathways that creates complex signaling.
Cross-Talk
________ are receptors for steroid hormones.
Nuclear Hormone Receptors
Nuclear hormone receptors are receptors for _______ such as________.
Steroid hormones:
glucocorticoids, mineralocorticoids, testosterone, estrogen, progesterone (also T3/T4, Vit.D, and retinoic acid)
Nuclear receptors are characterized as either _____ or _____.
Class I
Class II
Class I Nuclear receptors exist as a _______ with ______ in the absence of ligand.
complex
heat shock proteins
Class II Nuclear receptors _______ at a specific response element and binds __________ in the absence of ligand.
bind to target DNA
corepressors
(they are not in a huge complex like Class I)
Once ligand binds to Class I receptors, what will happen?
The complex falls apart, a homodimer forms and then it binds to a specific DNA response element. Binding to DNA stimulates transcription through coactivators.
True or False: Class I Nuclear Receptors bind to DNA and utilize corepressors to stimulate transcription.
False: COACTIVATORS
True or False: Class II Nuclear Receptors utilize coactivators and corepressors, whereas Class I only utilize coactivators.
True. Class I are inactive because they are complexed. Class II stay inactive with corepression
Glucocorticoids and androgens utilize ______ Nuclear Receptors.
Class I
Throid hormones, Vitamin D, and retinoic acid utilize _______ Nuclear Receptors.
Class II
Steriod hormones bind to receptors and then the ligand–receptor complex binds to ________ to increase its expression.
specific DNA sequences on target genes
What are the fourth methods of cell signaling?
- Ligand activated ion channels
- G protein coupled receptors
- Tyrosine Kinase Receptors
- Ligand activated Nuclear Receptors
