Unit 3 Flashcards
What are the two types of signaling molecules?
hydrophobic / hydrophilic
What are the two general classes of receptors
cell surface and intracellular
What is a gap junction and what type of signaling molecules can pass through it
small pore between cells, small signaling molecules only
What is required for a cell to respond to a signal
correct receptor and “signaling machinery” inside the cell
Acetylcholine
contraction in skeletal muscle cells
relaxation in heart muscle cells
signaling in secretory cells
3 responses from the same signal
Paracrine signaling
local signal
Synaptic signaling
long range - neurotransmitter signal from axons
Endocrine signaling
long range - hormones / blood stream
Autocrine signaling
short lived / self signaling
What are the classes of hydrophobic signaling molecules
steroids hormones
thyroid hormones
retinoids
Steroids
planar structure made from cholesterol
Examples of steroid hormones
cortisol (made by adrenal gland on top of kidney)
estradiol (ovary)
testosterone (testis)
vitamin D (made in skin)
Thyroids hormones
made from tyrosine
Hsp
heat shock protein
What are the domains of intracellular receptors
activation domain
ligand binding domain
DNA binding domain
When intracellular receptors are in the cytosol
They are bound to an inhibitory complex (chaperone)
What happens when a signaling molecule binds an intracellular receptor
molecule binds and displaces HSP
causes a conformational change and exposes DNA binding domain
Goes to nucleus and acts as a transcription factor
What is the first response of intracellular receptors
Early Primary Response
What happens in the early primary response?
signal binds to receptor
receptor goes to nucleus and acts as transcription factor
Increases transcription / translation of proteins in ~30 minutes
**Makes early response proteins
What is the second response of intracellular receptors
Secondary Response
What happens in the secondary response of intracellular receptors?
Early response proteins act in a neg. feedback loop turn off transcription of primary response genes.
Early response proteins increase transcription/translation of secondary response proteins.
**Cells can change behaviors
Hydrophilic signaling molecules aka
soluble signaling molecules
What are the two types of proteins in relay systems within cells
proteins that become phosphorylated
proteins that bind GTP (called G proteins)
Both phosphorylation / dephos and GTP - GDP act to
turn signal molecules on and off
Phos = on GTP = on
G Protein receptors can
activate adenyly cyclase
inhibit adenyly cyclase
activate phospholipase C (PLC)
Steps in G protein signaling
Receptor becomes activated when it binds the ligand
This receptor then interacts with the G protein
Binding activates the G protein
G protein then activates the next protein
G protein linked cell surface receptor structure
7 pass proteins N terminus binds ligand C3 look (3rd cytoplasmic) specifies which G protein interacts
What do GAPs and RGSs do to G proteins?
increase rate of GTP hydrolysis and turn G proteins off
Many G proteins regulate ________levels
cAMP
cAMP is a
secondary messengers
what are the 2 types of heterodimeric G proteins
stimulatory G proteins (Gs)
Inhibitory G proteins (Gi)
Which enzyme controls cAMP levels
adenylyl cyclase
cAMP cycles to what that is NOT a signaling molecule
5’AMP
What is contained on the alpha subunit of a Gs protein
nucleotide binding domain and GDP binding pocket
How does adenylyl cyclase make cAMP
from ATP
How do Gs proteins work
ligand binds and causes conformational change
G protein binds receptor and alpha subunit binds GTP
alpha subunit diffuses away from beta and gamma subunits.
alpha subunit moves through membrane and interacts with second enzyme
ATP becomes cAMP
alpha subunit hydrolyzes GTP back to GDP and associates with beta and gamma subunits
cycle will repeat
How does cholera work like a Gs protein
modifies subunit so that it can’t hydrolyze GTP
How does pertussis work like a Gi protein
locks the alpha subunit in the GDP phase
True or False: Many different G coupled protein receptors are able to turn on Gs proteins
True….means many different ligands can turn on the same receptors.
How do Gi proteins work
ligand binds receptor
receptor interacts with Gi protein
alpha subunit will interact with adenylyl cyclase but will inhibit it
How do they know it is the C3 loop of the G protein coupled receptor that makes it specific
Use recombinant DNA tech to swap out this sequence and you get a different receptor.
GPCR
G protein coupled receptor
What rises in the intracellular space when Gs activates adenylyl cyclase?
levels of cAMP
Kinases
phosphorylate proteins
PKA
protein kinase A
When is PKA inactive
When all 4 subunits are bound together
How is PKA activated
cAMP binds regulatory subunit and causes conformational change
This releases the catalytic domain
PKA then phosphorylates other proteins
What are some examples of cellular changes caused by PKA
glycogen breakdown
alterations in transcription
release of fluid across epithelial cells (membranes)
How are receptors involved in signal amplification
Each receptor can stimulate many different G proteins
How does cAMP activation cause glycogen breakdown in muscle cells?
Ligand binds receptor which activates cAMP.
cAMP turns on PKA
PKA phosphorylates phosphorylase kinase (activates it)
This enzyme activates glycogen phosphorylase
This enzyme turns glycogen to glucose 1 phosphate that feeds into respiration cycles.
WHY is cAMP generated in times of stress?
What signaling molecule is the ligand?
cAMP causes glycogen to break into glucose which then becomes ATP
Adrenaline is the ligand
How does PKA (due to cAMP) change gene expression
PKA enters nucleus and phosphorylates CREB
CREB (activated) binds P300/CBP to create transcription factors (loosens DNA around histones)
What does CREB stand for
cAMP response element binding protein
How does PKA (due to cAMP) release fluid in epi cells
after increase in cAMP and then in PKA…
This signaling creates a gradient that will draw water by osmosis
Movement of water across epithelial cells relies on what protein
CFTR = cystic fibrosis transmembrane conductance regulator
CFTR = membrane of ABC superfamily of proteins
Uses ATP but NOT a pump because moves things down the concentration gradient
What are the main domains of the CFTR protein
MSD = membrane spanning domain NBD = nucleotide binding domain R = regulatory domain *turns CFTR on / off
How is CFTR activated by cell signaling
PKA turns CFTR on (activates it)
CFTR normally
Moves Cl- ions from cells into mucus causing water to follow and thin mucus
How do mutations stop CFTR from working
Most common will delete Phe at 508
Causes misfolded protein
Induces unfolded protein response so receptor is degraded in cytosol
Most of the people with the mutation are missing the receptor all together.
If you are heterozygous for a mutation in the CFTR gene it gives you an advantage to survive
Cholera. Cholera locks the CFTR in the on position. Lower levels of CFTR means less water loss
How does cholera affect CFTR
Cholera turns off CFTR because it locks the Gs into the “on” position. So, constantly moving ions and you lose large amounts of water into intestines
How does pertussis affect CFTR
locks Gi in off position. So, CFTR continues to move ions and therefore water out of cells. Lungs fill with fluid.
PLC
Phospholipase C
IP3 and Ca +2 ions
cAMP
are secondary messengers
What is the basic pathway of signal transduction through membrane receptors
Ligand binds receptor (in membrane)
Receptor interacts with G protein
G protein activates and enzyme
The enzyme activates secondary messengers
Secondary messengers act on target molecules
PIP2 is cleaved to create
DAG and IP3 secondary messengers
What are some ways that Ca+2 levels are kept very low in cells
Ca-ATPase
Ca binding proteins
Pumps
Na+/Ca+2 antiporter
Why is Ca+2 concentration kept low in cells
It is a very powerful signaling molecule
Gq linked receptors generate
IP3
How does the Gq protein work
*like Gs
Activated alpha subunit interacts with PLC and activates it
Activated PLC cleaves into DAG and IP3
IP3 goes to the ER and releases Ca+2 ions into cytosol
PKC uses the Ca+2 ions and then goes on to change gene expression (usually)
Orail
plasma membrane associated Ca+2 channel
Stim =
stromal interaction molecule
An ER membrane protein that binds Ca+2 ions
What happens in ER after IP3 signal
ER moves Ca ions to cytosol
Decrease in Ca in ER triggers STIM dimers and conformational change
The STIM dimers interact with Orail
What is the G Protein-Ca/IP3 pathway that leads to activation of transcription factors and modulation of gene expression
DAG binds to PKC and activates it
PKC phosphorylates MAP kinase and activates it
MAP kinase moves to nucleus and phosphorylates transcription factors
PKC also phosphorylates IK-B and it releases NF-KB
NF-KB moves to nucleus and works as transcription factors
Enzyme linked receptors
Have catalytic activity and are active when bound to a ligand
Receptor tyrosine kinases are
an example of enzyme linked receptors
What are some examples of receptor tyrosine kinases receptors
NGF (nerve growth factor) PDGF (platelet derived growth factor) FGF (fibroblast derived growth factor) EGF (epidermal derived growth factor) VEGF (vascular endothelial growth factor)
What do receptor tyrosine kinases do
phosphorylate tyrosines
How are receptor tyrosine kinases activated
When no ligand bound they are monomers and when a ligand binds they dimerize. This dimerization will activate them.
What are the three domains of a RTK
extracellular ligand binding domain
transmembrane alpha helix
cytosolic domain with the tyrosine kinase activity
After RTKs are dimerized what is the first step
Autophosphorylation of multiple tyrosines on the receptor itself.
Ras is active / inactive when
active = bound to GTP inactive = bound to GDP
Ras is a monomeric G protein
GAP =
GTPase activating protein
Why does RAS need GAP to work
its own GTPase activity is very low.
The cell cycle is regulated by proteins within the cell at what points
in G1 just before S
in G2 just before M
in M just before metaphase
heterokaryon
has double the amount of DNA
MPF
mitosis promoting factor (a dimer)
CDK
cyclin dependent kinase
phosphorylates other proteins
WHat causes CDK to become active
binding to specific cyclins
different cyclins are made / degraded with every phase of every cell cycle
What are the main classes of cell cycle control system
G1-S phase CDKs
S phase CDKs
Mitotic CDKs
APC/C activity
Proteosomes
large protein complexes that degrade proteins that have been ubiquinated
Rb
retinoblastoma
an inhibitor of E2F transcription factor
Turned off by phosphorylation and releases E2F. This causes transcription of G1 cyclins
What can cause retinoblastoma tumors in the eye
No function of Rb so E2F is always active and G1 always moves into S because it induces S phase cyclins.
Role of Sic 1
keeps S phase cyclin-cdk “off” in G1
When sic 1 is phosphorylated and tagged for degradation then DNA replication is initiated by S phase Cyclin-CDK
Role of active S phase cyclins
phosphorylate proteins in ori rep. complex and cause conformational change.
Proteins fall off and ori remains active
What is the role of Mad2 in the spindle assembly checkpoint
Mad2 inhibits proteosome that degrades securin if the spindle is not properly formed
Chromosome segregation checkpoint
If chrs. not at poles, then inhibit cdc14
Cdc14 promotes degradation of mitotic cdks
ALL DNA damage checkpoints:
in G1, before S phase entry, During S phase, in G2
Use p53
IF DNA has not replciated
ATM/R activates p53 which activates P2ICIP which inhibits cyclin/cdk dimers and pauses cell cycle
ATR activates CHK 1 which inhibits Cdc25C. (This is the protein that moves cell to M phase)
p53
is a transcription factor
unstable unless there is DNA damage
Unipotent
can only form one differentiated cell type
Multipotent
can form multiple types of differentiated cells
Pluripotent
can form all of the different cell types
Totipotent
can form all of the differentiated cell types + specialized tissues
