Lecture 3: Signaling Flashcards
5 protein functions in cells
transport proteins structural proteins cell signaling proteins metabolic enzymes Genomic caretaker proteins
Metabolic enzymes
reaction catalysts control metabolic flux
transport proteins
have integral membrane proteins and soluble proteins
move ions and small molecs across HYDROPHOBIC membranes
signaling proteins
transmit extracellular and intracellular signals by functioning of molecular switches
genomic caretaker proteins
maintain integrity and accessibility of genomic info
structural proteins
maintain integrity of cell structures and promote changes in cell shape
passive transporter proteins
energetically INDEPENDENT
work in RESPONSE to chem gradients
active transporter proteins
require NRG from ATP hydrolysis to transport AGAINST chem gradient
structure of membrane lipid
polar head faces out of or into cell
hydrophobic fatty acid tails face eachother in center of membrane
tails form vanderwals interactions w/ each other
2 ways things can move across membrane (broad)
membrane diffusion
membrane transport proteins (polar molecs)
membrane diffusion
hydrophobic molecs diffuse across membrane
membrane transport proteins
passive transport
active transport
graphs:
diffusion and passive transport channels: rate of translocation incs with solute conc.
passive transport CARRIER and active transport CARRIER: inc then plateau
why do carrier transport rates plateau
b/c the carrier can only turn a molec over so fast. conf changes and carrying takes time. theres a point at which carriers are saturated.
Aquaporins
passive transporters
highly conserved
channles, water not bound to anything when going through
transport H2O across hydrophobic membranes
tatrameres (4 parts)
where are aquaporins abundant?
kidney, sweat gland, and RBC cells
active membrane transporter proteins ex
Ca2+-ATPase transporter protein
ATP hydrolysis used to pump Ca2+ ions across cell membrane AGAINS conc gradeint.
steps through lots of confs b/c of AtP binding and hydrolysis.
specific sequence of changes
for muscle contraction. big Ca conc on one side of cell
Prolosec
inhibs gastric H+/K+ ATPase protein
treats stomach ulcers
Zoloft
inhibits serotonin reuptake transporter protein
depression treatment
Cocaine
inhibits dopamine reuptake transporter protein
What is signal transduction?
sig. transduction transmits extracellular signals to intracellular places by ligand-activated receptor proteins
doesnt actually move molecs across cell membrane
G protein coupled receptors (GPCRs)
very abundant
controll sensory and hormone signaling in specialized cells
Glucagon
signals through membrane GPCR on liver cells
responds to low blood glucose levels. stims cyclic AMP prodiction to inc rate of glycogen degration and glucose export
signal transduction def
biochem mech. for “transmitting” signals from outside cells to inside
Signal transduction cascades/amplification
1 receptor on membrane response to 1st messenger leads to many targets proteins inside cell
amplification can happen wherever there is an enzyme
levels of signal transduction
1st messenger receptor protein on membrane upstream signalling proeins second messegners downstream signalling proteins target proteins
what is synonymous with first messenger
ligand
phosphorylation
addition of a phosphate group to a protein in order to turn an enzyme on or off
first messengersL
small diffusable biomolecs
hormones like insulin and glucagon
3 types of first messenger signalling
endocrine (far away)
autocrine (to same cell)
paracrine (to adjacent cells)
Insulin works by…
lowers blood sugar by stimulating glucose uptake
glucagon is opposite
Receptor proteins (cellular “gatekeepers”
G-protein-coupled receptors (membrane embedded)
Receptor tyrosine kinases (membrane embedded) (what insulin uses)
TNF receptor family (membrane embedded)
Nuclear receptors
Nuclear receptors
gene regulation
bind to hydrophobic compounds
often bind steroids, they can enter nucleus
steroids change conf of proteins to work on gene regulation
NOT found on membrane, found inside cells
How GPCRs work
1a. GPCR is ACTIVATED when 1st messanger/ligand binds to GPCR
Note: The part of GPCR that goes into cytoplasm associates with Heterotrimeric G protein
1b. Conf change at inside of cell due to ligand binding changes assocation with Heterotrimeric G protein
2a. GDP comes off of alpha subunit. GTP binds in its place
Note: When GDP is bound to subunit, the protein is INACTIVE
3. When GTP binds, subunits are dissociated and the protein is active
4. Downstream signalling signals another protein/enzyme
Note: GTP is basically a timing mechanism. For every G-alpha protein, theres a rate of GTP hydrolysis. When it hydrolyzes back to GDP, it goes back to being inactive
Heterotrimeric G-protein
has 3 subunits
alpha
beta gamma
Associate with either GDP or GTP
Downstream Signaling
Signal to some other enzyme
ex: adenelate cyclase.
enzyme that makes cylic AMP (second messanger)
cylic AMP signals another downstream target
How many transmembrane alpha helicies do GPCRs have?
SEVEN
where are GPCRs found?
embedded in the membrane
GPCR Protein Rhodopsin
light sesning
retinal molecule
retinal has conf change when light hits it
retinal burried within helicies of rhodopsin, so chaning its conf changes conf of helicies
Inactive sate of heterotrimeric G proteins
this is when it associates with the GPCR
G-alpha subunit has GDP bound to it
Active state of G proteins:
(after signal binds to GPCR)
GTP is bound to alpha helix of hetotrimeric G protein
GTP/GDP influence on proteins (adenylate cyclase ex):
ACTIVE state
G alpha-adenylate cyclase complex present
position of the switch helix of G alpha proteins changes when GTP is bound
G alpha protein is associated with enzyme adenylate cyclase through the switch helix of G alpha protein
adenylate cyclase produces second messenger
GTP/GDP influence on proteins (adenylatease cyclase ex):
INACTIVE state
the G alpha beta gamma complex is present
switch helix is associated with G beta and gamma proteins
After Ga protein activated…
interacts with adenylate cyclase
adenylate cyclase makes…
cyclic AMP
Cyclic AMP
activates protein kinase A (PKA)
phosporylates other molecs
when cAMP activated by adenlate cyclase
cAMP binds to regulatory subunit, making it fall off
then catalytic subunit is acvtive,
cAMP phosphylates molecs
cGMP
second messenger stimulated by G alpha stimulating enzyme PHOSPHODIESTERASE
light absorption into eye
some things G alpha proteins stimulates
cGMP
cAMP
IP3 and DAG
NOTE: there are different types of alpha subunits that do different things.
cAMP
second messenger stim by G alphas stimulating enzyme ADENYLATE CYCLASE in response to activation of OLFACTORY RECEPTORS
IP3 and DAG
second messenger stim by G alpha interacting with PHOSPHOLIPASE C in response to TASTER RECEPTOR activation on tounge
Glucagon signaling
binds to g-protein coupled receptor
stims signal transduction pathway: adenlate cyclate activated, cAMP produced, cAMP stims protein kinase A
protein kinase A has many targets in cell
Glucagon
“I’m Hungry” hormone
Protein Kinase A and glucagon signaling
target what it needs to as needed if glucagon signalling it: 1. turns off glycogen synthesis 2. turn ON glycogen degradation 3. turn ON glucose synthesis
glycogen
short term storage form of glucose
long term in fat
result of glucagon signaling
net glucose export so cell can have enough energy
insulin
tells cell to take in glucose to store as glycogen
