Exam 2 Flashcards
What does the plasma membrane do?
defines the cell and separates the inside from the outside
In eukaryotes, what else does the plasma membrane do?
defines intracellular organelles
What does the plasma membrane consist of?
a lipid bilayer that is semipermeable
What does the plasma membrane regulate?
the transport of materials into and out of the cell
What are the functions of the plasma membrane?
-hold structure
-protection
-transport
-communication through cell-cell signaling
-energy transportation
What is the basic structural unit of biological membranes?
phospholipid bilayer
What prevents water-soluble substances from crossing the membrane?
its hydrophobic core
What does the fluid mosaic model do?
keeps organelle shape and enables membrane budding and fusion/fission
What things give mosaic structure and fluid character?
phospholipids
cholesterol
proteins
carbohydrates
What are the principal building blocks of membranes?
phospholipids
What is the most common phospholipid in membranes?
phosphoglycerides
What does amphipathic mean?
molecules consists of 2 different properties
What makes phospholipids amphipathic?
hydrophobic tail made of fatty acids
hydrophilic head
What are the 3 amphipathic lipids in membranes?
phospholipids, glycolipids, cholesterol
What determines the structure of membranes?
the interactions between phospholipids with each other and water
How do phospholipids form bilayers?
hydrophobic tails align tightly together in the center, forming a hydrophobic core
hydrophilic heads face the outside
What stabilizes the close packing of non polar phospholipid tails?
van der Waals interactions
What stabilizes the interactions of the polar phospholipid head groups with water and each other?
ionic and hydrogen bonds
Exoplasmic face of bilayer
faces the outside
Cytosolic face of bilayer
faces the inside (cytosol)
What organelles are surrounded by two membranes (2 lipid bilayers)?
nucleus, chloroplast, mitochondria
Structure of phosphoglycerides
hydrophobic tail with 2 fatty acyl chains
polar head group attached to phosphate
What are plasmalogens?
a group of phosphoglycerides that contain one chain attached to C2 of glycerol by ester linkage and the other chain attached to C1 of glycerol by ether linkage
Where are plasmalogens abundant?
brain and heart tissue
What are the 3 principal classes of lipids present in biomembranes?
phosphoglycerides, sphingolipids, sterols
What are sphingolipids?
compounds derived from sphingosine that have a long chain fatty acid attached by amide linkage
What is the most abundant sterol in membranes of mammalian cells?
cholesterol
What do sterols provide?
structural support, prevent close packing of phospholipids, maintain membrane fluidity, give rigidity
How are sterols incorporated into the membrane?
intercalating between phospholipids
Transmembrane proteins
provide gateways to permit transport of specific substances
What do transporters do?
carry molecule from one side to the other
What do receptors do?
bind extracellular molecules
What do enzymes do?
transform molecule into another form
What do anchor proteins do?
physically link intracellular structures with extracellular structures
What phase transition in the membrane does lowering the temp cause?
from fluid state to gel state
What phase transition in the membrane does increasing the temp cause?
from gel state to fluid state
What does phase transition affect?
diffusion rates
3 factors that influence cell membrane fluidity?
temp, cholesterol, saturation vs unsaturation of fatty acids
What does composition of plasma membrane affect?
membrane fluidity, thickness, curvature
What causes curvature in the bilayer?
lipid asymmetry and cholesterol symmetry cause charge differences
Where are phophoglycerides synthesized?
cytosolic face of the ER membrane
Where is sphingomyelin synthesized?
ectoplasmic face of the Golgi
What does the cytosolic face of the ER become?
cytosolic face of the plasma membrane
What does the ectoplasmic face of the Golgi become?
exoplasmic face of the plasma membrane
What causes activation of the cytosolic enzyme?
stimulation of cell surface receptors by their ligands
What are lipid droplets?
vesicular structures composed of triglycerides and cholesterol esters
Where do lipid droplets originate from?
the ER
What do lipid droplets do?
store proteins for degradation
What are the 3 categories that membrane proteins can be classified into?
integral (transmembrane) proteins
lipid-anchored membrane proteins
peripheral membrane proteins
What are the 3 domains of transmembrane proteins?
cytosolic and ectoplasmic domains (have hydrophilic amino acids)
membrane spanning domain (have hydrophobic amino acids, one or more alpha helices/beta strands)
Transmembrane proteins span…
the entire bilayer
Lipid-anchored membrane proteins…
are bound covalently to one or more lipids with only the hydrophobic tail embedded into one leaflet of the membrane to anchor the protein
Peripheral membrane proteins do not…
span the whole membrane or have direct contact to the hydrophobic core
How are peripheral membrane proteins bound to the membrane?
by interactions with integral/ lipid anchored membrane proteins or by direct interactions with lipid head groups
What do peripheral membrane proteins do?
provide an interface between the cell and its environment, determine cells shape mechanical properties, and play a role in communication between cell interior and exterior
Examples of transmembrane proteins
aquaporins, T cell receptor for antigen, GPCR, glycophorin A
Which transmembrane protein contains only 1 membrane spanning alpha helix, forms dimers, and is the major protein for erythrocyte plasma membrane?
glycophorin A
Which transmembrane protein has 7 membrane spanning alpha helices and has pumps activated by light that results in the pumping of protons from the cytosol into the extracellular space?
GPCR
Which transmembrane protein has 4 subunits with 6 alpha helices in each, are water/glycerol channels, and are homo-tetramers?
aquaporins
Which transmembrane protein is composed of 4 separate dimers with interactions driven by charge-charge interactions between alpha helices?
T-cell receptor for antigen
Porins are found in the outer membranes of what?
gram-neg. bacteria
microchondria
chloroplasts
What is the shape of each subunit in porins?
barrel shaped
How are porins formed?
16 beta strands within a subunit form a sheet that twists into a barrel shape with a pore in the center
How do covalently attached lipids anchor some proteins to membranes?
acylation (cytosolic surface)
prenylation (cytosolic surface)
GPI anchor (exterior surface)
Transmembrane protein orientation and topology
cytosolic segments always face the cytosol, ectoplasmic segments always face the opposite
What is something that many transmembrane proteins contain?
carbohydrate chains covalently linked to serine, threonine, or asparagine that face the ectoplasmic domain
attached to the glycerol or sphingosine backbone of glycolipids in the ectoplasmic leaflet
Antibodies for A blood
anti-B
Antibodies for B blood
anti-A
Antibodies for AB blood
none
Antibodies for O blood
anti-A and anti-B
What blood types can type A receive?
A and O
What blood types can type B receive?
B and O
What blood types can type AB receive?
All blood types
What blood types can type O receive?
O
Which blood type is the universal donor?
type O
How do detergents remove proteins from membranes?
they disrupt membranes by intercalating into phospholipid bilayers
What completely denatures proteins at high concentrations?
sodium dodecylsulfate (SDS)
What are non-ionic detergents used for?
extracting proteins in their folded and active form
What are the various ways membrane proteins associate with the bilayer?
- a single alpha helix
- multiple alpha helices
- a beta barrel
- anchored to cytosolic surface by an amphipathic alpha helix
- covalently attached lipid chain
- oligosaccharide linker
- non covalent interactions with other membrane proteins
When do cells synthesize new membranes?
the expansion of existing membranes
What roles do fatty acids play in cells?
they are a fuel source, are key components of phospholipids and sphingolipids, and anchor some proteins to the membrane
Where does synthesis of phospholipids take place?
ER
What starts synthesis of fatty acids?
formation of acetyl CoA via esterificaiton
What are fatty acids bound to, that allows for transportation through the cytosol?
fatty-acid binding proteins (FABPs) that act as chaperones
Where are fatty acids incorporate into phospholipids?
ER membrane
Process for fatty acid incorporation into phospholipids
- two fatty acids are esterified to the phosphorylated glycerol backbone forming phosphatidic acid
- phosphatase converts phosphatidic acid into diacylglycerol
- polar head group is transferred to the exposed hydroxyl group
- flippase proteins catalyze the movement of phospholipids from the cytosolic leaflet to the exoplasmic leaflet
How are sphingolipids synthesized in the ER?
coupling of palmitoyl group to serine, second fatty acyl group is added to form ceramide, which is sent to the Golgi
How are sphingolipids synthesized in the Golgi?
polar head group is added to ceramide making sphingomyelin, which is then transported out of the golgi
What is the backbone for sphingolipids?
ceramides
What are other functions of ceramides?
serve as signaling molecules for growth, endocytosis, stress responses, apoptosis, and proliferation
Where is cholesterol synthesized?
in the liver
How is cholesterol synthesized?
- HMG-CoA reductase converts HMG-CoA into mevalonate
- mevalonate is converted into IPP
- IPP is converted into cholesterol
What is atherosclerosis?
distortion of the artery’s wall, leading to blockage of blood flow
What are statins?
anti-atherosclerosis medication
How do statins work?
bind to HMG-CoA and inhibit its activity
What is the bilayer largely impermeable to?
water-soluble molecules and ions
What can cross the membrane by simple diffusion?
gases and small uncharged molecules (urea, ethanol)
A higher concentration gradient causes a faster…
rate of movement across bilayer
What is the first and rate limiting step of diffusion?
movement across hydrophobic core
If a substance carries a net charge, what influences movement across a membrane?
substances concentration gradient and the membrane potential
Transport of most molecules requires the assistance of what?
membrane proteins
All transport proteins are what?
transmembrane proteins, generally alpha helices
3 main classes of transport molecules
channels, transporters (carriers), ATP-powered pumps
3 types of channels
non-gated and gated
Non-gated channels
open at all times
ex. aquaporins
Gated channels
selective for the type of molecule they transfer
Describe channels
transport proteins that transport water, specific ions, or small molecules down concentration gradient without the use of energy
What transports proteins slower than channels?
transporters (carriers)
3 types of carriers
uriporters, symporters, antiporters
Uniporters
transport single type of molecule
Symporters
coupled transport of molecules in same direction
Antiporters
coupled transport of molecules in different directions
Describe ATP-powered pumps
use ATP hydrolysis for energy to move ions or small molecules against their concentration gradient
What type of energy do cotransporters use and what is the process referred to as?
use energy stored in an electrochemical gradient, referred to as secondary active transport
Alternating access model of channels
channels switch between open and closed state with NO conformational change
has high rates of transport
Alternating access model of transporters and ATP-powered pumps
both undergo a cycle of conformational change which exposes a binding site in extracellular space and then changes again to expose cytosolic space, allowing the molecule in
has low rates of transport
What give a uniporter maximum transport rate (Vmax)?
large concentration gradient across membrane and uniporter working at maximum rate
What features distinguish uniport from simple diffusion?
-uniport moves substrates at a higher rate
-solubility is irrelevant
-there is limited number of uniport molecules
-transport is reversible
What transports glucose in mammalian cells?
GLUT-1
What are the two conformational states of GLUT-1 (alternating access model)?
glucose-binding site facing outside of cell or cytosol
What GLUT has the highest affinity (Km) for glucose?
GLUT-1
Where is GLUT-2?
in liver cells and insulin-secreting beta cells of the pancreas
Where is GLUT-3?
in neuronal cells of brain
have high glucose affinity (low Km)
Where is GLUT-4?
fat and muscle cells
Where is GLUT-5?
intestinal epithelial cells
What does GLUT-2 do?
has triggered activation
What does GLUT-3 do?
ensures cells have a high and constant supply of glucose
What does GLUT-4 do?
increases glucose uptake in response to insulin; unable to uptake glucose in absence of insulin
What does GLUT-5 do?
has high specificity for fructose, transports it from intestinal lumen to inside cells
What causes water to move across membranes?
osmotic pressure
Hypotonic
concentration of solutes lower than in the cytosol, water moves into cell, cell swelling
Hypertonic
concentration of solutes higher than in the cytosol, water moves out of the cell, cell shrinking
Aquaporins increase what?
the water permeability of cellular membranes
How many genes do humans have for aquaporins?
11
Where is aquaporin 1?
in erythrocytes
Where is aquaporin 2?
in kidney epithelial cells
What regulates aquaporin 2?
vasopressin
What aquaporin can transport molecules other than water?
aquaporin 3
What are the 4 main classes of ATP-powered pumps?
P-class
V-class
F-class
ABC superfamily
What are examples of P-class pumps?
Na/K ATPase pump
Ca ATPase pump
What do P-class pumps have?
2 identical catalytic alpha subunits that each contain ATP binding sites
Location of V-class pumps
animal lysosomal and eadosomal membranes
Function of V-class pumps
responsible for maintaining a lower pH inside organelles
pumps protons from cytosolic to extoplasmic face against electrochemical gradient
Where are F-class pumps?
bacterial plasma membranes, mitochondria, chloroplasts
What are F-class pumps considered as?
reverse proton pumps
What are the 4 core domains of ABC superfamily?
two transmembrane domains (T) that form a passageway and two cytosolic ATP binding (A) domains
What maintains intracellular Na and K concentrations?
Na/K ATPase
Na/K ATPase shares structural homology to what?
Ca pumps
For every 1 ATP molecules hydrolyzed, Na/K ATPase moves…
3 Na out and 2 K in
E1 conformation of Na/K pump
cytosolic sites have have affinity for Na and low affinity for K
E2 conformation of Na/K pump
the 3 bound Na gain access to exoplasmic face, sites have low affinity to Na and high affinity to K
Process for Na/K ATPase
- 3 Na out, 2 K in
- E1 conformation
- Phosphorylation and conformation change
- E2 conformation
- Phosphorylation and conformation changes
- E1 conformation, K released
What are the 2 abundant proteins in the lumen of the sarcoplasmic reticulum?
calsequestrin and high-affinity Ca binding protein
What regulates activity of Ca ATPase?
calmodulin
E1 state of Ca ATPase
2 Ca binding sites facing cytosol
E2 state of Ca ATPase
binding sites accessible to SR lumen
Process for Ca ATPase pumps
- E1 state, low cytosolic Ca but Ca still binds
- conformational change, ATP hydrolysis
- E2 state
- Ca dissociates
- E2-E1 conformational change
What do V-class H+ ATPases transport?
H+ only
The movement of H+ is accompanied by…
the movement of an equal number of anions in the same direction and an equal number of cations in the opposite direction
What do ABC proteins do?
use energy from ATP hydrolysis to export a wide variety of drugs and toxins from the cell
Which ABC proteins can move a hydrophobic or amphipathic substrate from the inner leaflet to the outer leaflet?
ABCB1 and ABCG2
Process of the Flippase model of ABC superfamily
- lipid tail of LLO binds to extracellular facing helix of flippase subunits
- exchange of ATP for ADP, dimer converts to an outward-open state
- hydrophilic oligosaccharide head of LLO enters positively charged pore of the transporter
- dimer returns to an inward-open conformation
- LLO tail dissociates
ABC cystic fibrosis transmembrane regulator (CFTR) is a…not a…
chloride channel, not a pump
What is protein targeting?
the delivery of newly synthesized proteins to their proper destinations
Where does signal based targeting go?
targeting of a newly synthesized protein from the cytoplasm to an organelle
Where does vesicle-based trafficking in the secretory pathway go?
transport of proteins from ER to a membrane-enclosed vesicle
For membrane proteins, where does targeting lead?
to insertion in the bilayer
For water-soluble proteins, where does targeting lead?
to translocation of protein across the membrane
What is a microsome?
a fragment of ER and attached ribosomes
Where does secretory protein synthesis begin?
on free ribosomes in the cytosol
During protein synthesis, translation and translocation occur…
simultaneously
How are proteins moved into membranes & organelles?
signal sequence, SRP, and SRP receptor docks the ribosome on an ER translocon & inserts the protein
Secretory proteins are synthesized in association with what membrane?
ER membrane
Process of co-translational translocation
- N-termial ER signal sequence emerges from ribosome
- SRP binds signal sequence & arrests protein synthesis
- SRP-nascent polypeptide chain-ribosome complex binds to SRP receptor in ER membrane
- GTP binds to SRP & its receptor
- translocation channel opens
- signal sequence goes to binding site next to central pore
- GTP hydrolyzed
- elongating polypeptide chain passes into ER lumen
- signal sequence is cleaved
- growing peptide chain continues through translocon into the ER, mRNA translated towards 3’ end
- translation stops, ribosome released
- translocon closes, nascent protein in ER lumen & folds
Process of post-translational translocation
- N-terminal segment of protein enter ER lumen
- BiP and Sec63 complex provide driving force for unidirectional translocation
- BiP ATP hydrolysis happens, BiP-ADP has conformational change & promotes binding to exposed polypeptide chain
- BiP binding prevents backsliding of peptide through translocon
- random inward sliding
- BiP-ADP binding directs protein into ER
- BiP released from protein
- protein folds
What uses post-translational translocation?
some yeast secretory proteins
What are the 3 single-pass membrane proteins?
types 1, 2, 3
Process of membrane insertion & orientation of type 1 transmembrane proteins
- translocation initiation & SS cleavage
- peptide elongates
- stop transfer anchor sequence enters translocon
- prevention of chain moving further into lumen
- stop transfer anchor sequence moves laterally
- translocon closes
- synthesis continues until stop codon
- nascent protein diffuses into ER membrane
Process of membrane insertion & orientation of type 2 transmembrane proteins
- SRP binds to internal signal-anchor sequence & interacts with SRP receptor; positively charged AAs on N terminal side orient chain
- chain elongation
- internal signal-anchor sequence moves laterally
- completion of protein synthesis
- peptide C-terminus released into ER lumen
Process of membrane insertion & orientation of type 3 transmembrane proteins
- SRP binds tot internal signal-anchor sequence & interacts with SRP receptor; positively charged AAs on C-terminal side orient chain
- C-terminal elongation
- ribosomal subunits released
Process of insertions of tail-anchored proteins
- Sgt2, Get4 and 5 take C-terminal tail of nascent protein & transfer it to Get3-ATP
- Get2-ATP-nascnet protein complex docks onto Get1/Get2 receptor on ER membrane
- Get3 ATP hydrolysis releases ADP and protein C-terminal tail into Get1/Get2 receptor, which releases tail-anchor sequence into ER membrane
4.
What determines orientation of type 1 proteins?
N-terminal signal sequence & STA sequence
What determines orientation of type 2 proteins?
high density of + charged AAs on N-terminal side of SA sequence
What determines orientation of type 3 proteins?
high density of + charged AAs on C-terminal side of
SA sequence
What determines orientation of type 4 A proteins?
N-terminus in the cytosol & alternating type 2 SA & STA sequences
What determines orientation of type 4 B proteins?
N-terminus in the ER lumen & type 3 SA sequence followed by type 2 SA & STA sequences
What proteins are considered multiples proteins?
Type 4
If multipass proteins have an even number of alpha helices, how will its N and C terminus be oriented?
towards the same side of the membrane
If a multipass protein has an odd number of alpha helices, how will its N and C terminus be oriented?
in opposite orientations
What 4 principal modifications do secretory proteins go through before they reach their final destinations?
- addition & processing of carbohydrates in ER & Golgi complex
- formation of disulfide bonds in the ER
- proper folding of chains in the ER
- proteolytic cleavages in ER, Golgi, and secretory vesicles
What are glycoproteins?
proteins with attached carbohydrates
O-linked oligosaccharides
have carbohydrate chains on hydroxyl side
N-linked oligosaccharides
have carbohydrate chains on amide side
What can promote folding and stability of glycoproteins?
oligosaccharide side chains
What does protein disulfide isomerase (PDI) do?
forms & rearranges protein cysteine disulfide bonds
Where are disulfide bonds formed and rearranged?
ER lumen
What facilitate folding & assembly of proteins?
chaperones & other ER proteins
What does peptide-prolyl isomerase (PPI) do?
accelerates rotation above peptide-prolyl bonds in unfolded segments of a polypeptide
What is the unfolded protein response?
- unfolded proteins accumulate in the ER lumen
- bind to Bip
- release Ire1
- Ire1 cuts unspoiled mRNA precursor making Hac1
- 2 Hac1 exons join
- Hac 1 translated into Hac1 protein
- transcription of chaperone encoding genes
Where are unassembled or misfiled proteins transported to for degradation?
cytosol
Process of protein import into the mitochondrial matrix
- precursor proteins are in unfolded state
- MTS binds to outer membrane receptor
- MTS inserted into TOM
- translocating protein inserted into TIM
- protein translocates through TIM
- MTS removed
- Hsp70 releases newly imported protein
- protein folds into its active form
What are the major structural features of the nuclear pore complex model?
membrane, structural, and FG- nucleoporins
FG nucleoporins form what kind of matrix?
gel-like
What are the nuclear proteins?
histones, transcription factors, DNA & RNA polymerases
What does the nuclear localization signal (NLS) do?
targets protein for import through nuclear pores
Process of NLS protein import in cytoplasm
- importin binds to NLS to form importin cargo complex
- importin cargo complex diffuses through
Process of NLS protein import in nucleoplasm
- Ran-GDP gets activated by GEF
- Ran-GTP forms & binds to importin causing conformational change that releases NLS-cargo protein
What does ran-dependent mechanism use for nuclear export of proteins?
NES
What does ran-independent mechanism use for nuclear export of proteins?
NXF1 or NXT1
The composition of the plasma membrane is determined by what two pathways?
secretory and endocytic pathways
Process of exocytosis
membranes & proteins are delivered to the membrane by exocytosis of coated vesicles that bud from the Golgi
Process of endocytosis
membranes & proteins are removed from the plasma membrane & coated vesicles bud from the membrane into the cytoplasm
Where does the first stage of the secretory pathway take place?
rough ER
How do cargo proteins get transported from the ER to the Golgi?
anterograde (forward-moving) transport vesicles
How do cargo proteins get returned back to the ER?
retrograde (backward-moving) transport vesicles
What is a cisterna?
flattened membrane bound compartments that hold liquid
made from fusion of transport vesicles
What is constitutive secretion?
proteins that are secreted continuously
What is regulated secretion?
proteins that are stored inside secretory granules that are not released until a signal for exocytosis
What is vesicle budding driven by?
polymerization of coat proteins
What is vesicle budding regulated by?
GTP binding proteins
What is cargo gathering?
interactions between cytosolic parts of integral membrane proteins & vesicle coat
What are 3 types of coated vesicles?
COPI, COPII, Clathrin
What do COPII vesicles do?
transport proteins from ER to Golgi
What do COPI vesicles do?
transport proteins in retrograde direction
What does Clathrin do?
transport proteins from cell surface to late endosomes
What does Sar1 do?
assembles & disassembles the COPII coat
What causes COPII disassembly?
Sar1-GDP being released from the vesicle
What do Rab GTPases do?
control docking of vesicles on target membrane
What do SNARE proteins do?
form stable coiled-coil complexes
Where is v-SNARE?
on target vesicle
Where is t-SNARE?
on target membrane
Process for docking & fusion of transport vesicles with their target membranes
- vesicle docking
- assembly of SNARE complexes
- membrane fusion
- disassembly of SNARE complexes
What is anterograde transport mediated by?
COPII transport vesicles
Mutation in what protein causes cystic fibrosis?
CTFR
What is retrograde transport mediated by?
COPI transport vesicles
What is the main function of KDEL receptor in retrograde transport?
to retrieve proteins containing the KDEL sorting signal to bring them back to the ER
How to proteins advance through Golgi?
by cisternal maturation
What is the role of adapter proteins (AP) complex?
transport from trans-golgi network directly to lysosome
What is the role of clathrin-coated AP complex?
transport from trans-golgi network to late endosome to lysosome
What is the role of constitutive and regulated secretory vesicles?
transport from trans-golgi network to cell surface
Clathrin molecules have what kind of shape?
three-limbed
What is dynamin essential for?
release of complete vesicle
What 3 proteins do regulated secretory vesicles contain?
chromogranin A & B, secretogranin II
Where can proteolytic maturation occur?
vesicles carrying protein, late endosome, in lysosome
What are the 2 types of endocytosis?
pinocytosis & receptor-mediated
What is pinocytosis?
nonspecific take up of small droplets of extracellular fluid & anything dissolved in it
What is receptor mediated endocytosis?
specific receptor on cell surfaces binds tightly to what is coming in, becomes a transport vesicle
2 types of receptor-bound ligands used for receptor-mediated endocytosis
LDLR & transferrin
How are lipids taken up from the blood to form lipoprotein complexes?
- LDLR binds LDL
- clathrin-coated pits pinch off
- vesicle sheds coat
- LDL particle released
- late endosome fuses with lysosome
Mutations in LDLR can cause what hereditary disease?
hypercholesterolemia
What is the main function of the lysosome?
to degrade extracellular material taken up by the cell
How are things delivered to the lysosome for degradation?
- vesicles fuse with the late endosome
- early endosomes fuse with late endosome
- proteins targeted for degredation bud into the interior of the late endosome forming multivesicular endosome
- multi vesicular endosome fuses with lysosome
Endocrine signaling
messengers reach target cells through blood stream
ex. hormones
Paracrine siganling
messengers travel short distance
ex. neurotransmitter
Autocrine signaling
cell has receptors on its surface that respond to messenger
What is signal transduction?
any process where cell converts one kind of stimulus to another
What carries out signal transduction?
enzymes
What activated signal transduction?
second messengers
3 main types of cell surface receptor proteins
GPCR, ion channel receptors, receptor tyrosine kinases
Examples of second messengers
cAMP and Ca2+
What are second messengers?
water soluble molecules or ions that spread throughout cell & activate responses
Process for activation of CREB
- receptor stimulation
- activation of PKA
- PKA subunits go to nucleus
- subunits phosphorylate & activate CREB
E1 state of Ca2+ ATPase pumps
two Ca binding sites, high affinity for Ca
E2 state of Ca2+ ATPase pumps
binding sites open to SR (after conformational change), Ca2+ dissociates
What can receptor tyrosine kinases (RTK) do?
simultaneously activate multiple signal transduction pathways
What do RTKs catalyze?
the transfer of a phosphate from ATP to tyrosine residues
What do ion channel receptors act like?
a gate
