biochem unit 4 Flashcards
Lipids
how many molecules does it include
are they defined by structure and if not how are they defined
arre they largely hydrophilic or hydrophobic
or what can they be, amphipathic or hydrophilic?
what are the 3 functions of lipids and examples of them
Lipids include many types of molecules
They are not defined by their structure; they are defined by having low solubility in water and high solubility in non-polar solvents
They are largely hydrophobic
OR they can be amphipathic (remember?)
Functions:
1. Energy Storage - Fats and oils- TAGs
- structural
- glycerophospholipids - membrane lipids
- spingolipids
- sterols (membranes) - Other/Specific Biological Activities
- enzyme co-factors
- electron carriers
- light-absorbing pigments like chlorophyll
- hormones, etc. like sterols
Storage Lipids: Fatty Acids
what are the simplest lipids
their basic structures exemplifies what lipid model and what are the parts of the model
what kind of acids are fatty acids, with what kind of chains
are most natural fatty acids branched or unbranched
what kind of bonds do some of them have
do most fatty acids have an odd or even number of carbons
The simplest lipids are fatty acids which are also constituents of many more complex lipids
Their basic structure exemplifies the amphipathic lipid model:
- A long hydrocarbon chain (“tail” – hydrophobic)
- A terminal carboxyl group (“head” – hydrophilic)
Fatty acids are carboxylic acids with highly reducedhydrocarbon chains
(4-36 carbons; C4 – C36)
Most natural fatty acids are unbranched
Some have double bonds (stay tuned)
Almost all natural fatty acids have an even numberof carbons (12-24)
Saturated and Unsaturated Fatty Acids
how many bonds in:
saturated
unsaturated
polyunsaturated
on what carbon is the carb. acid on
how many carbons and hydrogens do alkanes have and how do you know, is there a double bond
how many carbons and hydrogens do alkenes have and how do you know, is there a double bond
each time that we introduce a double bond, how many hydrogens do we lose
saturated means ____ amount of H’s possible
Saturated:
NO DOUBLE BONDS
Monounsaturated:
ONE DOUBLE BOND
Polyunsaturated:
MORE THAN ONEDOUBLE BOND
C1 = carboxylic acid
Most double bonds are at C9, C12, C15
alkane (no double bond)
CnH(2n+2)
so 2 carbons
H = 2(2 + 2) = 2 x 2 + 2 = 6!
alkene (one double bond)
CnH2n
so 2 carbons
H = 2 x 2 = 4
we lost 2 hydrogens when we introduced a double bond!
saturated = max. amount of H’s possible
Saturated and Unsaturated Fatty Acids
what conformation do saturated chains adopt
which is more abundant is nature, unsaturated or saturated
what configuration are the double bonds in for unsaturated fatty acids
what does unsaturated prevent and what does it increase
are there many or few van der waals in double bonds
what does this result in
The saturated chain adopts extendedconformations
- packed neatly
- max amount of van der waals
Unsaturated fatty acids areslightly more abundant innature
The double bonds in naturalunsaturated fatty acids arecommonly in the cis configuration
double bonds kink the chain
double bonds prevent close-packingand increases flexibility
with double bonds, there is fewer van der Waals interactions, changes in melting point
What is the impact of this? - more fluid membrane
Saturated and Unsaturated Fatty Acids: Naming
what is the first number
what is the number after the colon
what is teh number after the delta
what is omega
what does 18:1 delta 9 mean
what does 20:5 delta 5,8,11,14,17 omega 3 mean
The first number is how many carbons are present
The number after the colon is the number of double bonds present
The number(s) after the delta denotes which carbons have the double bonds
The ω (omega) numbers refer to how many carbons away from the methyl end of the fatty acid chain that the first carbon=carbon double bond appears
18:1 delta 9 =
- 18 carbons
- one double bond
- double bond is at the 9th carbon
20:5 delta 5,8,11,14,17 omega 3 =
- 20 carbons
- 5 double bonds
- double bond is at the 5,8,11,14,17 carbons
- omega 3 = starting from the last carbon, the first double bond we meet is at the 3rd carbon
which of the following fatty acids would have the lowest m.p
16:0
18:0
20:0
18:1
18:2
18:2
remember that double bonds have more impact than amount of carbons
Saturated and Unsaturated Fatty Acids
the longer the carbon chain, the higher the…
what do double bonds increase in the chain, how does this effect th evan der waals interactions and thus the melting point
what do double bonds decrease
more double bonds means what about the meltinng point
Let’s look at some trends of lipid propertiesas a function of lipid structure…
The longer the carbon chainthe higher the melting point
Double bonds increase kinks in the chain disruption in van der Waals associations and decreases the melting point
So, double bonds decrease themelting point
More double bonds, lower melting point
Energy Storage Lipids: TriAcylGlycerols (TAGs)
fatty acids are often incorporated in what
what kind of functional group connects the fatty acid to the ____
how many fatty acuds in each ester linnkage to how many glycerols
Fatty acids are often incorporated in Triacylglycerols (also called triglycerides, fats, TAGs)
These are fatty acid esters of glycerol
Three fatty acids each in ester linkage to 1 glycerol
Energy Storage Lipids: TriAcylGlycerols (TAGs)
advantages of storing energy lipids vs polysaccharides
are the carbon atoms highly reduced or oxidized, what does this mean for the energy density compared to polysaccahrides
arre they hydrophobic or hydrophilic, are they hydrated, what does this mean about the water weight
what do TAGs serve against the cold
carbon atoms are highly reduced (lots of hydrogens); this means that the energy density is 2x what it is in polysaccharides
these hydrophobic molecules are not hydrated, so the cells do not carry extra water weight
they serve as insulation against cold
Structural (Membrane) Lipids
what head group and tail do they have
what are the 3 things that Diversification can come from
properties of the head group can determine what
different organisms have different or the same lipid head group compositions
different tissues have different or the same lipid head group compositions
Contain a polar head group (variable) and nonpolar tails (usually fatty acids)
Diversification can come from:
Modifying a different backbone
Changing the fatty acids
Modifying the head groups
The properties of head groups determine the surface properties of membranes
Different organisms have different membrane lipid head group compositions
Different tissues have different membrane lipid head group compositions
Structural (Membrane) Lipids: Phospholipids
what is it called
what is the backbone
how many fatty acids, on which carbons, how many staurated or unsaturated
what functional group is the linkage
which carbon has a highly polar or charged group attached through what bond
(A) Glycerophospholipids
Backbone: Glycerol + Phosphate
Fatty Acids:2 Fatty Acids, 1 at C1, 1 at C2Usually one sat. and one unsat.
Ester linkage (whether TAGs or glycerophospholipids)
Head Group Attachment:C3 carbon has a highly polar or charged group attached through a phosphodiester bond
Glycerophospholipids contain _____ fatty acids and a _____.
1, sphingosine group
2, sphingosine group
1, polar head group
2, polar head group
3, polar head group
2, polar head group
Lipids as Signals
what is the name of the molecule that is a signal, and what is it
what are its derivatives involved in
activation of this pathway results in a variety of what
what is this required for
Phosphatidylinositol is a membrane lipid and is a signal!
It’s derivatives are involved in intracellular signal-transduction pathways such as the PIP2 IP3 DAG PKC pathway
Activation of this pathway results in a variety of cellular functions such as structure and metabolism regulation
Required for LTP
Structural/Signaling Lipids: (C) Sterols
what molecules can most bacteria not synthesize
what does the stroid nucleus contain
which ring is the polar head group in
how manyy non-polar sisde chains does it contain
what does it effect
what do Sterol + unsaturated FA’s do to motion
what do Sterol + saturated FA’s do to fluidity
Isoprenoids
Most bacteria cannot synthesizesterols
The steroid nucleus is four fusedrings (almost planar)
The polar head group (hydroxyl)is in the “A” ring
Often contain various non-polarside chains
Affects cell membrane fluidity
Sterol + unsaturated FA’s constrained motion
Sterol + sat FA increased fluidity
Steroids (Oxidized Sterols)
what are they used for
oxidized sterols =
what are they transported by from what site to target tissues
do receptors have a high or low affinity for them
what are the major types
what is the structure
Molecules used in intercellular signaling (makes sense because they are hydrophobic and can go through the membrane of cells)
Oxidized sterols = steroids
Transported by protein carriers from the site of synthesis to target tissues (long distance definition of “hormone”)
Receptors have a high affinity for them, so…
Major Types:
Sex Hormones (testosterone, estradiol
Adrenal Cortex Hormones (cortisol)
Anti-inflammatory drugs (Prednisone)
4 fused rings + oxygens = steroid
Eicosanoids (20-C Fatty Acid Derivatives)
what is it derived from, what kind of molecule is this
what is arachidonic acid derived from
what do they act on, what kind of signaling is this
what do they all serve as
what are the 3 classes their function
Derived from arachidonic acid (20-C PUFA)
Arachidonic acid is derived from membrane lipids cutwith a phospholipase
Act on cells near the site of synthesis Paracrine signaling
All serve as potent biological signaling molecules
Three Classes:
Prostaglandins (regulatory; fever, pain, inflammation)
Thromboxanes (made by platelets, aid in clotting)
Leukotrienes (3 conjugated double bonds; asthma)
Eicosanoids (20-C Fatty Acid Derivatives)
3 classes and their function
Prostaglandins:
Stimulate smooth muscle contraction
Elevate body temp, inflammation, pain
Thromboxanes:
Produced by platelets for clotting
Leukotrienes:
Stimulate smooth muscle contraction
In the airway asthma, anaphylaxis
The eicosanoids are _____ and derived from _____.
A. Intracellular messengers,Phosphatidylinositol
B. Paracrine hormones,Arachidonic acid
C. Steroids,Cholesterol
B. Paracrine hormones,Arachidonic acid
Testosterone, estradiol, cortisol, and prednisone are…
A. Prostaglandins
B. Thromboxanes
C. Leukotrienes
D. Steroids
E. Sphingolipids
D. Steroids
what are the 5 functions of the membrane
- Compartmentalization
Separate energy-producing reactions from energy-consuming ones - Keep proteolytic enzymes away from important cellular proteins
Import & Export
- Import (Selective import of nutrients) and Export (Selective export of waste/toxins)
Maintain electrical and chemical potent
- (retain metabolite and ion balance)
Sense external signals and transmit information into the cell
- Transporters
- Receptors (Pharmacology!)
- Adhesion Molecules (Glycoconjugates, lectins, and the like)
Fluid-mosaic model:
what is it mostly comprised of – what kind of lipids
what 2 other molecules are there too
what does the pohospholpid bilayer provide for the membrane
it contains proteins and modified protein to do what
is it semi or fully permeable and what does that mean
what can molecules move through
Comprised of a lipid bilayer of primarilyamphipathic phospholipids
Some sterols and carbohydrates too…
The phospholipid bilayer gives fluidity andelasticity to the membrane.
Contains proteins and modified proteinsto diversify functions
Semipermeable – what can and cannot move throughthe membrane is controlled
Through the lipid bilayer and through proteins
What’s in a Membrane: proteins
what do the proteins do and of what molecules
what are the 2 ways that membrane proteins interact with the lipids of the membrane
what are the targets of many drugs what do pharmacologists call these targets
Membranes have proteins that mediate and regulate the transport of metabolites, macromolecules, and ions
Membrane proteins interact with the lipidsof membranes in a variety of ways:
Electrostatic interactions w/polar groups
Hydrophobic regions embedded in thehydrophobic core
Membrane proteins are the targets of manydrugs, so pharmacologists call these“drug receptors”
membrane proteins interact with the phospholipids of the membrane through hydrophilic interactions (electrostatic interactions on the cytosolic sides) and hydrophobic interactions of the hydrophobic core
What’s in a Membrane: Proteins
what does integral membrane and through what interactions
how are integral proteins removed
what does monotropic mean
what does bitopic mean
what does polytopic mean
what are bitopic and polytopic also referred to as
what does amphitropic mean, do they associated reversibly or permeanantly, how are they attached, what regulated
Integral: embedded within the lipid bilayer through strong hydrophobic interactions. proteins are stuck in the membrane and cannot move from membrane
Removable only with agents that interfere with hydrophobic interactions (soaps)
Monotopic – interacts with one side of the membrane
Bitopic – Traverses the membrane once
Polytopic – Traverses the membrane more than once
Bitopic and Polytopic are also referred to as: Transmembrane Proteins (TM)
Peripheral: loosely associated with membrane via noncovalent interactions. Still proteins but connected through a loose connection and can still move
Amphitropic: associates reversibly with membranes; attached by weak interactions or through attached lipids; binding often regulated. Can be found in both membrane and cytosol
What’s in a Membrane: Integral Membrane Protein
are intregral proteins throughout the whole membrane or just in own spot, how many times can they weave in and out of the membrane
how are amino acids arranged in TM proteins
are TM segments mostly hydrophilic or hydrophobc
where are charged amino acds found
Integral/Transmembrane proteins span the entire membrane and may weavein and out several times.
Amino acids in TM proteins clusterin distinct regions
TM segments are predominantlyhydrophobic
Charged amino acids are only found in aqueous domains
What’s in a Membrane: Amphitropic
Tethered to a membrane through a covalent bond to a lipid anchor
Anchors are attached by specific enzymesand can later be removed
Reversible: sometimes associated,sometimes not
Transport Across Membranes
are biological membranes permeable
is the lipid bilayer hydrophilic or hydrophobic, what is it impermeable or permeable to
what do you need for ionic and polar substances
how are large things transported
Biological Membranes are selectively permeable
Also: semipermeable
The lipid bilayer is hydrophobic and is impermeable to most molecules exceptsmall non-polar molecules (like CO2, O2, N2, small steroids)
Need membrane proteins for ionic and polar substances
Endo/Exocytosis for big things!
Transport Across Membranes
Passive vs Active Transport
Simple vs Facilitated Passive Diffusion
Primary vs Secondary Active Transport
Uniport vs Cotransport
Symport vs Antiport Cotransport
Considerations of movement:
Is simple diffusion possible?
What is the membrane potential (Vm)?
Is there an electrochemical potential?
Passive (no energy required) vs Active (energy required) Transport
Simple (no protein required) vs Facilitated (protein required) Passive Diffusion
Primary (uses ATP directly for energy) vs Secondary (uses concentration from primary active transport) Active Transport
Uniport (transport 1 molecule) vs Cotransport (transport 2 molecules)
Symport (transport 2 molecules in the same direction) vs Antiport Cotransport (transport 2 molecules in the opposite directions)
Considerations of movement:
Is simple diffusion possible?
What is the membrane potential (Vm)?
Is there an electrochemical potential?
Simple Diffusion
involves the movement of what from an area of what amoutn of concentration to an area of what other concentration
diffusion of what kind of molecule is proportional to what
does it require a protein channel
where do molecules go through
Simple diffusion involves the movement of each solute byrandom molecular motion from an area of high solute concentrationto an area of low solute concentration
Diffusion of small, nonpolar molecules (such as gases O2 and CO2)is proportional to their concentration gradients
Does not require a proteinchannel
Through the membrane!
Facilitated Diffusion
what do passive transport proteins move
what are the two types
what do transport proteins decrease and how
what do transporters and channels provide for the diffusion of the solute across the membrane
is the solute guaranteed to cross
Passive transport proteins move uncharged, polar solutes down concentration gradient
two types:
Transporters
Channels
Transport proteins decrease the activation barrier (energy) of transport (∆G‡) by binding solute noncovalently
Transporters and channels provide a more chemically favorable environment for the diffusion of the solute across the membrane
The solute is not guaranteed to cross. Like the transitionstate of enzymatic reactions, it could go either way
no energy required
Facilitated Diffusion: Channels
are they faster or slower than transporters
do they saturate
do they undergo conformational changes
how many gates
what is the gate opening/closing regulated by (3 things)
is the opening/closing fast or slow
what are they somewhat specific to
what do many drugs target
Channels/Ion channels are much faster than transporters, they do not saturate, and do not undergo conformational changes
They allow movement (driven by a gradient – millions of ions/second if right)
Have one gate
Gate opening/closing is regulated by ligands, voltage, mechanical stress
Opening/closing is very quick
Are somewhat specific for ions
MANY DRUGS TARGET ION CHANNELS
Facilitated Diffusion: Transporters
what do transport proteins decrease or increase and how do they do that, is it slower of faster than channels
how many gates
are they specific or non-specific
what kind of transport
what are the 4 steps
- what binds
- what does the transporter change
- what does it release
kinetics of transport are similar to what
Transport proteins decrease the activation barrier (energy) of transport (∆G‡) by binding solute noncovalently (slower than channels!)
Transporters have 2 gates
Bind specifically (more so than channels)
Passive or Active (1°, 2°)Transport
Straightforward “steps”:
- “Substrate” binds
- Transporter changes conformation
- Releases substrate on the inside of the cell
Kinetics of transport are similar to enzymes!
for the Kt values below,
which molecule is the enzyme specific for
(has the highest affinity for)
D-glucose: 6mM
D-mannose, D-galactose: 20, 30 mM
L-glucose: 3000+ mM
D-glucose because it has the smallest Kt
low Kt: bind well, left of curve
high Kt: bind poorly, right of curve
Active Transport
what is the transport against
does it require energy
what is a
uniport
symport
antiport
Transport against a concentration gradient
Requires input of energy!
uniport: transport 1 molecule
symport: transport 2 molecules in same direction
antiport: transport 2 molecules in opposite directions
Active Transport
primary active transport,
- what proteins provide the energy to drive the transport of what molecules
secondary active transport,
- what concentration gradient is used and what happens to substances
In primary active transport, transmembrane ATP-hydrolyzing enzymes provide the energy to drive the transport of ions or molecules
In secondary active transport, concentration gradients formed by primary active transport are used to move other substances across the membrane
Active Transport: Na+/K+ ATPase
is it a uniport, symport, antiport
how much energy does this system use when a person is at rest
what happens if it stops working
an antiporter:
ATP hydrolysis drives 2K+ in, 3Na+ out
these pumps consume ~25% of the energy consumed by humans at rest
if it stops working then Na+ builds up in the cell and so water will follow the salt and go inside the cell and cause it to swell
Secondary Active Transport: Lactose Transporter
lactose transporter (permease) transports H+ and lactose in the cell
proton pump transports H+ out of the cell and at the same time, converts fuel into CO2
Secondary Active Transport: Na+-glucose Symporters
3 transporters system
all in the intestinal epithelial cells
1- Na+ K+ ATPase - primary antiporter
- move 3 Na+ out and 2 K+ in
2- Na+ glucose symporter (driven by high extracellular [Na+]) - secondary symporter
- move 2 Na+ and 1 glucose in
3- glucose uniporter GLUT2 facilitates downhill efflux
- move 1 glucose out of cell
Summary of Transport Types
simple diffusion
protein carrier
saturable with substrate
movement relative to concentration gradient
energy input required?
facilitated diffusion
protein carrier
saturable with substrate
movement relative to concentration gradient
energy input required?
channels and pores
protein carrier
saturable with substrate
movement relative to concentration gradient
energy input required?
transporters and carriers
protein carrier
saturable with substrate
movement relative to concentration gradient
energy input required?
active transport
protein carrier
saturable with substrate
movement relative to concentration gradient
energy input required?
primary
protein carrier
saturable with substrate
movement relative to concentration gradient
energy input required?
secondary
protein carrier
saturable with substrate
movement relative to concentration gradient
energy input required?
simple diffusion
protein carrier- no
saturable with substrate- no
movement relative to concentration gradient- down
energy input required?- no
channels and pores
protein carrier- yes
saturable with substrate- no
movement relative to concentration gradient- down
energy input required?- no
transporters and carriers
protein carrier- yes
saturable with substrate- yes
movement relative to concentration gradient- down
energy input required?- no
primary
protein carrier- yes
saturable with substrate- yes
movement relative to concentration gradient- down
energy input required?- yes (direct source)
secondary
protein carrier- yes
saturable with substrate- yes
movement relative to concentration gradient- up
energy input required?- yes
passive transport (no energy required)
- simple diffusion
- facilitated diffusion
- channels and pores
- transporters & carrier
active transport
- active transport
- primary
- secondary
what is Kt
the concentration of a substrate, in this case glucose, at which the transport protein is at half capacity. A low Kt would mean a high affinity transporter a high Kt means a Low affinity. a lower Kt means it takes less substrate to occupy half the transport space of a protein.
Features of Signal
Transduction
is it specific or not
why is it sensitive, what is it due to
- is there high affinity
- is there cooperativity
- is there ampplification
are things rigid if not is it modifiable
is there integration
specific
sensitive, due to
- high affinity
- cooperativity
- amplification
modifiable (desensitization)
integration
signal transduction pathway
___ protein ____ receptor
- where does the external ligand (L) bind
- what does it activate
- what does that molecule regulate
- what does it generate
G-protein coupled receptor
- external ligand (L) binding to receptor (R) activates an intracellular GTP-binding protein (G) which regulates an enzyme (Enz- Adenylyl cyclase right?) that generates an intracellular second messenger (cAMP right?)
So Let’s Do an Example: Adrenergic Receptors
what kind of illnesses are GPCRs apart of
how many drugs on the market target GPCR
what are the 4 drugs examples of this
- for HTN
- for stomach acid
- for airway
- for depression
GPCRs implicated in allergies, depression, blindness, diabetes, Cardiovascular defects
more than 1/3 of all drugs on the market today target a GPCR
examples of drugs:
- blood pressure reducers (beta-blockers such as propranolol)
- stomach acid suppressors (ranitidine)
- bronchodilators (albuterol)
- antidepressants (paroxetine)
So Let’s Do an Example: Adrenergic Receptors
which of the drugs has the highest affinity for the receptor
epinephrine Kd: 5
isoproterenol. Kd: 0.4
propranolol (antagonist) Kd: 0.0046
what drug bind onto the adrenergic receptor
what are the 4 types of epinephrine or adrenaline molecules
what is an agonist
what is an antagonist, are they inhibitors
where are the different types found
propranolol (antagonist) Kd: 0.0046 does!
binding site for epinephrine (adrenaline)
four types a1, a2, B1, B2 - defined by differences in affinities and response to:
agonists: molecules (ligands) similar to the natural ligand, that mimic the ligand’s effects
antagonists: analogs that bind but have no effect, blocking the effects of agonists - they are inhibitors
different types are found in different tissues and have different effects
G Protein-Coupled Receptor (GPCR) Systems
the 3 parts of these systems
- where is the receptor
- what is the full name of the protein that starts everything
- what protein in the membrane is activated and what does it generate
how many knowns types of GPCRs are there and what do they trandsduce
3 Components of these systems:
- Plasma Membrane Receptor
- Guanosine nucleotide-binding protein (G protein)
- In-membrane effectorenzyme that generates anintracellular 2nd messenger
There are 800+ known GPCRs transducing messages such as hormones, growth factors, smells, taste, etc.
G Protein-Coupled Receptor (GPCR)
how many proteins are they
what does that mean - are they mono, bi or polytopic, where are the hydrophobic and hydrophlic A.A.
what is an example of thiss
GPCRs are spots for
- what kind of binding
- ___ interaction sites
- ___ interaction sites
- ____ interaction sites
GPCRs are 7-TM (transmembrane) (7 amino acid chains, polytopic because it goes through the membrane 7 times, hydrophobic amino acids insde and hydrophlic ones outside) domain α-helical integral membrane proteins
Example:
- Β-adrenergic receptor
Spots for:
Ligand-binding
Gα interaction sites
Gβ interaction sites
Regulatory (β-arrestin) interaction sites
G Proteins
what is the name that is used to describe them
what side of the membrane are they on
can they be stimilatory or inhibtoriy and what symbols do we use to classify this
initally, what is G-protein bound to
what are the 3 subunits
what is it initally bound to
what is the G protein a subunit of
- what does that subunit separate from
- what molecules does it move to
GPCR Michelle definition
Heterotrimeric
on the cytosolic side of the membrane
stimulatory: Gs (others are inhibitory)
initially, G-protein has GDP bound (thus the name)
3 subunits: a (can either be Gi or Gs), B, Y
initially, bound to the receptor
The G protein is a subunit of Gsa that separates from the B and Y subunits and moves (‘slides along’) to the effector enzyme (AC).
after receptor binds epinephrine, GDP is replaced by GTP
GPCR: G protein coupled receptor so it is a receptor on a cell that effects a G prootein to cause an intracellular signal
In-membrane Effector Enzyme
what molecule effector enzyme we talk about
what do other pathways have
G-proteins can either ___ (what is this molecule called) or ___ (what is this molecule called) what molecule and therefore the production of what molecule
which subunit of G protein separates from what 3 other subunits and moves to AC
- what does this activate AC to do
- what type of molecule is created
In our present discussion, we will talk about adenylyl cyclase (AC)
Other pathways have other effector enzymes
G-proteins can either stimulate (Gs) or inhibit (Gi) AC production of…
Cyclic AMP (cAMP)(second messenger)
The G protein’s a subunit of Gsa separates from the B and Y subunits and moves ‘slides along’ to adenylyl cyclase (AC) and activates it so that AC catalyzes the synthesis of cAMP 2nd messenger
Gs and the enzyme go their separate ways
after Gsa activates AC, the ___ is converted to ___
what kind of enzyme is Gsa, what can it do, what does thsi do to Gsa
- what is a term for this
what does Gsa do with AC, what does it do with the other subunits of the G-protein
- and is ready to go again!
after activating AC, the GTP bound by Gsa is converted to GDP. Gsa is a GTPase: it can convert GTP to GDP. This inactivates Gsa. Self-inactivation
Gsa dissociates from AC, re-associates with its B and Y subunits, and is ready to go again Gs
summary: G protein activation and inactivation
what is bound to Gsa, can it actiavte AC
contact of Gs with what complex causes what to the bound GDP to GTP
Gs with GTP bound dissociates into what
- Gsa GTP is turned on what can it now do
GTP bound to Gsa is hydrolyzed by what
- what does Gsa do to itself
- the inactive a subunit reassociates with what
Gs with GDP bound is turned off; it cannot activate adenylyl cyclase
contact of Gs with hormone receptor complex (the complex would have to chnage shape to come in contact with G-protein) causes displacement of bound GDP to GTP
Gs with GTP bound dissociates into a and By subunits. Gsa -GTP is turned on; it can activate adenylyl cyclase
GTP bound to Gsa is hydrolyzed by the protein’s intrinsic GTPase; Gsa thereby turns itself off. The inactive a subunit reassociates with By subunits
What is the correct order of action for GPCR’s?
G-protein, receptor, AC
G-protein, AC, receptor
Receptor, G-protein, AC
Receptor, AC, G-protein
Receptor, G-protein, AC
steps
what does epinephrine bind to
what change does the complex go through
- what does this cause
what does Gsa separate from what and moves where and does what to the effector enzyme
what does AC do
what does cAMP to
what does PKA do
what happens to cAMP and how does this effect PKA
epinephrine binds to its specific receptor
allosteric change in hormone-receptor complex causes the GDP bound to Gsa to be replaced by GTP activating Gsa
activated Gsa separates from By subunits of G-protein and moves to adenylyl cyclase and activates it. Many Gsa subunits may be activated by one occupying receptor
adenylyl cyclase catalyses the formation of cAMP
cAMP activates PKA
phosphorylation of cellular proteins by PKA causes the cellular response to epinephrine
cAMP is degraded, reversing the activation of PKA
cAMP and PKA
what kind of molecule is cAMP
a large amount of GPCRs do what
what does cAMP do to PKA
cAMP is a common secondary messenger
A large number of GPCRs mediate their effects via cAMP (Gs or Gi)
allosterically activates cAMP-dependent protein kinase A (PKA)
cAMP activates PKA
What do kinases do
what is PKA
- what does it target
- what does it lead to
some targets of PKA lead to what in what organ
Kinases are enzymes that catalyze the phosphorylation of hydroxyl groups on Ser, Thr, or Tyr amino acids in target proteins
Protein Kinase A (PKA) is a cAMP-dependent protein kinase that targets many proteins in the cell leading to their activation
Some targets of PKA lead to glycogen glucose in the liver (next semester)
Adenylyl cyclase catalyzes the formation of _____, which then activates _____.
ATP, PKA
cAMP, PKA
PKA, cAMP
GTP, PKA
cAMP, PKA
Specificity Through Localization
what do AKAPs hold together
- how does this effect the cAMP
what can cAMP do
what is PKA localized to by what protein
different __ are expressed in ___ cell types,
- what does this determine
what cascade causes amplification
with amplification, 1 molecule produces how many molecules
AKAPs (PKA anchoring protein) hold together specific ACs, PKAs, and PKA targets so that the cAMP generated by an AC activates (or inactivates) the right PKA and its target enzyme
cAMP can mediate multiple signals due to the localization of PKA
PKA is localized to particular structures by an anchoring protein
different anchors are expressed in different cell types –> determines downstream effect of cAMP
amplification: epinephrine cascade
This is where the amplification theme comes in.
We go from 1 molecule to 100,000
epinephrine cascade
how many of what molecule do you start with
what does it bind to what does it do
how many Gsa molecules are produced
- what is replaced on Gsa
- what does Gsa then go onto activate
how many molecules are produced
how many molecules of PKA are produced
how many molecules of phosphorylase b kinase is activated
how many molecules of glycogen phosphorylase a is activated
how many molecules of glucose 1-phosphate is produced
1 molecule turns into how many molecules
1 molecule epinephrine
1 molecule epinephrine receptor complex (change shape)
10 molecules Gsa (GDP attached to Gsa is replaced by GTP and activates Gsa. Gsa then goes on to activate cAMP)
200 molecules of cyclic AMP (which activates PKA)
100 molecules active PKA
1000 molecules active phosphorylase b kinase
10000 active glycogen phosphorylase a
100000 molecules glucose 1-phosphate
This is where the amplification theme comes in.
We go from 1 molecule to 100,000
Terminating the Response
what [molecule] drops in the blood
- what molecule dissociates from the receptor
- is G protein activated
what do GTPase activators (GAPs) accelerate
what does cyclic nucleotude phosphodiesterase do
what do methyl xanthines do, what are examples of them
when blood [epi] falls, epi dissociates from the receptor, and G is no longer activated
GTPase activator proteins (GAPs) accelerate G protein inactivation
cAMP can be hydrolyzed to 5’-AMP (which is not active) by cyclic nucleotide phosphodiesterase
- methyl xanthines (caffeine, theophylline [tea]) block the degradation of cAMP, increasing the half-life of cAMP so it is around longer!!!
GAPs & GEFs
what is the full name of GEF, what does it do
what are GAPs and GEFs potential targets for
are they regulators
guanine exchange factor (GEF) - helps exchange GDP for a new GTP
GAPs and GEFs - potential drug targets in cancer
these are also regulators
The breakdown of cAMP is blocked by
ATP
Caffeine
GTP
PKA
Caffeine
a methyl xanthine!
phosphorylation
what are the two processes that regulate enzyme activity
what are the names of the enzymes that do both of the processes
what are examples of these enzymes
what can phosphorylation do
enzyme activity is often regulated by phosphorylation (enzyme = kinase) and de-phosphorylation (end = phosphatase)
- modified AA = Tyr, Der, Thr
examples: PKA, Receptor Tyr kinases
phosphorylation may increase or decrease activity
what are the simplified parts of the epinephrine pathway
epinephrine
B-adrenergic receptor
G-protein
adenylyl cyclase
cAMP
PKA
