Exam 2 Flashcards
What are mechanisms for restricting the movement of proteins in the membrane?
Tethering proteins to the cell cortex, using barriers such as tight junctions, tethering proteins to the surface of another cell, and tethering proteins to the extracellular matrix
What type of molecules can readily (without the help of a protein) pass the lipid bilayer?
Small polar molecules that have no charge, such as ethanol and small hydrophobic molecules like gases
How does Ca2+ get removed from the cytoplasm of a muscle cell after a contraction?
Active transport using Ca2+ pump (ATPase)
Movement of glucose out of intestinal epithelial cells in order to enter into the bloodstream is via what mechanism (or transporter type)?
Passive transport/facilitated diffusion
In animals, the concentration gradient of what ion is often used to drive the movement of other molecules against their concentration gradients?
Na+
What are properties of a passive transporter?
The transporter binds to the molecule prior to transferring it across the membrane and the molecule transported can go either direction across the membrane, depending on the concentration gradient.
What is osmosis?
The movement of water from an area of low solute (high water) concentration to an area of high solute (low water) concentration.
What is the difference between transporters and channels?
Channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.
Where are sugars located in the intestinal epithelial cell?
In the lumen in the gut; they enter in to the cell and diffuse out the other side
Why are transporters kept in their place in epithelial cells?
Because they have diffusion barriers called tight junctions that prevent the movement of transporters because it’s important that transporters maintain in either the apical membrane or the basal/lateral membrane
Why do amino acids have a harder time getting across a membrane?
Their side chains are charged
What is a difference between flow in channels and passive transporters?
Transporters can open either direction via a confirmation change and move the molecule in either direction but channels can open or close but when they’re open the molecules just flow through the poer
What are ways to achieve active transport?
Coupled pump, ATP-driven pump, and light-driven pump
What are the natural concentration of Na and K in the cytosol?
Low Na concentrations and high K concentrations
What is the process of the Na/K pump?
Na ions enter binding sites on cytosolic sides to pump Na against concentration gradient and pump is phosphorylated to expose the Na ions to the cell. Binding of K allows the pump to return to normal
What is a uniport?
Carries one type of molecule
What is a symport?
Coupled transporter that carries two types of molecules in the same direction
What is an anti port?
Coupled transporter carries two types of molecules in different directions
What is the difference between a pump and a coupled transporter?
A pump requires ATP to drive the reaction
What is the Na/glucose co-tranporter?
Na movement down its electrochemical gradient drives glucose transport against its concentration gradient
What transporters are required for moving glucose from the intestine to the bloodstream?
Na/glucose symport and glucose uniport
Why do we have different ion concentrations inside the cell?
Transport molecules across the membrane, regulate cell volume/turgor, regulate absorption or release of water, and electrical signaling
What are the three types of gated ion channels?
Voltage-gated, ligand-gated, and mechanically-gated
Why are excitable membranes necessary?
Diffusion is inefficient over distance and very rapid signaling can occur through voltage changes
When do voltage gated K+ channels and K+ leak channels open during induction?
When the action potential is reached
What would happen if voltage gated Na+ channels were blocked?
The cell would be depolarized to the threshold potential of ~-40mV and then return to the resting potential of ~-60mV
What would happen if K+ channels are blocked?
Once action potential is reached, repolarization would be very slow
What would happen if the Na+/K+ pump was blocked?
Nothing because the pump sets up the concentration gradient but the action potential doesn’t really change concentration (would need many action potentials to have an effect if Na+/K+ pump was blocked)
What is the process of an action potential?
Local depolarization to threshold, depolarization opens nearby voltage-gated Na+ channels, initiating action potential, and resting potential is restored by rapid inactivation of Na+ channels and slower opening of voltage-gated K+ channels
What is the signaling pathway for a muscle contraction from the brain to the contraction?
Neurotransmitter released onto post-synaptic motoneuron in spinal cord, neurotransmitter opens receptor (ligand-gated) channels and depolarizes membrane, depolarization triggers action potential which is propagated to the synapse using voltage-gated Na+ and K+ channels, depolarization at the presynaptic terminal opens voltage-gated Ca2+ channels, Ca2+ influx triggers ACh release, and ACh binds ACh receptors and triggers a contraction
What is a neurotransmitter at the neuromuscular junction?
Acetylcholine
What is the most common excitatory neurotransmitter in the brain?
Glutamate
What is the most common inhibitory neurotransmitter?
GABA
What are some “slow” neurotransmitters?
Serotonin, dopamine, norepinephrine, etc. that signal through G proteins and 2nd messengers
What is an endocrine signal?
Transmits through the whole body like hormones
What is a paracrine signal?
Transmits locally like inflammatory sites
What is a synaptic signal?
Signal at the synapse where there’s locality but it’s transmitted far
What is a contact-dependent signal?
Membrane-bound signal
How is specificity determined?
Type of receptor expressed, location of signal, signal transduction pathways in the cell, and combinatorial effects with other signals
How does nitroglycerin avert heart attacks?
Nitroglycerin converted to NO and dilates blood vessels so there’s increased flow through arteries
What is the general process of cell signaling?
Extracellular signal molecule attaches to the receptor which generates other intracellular signal molecules to activate which alters the target protein which produces effector proteins and alters cell behavior
What are the two types of extracellular signal molecules?
Cell-surface receptors for molecules too large or hydrophilic and intracellular receptors that are small or hydrophobic enough
What are the intracellular receptors that bind to receptor proteins in the cytosol or nucleus called and why?
Nuclear receptors because when they’re activated by hormone binding, they act as transcription regulators in the nucleus
What is the process of dilating blood vessels in the smooth muscles?
Acetylcholine activates NO synthase which produces NO which diffuses to the smooth muscle cells where NO binds to the guanylyl cyclase that converts GTP to cyclic AMP that relaxes the blood vessel
What are the functions of an intracellular signaling molecule?
Relay signal, amplify signal, detect signals from more than one pathway and integrate before relaying, and distribute signals to more than one effector protein
How do intracellular signal molecules act as molecular switches?
Phosphorylation by kinase or dephosphorylation by phosphatase and GTP-binding proteins switching between active (GTP) and inactive (GDP) forms
What do ion-channel-coupled receptors do?
Change permeability of membrane to selected ions which changes membrane potential which creates an electrical current
What do G-protein-coupled receptors do?
Activate membrane-bound G proteins which activate or inhibit an enzyme or ion channel in the membrane which activates and intracellular signaling cascade
What do enzyme-coupled receptors do?
Act as or associate with enzymes that, when stimulated, enzymes can activate a variety of intracellular signaling pathways
What are some characteristics of G-protein coupled receptors (GPCRs)?
All have similar structures (seven-pass transmembrane proteins), most drugs work through GPCR proteins, and many are involved in the sense of smell
How are GPCRs stimulated?
Extracellular signal binds to GPCR which changes the confirmation of receptor protein which activates the G protein on the other side of the membrane
How does GTP bind to the G protein?
When the receptor activates the G protein it causes the alpha subunit of the protein to decrease its affinity for GDP which is the exchanged for GTP
How do some bacteria cause disease through GPCRs?
They alter the activity of G proteins by changing their conformation
How is the G protein inactivated?
Hydrolysis of GTP to GDP
What is an example of how G proteins regulate ion channels?
The beta-gamma complex binds to the K+ channel and causes it to open when GPCR activates the G protein which slows heart rate by increasing membrane permeability to K+ and making it more difficult to electrically activate
What are the two enzymes that most frequently are targeted by G proteins?
Adenylyl cyclase (produces cyclic AMP) and phospholipase C (produces inositol triphosphate and diacyl glycerol)
What is the process involving adenylyl cyclase?
ATP is converted to cyclic AMP that is catalyzed by adenylyl cyclase (removes 2 phosphates) then cyclic AMP is converted to AMP via cAMP phosphodiesterase
What does cAMP activate?
cAMP activates cyclic-AMP-dependent protein kinase (PKA) by forcing a conformational change that unleashes active kinase; PKA then catalyzes phosphorylation of particular serines or threonines
What is an endocrine extracellular signaling mechanism?
It broadcasts throughout the whole body in the bloodstream like hormones
What is a paracrine extracellular signaling mechanism?
It is local like inflammation sites
What is a synaptic signal?
Neuronal signals are transmitted electrically along a nerve axon and releases neurotransmitters on adjacent target cells
What is a contact-dependent signal?
A cell-surface-bound signal molecule binds to a receptor protein on an adjacent cell
What are some GPCRs?
Sensory receptors (rhodopsin (eyes), odorant, and taste), muscarinic acetylcholine receptor, serotonin receptors, and adergenic receptors
How do you stop a neurotransmitter?
Degradation or reuptake by transporters
What happens if you inhibit transporters?
Neurotransmitters work longer
What type of receptors do the neurotransmitters dopamine, serotonin, and norepinephrine bind to?
GPCRs
What do amphetamines do?
Block dopamine, serotonin, and norepinephrine transporters so the neurmodulators work longer
How do anti-anxiety drugs work?
Tone down excitatory nerve transmission in the brain by enhancing the GABAa receptor
What do protein kinases do?
Catalyze transfer of phosphate from ATP to OH group on substrate (serine, threonine, or tyrosine) which alters protein conformation, altering enzyme activity or interactions with other molecules
What is the specificity of kinases?
Depends on amino acid sequence of substrate, different kinases are activated differentially, and location
What is the general signaling through the G alpha subunit?
Extracellular molecule binds to receptor, activation of trimeric G protein, alpha subunit changes activity of enzyme in membrane, change in levels of 2nd messengers, and 2nd messenger binding turns on/off effector
What do 2nd messengers do?
Pass info received @ receptor to effector and their binding changes the conformation and activity of the target
What are some 2nd messengers?
IP3, cAMP, cGMP, and Ca2+
What is the info for Gs (stimulatory)?
Target = adenylyl cyclase; effect = increase in cAMP; bacterial toxin = cholera activates
What is the info for Gi (inhibitory)?
Target = adenylyl cyclase; effect = decrease in cAMP; bacterial toxin = pertussis inhibits
What is the info for Go?
Target = phospholipase C; effect = increase in IP3 and DAG; bacterial toxin = pertussis inhibits
What is the info for Gt (vision)?
Target = cGMP phosphodiesterase; effect = decrease in cGMP; bacterial toxin = cholera and pertussis
What is the info for Golf (smell)?
Target = adenylyl cyclase; effect = decrease in cAMP; bacterial toxin = cholera activates
What is the info for Gq?
Target = phospholipase C; effect = increase in IP3 and DAG; bacterial toxin = no effect
How does calcium enter the cell?
From extracellular space via ligand or voltage-gated ion channels or released from intracellular stores (ER)
What are some Ca2+ activated targets and responses?
Muscle contraction, kinase activation (PKC and CaM kinase), phosphatase activation, ion channel opening, phospholipase A2 activation, etc.
How are proteins activated via RTKs?
Proteins contain gin SH2 domains bind to phosphotyrosines (phosphorylated tyrosine) on receptor, causing activation
What is the pathway that leads to activated Tor?
Activated RTK by a growth factor activates PI 3-kinase which activates PKB which activates Tor and Tor leads to inhibition of protein degradation or stimulation of protein synthesis and promotes cell growth
