Chapter 12

Transmembrane Transport

O2, Co2, steroids, hormones

what is able to simple diffuse through the membrane (hint: cell respiration and cell signaling)

water, ethanol, amino acids, glucose

what molcules can simple diffuse through a cell membrane but the membrane is much less permeable and rate is dependent on size

• facilitated transport is necessary for the quantities a cell needs

H+, Na+, K+, Ca2+, Cl-

what molecules are not able to diffuse across a membrane and require facilitated transport

membrane potential

this term refers to voltage difference at the membrane 

0

what is the membrae potential equal to when charges are balanced on both sides of the cell membrane

less than

is the membrane potential greather or less than 1 when there are more cations outside the membrane

-20 to -200 mV (a small vaue!)

what is the average resting membrane potential of a cell membrane

concentration gradient and charge gradient

what two components make up an eletrochemical gradient in a cell

concentration gradient

this term refers to the relative concentrations of a specific solute

• component of the electrochemical gradient

• unique to each solute; important for charged, polar, and neutral molecules

charge gradient

this term refers to the balance of all charged molecules

• component of the electrochemical gradient

• is equal to the membrane potential; important for ions

true

true or false: both ion channels and transporters are usually highly specific

size and charge of channel’s pore

what determines the selectivity of a channel protein

pore opens or shuts

by what method does an ion channel transport ions

ion channel

which is faster: an ion channel or a transporter

down the gradient

in what direction does an ion channel move ions always

the specific binding site in it

what determines the selectivity of a transport protein

via conformation changes of protein

by what method does a transport protein move molecules

can be either with or against gradient

in what direction does a transport protein move molecules

passive transport (facilitated diffusion)

ion channels and transport proteins are both examples of what kind of transport (note: pumps are a subclass of a transporter and are not this type of transport)

active

pumps are an example of what kind of transport

osmolarity (most cells have a high internal osmolarity)

this term refers to the total solute concentration

osmosis

this term refers to the passive diffusion across the lipid bilayer

the expelling of 3 Na+ via a Na+/K+ pump reduces the rate of osmosis (too much Na+ in a cell can lead to cell lysis)

how does a Na+/K+ pump help a cell manage its rate of osmosis

kidneys, plant roots

what types of cells need to move a lot of water

perfectly sized for water, alternates partially negative and positive polar groups (to exclude all ions)

how is an aquaporin made that makes it so highly selective for water

rapid random

a passive transporter has ___ and ___ transitions between conformations independent of ligand binding

• allows for solutes to flow down concentration gradient

• mechanism is similar to turnstile

no (highly specific only for glucose and its isomers; G6P remains trapped in cell)

could a glucose-6-phosphate travel through a glucose transporter?

glucose is imported into cell

what is the flow of glucose when a person has high or normal blood sugar

glucose is exported from liver cells (other cells import less glucose)

what is the flow of glucose when a person has low blood sugar

retinal

what type of pump is a light energy pump that transporters H+ out of the cell (found in a few prokaryotes)

powers gradient driven pumps, required for electrical signaling, regulates osmolarity

what are the functions of the concentration gradient created by Na+

membrane potential, required for electrical signaling

what are the functions of the concentration gradient created by K+

3 Na+ binds to the pump, ATP is phosphorylated causes a conformational change releasing Na+ into the ECF, 2K+ from the outside binds to the pump, the pump is dephosphorylated (only ever after K+ binds) causing a conformational change and releasing K+ into the cell

how does a sodium potassium pump work

so ATP hydrolysis is not wasted on an empty pump

why will a sodium potassium pump only phosphorylate or dephosphorylate when a solute is bound to the pump

pumps 2 Ca2+ out of the cell via the phosphorylation of ATP after Ca binds and then dephosphorylates to return to original conformation

how does a Ca2+ pump work

plasma membrane, sarcoplasmic reticulum (smooth ER)

where can you find Ca2+ pumps

exocytosis of neutrotransmitters, motor proteins for use in muscle contraction, fertilization, secretion

what are the functions Ca2+ is able to fulfill by being excreted from the cell via the active transport of a Ca2+ pump

Na+ and glucose

what is an example of a symport (the movement of one solute down its gradient drives the movement of another solute with it)

Na+ and H+; pH regulation

what is an example of an antiport (the movement of one solute down its gradient drives the movement of another solute in the opposite direction); also what is its purpose

epitheial cells of small intestine

what type of cell must important glucose from gut even when glucose is scare via Na+/glucose symport

both Na+ and glucose are bound, the symport is empty

a Na+/glucose symport is capable of random conformational changes only if: (two possible situations)

the direction of the Na+ chemical gradient (usually flows into the cell, Na+/K+ pumps then remove the introduced Na+)

what determines the direction of a Na+/glucose symport

apical surface

where can Na+/glucose symporters be found within an epithelial cell in the small intestine

tight junction

this term refers to the junctions found within epithelial cells that separate the cell into two domains

• functions to prevent molecules from flowing between cells and specifically helps tightly regulate glucose concentration to be high inside the cell

  • apical and lateral/basal domain

apical

this domain (created by a tight junction) and found within epithelial cells in the small intenstine uses Na+/glycose symporters to bring in glucose from the gut lumen into the cell

lateral/basal

this domain found in the epithelial cells in the small intestine uses glucose uniporters to move the glucose from within the epithelial cell out to the ECF/rest of the body

• also uses Na+/K+ pumps to push out Na+ brought in by the Na+/glu symport

drives symports that import sugars and amino acids

what is the purpose of the electrochemical gradient created by an H+ pump or Na+/H+ antiport found only in plant, fungi, and bacteria

random, independent of solute binding

in regards to a glucose uniport: is the movement random or directional; is it independent or regulated by solute binding

random, regulated by solute binding

in regards to a Na+/glucose symport": is the movement random or direction; is it independent of or regulated by solute binding

Na+/K+ pump

which of these transport proteins uses ATP: glucose uniport, Na+/glucose symport, Na+/K+ pump

selectivity filter, gate

what two components does an ion channel have

cation

what kind of ion can flow through an ion channel with a negatively charged selectivity filter

gap junction

this is a type of junction that is a hydrophiilc channel that connects between two membranes of neighboring cells 

• cannot connect directly to cytosol or ECF, only can link two cytosols

porin

this type of channel is found in the outermembrane of mitochondria and some chloroplasts

passive

what kind of transport is a channel protein only capable of

specific stimuli

what triggers an ion channel to open its gate (*remember passive transport only)

voltage, ligand, mechanical

what types of stimulus is capable of regulating an ion channel (3 kinds)

patch clamp experiment

this experiment is capable of measuring a single ion channel

• proves that channel opening is all or none

  • a gate is either opened or closed, no in-between state occurs

change

a signal is transfered via a ___ in membrane potential (action potentials)

membrane potential

this term refers to the slight and localized voltage difference across the membrane

• can be altered to relay action potentials across the body

resting membrane potential

this is the steady state membrane potential in an unstimulated cell

• restored by K+ leak channels

concentration gradients

what does a Na+/K+ pump establish in regards to membrane potential

resting membrane potential

what does a K+ leak channel establish in regards to membrane potential

• moves K+ out of cell

concentration gradient (less K+ outside of cell than inside)

since a cell has a negative charge inside of it (voltage gradient), K+ ions should not want to flow out of a K+ leak channel during repolarization, what force drives the K+ ions out then

inhibitory

what type of neurotransmitter is a Cl- channel

• when with tetanus toxin it causes unconcontrollable muscle contractions/spams

sound vibrates basilar membrane sterocilia tilt, cation channels open and alter membrane potential, hair cells pass signal to nerve fiber; mechanical gate

how do auditory hair cells pass signals to nerve fibers in the ear; what type of gate is this an example of

cell body, dendrite, axon, terminal branches, nerve terminal

what are the components of a neuron

dendrite

this component of a neuron is responsible for receiving incoming signals from the body

action potential

this is the actively speading wave of electrical excitation that travels down an axon via voltage gated ion channels

voltage gated ion channels

what does an axon use to spread action potentials

spead rapdily and not weaken, be unidirection, restore resting membrane potential (terminate)

what three features must be action potential be able to do

depolarized

the membrane is ___ during the peak of an action potential

• when the Na+ driving force aproaches 0 as the Na+ channels are open

the initial stimulus raises the plasma membrane potential to the threshold potential

what triggers the opening of Na+ ion channels during the generatio of an action potential

all or none (either reaches threshold potential or doesn’t), self limiting (refractory period occurs and resting membrane potential is restored)

what two aspects of action potentials are key when understanding their behavior in regards to Na+ and K+ channels

the Na+ channel is inactivated as K+ leak channels open, letting K+ flow into the ECF and restoring the membrane potential

what happens during the refractory period

trailing edge of refractory Na+ channels

when observing an action potential traveling down an axon, what is seen trailing behind the currently opened/depolarizing ion channel

gap junction (fastest but simple), synaptic cleft (slow, requires conversion of signal, more complex possibilities)

what are the two ways an electrical signal (action potential) can transfer to a neighboring cell

synaptic cleft

this refers literally to the space between a nerve terminal and the target cell

• requires an electrical signal within the nerve terminal to be converted in a chemical signal (neurotransmitter) that can cross this space and bind to receptors on the target cell

neurotransmitter

this is a small signaling molecule found within synaptic vesicles within nerve terminals that are released via stimulus from an action potential and then travel to target cells

an action potential arrives at a nerve terminal and triggers a voltage gated Ca2+ channel to open and bring Ca2+ into the cell, these promote vesicle fusion of synaptic vesicles which then release neurotransmitters into the ECF and cross the synaptic cleft to bind to receptor proteins on the target cell

how does an action potential trigger the conversion of its electrochemical signal into the release of a neurotransmitter from a nerve terminal

fast

are ligand gated ion channels (ex: neurotransmitter receptors) fast or slow

okay

know how acetylcholine works and how they are the second part to a nerve terminal releasing a neurotransmitter

enzymes degrade neurotransmitter, neurotransmitter is imported into cell

how is a neurotransmitter signal terminated once it has reached a target cell and elicited a response

excitatory

this type of neurotransmitter triggers depolarization and generates an action potential

• usually does this via Na+ channels

inhibitory

this type of neurotransmitter hyperpolarizes a membrane (makes it even more negative) and in doing so opposes the generation of action potentials

• makes it harder for a stimulus to reach the threshold potential

  • usuallly anion (Cl-) channels

receptor antagonist

this molecule binds to a receptor on a target protein and prevents the excitatory neurotransmitter from binding

bolutinum

this toxin blocks the release of acetylcholine from a nerve terminal and results in flaccid muscle paralysis

acetylcholinesterase

this enzyme degrades acetylcholine

• can be inhibited by many different molecules which will result in increased muscle contraction

tetanus

this type of toxin will block inhibitory neutrotransmiter signaling (Cl-) channels and results in uncontrolled muscle contractions

• makes cell hypersensitive