Chapter 12 -> Membrane Transport Flashcards by Claire Kammerer

Rank from easiest to most difficult to get into the cell
1) Small, non polar molecules
2) Small, uncharged polar molecules
3) Larger uncharged polar molecules
4) Ions

1, 2, 3

Ions can even get in the molecule without SERIOUS help

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What are the 2 Categories of Proteins that transport molecules?
How do they transport proteins in general?

Channel Proteins and Transporter Proteins
Channel Proteins involve ion channels while Transporter Proteins involve the changing of the protein to grab the ion and move it

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Give 2 Examples of Passive Transport options

Channel Mediated and Transporter Mediated

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What occurs during active transport

Goes against the concentration gradient

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Where does the energy to actively transport molecules come from? (List 3)

1) ATP
2) A transmembrane ion gradient
3) Sunlight

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Total ion concentrations leave most cells with most (+) charges ______ of the cell

Outside

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Describe where K+, Cl-, and Na+ tend to congregate in a typical mammalian cell

K+ is higher inside the cell, Na+ and Cl- are higher outside of the cell

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What is an electrochemical gradient?

the combination of the charges on a molecule and its size/ general ability to pass through the membrane

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When moving into the cell, positive charges have an _______ time getting in due to the inside of the cell being more ______

Easier, Negative

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When moving out of the cell, positive charges have a _______ time getting out due to the outside being _____

Difficult, Positive

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What is an example of a passive transport carrier protein?
Explain what happens when sugar is plentiful on the outside of cell after meal
Explain what happens when glucose levels in blood are low

Glucose Carrier- found in liver cells, crosses membrane at least 12 times, can adapt 2 conformations
Glucose binds to external binding sites, protein switches conformation and carries glucose inside cell
Glucagon stimulates liver to produce glucose from glycogen, glucose binds to internal binding sites and is exported from cell

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How do cells obtain energy for active transport (list 3)

ATP, Transmembrane Ion Gradient, Sunlight

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What do transporter proteins do?
How to they discriminate?

Transport small molecules from one side of the membrane to the other by CHANGING SHAPE
Only allow molecules that fit into specific binding sites on the protein

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What do Channel Proteins do?
How do they discriminate?

Form Pores across the membrane through which substances pass by diffusion
Discriminate based on size and electric charge

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Small, non polar molecules like O2, Co2 etc diffuses ______ across cell membrane
Uncharged polar molecules like H2O also diffuse ______ across bilayer but ONLY if they are small enough (bigger ones have a harder time)
All charged substances such as inorganic ions have a really hard time crossing because________ (for this reason, ions must have carrier protein channels)

Rapidly
Rapidly
The charges on these solutes inhibit entry

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What is a membrane potential?

An electrical imbalance that generates a voltage difference across the membrane

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Total ion concentration can be represented with more __ charges outside of the cell

Positive

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Where are K+, Cl-, and Na+ found with respect to the cell

K+ is inside, the other two are outside

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What is the electrochemical gradient?

Concentration gradient + Voltage gradient
Determines the direction in which each solute will flow across the membrane

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How does K+ electrochemical gradient work?

It has opposing voltage gradient and concentration gradient and therefore movement is minimized
( K+ stays in the cell because the cell is negatively charged)

Taking a positively charged molecule out of the cell is ______ because…
Taking a positively charged molecule to the inside of the cell is _______ because

Difficult because the outside is positively charged
Easy because the the inside is negatively charged

What is an example of a transporter that mediates passive transport and is a carrier protein?
How does the system work?
When sugar is plentiful on outside of cell…

When glucose levels in blood are low, ______ stimulates liver cells to produce ____
Glucose then binds to internal binding sites and is exported from cell

Glucose Transporter
Determined by concentration gradient alone making it passive

Glucose binds to the external binding site, protein switches conformation and carries glucose inside
Glucagon, Glycogen

What are three examples of transmembrane pumps which carry out active transport

1) Gradient-driven pumps
2) ATP-driven pumps
3) Light-driven pumps

Na+ K+ Pump

For Na+, the Na+ tends to want to go ______ the cell, and it is also positive so it also will get pulled ______ the cell as well.
All this to say that the ______ and ______ gradients are working in the same direction
So if Na+ tends to enter the cells easily, it must continuously actively get pumped out

into, into
Voltage, Concentration

Na+ K+ Pump Concentration inside the cell is greatest so it tends to want to move ____ of the cell K+ is positive, however, so it tends to get pulled _____ the cell All this to say that the ______ and _______ gradients are working in opposite directions leading to ______ movement of K+

out, into, concentration, voltage, little

Na+ K+ Pump Animal cells use the energy of _______ ____ to pump out Na+ ATP driven Na+ pump hydrolyses ATP to ________ and uses the energy to transport Na+ out of the cell At the same time, the pump transports ______ inward This pump keep internal Na+ ____ to _____ times lower than the external concentration and keeps the K+___ to _____ times higher internally than externally

ATP Hydrolysis ADP K+ 10, 30, 10, 30

Steps of Na+ K+ Pump 1) Na+ binds to pump at sites exposed ______ the cell 2) ATP is split into _______ and __ 3) P group is transferred to pump itself 4) Phosphorylation causes pump to switch conformation releasing ____ at exterior of cell 5) ___ binds and triggers removal of _ group 6) Pump switches back conformations, discharging _ into cell

1) inside 2) ADP, P 3) 4) Na+ 5) K+, P 6) K+

Symport Definition Example of a Symporter

Both molecules move in the same direction across a membrane Na+ Glucose Symporter

Antiport Definition Example of an Antiporter

Both molecule move in opposite directions across a membrane Na+ K+ Pump

Uniport Definition Example of a uniporter

Ferries one solute across membrane and down its concentration gradient Passive Glucose Transporter

Coupled transport Definition

downhill movement of one solute down its gradient proved energy for uphill transport of a second solute

Glucose- Na+ Symport This involves _____ transport using concentration gradients It is a _____ type of transport between two molecules Essentially moves glucose from the gut even when glucose concentration in cells is higher than in the gut It is necessary to have both active and passive versions of this to balance out the sugar The cell membrane that faces the gut has ______ glucose carrier leading to high amounts of glucose being taken up from the gut The cell membrane that faces other cells have ______ glucose carriers that release glucose down its concentration gradient

Active Symport Active Passive

Channel proteins form transmembrane ________ that allow the passive movement of small water soluble molecules into or out of the cell Channel proteins have high selective pores that transport mainly _____, _____, ______, and ______

Pores K+, Cl-,Ca2+, Na+

What two properties distinguish ion channels from simple pores?

Ion selectivity and Gated (open briefly and then close again)

What is ion selectivity?

The ability of ion channels to permit some inorganic ions to pass through but not other Channels are selective for just one type of ion like Cl- or K+

What are the three types of ion channels and give a little info about each

Voltage gated channel (change in voltage difference across the membrane allow movement through channel) Ligand gated channel (binding of a ligand to the channel either inside or outside of cell allows movement through channel) Mechanically gated channel (completely switched conformation to allow shit through)

What is an example of a stress-activated (Mechanically gated) channel and tell me how it works

Auditory hair cells in ear, sound vibrations pull channels open causing ions to flow into hair cells creating an electrical signal that is transmitted from the hair cell to the auditory nerve, converting the signal to the brain

Important fact: Ion channels _____ carry out active transport Instead, ions diffuse down their __________ gradient when ion channels are open, making the concentration of the membrane ______. The flow of ions changes the voltage across the membrane, changing the _______ potential The resulting flurry of electrical activity spreads rapidly from one region to another conveying an electrical signal to nerve cells

DON'T Concentration unequal Membrane

_______ gated ion channels respond to the membrane potential by switching from a closed state to open or vice versa

Voltage

What control membrane potential?

Ion channels

Action Potentials 1) Neuron is stimulated by signal 2) Signal initiates a change in membrane potential at site to ______ signal onward 3) The change in membrane potential will passively spread along axon, but becomes _____ with increasing distance

2) transmit 3) weaker

Action potentials are mediated by ________ ______ __ ______

Voltage Gated Na+ Channels

Neuron Stimulated When neuron is stimulated, membrane potential shifts to a less negative value, causing _________ _______ __ ______ to open causing Na+ ions to enter cell, making the membrane potential even _____ negative, which causes more Voltage gated Na+ channels to open and further depolarize. Because of this, the membrane potential shifts from _______mV to about +______mV. Here, the electrochemical driving force for ____ ions is zero. Although there is no tendency for Na+ ions to move anymore, the channels are still open but have an automatic _______ _____ and therefore become inactivated.

Voltage Gated Na+ Channels, less, -60, 40, Na+, inactivating system

What ion helps to return membrane to resting state during neuron stimulation?

K+ ion

When transmitting a signal from one neuron to another, the electrical signal must be converted to a ________ signal then back to an electrical signal

chemical

When the action potential arrives, the nerve terminal _________, opening voltage gated Ca2+ channels that are located in the ____ _______ nerve terminal. From there, ____ rushes into nerve terminal, triggering fusion of synaptic vesicles with presynaptic membrane and releasing _________ into synaptic cleft. The released neurotransmitter diffuses across the ______ cleft, binds to receptors causing a change in membrane potential, triggering cell to produce action potential only if it is _____ enough of a signal.

Depolarizes, presynaptic, Ca2+, Neurotransmitters, Synaptic, Large

How are neurotransmitters removed?

Destroyed by enzymes or taken up by nerve terminals

Neurons receive both _______ and ________ inputs

Excitatory, Inhibitory

What are the main excitatory receptors?

Acetylcholine and Glutamate