Biochem Unit 1 Lecture 5 Functions of Channels and Transporters

The --- is the formula for calculating the membrane potential based on internal and exterior concentrations of ion distributed differentially across a bilayer

Nernst equation

In most animal cells, the Na+/K+-ATPase is responsible for about --- of the cell's energy expenditure.

For neurons, the Na+/K+-ATPase can be responsible for up to --- of the cell's energy expenditure.

1/5; 2/3

In most --- cells, the Na+/K+-ATPase is responsible for about 1/5 of the cell's energy expenditure.

For ---, the Na+/K+-ATPase can be responsible for up to 2/3 of the cell's energy expenditure.

animal; neurons

A --- is a structure that permits a neuron (nerve cell) to pass an electrical or chemical signal to another cell.

synapse

--- is the transport of materials from inside the cell to the outside.

Exocytosis

--- is the transport of materials from outside the cell to inside the cell.

Endocytosis

--- channels are a specialized type of channel in the cell membrane that are found in all animal cells, also in plant cells and microorganisms.

Ion

Ion channels show --- and are NOT ---.

ion selectivity; continuously open

Ion channels (especially the --- and --- ones) are very important in establishing membrane potential.

potassium and sodium

Ion channels (especially the potassium and sodium ones) are very important in establishing ---

membrane potential

Ion Channels are selective and fluctuate between open and closed states.

What are the 3 types of "gates?"

voltage-gated

ligand-gated

mechanically-gated

Ion Channels

--- channels are typically located in plasma membrane of most animal cells and are responsible for maintenance of resting membrane potential.

K+ Leak channels

Ion Channels

K+ Leak channels are typically located in plasma membrane of most --- cells and are responsible for ---

animal; maintenance of resting membrane potential.

Ion Channels

--- channels are typically located in plasma membrane of nerve cells and are responsible for generation of action potentials.

Voltage-gated Na+ channels

Ion Channels

Voltage-gated Na+ channels are typically located in plasma membrane of --- and are responsible for ---

nerve cell axons; generation of action potentials.

Ion Channels

--- channels are typically located in plasma membrane of nerve cell axons; cells and are responsible for return of membrane to resting potential after initiation of an action potential.

Voltage-gated K+ channels;

Ion Channels

Voltage-gated K+ channels are typically located in plasma membrane of ---; cells and are responsible for ---.

nerve cell axons; return of membrane to resting potential after initiation of an action potential.

Ion Channels

--- channels are typically located in auditory hair cell in inner ear and are responsible for detection of sound vibrations.

Stress-activated cation

Ion Channels

Stress-activated cation channels are typically located in --- and are responsible for ---.

auditory hair cell in inner ear; detection of sound vibrations.

A --- can result from active pumping or passive ion diffusion through certain channels.

membrane potential

A membrane potential can result from --- or --- through certain channels.

active pumping; passive ion diffusion

Normally the Na + -K+ pump helps maintain --- across the cell membrane, keeping the intracellular Na+ concentration low

osmotic balance

Normally the Na + -K+ pump helps maintain osmotic balance across the cell membrane, keeping the intracellular Na+ concentration ---.

low

The --- channel is one of the ion channels important in establishing a membrane potential

potassium leak

Because intracellular --- concentrations are low (due to being pumped out!), other positively charged ions have to be plentiful to balance the negatively charged ions

Na+

Balancing role mainly performed by K+ ions, which are pumped into the cell by the Na + -K+ pump, but can also move freely in or out through --- Channels

K+ Leak

The Na+ -K+ ATPase

The specific inhibitor --- and K + compete for the same site on the extracellular side of the pump.

ouabain

The Na+ -K+ ATPase

The specific inhibitor ouabain and ---compete for the same site on the extracellular side of the pump.

K +

The Na+ -K+ ATPase

The specific inhibitor ouabain and K + compete for the same site on the --- side of the pump.

extracellular

--- can be used in low doses to treat hypotension. It can also cause cardiac arrest in high doses due to too much Na+ in the cell.

Ouabain

For a typical cell, 1 microcoulomb of charge (6 × 10 12 monovalentions) per square centimeter of membrane, transferred from one side of the membrane to the other, changes the membrane potential by roughly ---.

1 V

Resting Membrane Potential

When the potassium leak channel opens, the high --- concentration of K + will cause it to flow out of the cell.

intracellular

Resting Membrane Potential

When the potassium leak channel opens, the high intracellular concentration of K + will cause it to flow out of the cell.

As K+ moves out this leaves behind an unbalanced --- charge creating a membrane potential.

negative

The resting membrane potential for most neurons it is about ---

-70mV

An action potential can only travel away from the site of depolarization, because --- prevents the depolarization from spreading backward.

Na+ channel inactivation

On myelinated axons, clusters of Na + channels can be --- apart from each other

millimeters

When an action potential reaches the nerve terminal in a presynaptic cell, it stimulates the terminal to release its ---.

neurotransmitter

When an action potential reaches the nerve terminal in a --- cell, it stimulates the terminal to release its neurotransmitter.

presynaptic

The neurotransmitter molecules are contained in --- and are released to the cell exterior when the --- fuse with the plasma membrane of the nerve terminal.

synaptic vesicles; vesicles

The released neurotransmitter binds to and opens the transmitter-gated ion channels concentrated in the --- of the postsynaptic target cell at the synapse.

plasma membrane

Hearing uses --- channels

mechanically gated

Hearing uses mechanically gated channels.

In resting state, the bundle is --- and the channel is closed.

When the --- moves, the bundle is ---, causing the linking filament to tug open the channel and allow entry of positively charged ions.

not tilted; cilia; tilted

Hearing uses mechanically gated channels.

In resting state, the bundle is not tilted and the channel is closed.

When the cilia moves, the bundle is tilted, causing the --- to tug open the channel and allow entry of ---.

linking filament; positively charged ions

Lidocaine and novocaine anesthetics block --- ion channels

sodium

--- can be cause by mutations in potassium channel genes (KCNQ1, KCNA5, KCNE1, KCNE2, KCNJ2)

Familial atrial fibrillation

--- can be caused by mutations in KCNA1, potassium channel

Episodic ataxia

--- is caused by ventricular arrhythmia caused by mutations in voltage gated sodium channel (SCNA5)

Brugada syndrome

--- is caused by mutations in CFTR gene which is a chloride channel

Cystic fibrosis

Cystic fibrosis is caused by mutations in CFTR gene which is a --- channel

chloride

--- is caused by autoantibodies that block the action of acetylcholine receptors and lead to muscle weakness.

Myasthenia gravis

Tetrodotoxin blocks --- channels

sodium

--- are a superfamily of integral membrane proteins responsible for ATP-powered translocation of molecules such as sugars, amino acids, lipids, toxins, drugs, antibiotics, etc.

ATP-Binding Cassette (ABC) Transporters

ATP-Binding Cassette (ABC)Transporters are a superfamily of --- responsible for ATP-powered translocation of molecules such as sugars, amino acids, lipids, toxins, drugs, antibiotics, etc.

integral membrane proteins

ATP-Binding Cassette (ABC)Transporters are a superfamily of integral membrane proteins responsible for --- translocation of molecules such as sugars, amino acids, lipids, toxins, drugs, antibiotics, etc.

ATP-powered

--- have 4 domains: 2 hydrophobic and 2 ATP-binding.

ATP-Binding Cassette (ABC) Transporters

ATP-Binding Cassette (ABC) Transporters have 4 domains: 2 --- and 2 ---

hydrophobic; ATP-binding.

ATP-Binding Cassette (ABC) Transporters

Interface between ATP-binding domains is in --- state when ATP is bound and an -- state when ATP is hydrolyzed

closed; open

ATP-Binding Cassette (ABC) Transporters

Some ABC transporters are the cause of drug resistance which develops in many ---, or which frequently develops in ---.

human cancers; malaria parasite

ATP-Binding Cassette (ABC) Transporters

Mutation in ABC chloride carrier is cause of ---.

cystic fibrosis

ATP-Binding Cassette (ABC) Transporters

Mutation in ABC --- carrier is cause of cystic fibrosis.

chloride

The deficiency of Glut1 primarily affects the ---.

brain

The 3 possible fates for transmembrane receptor proteins following endocytosis are ---, ---, and ---.

recycling, degradation, and transcytosis

Transferrin Cycle

After ---, iron is released from the receptor-ferrotransferrin complex in the --- late endosome compartment.

endocytosis; acidic

Transferrin Cycle

After endocytosis, iron is released from the receptor-ferrotransferrin complex in the acidic late endosome compartment.

The --- protein remains bound to its receptor at this pH, and they recycle to the cell surface together where the --- pH of the exterior medium causes release of the iron-free ---.

apotransferrin; neutral; apotransferrin