Chapter 13 Flashcards by Kian Derck

What type of molecules can diffuse on their own across membranes?

Non-polar molecules

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What type of transport do proteins provide for polar compounds and ions?

Facilitated diffusion

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What is the result of the uneven distribution of cations in cells?

Cells are polarized (ΔV across the plasma membrane)

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What are the three mechanisms that move polar compounds across membranes?

Pumps * Carriers * Channels

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What are the two types of pumps that use ATP to move ions against the gradient?

P-type pumps * ABC transporters

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What is the primary active transport mechanism?

Pumps use ATP to move ions against the gradient

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How do carriers facilitate secondary active transport?

By using the gradient of one ion to drive the transport of another molecule or ion

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What type of transport do channels facilitate?

Passive transport

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What is ΔG for uncharged solutes based on?

Concentration gradient

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What additional factor affects ΔG for charged solutes?

Electrical potential

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What is the formula for calculating ΔG?

ΔG = ±RT ln(C2/C1) ± ZFΔV

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What is the ΔG for inward diffusion of potassium in a specific cell condition?

1.6 kJ/mol

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What type of transporters are ABC transporters?

ATP-driven ion pumps

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What is the role of ATP in the function of ABC transporters?

ATP binding brings ABC together to interact

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Inside cell, K+ is ______, Na+ is _______

high, low

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What is the sodium/potassium ATPase’s action in the cell?

Pumps three Na+ out and two K+ in

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What happens after K+ binds to the phosphorylated pump?

Dephosphorylation of the pump occurs

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Dephosphorylated pump has ______ affinity for K+ and ______ affinity for Na+

low, high

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What role does the sarcoplasmic reticulum Ca-ATPase (SERCA) play?

Regulates Ca+2 levels in muscle cells

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Describe the steps of SERCA

Steps of the SERCA cycle:

E1 state: The pump binds two calcium ions from the cytosol and one ATP molecule.
E1-2Ca2+ complex: The pump’s structure changes to facilitate the coupling of ATP hydrolysis and calcium transport.
E1~P-ADP-2Ca2+ state: The pump becomes phosphorylated after ATP hydrolysis.
E2P-2Ca2+ state: The pump’s structure changes to a low-calcium affinity state.
E2-P state: The pump releases two calcium ions into the SR lumen and binds two protons from the lumen.
Dephosphorylation and dehydrogenation: The pump returns to the E1 state, which can then start another transport cycle.

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What is a symporter?

A symporter is a type of membrane protein that transports two different molecules across a cell membrane in the same direction

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What is an antiporter?

An antiporter is a protein that moves two or more molecules across a cell membrane in opposite directions

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What is a uniporter?

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A uniporter is a type of membrane transport protein that facilitates the movement of a single type of molecule across a cell membrane

What is the main function of the lactose permease?

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The primary function of lactose permease is to transport lactose, a sugar found in milk, across the cell membrane into the cell by utilizing a proton gradient as the driving force for active transport

What is the main function of the sodium-calcium exchanger?

Removes Ca+2 from the heart quickly to stop contraction

What are voltage-gated channels?

Voltage-gated channels are proteins that open and close in response to changes in a cell's electrical potential

What are ligand-gated channels?

Ligand-gated ion channels (LGICs) are proteins in cell membranes that open and close in response to chemical messengers

What are tension-gated channels?

Tension-gated channels, also known as mechanosensitive channels (MSCs) or stretch-gated ion channels, are membrane proteins that open and close in response to mechanical stress

What is the effect of Digitalis on heart function?

Inhibits Na/K ATPase, increasing intracellular Na+ and Ca+2

What technique allows measurements of ion conductance through a cell membrane?

Patch clamp

What is the role of thermoreceptors in sensory neurons?

Open to let Ca+2 in, starting local depolarization

What initiates the propagation of an action potential in neurons?

Opening of voltage-gated sodium channels

How are neurotransmitters involved in neuron signaling?

Bind to K+/Na+ channels in the interneuron and motor neuron

What is the role of voltage-gated K+ channels in neuron resetting?

Allows K+ to flow out, bringing the charge back to normal

What Nobel Prize was awarded for discoveries related to channel structures?

Nobel Prize in Physiology or Medicine 2003 to Roderick MacKinnon

Channel structures reveals basis of...

ion specificity

What is the size of the selectivity filter in potassium channels?

3 Å

What is the reason Na+ cannot pass through the selectivity filter?

Too small and remains partially hydrated

How do carbonyls in the selectivity filter assist in K+ transport?

Re-solvate K+ ions after desolvation

What happens to K+ ions during rapid transport through channels?

Move in single file

How many K+ bindings sites are in the selectivity filter?

What is the cost of dehydration for Na+?

The cost of dehydration for Na+ is not paid in full ## Footnote This means Na+ remains partially hydrated and is too big to pass.

Describe the model of rapid K+ transport.

K+ ions move in a single file through a narrow channel with four K+ binding sites in the selectivity filter ## Footnote Electrostatic repulsion moves ions to the next site.

What do voltage-gated channels react to?

Voltage-gated channels react to changes in membrane potentials ## Footnote They are involved in action potentials in neurons.

What forms the 'Paddles' in voltage-gated channels?

Segments S1-S4 form the 'Paddles' ## Footnote Segment S4 is an α-helix with basic residues.

What occurs during depolarization in cells?

During depolarization, the interior of the cell becomes more positive ## Footnote This causes S4 to move to a parallel position to minimize electrostatic repulsion.

What happens to ion channels during inactivation?

Channels are quickly inactivated by blocking the pore even when open ## Footnote This resets the system.

What is the role of the first 20 amino acids in ion channels?

The first 20 amino acids form a plug (the ball) attached by a flexible linker (the chain) ## Footnote The ball acts like a big cation.

What triggers the release of acetylcholine in neurons?

Depolarization of a neuron triggers the release of acetylcholine ## Footnote Two acetylcholine molecules bind and activate non-specific ligand-gated channels.

What is the equilibrium potential?

Equilibrium potential is reached when the concentration gradient force is balanced by the repulsion of similar charges ## Footnote For most cells, V_eq for Na+ is +62 mV and for K+ is -98 mV.

What happens as the membrane potential approaches -40 mV?

As the membrane potential approaches -40 mV, the Na-channels open ## Footnote This causes [Na]i to increase rapidly.

What is Long QT syndrome?

Long QT syndrome is a heart condition characterized by delayed repolarization ## Footnote It can cause fainting spells, arrhythmia, and sudden deaths.

What is the effect of lidocaine on ion channels?

Lidocaine blocks both K- and Na-channels ## Footnote This affects the action potential of neurons.

What are 'Funny' channels?

'Funny' channels are hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels ## Footnote They regulate cardiac pacemaker current, I(f), and heart rate.

What is the role of connexons in gap junctions?

Connexons connect cytoplasm to cytoplasm and can stay open for minutes ## Footnote They are made of 12 connexins and can be closed by high [H+] and [Ca+2].

How is water moved quickly through aquaporins?

Water moves through aquaporins in single file, lined with hydrophilic residues ## Footnote Positive charge traps prevent disruption of proton gradients.

Chapter 13 Flashcards

(56 cards)