Term
| Do free ions exist in solution and why? |
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Definition
| No, electrostatic forces are very large and their large charge is screened by water molecules (waters of hydration). |
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Term
| Small charged ions such as Na+, K+, Ca2+, & Cl- do not enter the lipid bilayer because... |
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Definition
| the energy requirements are too great (dielectric constant of aqueous solution >> dielectric constant of lipids) |
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Term
| What is larger the hydrated radius or ionic/atomic radius? |
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Definition
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Term
| What are pore-forming membrane proteins that facilitate the movement of small ions across the membrane? |
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Definition
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Term
| The ion channel pore is a ___________ channel which allows the passage of _________ ions. |
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Definition
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Term
| Ions flow through the pore by... |
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Definition
| diffusion, down their concentration gradient |
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Term
| The movement of ions through an ion channel generates... |
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Definition
| an electrical potential difference, ie a voltage, across the membrane |
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Term
| Most cells have a basal PD across the membrane, this is called? |
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Definition
| RMP (resting membrane potential) |
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Term
| Many cells also use ion channels and ion currents to generate rapid changes in the membrane potential. These changes are the basis of... |
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Definition
| electrical signaling in the body |
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Term
| Ion channel PORES select the permeant ion by? |
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Definition
-size constraints
-charged amino acids lining the pore |
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Term
| What is the term for the permeant ion is determined mainly by the diameter of the narrowest part of the pore and by electrostatic interactions amino acids which line the pore? |
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Definition
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Term
| Ion channel proteins share common structural features... |
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Definition
| -Most are formed from 4-6 homologous protein domains, which assemble like a rosette to form a protein with a central pore (inset) |
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Term
| -The channel can be made up of... |
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Definition
1) identical, distinct subunits
2) distinct subunits that are homologous but not identical
3) repetitive subunit-like domains with a single polypeptide |
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Term
| Each subunit in a voltage-gated channel consists of? |
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Definition
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Term
| Tetramer oligomeric complexes are good for what type of channel? |
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Definition
| Voltage-gated Na+, Ca2+ and K+ channels; Ca-release channel |
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Term
| Pentamer oligomeric complexes are good for what type of channel? |
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Definition
| Nicotinic ACh receptor channel |
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Term
| Hexamer oligomeric complexes are good for what type of channel? |
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Definition
| A half-gap junction channel, made up of six connexins |
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Term
| Note that each subunit is composed of alternating... |
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Definition
| hydrophobic and hydrophilic strands. The hydrophobic strands consist of 22-23 amino acids arranged in an alpha helix. The more hydrophilic strands connect the alpha helices to form intracellular and extracellular linker domains. |
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Term
| Note that each subunit is composed of alternating... |
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Definition
| hydrophobic and hydrophilic strands. The hydrophobic strands consist of 22-23 amino acids arranged in an alpha helix. The more hydrophilic strands connect the alpha helices to form intracellular and extracellular linker domains. |
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Term
| An ion channel protein can exist in more than one conformation. They are... |
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Definition
Closed state: pore is closed
Open state: pore is open
Inactive state(desensitized state): pore is open but occluded by another region of the protein |
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Term
| Are all channels always closed? |
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Definition
No
Some channels are open when the cell is under basal conditions, e.g. resting K+ channel
Some channels are CLOSED most of the time and OPEN only briefly, when the cell is active, e.g. nerve Na channel
Switching between states is FAST, typically < 1/1000 of a second |
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Term
| Two common mechanisms of ion channel gating are... |
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Definition
| ligand binding and membrane depolarization |
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Term
| Membrane potential refers to a... |
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Definition
| voltage across the cell membrane |
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Term
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Definition
| that charges are separated, there is an energy difference |
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Term
| There exists an energy difference of about ____ volt across every cell membrane in your body. |
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Definition
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Term
| Ion channel proteins are ubiquitous. Typically, they control physiological functions where... |
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Definition
| speed and synchronization are important |
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Term
| Why use electrical signals? |
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Definition
-Control Physiological functions
-are used where Speed and Signal Propagation are needed |
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Term
| Most cells maintain an electrical potential difference across the plasma membrane at rest. This potential difference is called |
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Definition
| Resting Membrane Potential (RMP) |
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Term
| During cellular activity, the membrane potential changes transiently, then returns to the resting level. These brief changes in membrane potential, called... |
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Definition
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Term
| Action potentials control important cellular functions including... |
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Definition
-communication in the brain and nervous systems
-sensory transduction
-muscle contraction
-hormone secretion |
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Term
| What is an extremely rapid method of inter- and intra-cellular signaling? |
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Definition
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Term
| Two membrane proteins, at a minimum, are needed to generate a resting membrane potential. They are... |
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Definition
1) resting K channel
2) Na, K ATPase (NA/K pump) |
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Term
| The major charged ions which participate in membrane potentials and electrical signaling are: |
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Definition
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Term
| What is normally found outside the cell? |
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Definition
Cations: Na+
Anions: Cl- & HCO3- |
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Term
| What is normally found inside the cell? |
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Definition
Cation: K+
Anion: Cl- & HCO3-, PO4- and negatively charged proteins |
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Term
| What balances the cations? |
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Definition
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Term
| The extracellular and intracellular solutions (ECF and ICF) are ... |
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Definition
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Term
| To generate a potential difference across a cell membrane, need: |
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Definition
- UNEQUAL CONCENTRATIONS of a PERMEANT ion. This is generated by the Na,K-ATPase.
-a PORE or pathway for the permeant ion to cross the membrane. In most cells, this is provided by a K+ channel which is OPEN at rest. |
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Term
| What is more concentrated inside the cell as a result of the Na,K pump? |
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Definition
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Term
| The resting membrane has a K channel which is _____ at rest, providing a K+-selective diffusion pathway |
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Definition
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Term
| The outward movement of K+ immediately generates an _________ _______ difference tending to pull the K+ ion back (inward gradient). |
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Definition
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Term
| How far will K+ diffusion proceed? |
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Definition
| K+ ions diffuse outward until the electrical gradient which builds up as a result of the charge separation is equal to the diffusion gradient. |
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Term
| There are TWO gradients acting on a K+ ion: they are? |
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Definition
-CONCENTRATION GRADIENT (also called chemical gradient, diffusion gradient) tends to pull K+ OUT of the cell
-ELECTRICAL GRADIENT attracts the K+ ion back IN |
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Term
| The RMP is most sensitive to changes in plasma ____. |
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Definition
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Term
| Electrical Potentials across Cell Membranes Are Generated by the Transfer of (Very Few/ Many/ Hundreds) Ions |
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Definition
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Term
| Heart muscle cells have a Resting membrane permeability to which ions? |
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Definition
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Term
| Skeletal muscles cells have a Resting membrane permeability to which ions? |
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Definition
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Term
| What is the source of the resting permeability to Na+ ions? |
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Definition
| ? Typically it arises from a resting K channel which does not discriminate perfectly for K+ over Na+ ions (i.e. some Na+ ions get in the pore and, once there, move down their electrochemical gradient). It may also arise from a Na channel subtype which opens at more negative membrane potentials, such as the pacemaker channel in the heart sinoatrial node. |
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Term
| Cl- permeability is due to the presence of... |
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Definition
| anion-selective Cl- channels |
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Term
| Cl- ions distribute _________ across the cell membrane. They (are/are not) actively concentrated by a pump. |
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Definition
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Term
| Consequently, the Cl- concentrations _______ inversely as the K+ concentrations. i.e. as the pump concentrates K+ inside the cell, Cl- ions follow to maintain electroneutrality, |
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Definition
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