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Excitable Cells > Water, Ions & Membranes > Flashcards

Water, Ions & Membranes Flashcards

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1
Q

What is the basic meaning of polarity in water?

A

Ends/sides are different

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2
Q

What is an ion?

A

Any atom or molecule that has gained or lost one or more electrons

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3
Q

True or False: Ions are by definition uncharged.

A

False

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4
Q

Why are ions important in biological systems?

A

They carry signals in the body, act as an energy store, and interact biochemically with proteins and other molecules

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5
Q

List two classes of biologically important ions.

A
  • Physiologically useful ions - charge carries or exert osmotic pressure
  • Biochemically useful ions - involved in enzymatic reactions or form parts of proteins
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6
Q

Which ions are both physiologically and biochemically useful?

A
  • Na+
  • K+
  • Cl-
  • Ca2+
  • Mg2+
  • Trace metals (e.g., Fe3+, Zn2+)
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7
Q

What is the structure of biological membranes?

A

Lipid bilayers with hydrophilic polar heads and hydrophobic tails

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8
Q

What drives the formation of lipid bilayers in membranes?

A

The amphipathic nature of lipids

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9
Q

Fill in the blank: Membranes are essentially impermeable to _______.

A

[ions]

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10
Q

What is the role of pumps in membrane transport?

A

They establish ion gradients using energy, usually from ATP hydrolysis

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11
Q

What is the function of the sodium-potassium ATPase?

A

Generates a Na+ and K+ gradient by moving 3 Na+ out and 2 K+ in

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12
Q

What type of transport do pumps perform?

A

Primary active transport

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13
Q

True or False: Ion gradients can be used to power cellular processes.

A

True

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14
Q

What are cotransporters?

A

Proteins that facilitate secondary active transport of ions

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15
Q

What is an antiporter?

A

A transporter that moves two different ions in opposite directions

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16
Q

What is the maximum rate of ion transport through ion channels?

A

Approximately 1,000,000 ions per second

Passive transport down the gradient

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17
Q

What characterizes ion channels?

A

Transmembrane proteins that are selectively permeable with gated openings

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18
Q

What are the types of gating mechanisms for ion channels?

A
  • Mechanical
  • Second messenger
  • Phosphorylation
  • Ligand-gated
  • Voltage-gated
  • Temperature-gated
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19
Q

Fill in the blank: Ion channels are characterized by their _______ and ion selectivity.

A

[gating]

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20
Q

What is the difference between cation and anion selectivity in ion channels?

A

Cation channels allow passage of positive ions (e.g., K+, Na+, Ca2+), while anion channels allow passage of negative ions (e.g., Cl-)

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21
Q

What is a hydration shell?

A

The effective size of an ion in solution, influenced by surrounding water molecules

Smaller ions have a bigger hydration shell as they have a higher charge density

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22
Q

What does the term ‘electrogenic’ refer to in the context of sodium-potassium ATPase?

Study These Flashcards
A

It refers to the pump generating a net charge difference by moving 2+ charges in and 3+ charges out

23
Q

What is hyperpolarization in the context of ion concentration?

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A

Hyperpolarization occurs when K+ is at 5 mM and Cl- is at 150 mM.

24
Q

What ion concentrations are associated with depolarization?

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A

Depolarization occurs when Na+ is in and K+ is out.

25
What is the typical concentration of K+ in a mammalian cell?
100 mM K+ outside the cell.
26
What are ligand-gated ion channels?
Channels that open in response to binding of an activating ligand (agonist).
27
Which receptors are classified as ligand-gated ion channels?
* Nicotinic AChR * GABA A * 5HT3 receptor * Inhibitory glycine receptor These are Cys loop receptors * Ionotropic glutamate receptors - located in CNS and are all cation channels
28
What are the four key components of all ligand-gated channels?
* Pore * Ligand binding site * Coupling mechanism * Desensitization mechanisms.
29
What is the structure of the nicotinic acetylcholine receptor?
A pentamer of five similar subunits.
30
What triggers energy release in the nicotinic acetylcholine receptor?
A molecular switch.
31
What is the structure of voltage-gated ion channels?
They have complex structures, such as the tetramer of four equivalent subunits in potassium channels.
32
How many Kv channel genes are present in the human genome?
40 Kv channel genes.
33
What are the main types of voltage-gated ion channels?
* Calcium channels (CaV) * Sodium channels (NaV) * Potassium channels (KV)
34
What is the potential structure of a native sodium channel?
1 α: 1/2 β.
35
Fill in the blank: Ligand-gated channels have a _______ that lets ions through.
Pore.
36
True or False: Voltage-gated potassium channels are present in prokaryotes.
True.
37
What is the role of the coupling mechanism in ligand-gated ion channels?
It couples channel opening to ligand binding.
38
What is desensitization in the context of ligand-gated ion channels?
The closure of the channel if the ligand binds for too long.
39
What is the significance of voltage-gated channels in evolution?
Kv channels appear early in evolution.
40
What subunits are involved in calcium channels?
* α CaV 1.1-1.4 * α CaV 2.1-2.3 * α CaV 3.1-3.3 * 4β * α2δ * γ.
41
What is the basic structure of voltage-gated potassium channels?
They consist of a tetramer of four equivalent subunits. 6 transmembrane domains - each one is an alpha helix 4th one is the voltage sensor The little dip forms the lining of the channel’s pore
42
What happens to the extracellular domain of sodium channel subunits?
A disulfide bond is formed and the extracellular domain is cleaved to yield two linked peptides.
43
What is the primary function of the sodium pump in muscle cells?
To store energy in electrical gradients.
44
Effects of hydration shells
- affects mobility in solution - affects interactions with proteins (some proteins remove the hydration shell before interacting)
45
Ion concentrations in cells
*Na+* Inside = 150 mM Outside = 15 mM Ratio = 10:1 *K+* Inside = 5 mM Outside = 100 mM Ratio = 1:20 *Ca2+* Inside = 2 mM Outside = 0.0002 mM Ratio = 10000:1 *Cl-* Inside = 150 mM Outside = 13 mM Ratio = 11.5:1
46
Basic features of pumps
- live in membranes - move ions against the gradient - couple to ATP - fairly slow - nearly always move cations (positively charged ions) - e.g. Calcium pump
47
Importance of ion gradients
- source of energy - can be used to transmit information (e.g. signalling via ion channels) - can be used to power cellular processes (e.g. secondary active transport)
48
Example of a co-transporter
Secondary active transport Sodium-calcium exchanger = an antiporter
49
What is a selectivity filter?
Part that selects which ions will pass Has a ring of charge around it = charged amino acids that will have the opposite charge to the type of ion the channel is selective to
50
Structure of CaV and NaV channels
Repeating pseudosubunit (each segment) Alpha subunit = pore forming subunit - consists of 4 copies of voltage-gated K+ channels-like structures
51
Subunits of CaV channel
α CaV 1.1-1.4 α CaV 2.1-2.3 α CaV 3.1-3.3 accessory subunits 4β α2δ 8gamma
52
Subunits of NaV channel
α NaV 1.1-1.9 Accessory subunits 4β
53
What are accessory subunits?
Modify the alpha subunit
54
Importance of α2δ subunits
Important in drug targeting = site of action in drugs used to treat epilepsy, anxiety & pain 1. Gene produces a single polypeptide which is cut into 2 pieces 2. Disulfide bond formed in extracellular domain 3. Extracellular domain cleaves to yield 2 linked peptides

Excitable Cells (22 decks)

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