Week 2 ELM 4: Water, Ions, and Membranes

Flashcards covering water structure, ions, membrane properties, and ion channels, including their structure, function, and regulation.

Polarity

Basic meaning: ends/sides are different. Examples include Epithelial cell (structural), Magnet (magnetic), and Membrane (electrical).

Ion

An atom or molecule that has gained or lost one or more electrons, resulting in a charge.

Importance of Ions

Carry signals in the body (action potentials), act as an energy store (secondary active transport), and interact biochemically with proteins and other molecules.

Physiologically Useful Ions

Na+, K+, Cl-, Ca2+ (Never Kiss Clammy Cats)

Biochemically Useful Ions

Mg2+, Trace metals (e.g., Fe3+, Zn2+), and Ca2+ (MaGgots Fear Zinc Cats)

Membranes

Hydrophilic polar head and Hydrophobic tail. All biological membranes are lipid bilayers. Essentially impermeable to ions

Membrane Proteins Function

Allow cells to establish ion gradients and use them.

Pumps Basic Features

Proteins that live in membranes, move ions "uphill", couple to ATP, are fairly slow, and nearly always move cations. PRIMARY ACTIVE TRANSPORT

Primary Active Transport - Pumps

Sodium-potassium ATPase (sodium pump). Generates a Na+ and K+ gradient, electrogenic (2 K+ in, 3 Na+ out). Cells use 25% of ATP to keep this pump going

Ion Gradients as Batteries

Gradients represent a source of energy. Can be used to transmit information (e.g., signaling via ion channels) or to power cellular processes (e.g., transport of other ions via cotransporter —> Secondary active transport).

Cotransporters

Transports 2 or more molecules simultaneously. Secondary active transport. Sodium-calcium exchanger: an antiporter (opposite directions)

Ion channel Maximum rate

1000000/s, Passive transport

Basic properties of ion channels

Transmembrane proteins, selectively permeable, opening controlled somehow, diverse.

Gating types

The regulated opening and closing of ion channels. Mechanical, Second messenger, Phosphorylation, Leak, Ligand-gated, Voltage-gated, Proton-gated, G protein-gated, Temperature-gated.

Naming of ion channels

Classified by Gating and Ion selectivity. Eg Voltage-gated potassium channel

Ligand-gated ion channels

Open in response to binding of an activating ligand (agonist).

All ligand gated channels have:

Pore, Ligand binding site, Coupling mechanism, Desensitization mechanisms.

Voltage-gated ion channels types

Calcium channels (Cav), Sodium channels (Nav), Potassium channels (Kv)

Hydration shell

Affects mobility in solution, is the effective “size” of an ion, and it affects interactions with proteins

Carrier/ transport protein

Maximum rate - 10000/s, can be active or passive. Example is Na+/K+ ATPase

Characterization of the nAChR

Electric organ is similar to muscle, muscle stores energy in electrical gradients (sodium pump), energy release triggered by “molecular switch” (nicotinic acetylcholine receptor)