Water, Ions & Membranes Flashcards
What is the basic meaning of polarity in water?
Ends/sides are different
What is an ion?
Any atom or molecule that has gained or lost one or more electrons
True or False: Ions are by definition uncharged.
False
Why are ions important in biological systems?
They carry signals in the body, act as an energy store, and interact biochemically with proteins and other molecules
List two classes of biologically important ions.
- Physiologically useful ions
- Biochemically useful ions
Which ions are both physiologically and biochemically useful?
- Na+
- K+
- Cl-
- Ca2+
- Mg2+
- Trace metals (e.g., Fe3+, Zn2+)
What is the structure of biological membranes?
Lipid bilayers with hydrophilic polar heads and hydrophobic tails
What drives the formation of lipid bilayers in membranes?
The amphipathic nature of lipids
Fill in the blank: Membranes are essentially impermeable to _______.
[ions]
What is the role of pumps in membrane transport?
They establish ion gradients using energy, usually from ATP hydrolysis
What is the function of the sodium-potassium ATPase?
Generates a Na+ and K+ gradient by moving 3 Na+ out and 2 K+ in
What type of transport do pumps perform?
Primary active transport
True or False: Ion gradients can be used to power cellular processes.
True
What are cotransporters?
Proteins that facilitate secondary active transport of ions
What is an antiporter?
A transporter that moves two different ions in opposite directions
What is the maximum rate of ion transport through ion channels?
Approximately 1,000,000 ions per second
What characterizes ion channels?
Transmembrane proteins that are selectively permeable with gated openings
What are the types of gating mechanisms for ion channels?
- Mechanical
- Second messenger
- Phosphorylation
- Ligand-gated
- Voltage-gated
- Temperature-gated
Fill in the blank: Ion channels are characterized by their _______ and ion selectivity.
[gating]
What is the difference between cation and anion selectivity in ion channels?
Cation channels allow passage of positive ions (e.g., K+, Na+, Ca2+), while anion channels allow passage of negative ions (e.g., Cl-)
What is a hydration shell?
The effective size of an ion in solution, influenced by surrounding water molecules
What does the term ‘electrogenic’ refer to in the context of sodium-potassium ATPase?
It refers to the pump generating a net charge difference by moving 2+ charges in and 3+ charges out
What is hyperpolarization in the context of ion concentration?
Hyperpolarization occurs when K+ is at 5 mM and Cl- is at 150 mM.
What ion concentrations are associated with depolarization?
Depolarization occurs when Na+ is in and K+ is out.
What is the typical concentration of K+ in a mammalian cell?
100 mM K+ outside the cell.
What are ligand-gated ion channels?
Channels that open in response to binding of an activating ligand (agonist).
Which receptors are classified as ligand-gated ion channels?
- Nicotinic AChR
- GABA A
- 5HT3 receptor
- Inhibitory glycine receptor
- Ionotropic glutamate receptors.
What are the four key components of all ligand-gated channels?
- Pore
- Ligand binding site
- Coupling mechanism
- Desensitization mechanisms.
What is the structure of the nicotinic acetylcholine receptor?
A pentamer of five similar subunits.
What triggers energy release in the nicotinic acetylcholine receptor?
A molecular switch.
What is the structure of voltage-gated ion channels?
They have complex structures, such as the tetramer of four equivalent subunits in potassium channels.
How many Kv channel genes are present in the human genome?
40 Kv channel genes.
What are the two main types of voltage-gated channels?
- Calcium channels (CaV)
- Sodium channels (NaV).
What is the potential structure of a native sodium channel?
1 α: 1/2 β.
Fill in the blank: Ligand-gated channels have a _______ that lets ions through.
Pore.
True or False: Voltage-gated potassium channels are present in prokaryotes.
True.
What is the role of the coupling mechanism in ligand-gated ion channels?
It couples channel opening to ligand binding.
What is desensitization in the context of ligand-gated ion channels?
The closure of the channel if the ligand binds for too long.
What is the significance of voltage-gated channels in evolution?
Kv channels appear early in evolution.
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.
What is the basic structure of voltage-gated potassium channels?
They consist of a tetramer of four equivalent subunits.
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.
What is the primary function of the sodium pump in muscle cells?
To store energy in electrical gradients.
