1. Cell Transport Flashcards
Describe the structure of the cell membrane.
Final Answer: Composed of; phospholipids that consists of hydrophilic heads and hydrophobic tails (which their tails facing each other and their heads being at polar opposite ends), proteins that are used as receptors and channels (to name a few), and cholesterol to maintain some rigidity whilst still remaining somewhat fluid.
Forms a complete boundary
Composed of phospholipids, proteins and cholesterol
It is a fluid and flexible structure - Not rigid
What are the functions of the cell membrane?
Barrier between compartments
Provides an area for contact
Provides receptors for chemicals
Mediates the entrance and exit of materials
Has the property of SELECTIVE PERMEABILITY
Highly impermeable barrier
Permeability is a function of several factors:
Solubility in lipids
In breif, how do lipophilic substances cross the cell membrane?
Passive diffusion (Obey’s Fick’s Law of Diffusion)
They are soluble in lipids, so they can pass straight through without a carrier protein
Small substances such as respiratory gas will move much quicker than larger substances (Fick’s Law)
Describe those factors affecting Fick’s law of diffusion.
Fick’s Law of Diffusion = (Surface area x concentration gradient x membrane permeability)/ Membrane thickness (or diffusion distance)
Where membrane permeability = lipid solubility/size of the molecule
Also note that if and of the numerator values in the above equation = 0 then by definition the final value must be 0
Fick’s Law can also be affected by things such as temperature, pressure, etc.
Ficks law basically states that the diffusion rate increases when surface area, the concentration gradient, or the membrane permeability increase.
O2 is smaller than CO2 but CO2 is more soluble (quicker movement)
What are the differences between volatage-gated and ligand-gated channels?
Voltage-Gated Channels (pictured below): - Open in response to a change in mpot (VOLTAGE; I.e. when the cell gets depolarized) - Gated channels have self-closing mechanisms that rapidly reclose, even if the stimulus that opened them is still operating (absolute refractory period)
Ligand-Gated channels: - Open in response to an extracellular ligand (A chemical signal) binding to a specific cell surface receptor - E.g. Acetylcholine
The sodium potassium pump is said to be “electrogenic”, What does this mean and what does it relate to?
That it makes a small contribution to the membrane potential. Most of the membrane potential is generated by the Sodium and Potassium gradients maintained by the sodium potassium pump, combined with the greater permeability of the plasma membrane to potassium. Basically, for every transport cycle (an efflux of 3 x sodium and influx of 2 x potassium) it leads to the movement of one net positive charge out of the cell. (the electrogenic part of it all)
Important feature making it electrogenic is the imbalance of ions being pulled in vs being pushed out helping to creating a membrane potential.
What is the difference between primary and secondary active transport?
Primary: Energy derived DIRECTLY from the breakdown of ATP
Secondary: Energy is derived INDIRECTLY from energy that has been stored in the form of ionic concentration differences between the two sides of a membrane.
