deck_501302 Flashcards
What is required to move a small hydrophillic molecule or ion across a semi permeable membrane?
A large free energy change
What does the difficulty involved in movement of small hydrophillic molecules across a membrane mean?
The transverse movement of hydrophilic molecules across a membrane is a rare event
How is the movement of ions and hydrophillic molecules mediated and regulated?
By specific membrane transport systems.
Give six roles of transport processes in cell membrane
PIE Can’t Make Gravy pH, Ionic, Extrusion, Cell volume, metabolic fuels + building blocks, Generation of ionic gradients-Maintenance of pH-Maintenance of ionic composition-Regulation of cell volume-Concentration of metabolic fuels and building blocks-Extrusion of waste products of metabolism and toxic substances-Generation of ionic gradients necessary for the electrical excitability of nerve and muscle
How do hydrophobic molecules move through cell membrane?
easily diffuse through the lipid bilayer – including O2 and CO2
How do small, uncharged polar molecules move through membrane?
Diffuse
How do large, uncharged polar molecules move?
e.g. glucose and sucrose, are not able to diffuse through the lipid membrane – transport proteins required
How do ions move through membrane?
Not able to diffuse, require transport proteins
Complete the sentence The smaller the membrane coefficient…
… the larger the net rate of transport
What is the rate of diffusion of molecules proportional to?
Concentration gradient
What is the term for the diffusion of water across a membrane up concentration of solute?
Osmosis
What is different about osmosis in cells such as those that line the kidney proximal tubule?
Facillitated by water channels - aquaporins
Define diffusion
Passive (i.e. spontaneous), non-energy requiring, movement of molecules across the lipid bilayer
Describe facilitated transport Give an example of facilitated transport
Specific proteins increase the permeability for a polar substance e.g Band 3 and Cl-
Why can water move the lipid bilayer easily?
Because it is a very small molecule
What does the band 3 protein do in cells?
HCO3- out, Cl- in anion exchange. Example of facilitated diffusion
Why is facilitated diffusion described as a saturatable process?
Because each carrier can interact with a few ions at any moment, and there are a finite number of transporters in membrane.
What is the Vmax for facilitated diffusion?
When all transporters are saturated
What is not altered by facilitated transport and why?
Equilibrium - Speeds up the rate at which equilibrium is reached, does not modify it
Name three types of pores in facilitated diffusion
Ligand gated ion channelsVoltage - gated ion channelsGap junction
What is a ligan gated ion channel?
Opens or closes in response to ligand binding to a receptor site
What is a voltage fated ion channel?
Open/close in response to potential difference across the membrane
What is a gap junction (connexin)
Closed when cellular calcium concentration rises above 10 micromoles or cell becomes acid
What is the difference between passive and active transport?
If the transport of an ion or molecule can occur spontaneously or requires energy (active transport)
