Exam 3- Transport of Small Molecules Flashcards
Which molecules are able to cross freely through the plasma membrane? Why?
Gases : O2 and CO2
Lipids / hydrophobic
Steroid Hormones
Small Polar Molecules: H2O, Ethanol
Which molecules are unable to cross freely through the plasma membrane? Why?
Glucose and sugars
Amino Acids
Ions: Na+ K+ Cl- H+ Ca2+ / other small charged ions
nucleosides
What’s the “force” that drives Diffusion (both, passive and facilitated)?
A concentration gradient across the membrane.
What’s a “concentration gradient”?
Unequal distribution of ions across the cell membrane
How does the Glucose Transporter work? What’s the mechanism behind its activity?
has 12 alpha-helical transmembrane domains made of hydrophobic amino acids but have polar residues that can bind glucose.
When glucose binds a conformational change occurs moving the binding site into the cell and releasing glucose. `
what is facilitated diffusion?
uses no energy, molecules move relative to [gradients] or electric potentials.
what does facilitated diffusion require?
carrier protein or channel protein
what are the molecules that require facilitated diffusion?
Polar, charged, sugars, AA, nucleosides, ions
what is a carrier protein?
binds specifically
changes conformation to allow molecule to travel
what molecules need a carrier protein?
Sugars, AA, nucleosides
What is a channel protein?
A pore that only allows the correct size and charge to pass freely with the concentration gradient
two examples of channel proteins
ion channels
aquaporins
3 features of ion channels?
- Fast! more than 1M ions per second
- very selective to m/z
- most are closed and must be opened
What are the two mechanisms that regulate the opening of ion channels?
Voltage- gated and Ligand- gated
How is specificity achieved for the Na+ channel?
the Na channel is 10x more permeable to Na than K.
The specificity is based on Na’s small size
