Flashcards in Topic 6 - chapter 12 Membrane transport Deck (43)
The difference between a transporter and a channel?
A transporter has moving parts and can shift small molecules (inorganic ions & small molecules) from one side to the other by changing its shape.
Channels, in contrast, form tiny hydrophilic pores thru which solutes (inorganic ions) can pass by diffusion
Most plentiful inorganic ions?
Na+, K+, Ca2+, Cl-, H+
Highest ion inside/outside the cell? Concentrations?
inside cell K+ 140mM, outside cell K+ 5mM
outside Na+ 145mM, outside cell 5-15mM
What prevents the cell from being torn apart by electrical forces?
the quantity of +ve charge inside cell must be balanced by almost equal amount of -ve charge inside. Same applies to outside the cell
High [Na+] outside the cell balanced with ...?
High [K+] inside the cell balanced by ...?
a variety of -vely charged ions (anions)
The plasma membrane acts as ... ... membrane?
selectively permeable membrane
List some small nonpolar molecules
O2, CO2, N2, benzene
List some uncharged polar molecules
water, ethanol, glycerol
Do uncharged polar molecules diffuse across the membrane rapidly?
yes, if they are small enough
List some large uncharged polar molecules
AAs, glucose, nucleosides
T or F - lipid membranes are impermeable to all ions and charged molecules, no matter how small
On what basis do channels discriminate?
size & electric charge ie. if a channel is open, an ion or molecule small enough with the appropriate charge can freely pass thru
Molecules or solutes that require no energy get into cells by ...?
passive diffusion or facilitated diffusion
Plasma membrane contains transporters that import which nutrients?
sugars, AA's, nucleotides, Na+ (out of cell)
Lysosome membrane contains a transporter for which molecule?
H+ to acidify the lysosome interior
Mitochondrion membrane contains a transporter for which molecule?
pyruvate & ATP
A transporter that mediates passive transport?
glucose transporter (at least 2 conformations)
binds only D-glucose
The electrochemical gradient is best described as...?
the net driving force as a composite of 1. concentration gradient 2. voltage across membrane
The charge inside the cell is ...?
more -ve than the outside
3 main ways cells carry out active transport...
1. Coupled transporters: one solute goes down [ ] gradient transferring other solute up [ ] gradient
2. ATP-driven pumps: ATP hydrolysis drives pump
3. Light-driven pumps: energy from light (bacterial cells eg. bacteriorhodopsin)
The main role of the Na+-K+ ATPase is...?
to maintain high Na+ outside the cell (energy store) and high K+ inside the cell maintaining the concentration gradient and also accounts for 30% of total ATP consumption
Describe the Na+-K+ ATPase cycle...
1. Na+ binds to pump (from inside cell) 2. ATP phosphorylates pump -> ADP + Pi 3. Pi causes pump to release Na+ into extracellular space 4. K+ binds to pump from outside cell 5. pump dephosphorylated 6. pump returns to normal conformation & K+ ejected into cell
How do animal cells maintain osmotic equilibrium?
keeping intracellular solute [ ] low by pumping out ions
How do protozoans maintain osmotic equilibrium?
by periodically ejecting water that moves into the cell via contractile vacuoles
How do plant cells maintain osmotic equilibrium?
cell walls prevent swelling as osmosis & active transport into cell -> turgor pressure
Is Ca2+ high or low inside the cell? Why?
low, because of Ca2+ pumps that move them from cytosol to SR
A bit more about the Ca2+ pump...
polypeptide of protein crosses membrane as 10 alpha helices
Ca2+ binds to binding cavity -> ATP phosphorylates aspartic acid -> conformational change (activator domain & phosphorylation domain move closer together) -> Ca2+ back into SR
Can Ca2+ be used for any other reason?
yes - second messenger