11: Membrane Transport

What is simple diffusion? examples?

molecules go directly through the lipid

• no E

• only small non polar molecules like O2 and CO2

What is facilitated diffusion? examples?

across the membrane by specialized membran transport proteins

• hydrophillic molecules (sugars, aa, nucleotides) ions

What affects diffusion of a molecule?

1. size

2. hydrophobicity

explain small + NP and provide examples

• can go thru

• ex. O2, Co2, N2, steroid hormones

explain small + uncharged + P ? provide examples

slowly gets thru, but needs help of membrane transport protiens

ex. H2O, ethanol, glycerol

large + uncharged + P? provide examples

some can lose polarity in a split sec so some goes in

• glucose, nucleosides, some aa

explain Ions diffusing?

cannot go in at all

• H+, Na+, K+, Ca2+, Cl-, Mg2+, HCO-3

what are Transport Proteins? what structure passes thru the membrane?

• multipass transmembrane proteins

• alpha helices

What are channels? if the channel has a lot of negatives what will go thru?

hydrophillic pores across the membrane, that discriminates sizes and charges

• positive!

What are transporters? how?

selectively shifts solutes across the membrane by changing conformations

• transfer ions or molecules that fit into specific binding sites

Important ions in cell?

1. Ca

2. Na

3. K

4. Cl

5. H

what is Na+? balanced by?

most abundant cation outside the cell

• mostly balanced by Cl-

What is K+? balanced by?

most abundant cation inside a cell

• balanced by variety of anions and large molecules such as nucleic acids (due to phosphate groups) and protiens

What is Membrane potential

• electrical imbalances that generate a voltage difference across the membrane

What is an unstimulated cell? explain animal cells

anions and cations are balanced across the membrane

• resting membrane potenial is steady, but not zero (nothing moves in any direction)

-20 to -200 mV

• more negtaive inside than outside of cell

What is passive tranpsort? energy used? examples?

substances diffuse spontaneously down their concentration gradient until eq is reached

• NO E

• channels or transporters

what are channels and transporters?

channels - tunnels

transporters - changes conformation when something binds

What is the electrochemical gradient? explain how uncharged and charged solutes move

driving force that determines the direction of a charged solute flowing across the membrane

1. uncharged - moves based on concentration gradient (high to low)

2. charged - diffuses based on charge and [ ]

• usually cations diffuse in and anions out

What is aquaporin?

protein that facilitates the flow of water

• get water in and out of cell fast

   

What is Osmolarity

total concentration of solute particles inside the cell

What is osmosis?

movement of water from an area of low solute concentration to high solute concentration

• high free [water] to low

Explain isotonic, hypertonic, and hypotonic. What are cells usually?

1. Isotonic = [ ] in and out same

2. Hypertonic = outside has [high] + inside has [low]

• flows out of cell = shrivels

• High osmolarity

3. Hypotonic = low [ ] out + high [ ] in cell

• water goes in = swells  BOOM! (osmolysis)

• Low osmolarity

cells are usually hypotonic

example of H2O moving into cell to swell or hypotonic

1. contractile vacuoles in paramecium

2. transmembrane pumps in animal cells - grabs water and pumps it so it doesnt burst

3. rigid cell walls in plant cells (turgor pressure) - builds box around so interior swells as far as it can and doesn’t burst

What are passive transporters? example?

have several conformations that switches reversibly and randomly

• can be open to external and cell interior

• usually no E

ex. uniport

Whats a uniport?

moves one single type of solute at a time

• glucose from extracellular space binds to uniport and gets released to the cytosilic side of membrane

What is Active Transport?

the movement of a solute against its [gradient] by its transporters called pumps

• uses E from the hydrolysis of ATP

Examples of active transporters and explain

1. Gradient driven pumps - links the uphill transport of one solute to downhill movement of a diff solute (red goes down [gradient] so yellow moves up)

2. ATP driven pumps - E released from ATP hydrolysis drives uphill transport

3. Light driven pumps - E from sunlight drives uphill transport

What can Na+ transport be called? what is it? how?

• Na+ - K+ ATPase or Na+ - K+ pump

• pumps 3 Na+ out and 2 K+ in against its [gradient] so its more negative outside than inside maintaining membrane potential due to its imbalance

1. Na pumped against conc gradient and binds on transport protein so ATP phosphorylates it

2. Which triggers conformation change and sodium is pushed outside the cell

3. K can bind to it since its open

4. Dephosphorylate occurs and causes a conformation chagne to its orginal shape, which is opening pump inside

What is Ca2+ transport’s cocnetration like? what about how it flows? how does it work

concentrations are low in cytosol since Ca is stored in SER

• flows into cytosol triggers muscle contraction and nerve cell signalling

• ATP driven ca2+ pumps in plasma membrane and ER membrane

  • doesnt require binding of a second ion to go back to its og conformaiton

Example of gradient driven pumps? explain. example?

1. symport - moves solutes in the same direction

2. antiport - moves solutes in the opposite direction

ex. glucose-Na+ symport

• Na(positive) binds and drags glucose (partial neg) in symport if they are tgt

  • Then Na moves down [gradient] forces the shape so glucose is dragged too

  • So it moves glycose up [gradient] BUT BOTH MOVING SAME DIRECTION

  • As soon as both come out, the symport will go back to its conformation shape

example of antiport?

H+ gradients - Na floats down in the cell which pumps H outside the cell

What are H+ gradients?

cells control the pH in cytosol

so if its a lot of H = acidic

low H = basic

Explain Animal, plants, bacteria, fungi’s H+ gradients?

na+ - H+ exhcnager: pumps H+ out of cell

PLANT, bacteria, fungi:

• no Na+ pumps, but have H+ pumps to set electrochemical proton gradients

  • overall creating an acidic environment around the cell

• usually light driven H+ pimps or ATP driven H+ pumps