1. Size: small easier than large
2. Charge: uncharged pass unaided
3. Polarity: polar with no charge pass weakly
4. Hydrophobicity: no assistance needed (hydrophilic-NO)
5. Concentration of solute: down gradient (H-->L)

Solute can pass down its concentration gradient without expending energy (H-->L)

Passive Active

No energy needed Energy required

Use channels or carriers Use carrier

-Ach gated ion channel -Na+/K+ ATPase

-GLUT -Na+ and glc symport

Channel                                         Carrier

-Does not bind solute                  -Does bind solute

-Hydrophilic tunnel                      -Active or passive

 transport down conc.                  -3 classes

 gradient (passive)                      (1) uniport

-Gated-need ligand                     (2) symport

-Multipass                                 (3) antiport

-Multisubunit                              -GLUT, Na+/K+ ATPase

-Ach gated ion                              Na+ and glc symport

 channel

Uniport

Symport

Antiport

[image]

Uniport- one molecule on direction

Symport- 2 molecules simultaneously same direction

Antiport- 2 molecules simultanesouly opposite direction

transport of a charged molecule into the cell is influenced by two characteristics:

(1) concentration gradient

(2) electrostatic environment on each side of the PM

(generally, the interior is more negative)

[image]

Passive diffusion

Found in muscle cells

Ach binds to alpha subunit and allows Na⁺ to flow in

Can cause depolarization of cell membrane causing muscle contractions

Uniport of glucose 

Varying Km values

brain-->other cells-->liver (lowest Km)

[image]

RBC, brain, placenta, fetal tissue

Low Km

Glc concentration higher in plasma than in RBC

No regulation

ability to bind solute

higher--bind poorly

low--bind well

GLUT 2

Transport glc across basal membrane of enterocyte to touside of cell

Passive transport

High Km

Liver, kidney, intestine, pancreatic Beta cells

Brain

Low Km

[image]

Insulin regulated

Found in adipose and muscle tissue

Unstimulated: receptor in vesicles in cytoplasm

Stimulaed: receptors fuse with PM to increase glc uptake

[image]

Solute passes between adjacent cells through tight junctions

Tight junctions loosen in response to a meal

[image]

Solute transported into cell at apical side and out of cell at basal side

[image]

Pump is open to interior and binds 3 Na+

ATP then binds causing change in conformation

Pump opens to outside and dumps Na+

Pump grabs 2 K+ and dephosphorylates causing it to open to inside of cell where K+ are released

Forms an electrochemical gradient--primary active transport

[image]

Na+ outside of cell due to  ATPase activity uses its electrochemical gradient to bring glc into the cell

Secondary active transport

Primary Active Transport

Secondary Active Transport