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

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)

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)

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

Insulin regulated

Found in adipose and muscle tissue

Unstimulated: receptor in vesicles in cytoplasm

Stimulaed: receptors fuse with PM to increase glc uptake

Solute passes between adjacent cells through tight junctions

Tight junctions loosen in response to a meal

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

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

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