Transport Across Membranes Flashcards
Simple Diffusion Properties
no specific protein
no transport against gradient
no ATP hydrolysis
example = O2 and CO2
Facilitated Transport Properties
requires specific protein
no transport against gradient
no ATP hydrolysis
glucose and amino acids = uniporter
ions and water = channel
Cotransport Properties
requires specific protein
requires transport against gradient
no ATP hydrolysis
movement with a cotransported ion
glucose and amino acids = symporters
ions and sucrose = antiporters
Active Transport Properties
requires specific protein
requires transport against gradient
requires ATP hydrolysis
ions, small hydrophilic molecules, lipids
Channels
- down gradient
- closed vs open
Transporters
- uniporter = move one down gradient
- symporter = one down, one against (both enter)
- antiporter = both down gradient (one enter, one exit)
ATP-Powered Pumps
- against gradient
- ATP-hydrolysis
Facilitated Transport
- concentration gradient
- move hydrophilic substances through protein-lined pathway
- faster than predicted by passive diffusion
- specific
- saturable
Glucose Importer
- glucose binds to GLUT1 = conformation change
- molecules released
- conformation change
Pores and Channels
- integral membrane proteins
- size-based exclusion
K+ Resting Channel
- K+ bound to water LARGER than Na+ bound to water
- oxygens in channel in same configuration as K+ bound to water
- move down concentration gradient
Electric Potential
- due to selectivity of the channels
- movement of K+ –> charge gradient
Ligand-Gated Channels
- binding of specific ligand — open channel
- example = GLUT1
Voltage-Gated Channels
- membrane potential change — open channel
- example = calcium release channel
Primary Active Transport
ATP-Powered Pumps
- P Class = H+, Na+, K+, Ca2+
- V Class = H+
- F class = H+
- ABC Type = small molecules
Ion Concentrations
- Ca2+ low levels in cell
- Na+ high levels in/out of cell
Sodium Potassium ATPase
- P Class Pump
- 3 Na+ out and 2 K+ in per ATP
- high level Na+ out cell & K+ in cell
- Na+ and ATP binding –> phosphorylate aspartate
- conformation change –> Na+ release and K+ binds
- dephosphorylation and conformation –> release K+
Muscle Calcium ATPase
- P Class Pump
- 2 Ca2+ out per ATP
- Ca2+ and ATP binding –> phosphorylate aspartate
- conformation change –> Ca2+ release
- dephosphorylation and conformational change
ABC Class Pumps
- move large molecules
- “flippase” mechanism — flip from one leaflet
Co-Transporters
- antiporters and symporters
- coupled transport btwn 2 different molecules
- use energy from ions going along concentration gradient to import molecules against gradient
Sodium Glucose Symporter
- glucose move in cell against gradient
- energy from Na+/K+ ATPase and K+ Resting channel
- 2 Na+ down and 1 glucose against (both enter cell)
Mechanisms in Epithelial Cells
Tight Junctions - prevent movement btwn cells
Gap Junctions - allow ions flow btwn cells
Na+/K+ ATPase - bring Na+ out and K+ in
K+ Channel - K+ leaks out
Na+/Glucose Symporter – brings glucose in (against)
Facilitated Transport GLUT2 – glucose to bloodstream
ECM in Epithelial Cells
Hemidesmosomes – send signals
Desmosomes – hold cells together
Microvilli – actin bundles extend surface area
