Transport Across Membranes

Question 1

Simple Diffusion Properties

Answer 1

no specific protein
no transport against gradient
no ATP hydrolysis
example = O2 and CO2

Question 2

Facilitated Transport Properties

Answer 2

requires specific protein
no transport against gradient
no ATP hydrolysis

glucose and amino acids = uniporter
ions and water = channel

Question 3

Cotransport Properties

Answer 3

requires specific protein
requires transport against gradient
no ATP hydrolysis
movement with a cotransported ion

glucose and amino acids = symporters
ions and sucrose = antiporters

Question 4

Active Transport Properties

Answer 4

requires specific protein
requires transport against gradient
requires ATP hydrolysis

ions, small hydrophilic molecules, lipids

Question 5

Channels

Answer 5

• down gradient

- closed vs open

Question 6

Transporters

Answer 6

• uniporter = move one down gradient
• symporter = one down, one against (both enter)
• antiporter = both down gradient (one enter, one exit)

Question 7

ATP-Powered Pumps

Answer 7

• against gradient

- ATP-hydrolysis

Question 8

Facilitated Transport

Answer 8

• concentration gradient
• move hydrophilic substances through protein-lined pathway
• faster than predicted by passive diffusion
• specific
• saturable

Question 9

Glucose Importer

Answer 9

• glucose binds to GLUT1 = conformation change
• molecules released
• conformation change

Question 10

Pores and Channels

Answer 10

• integral membrane proteins

- size-based exclusion

Question 11

K+ Resting Channel

Answer 11

• 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

Question 12

Electric Potential

Answer 12

• due to selectivity of the channels

- movement of K+ –> charge gradient

Question 13

Ligand-Gated Channels

Answer 13

• binding of specific ligand — open channel

- example = GLUT1

Question 14

Voltage-Gated Channels

Answer 14

• membrane potential change — open channel

- example = calcium release channel

Question 15

Primary Active Transport

Answer 15

ATP-Powered Pumps

• P Class = H+, Na+, K+, Ca2+
• V Class = H+
• F class = H+
• ABC Type = small molecules

Question 16

Ion Concentrations

Answer 16

• Ca2+ low levels in cell

- Na+ high levels in/out of cell

Question 17

Sodium Potassium ATPase

Answer 17

• 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+

Question 18

Muscle Calcium ATPase

Answer 18

• P Class Pump
• 2 Ca2+ out per ATP
• Ca2+ and ATP binding –> phosphorylate aspartate
• conformation change –> Ca2+ release
• dephosphorylation and conformational change

Question 19

ABC Class Pumps

Answer 19

• move large molecules

- “flippase” mechanism — flip from one leaflet

Question 20

Co-Transporters

Answer 20

• antiporters and symporters
• coupled transport btwn 2 different molecules
• use energy from ions going along concentration gradient to import molecules against gradient

Question 21

Sodium Glucose Symporter

Answer 21

• 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)

Question 22

Mechanisms in Epithelial Cells

Answer 22

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

Question 23

ECM in Epithelial Cells

Answer 23

Hemidesmosomes – send signals
Desmosomes – hold cells together
Microvilli – actin bundles extend surface area