Membrane Dynamics contd

1
Membrane Dynamics contd

• How many substrates can a carrier move?
• Active Transport
• Secondary Active Transport
• Transepithelial transport

2
How many substrates can a carrier move?
3
How many substrates can a carrier move?
4
Direction of substrate movement.
5
Carrier mediated transport into cells- net
movement as long as there is a concentration
gradient across the mb ? Facilitated Diffusion
Diffusion and carrier proteins
6
Disequilibrium drives facilitated diffusion of
glucose.
7
Function during disequilibrium
Ca
Ca
Ca

• Calcium entry

8
Some molecules need to be in disequilibrium.

• Levels of extracellular calcium and extracellular
  sodium (Na) are high.

Na Ca
Na Ca
9
Active Transport

• Na is removed from cells against its
  concentration gradient
• Need ATP energy for this work

10
Active Transport Na/K ATPase
Na K
Low levels of intracellular Na
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Active Transport Na/K ATPase
1.
3 Intracellular Na Ions bind Onto Na/K ATPase
12
Active Transport Na/K ATPase
2.
ATP hydrolysis
13
Active Transport Na/K ATPase

• 3.

The 3 Na ions are released Into the ECF
14
Active Transport Na/K ATPase

• 4.

Binding of 2 K ions from ECF
15
Active Transport Na/K ATPase

• 5.

Intracellular release of 2K ions
16
Active Transport Na/K ATPase
17
Secondary (indirect) Active Transport
Symport driven by Na concentration gradient for
trans-epithelial transport,
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Sodium-glucose symporter
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Sodium-glucose symporter
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Sodium-glucose symporter
21
Transepithelial transport

• Primary active transport
• Secondary active transport
• Facilitated diffusion

Must have low levels of intracellular Na To
drive transepithelial transport
22
Intracellular glucose provide energy for primary
and secondary active transport.
23
Where does transepithelial transport occur?

• Glucose absorption in the intestine
• Glucose absorption in the nephron
• Glucose is moved from the mucosal surface of the
  epithelium to the serosal surface.
• Glucose is moved from the apical surface of the
  cells to the basal surface of the cells.