cell membrane transport types of membrane transport Active transport passive transport simple diffusion osmosis facilitated diffusion protein channels carrier proteins

1. Overview of
membrane
transport
Dr. Irtaza Rehman
(Author of the book The Extraordinary Life)

3. • To revise & memorize concepts of membrane
transport
• To answer a MCQ correct at the end of lecture
Learning objective

4. Q. Do you
remember the
magical numbers of
cell membrane?
• 55%
• 25%
• 13%
• 4%
• 3%

5. Biomolecule Quantity
Protein 55 %
Phospholipid 25 %
Cholesterol 13 %
Other lipids 4 %
Carbohydrate 3 %
Composition of cell membrane

6. Q. What am i?
• describes the ease with which a
solute diffuses through a
membrane
• depends on the characteristics of
the solute and the membrane.
Ans. Permeability

7. Factors that increase permeability:
↑ Oil/water partition coefficient of the solute increases
solubility in the lipid of the membrane
↓ Radius (size) of the solute increases the diffusion
coefficient and speed of diffusion.
↓ Membrane thickness decreases the diffusion distance
Permeability

8. • Small hydrophobic solutes (O2
CO2) have the highest
permeabilities in lipid membranes.
• Hydrophilic solutes (Na+ K+) must cross cell
membranes through water-filled channels,
or pores, or via transporters.
• If the solute is an ion (is charged), then its
flux will depend on both the concentration
difference and the potential difference
across the membrane
Permeability

9. Rate of diffusion
• Rate of diffusion: (Surface area) (Concentration gradient)
(Thickness) (Weight of molecule)

10. The Size effect

11. Transport
Simple diffusion Carrier Mediated
Facilitated diffusion
Active transport
Primary active secondary active

12. Factors affecting diffusion
• Concentration difference
• Potential difference
• Pressure difference
“If forces oppose each other = forces will
balance each other = No net movement”

13. • Why Glucose can’t be diffused?
• Why Na, K, Ca can’t be diffused?
• Why Aminoacids/Nucleic acids can’t be diffused?
 Large
 charged
 Large/
charged

14. Osmosis
Q. Why volume of the cell
remains constant?
Q. Why water moves from
hypotonic to hypertonic
solution?
Net movement of water caused by
concentration difference of water is called
osmosis

16. Carrier-mediated transport
• Stereospecificity:
• Saturation:
• Competition:
SSC

17. Stereospecificity
Carrier-mediated transport

18. Saturation
Carrier-mediated transport

19. Competition
Carrier-mediated transport

20. Carrier-mediated transport
SSC

21. Facilitated diffusion
Rate of transport
depends upon how
rapid carrier protein
can change its states
back and forth

22. Channels are highly selective
• Hydrated K binds with
carbonyl oxygen lining
selectivity filter.
• Shed their water
molecules and
dehydrated K pass
through channel.

23. • Glucose transport in muscle
and adipose cells is through
facilitated diffusion.
• In diabetes mellitus, glucose
uptake by muscle and
adipose cells is impaired
because the carriers for
facilitated diffusion of
glucose require insulin.
Carrier-mediated transport

24. Note: Na-Glucose transporters in small intestine & renal
tubules are active
Facilitated diffusion

25. Defect results in
Diabetes insipidus
Facilitated diffusion

26. Types of channels
• Leaky channels/Non gated channels
• Voltage gated
• Ligand gated
• Mechanically gated
• Aquaporins
• GLUT-4
Facilitated diffusion

28. Q. What type of
transport is
more rapid?
A. Simple diffusion
B. Facilitated diffusion
Ans. Facilitated diffusion

29. Dialysis is an example of simple diffusion

30. Primary active transport
• requires direct input of metabolic energy in the
form of adenosine triphosphate (ATP)
• occurs against an electrochemical gradient
(“uphill”)
• is carrier mediated and therefore exhibits
stereospecificity, saturation, and competition

31. 3Na-Out-2K-In
Controls cell volume
Prevents cell burst from swelling
Makes inside cell negative &
outside positive

32. Q. Why Sodium
Potassium pump is
called as
Electrogenic?
Ans. because it creates an
electrical potential across the
cell membrane by making
outside + and inside -

33. • SERCA
Sarcoplasmic Endoplasmic Reticulum Calcium ATPase
(pump)
Primary active transport
• H+ K+ATPase (or proton pump)
gastric parietal cells and renal α-intercalated cells
transports H+ into the lumen (of the stomach or renal
tubule) against its electrochemical gradient
Energy is utilized by the breakdown of ATP
Uses external chemical energy

34. • Uses Electrochemical energy
• Electrochemical Gradient exists when there is
net difference in charges
Secondary active transport

35. • The transport of two or more solutes is coupled
• One of the solutes (usually Na + ) is transported
“downhill” and provides energy for the “uphill” transport
of the other solute(s)
Secondary active transport
Cotransport/Symport
Solutes move in Same direction
Counter transport
Solutes move in opposite direction

36. Secondary active transport
Na-Glucose Cotransport

37. Secondary active transport
Na–Ca countertransport (antiport)

38. Counter transport
Secondary active transport

39. Examples of Active Transport
• Phagocytosis
• Movement of Calcium ions out of cardiac cells
• Transport of aminoacid in intestinal lining
• Secretion of enzyme, peptide hormones,
antibodies

40. Which of the following
would occur as a result of
the inhibition of
Na+K+ATPase?
(A) Decreased intracellular Na concentration
(B) Increased intracellular K concentration
(C) Increased intracellular Ca concentration
(D) Increased Na glucose cotransport
(E) Increased Na Ca exchange
Ans. C

41. Summary

43. Jazakumullahu Khair ♥
(May ALLAH swt reward you with goodness)