Active transport moves molecules or ions against their concentration gradient using energy. There are two types: primary active transport which directly uses ATP as an energy source, and secondary active transport which uses the concentration gradient of another substance like sodium. Primary active transport examples include the sodium-potassium pump and calcium pumps. Secondary active transport occurs by co-transport or counter-transport using the sodium gradient. Passive diffusion requires no energy and occurs down a gradient, while active transport is an uphill process requiring a carrier protein and energy. Vesicular transport involves endocytosis which brings substances into cells through pinocytosis or phagocytosis, and exocytosis which releases substances from cells.

1. Dr Asma Jabeen
Assistant professor

2.  Define active transport and describe its general
mechanism.
 Identify the types of active transport(primary and
secondary) and contrast the differences in between.
 Give examples for the substances using active
transport as a method of transport
 Compare and contrast passive diffusion, facilitated
diffusion and active transport
 Brief the mechanism of vesicular transport(exocytosis
& endocytosis)

3. Active transport
When a cell membrane moves molecules or ions “uphill”
against a concentration gradient (or uphill against an
electrical or pressure gradient), the process is called
Active transport.
Types:
 Primary active transport
 Secondary active transport

4. Substances that use active transport mechanism
 Sodium ions
 Potassium ions
 Calcium ions
 Iron ions
 Hydrogen ions
 Chloride ions
 Iodide ions
 Urate ions
 Several sugars and amino acids

5. Role of Carrier proteins
 In active transport, the transport depends on carrier
Proteins that penetrate through the cell membrane
 The carrier protein is capable of imparting energy to
the transported substance to move it against the
electrochemical gradient

6. Primary active transport
The energy for the process is derived directly from the
breakdown of adenosine triphosphate (ATP) or of some
other high energy phosphate compound.
Examples:
 Na K pump
 Primary active transport of Calcium
 Primary active transport of Hydrogen ions

7. Sodium Potassium Pump

8. Carrier protein with 2 globular subunits:
Alpha and beta
Alpha subunit (100,000 mol. Wt.)
(larger)
1.Has 3 receptor sites for Na on inside
2.Has 2 receptor sites for K on outside
3.Inside portion has ATPase activity
Beta subunit ( 55,000 mol. Wt.)
(smaller)
Anchors the protein complex in the
lipid membrane.
Na-K pump…..General Characteristics

9. How the Na K pump works?
 Binding of three sodium inside and two potassium
outside activates ATPase function, cleaves ATP , splitting
it to ADP and liberates high energy phosphate bond of energy.
 The liberated energy then cause a chemical and conformational
change in protein carrier molecule, extruding the three sodium
out and two potassium to inside.

10. Reverse function of Na K Pump
If the electrochemical gradients for Na and K are
experimentally increased enough,,so that the energy stored in
Their gradients is greater than chemical energy of ATP
hydrolysis, ions will move down their conc gradient and ATP
will be formed from ADP and phosphate.

11. Significance of sodium potassium pump
 For some cells such as electrically active nerve cells,
60 to 70% of the cell’s energy requirement may be
devoted to pumping sodium out of cell and K into the
cell
 This pump performs a continual surveillance role in
maintaining normal cell volume

12.  By the movement of sodium and potassium ions,
a net of one positive charge is moved from the
Interior of the cell to the exterior for each pump
cycle creating negativity on the inside.
It is said to be Electrogenic because it creates an
electrical potential across the cell membrane
Significance of sodium potassium pump

13. Primary active transport of Calcium ions
Calcium ions are normally maintained at extremely low
Concentration in the cytosol of virtually all cells in the
Body…about 10,000 times less than that in ECF.
This is achieved by two primary pumps:
 One is in cell membrane, pumps calcium to outside
 Other one pumps calcium into one of the vesicular
organelles such as SR of muscle, mitochondria of all
cells
 The carrier protein acts as an ATPase enzyme

14. Primary active transport of Hydrogen ions:
At two places in the body, primary active transport
Of hydrogen ions is important:
1. In the gastric glands of the stomach
2. In the late distal tubules and cortical collecting ducts
of the kidneys

15. Energetics of Primary active transport
The energy required is proportional to the logarithm of
The degree that the substance is concentrated:
Energy(in calories per osmole) = 1400 log C1/C2
The energy required to concentrate a substance 100 folds
is twice as compared to concentrating a substance 10
times

16. Secondary Active Transport
The concentration gradient developed due to diffusion
of sodium is a storehouse of energy..This diffusion energy
of sodium can pull other substances along with sodium
through the cell membrane.
Types of Active transport:
 Co transport
 Counter transport

17. Co- Transport
 The carrier serves as an attachment point for both the
Sodium ions and the substance to be transported.
 Once attached, the energy gradient for sodium causes
both the sodium ions and other substance be transported
together to interior of cell
 e.g. Co transport of glucose and amino acids along
with sodium

18. Co- Transport

19. Na+
AA Na+ gluc 2 HCO3
-
Na+

20. Counter transport
The type of active transport in which the sodium ions
move in one direction and other ions in the opposite
direction
 Sodium - hydrogen counter transport
 Sodium – calcium counter transport

21. Counter Transport

22. Na+
Ca2+
Na+
H+
Cl-/H+
Na+/HCO3
-

23. Passive diffusion, facilitated diffusion & Active transport

24. • Occurs down a concn.
gradient
• No mediator or involves
a “channel” or “carrier”
• No additional energy
• Occurs against a concn.
gradient
• Involves a “carrier”
• Requires ENERGY

25. Vesicular Transport

26. Ingestion by the cell -Endocytosis
Very large particles enter the cell by a specialized function
Of the cell membrane called endocytosis.
 Pinocytosis
 Phagocytosis
 Pinocytosis means ingestion of minute particles that
form vesicles of extracellular fluid and particulate
constituents inside the cell cytoplasm
 Phagosytosis means ingestion of large particles, such
as bacteria, whole cells or portions of degenerating
tissue

27. • Molecules attach to
cell-surface receptors
concentrated in clathrin-
coated pits
• Receptor binding
induces invagination
• Also ATP-dependent
and involves recruitment
of actin and myosin
Receptor-mingestediated
endocytosis:
Figure 2-11
Ingestion by the cell -Endocytosis

28. Digestion of Substances in
Pinocytotic or Phagocytic
Vesicles
Figure 2-12
Endocytosis

30.  Define active transport and describe its general
mechanism.
 Identify the types of active transport(primary and
secondary) and contrast the differences in between.
 Give examples for the substances using active
transport as a method of transport
 Compare and contrast passive diffusion, facilitated
diffusion and active transport
 Brief the mechanism of vesicular transport(exocytosis
& Endocytosis)

31. Thank You