Transport of molecules

2.  active transport :Movement of materials through
a membrane against a concentration gradient
and requires energy from the cell.
Concentration
gradient
Plasma
membrane
Carrier
proteins
Cellular energy
Cellular
energy

3.  Cells may need molecules to move
against concentration “hill”
◦ need to pump “uphill”
 from LOW to HIGH using energy
◦ protein pump
◦ requires energy
 ATP
ATP

4.  Also called sodium potassium ATPase pump
or sodium potassium ATPase.
 A transport process that pumps sodium
ions outward through the cell membrane of
all cells and at the same time pumps
potassium ions from the outside to the
inside.
 Sodium & potassium ions are transported
by means of a common carrier protein
called Na+-K+ pump and ATP is used as
energy.

5.  The carrier protein has 3 important features:
 1. It has three receptor sites for binding
sodium ions on the portion of the protein
that protrudes to the inside of the
cell.(towards cytoplasm)
 2. It has two receptor sites for potassium ions
on the outside.(towards ECF)
 3. The inside portion of this protein near the
sodium binding sites has ATPase activity

7.  Three sodium ions get attached to the respective
receptor site on the inner surface of carrier
protein.
 Two potassium ions get attached to respective
receptor sites on the outer surface of the carrier
protein.
 Binding of sodium and potassium ions activates
the enzyme ATPase (located near sodium sites on
inner surface of carrier protein).
 ATPase causes breakdown of ATP into ADP with
the release of high enery phoshate
bond.(Phosphorylation of ATP).

8.  The energy liberated causes conformational
change in carrier protein.
 Outer surface of molecule(with potassium
ions) now faces the inner side of cell & inner
surface of protein molecule (with sodium
ions) now faces the outer side of cell.
 Dissociation & release of ions take place so
that the sodium ions are released outside the
cell &potassium ions are released inside the
cell.

9.  Maintains sodium and potassium concentration
differences across the cell membranes. It
maintains high levels of Na in the ECF(major
cation of ECF) and maintains high levels of K in
ICF(major cation in ICF)
 Establishes negative electrical voltage inside the
cells because it pumps more positive ions
outwards than inwards(3 Na outwards and 2 K
inwards)
 Maintains cell volume by throwing Na outwards
in ECF against the concentration gradient and Na
carries water with it outside and cell volume is
maintained.

11.  The movement of macromolecules such as
proteins or polysaccharides into or out of the
cell is called bulk transport/vesicular transport
 There are two types of bulk transport
 Endocytosis : taking in of material into the cell
 Exocytosis : taking out of the material from
cell.
 both require the expenditure of energy (ATP).

13.  The taking in of material by a living cell by
invagination of its membrane to form a
vacuole/vesicle.
 Receptor-mediated endocytosis is an
extremely selective process of importing
materials into the cell. This specificity is
mediated by receptor proteins located on
depressed areas of the cell membrane
called coated pits.
 It is a specialized function of the cell
membrane by which very large particles
especially enter the cell.

14.  The principal forms of endocytosis are
 Pinocytosis and
 Phagocytosis.
 Pinocytosis means ingestion of minute particles
that form vesicles of extracellular fluid and
particulate constituents inside the cell cytoplasm.
(cell drinking). Formation of pinocytotic vesicle
 Phagocytosis means ingestion of large particles,
such as bacteria, whole dead cells, or portions of
degenerating tissue by formation of phagosome
(cell eating)

15.  Pinocytosis- Greek word , Pin means to drink
 Occurs continually in the cell membranes of most
cells, but it is especially rapid in some cells.
 Pinocytosis is the only means by which most large
macromolecules, such as most protein molecules,
can enter cells.

16.  Molecules attach to specialized protein
receptors on the surface of the membrane that
are specific for the type of protein that is to be
absorbed.
 The receptors are concentrated in small pits on
the outer surface of the cell membrane, called
coated pits.
 On the inside of the cell membrane beneath
these pits is a latticework of fibrillar protein
called clathrin.

18.  Once the protein molecules have bound with the
receptors, the whole pit invaginates inward.
 The fibrillar proteins surrounding the invaginating
pit cause its borders to close over the attached
proteins as well as over a small amount of
extracellular fluid.
 The invaginated portion of the membrane breaks
away from the surface of the cell, forming a
pinocytotic vesicle inside the cytoplasm of the cell.

19. 1: ATP:
 This process requires energy from within the
cell supplied by ATP.
2: Calcium ions:
 It requires the presence of calcium ions in the
extracellular fluid, which react with contractile
protein filaments beneath the coated pits to
provide the force for pinching the vesicles away
from the cell membrane.

21.  Greek word, phago means to eat
 Same as pinocytosis except that it involves large
particles rather than molecules.
 Only certain cells have the capability of
phagocytosis, most notably the tissue
macrophages and some of the white blood cells.
also a characteristic of Ameoba.
 Phagocytosis is initiated when a particle such as a
bacterium, a dead cell, or tissue debris binds with
receptors on the surface of the phagocyte.

22.  The cell membrane receptors attach to the
surface ligands of the particle.
 The edges of the membrane around the points
of attachment evaginate outward to surround
the entire particle;
 progressively more and more membrane
receptors attach to the particle ligands.
 All this occurs suddenly in a zipper-like
manner to form a closed phagocytic
vesicle.(phagosome)

23.  Actin and other contractile fibrils in the
cytoplasm surround the phagocytic vesicle and
contract around its outer edge, pushing the
vesicle to the interior.
 The contractile proteins then pinch the stem of
the vesicle so completely that the vesicle
separates from the cell membrane, leaving the
vesicle in the cell interior in the same way that
pinocytic vesicles are formed.

26.  Almost immediately after a pinocytotic or
phagocytic vesicle appears inside a cell,
one or more lysosomes become attached to
the vesicle and empty their acid hydrolases
to the inside of the vesicle.
 A digestive vesicle is formed inside the cell
cytoplasm in which the vesicular hydrolases
begin hydrolyzing the proteins,
carbohydrates, lipids, and other substances
in the vesicle.

27.  What is left of the digestive vesicle, called the
residual body, represents indigestible
substances.
 In most instances, this is finally excreted
through the cell membrane by a process called
exocytosis, which is essentially the opposite of
endocytosis.
 Thus, the pinocytotic and phagocytic vesicles
containing lysosomes can be called the
digestive organs of the cells

29.  In exocytosis, materials are exported out of the
cell via secretory vesicles.
 In this process, the Golgi complex packages
macromolecules into transport vesicles that
travel to and fuse with the plasma membrane.
This fusion causes the vesicle to spill its
contents out of the cell.
 Exocytosis is important in expulsion of waste
materials out of the cell and in the secretion of
cellular products such as digestive enzymes or
hormones.