2. Phospholipid bilayer is a good barrier around the cell especially
for polar hydrophilic molecules
However, for cell survival; some
material need to be able to enter
and leave the cell
Cell membrane is selectively permeable (semi permeable).
Certain molecules as glucose, amino acids and lipids can easily
enter and exit the cell.
3.
4. 1- Concentration gradient of the substance.
2- Size of the substance.
3- Relative solubility of the substance in oil.
In general, the smaller the molecule and the more
soluble in oil (the more hydrophobic, or
nonpolar), the more rapidly it will diffuse across a
lipid bilayer.
Factors affecting membrane transport
5. Molecules can be transported across membrane by the
following mechanisms:
A- transfer of small molecules
1-Simple diffusion
2- Active transport
A-Passive
Simple
diffusion
B-Facilitated
Simple
diffusion
B- transfer of large molecules
1-Endocytosis
2-Exocytosis
6. 1-Simple diffusion
Movement of molecules or ions across the membrane from
a region of their higher conc. To a region of their lower
conc.
i.e. the molecules moves down a
conc. Gradient
Diffusion stops when
equilibrium is reached
A- Passive Simple diffusion
Passive Simple diffusion needs
no energy
7. Rate of transport depends on
solubility of the transported
molecules in the hydrophobic core
of lipid bilayer
Transmembrane ion channels
(protein containing pores) is ex. of
passive transport…..transport
several ions like Na, K , Ca ion
from their region of high conc. To
low conc.
Some channels are open continuously, others like Ca
channels open only in response to signals. So, it is called
Gated channels
Passive diffusion
8. B- Facilitated Simple diffusion
Need no energy
Transport of small molecules in
the direction of the
concentration gradient with the
help of specific carrier protein
Passive diffusion
Simple diffusion
E.g glucose carrier protein
Differ from passive simple
diffusion that when all carrier
proteins are saturated
transport is stopped
9. 2- Active transport
Active transport is the pumping
of molecules against their
concentration gradient by
binding to membrane protein
(called Ion pumps)
These pumps transport the molecules
with the use of ATP (Energy) gained
from sodium - potassium pump ,where
hydrolysis of ATP in presence of (ATPase
enzyme) occur to produce energy
10. The protein act as a pump
using ATP to transport the H+
ion against its conc. gradient
11. Examples of carrier protein
Glucose transporters (GLUTs): A family of glucose
transport proteins catalyze facilitated transport of glucose
in most cells for glucose uptake according to the
concentration gradient between extracellular fluids and
the cytoplasm.
Sodium glucose transport proteins (SGLT): A family of
transport protein in intestinal epithelial cells where
glucose must be transported against conc. gradient
(active transport) from intestinal lumen to the intestinal
epithelial cells.
12. B- transfer of large molecules
1-Endocytosis
The process by which cells take up large molecules
The cell uptakes extracellular macromolecules
to form endocytic vesicle
13. There are 2 types of endocytosis:
1- Phagocytosis
(cell eating)
Occur only in specialized
cells as macrophages and
granulocytes as they ingest
bacteria and fungi
They extend pseudopodia
and surround the bacteria
to form phagosomes which
fuse with lysosomes
forming phagolysosomes to
digest the particles
2- Pinocytosis
(cell drinking)
It occurs in all cells and
lead to uptake of fluid
vesicles of fluid are
formed in the cell
membrane without the
formation of pseudopods.
14. 2-Exocytosis
used to release macromolecules to outside the cell
e.g. release of insulin hormones from beta cells of islet of
Langerhans in pancrease
An opposite process to endocytosis
15. Osmosis is the same thing as diffusion but it refers
specifically to water molecules.
Osmosis is the passage of water across the membrane
from the area of high concentration of water to the
area of low concentration of water.
Protein channels in the phospholipids of the membrane
known as aqua porins to enable water to pass through
the hydrophobic core of the membrane.
Osmosis
16. Difference in solute concentration on opposite sides of the cell
membrane generate an osmotic pressure which is often used to
express the concentration of the solution.
Osmotic pressure:
17. Isotonic solution Hypertonic Hypotonic
The hypertonic solution is the
solution with a greater solute
concentration compared to the
hypotonic solution. كميه
المياه
اقل
في
المحلول
المركز
مقارنه
ب
المحلول
المخفف
Three important terms related to osmosis
isotonic solution is the external
solution surrounding the cell,
where the osmotic pressure is the
same in both inside and outside
the cell, Cells maintain their
volume in isotonic solutions.
18. Facilitated diffusion
differ than simple
diffusion in
requirement of
A. Carrier Protein
B. Energy
C. Both of them
D. No difference
When the concentration of
molecules on both sides of a
membrane is the SAME, the
solution:
A. moves from an area of higher
concentration to an area of
lower concentration.
C. has reached an equilibrium
D. is hypertonic.
19. If a large cell consumes or
eats another smaller cell,
say a tiny bacterium, this
process known as
A-Exocytosis
B-Phagocytosis
C- Osmosis
D-pinocytosis
Pseudopods surround the food
item forming a vesicle to take
the food into the cell
A-phagocytosis
B- Pinocytosis
C-Exocytosis
D- osmosis
20. Glucose transported from
intestinal lumen to the
intestinal epithelial cells
by:
A- Active transport
B- SGLT transport protein
C- pinocytosis
D- A&B is correct
In general, which of the
following will diffuse across
a lipid bilayer most rapidly?
A-Small hydrophilic molecule
B- Small hydrophobic
molecule
C- Large hydrophilic
molecule
D- Large hydrophobic
molecule
21. A solution in which the salt
concentration is LOWER
outside the cell than the salt
concentration inside the cell
is called
A- isotonic
B- hypotonic
C- hypertonic
D- A&B is correct
c
Red blood cells shrunk
in
A- isotonic
B- hypotonic
C- hypertonic
D- A&B is correct
c
