Types of cell membrane transport
Factors affecting transport
Cell membrane
Chemical gradient
Electrical gradient
Rate of transport
Passive transport
Facilitated diffusion
Active transport
Factors affecting transport: cell membrane
 The cell needs to absorb and excrete various compounds throughout its life.
 These compounds need to pass through the membrane which is made from a
phospholipid bilayer
 The phospholipid bilayer is formed by phospholipid molecules bipolar
molecule: the fatty acid side is hydrophobic, the phosphoric side is
The membrane is
permeable to:
 H2O
 Gases (O2, CO2, N2)
 Lipids
 Small, neutral molecules (such
as urea)
The membrane is
impermeable to:
 Small, charged molecules
 “large molecules” such as
amino acids, glucose and
 These compounds must go
through channels present in the
membrane in order to enter or
exit the cell
Factors affecting transport: Chemical gradient
 Compound moves from an
area of high concentration to
low concentration (or
concentration gradient)
 All compounds permeable to
the phospholipid bilayer will
move this way
Factors affecting transport: Electrical force
 Positive ions are attracted to
negative ions and vice versa
 Ions are repelled by ions of
the same charge (+ against +
and – against -)
Movement across the cell membrane
 Both chemical and electrical forces (electrochemical
force) drive the movement of compounds across the cell
Factors affecting the rate of transport
 The rate of transport will depend on:
 The concentration gradient
 The compound permeability to the membrane
 The type and number of charges present on the compound
Crossing of cell membrane
 fats and oils can pass directly through
inside cell
outside cell
Types of Transport Proteins
 Channel proteins are embedded in the cell membrane &
have a pore for materials to cross
Carrier proteins can change shape to move material from one
side of the membrane to the other
Cell membrane channels
 Need to make “doors” through membrane
 protein channels allow substances in & out
 specific channels allow specific material in & out
 H2O channel, salt channel, sugar channel, etc.
inside cell
outside cell
Protein channels
 Proteins act as doors in the membrane
 channels to move specific molecules through cell
Passive transport
Compounds will move from area of high concentration
toward area of lower concentration
 No ATP is needed for this type of transport
 Passive transport mainly TWO types
B-Diffusion-diffusion again two types
a-simple diffusion- no energy needed
b- facilitated diffusion- no energy needed
-help through a protein channel
 Each compound obeys the law of diffusion
 diffusion of water from HIGH concentration of water to LOW concentration
of water
 across a semi-permeable membrane
 However, some compounds are unable to cross the cell membrane (glucose,
 Water can cross  will enter or exit the cell depending its concentration
Cells in Solutions
Isotonic Solution
H2O (equal amounts
entering & leaving)
Simple diffusionno energy needed
Movement across higher to lower concentration gradient.
Facilitated diffusionSome compounds are unable to diffuse through the membrane.
They will be allow to cross if the membrane has proteins that
can bind these compounds and enable to cross toward the area
of lower concentration
Simple and facilitated diffusion
simple diffusion
inside cell
facilitated diffusion
inside cell
protein channel
outside cell
outside cell
Simple Diffusion
 Doesn’t require energy
 Moves high to low
Example: Oxygen or water
diffusing into a cell and carbon
dioxide diffusing out.
Simple Diffusion
The rate of diffusion will be increased when there is :
Concentration: the difference in between two areas (the gradient) causes
diffusion. The greater the difference in concentration, the faster the
Molecular size: smaller substances diffuse more quickly. Large molecules
(such as starches and proteins) simply cannot diffuse through.
Shape of Ion/Molecule: a substance’s shape may prevent it from diffusing
rapidly, where others may have a shape that aids their diffusion.
Viscosity of the Medium: the lower the viscosity, the more slowly molecules
can move through it.
Movement of the Medium: currents will aid diffusion. Like the wind
in air, cytoplasmic steaming (constant movement of the cytoplasm)
will aid diffusion in the cell.
Solubility: lipid - soluble molecules will dissolve through the
phospholipid bilayer easily, as will gases like CO2 and O2.
Polarity: water will diffuse, but because of its polarity, it will not pass
through the non-polar phospholipids. Instead, water passes though
specialized protein ion channels
Facilitated diffusion
Doesn’t require energy
Uses transport proteins to move
high to low concentration
Examples: Glucose or amino
acids moving from blood into a
Active Transport
- Pumps
- phagocytosis
- Endocytosis/exocytosis
Active transport
ATP (energy) is needed 
Moves materials from LOW to
HIGH concentration
AGAINST concentration
Example-1 ATPase pumps
 The most common: Na/K pumps  reestablish membrane
potential. Present in all cells.
 Two K+ ions are exchanged with 3 Na + ions
 Example 2: the thyroid gland accumulates iodine as it is needed
to manufacture the hormone thyroxin.
 The iodine concentration can be as much as 25 times more
concentrated in the thyroid than in blood.
 Example 3: In order to make ATP in the mitochondria, a
proton pump (hydrogen ion) is required.
 Endocytosis: (“Endo” means “in”).
 Endocytosis is the taking in of molecules or particles by invagination of the
cell membrane forming a vesicle. Integrity of plasma membrane is
 This requires energy.
 Endocytosis is fallowed by exocytosis on the other side. – Transcytosis,
vesicle trafficking, or cytopempsis.
Types of endocytosis
1. pinocytosis (cell drinking): small molecules are ingested and
a vesicle is immediately formed. This is seen in small intestine
cells (villi)
2. phagocytosis (cell eating): large particles, (visible with light
microscope) are invaginated into the cell (ie: white blood cells
‘eat’ bacteria
 Used to engulf large particles such as food, bacteria, etc. into
 Called “Cell Eating
 Capture of a Yeast Cell (yellow) by Membrane Extensions of
an Immune System Cell (blue)
Receptor-Mediated Endocytosis
Some integral proteins have receptors on their surface to
recognize & take in hormones, cholesterol, etc.
 Exocytosis: (“Exo” means “out”.)
• Exocytosis is the reverse of endocytosis.
• This is where a cell releases the contents of a vesicle
outside of the cell.
• These contents may be wastes, proteins, hormones, or
some other product for secretion.
• This also requires energy.
• Example: vesicles from the Golgi fuse with the plasma
membrane and the proteins are released outside of the cell.
 Fusion of vesicle with plasma membrane is mediated
by a number of accessory proteins- SNARE protein.
 Require stimulus and Ca.
 Exception- Renin from JG cells and PTH from
parathyroid gland by decrease in intracellular Ca.
 Constitutive Secretion- Immunoglobulin from plasma
Cells and collagen from fibroblast.
 Regulated- endocrine gland, pancreatic acinar cells
Membrane Transport Proteins
1. Water Channels or Aquaporins (AQPs) –
12 types
Amount of water is regulated by No. of AQPs
They are known as gated channel although
they are pores.
Two types a) Aquaporins- only water.
b) Aquaglyceroporins- also for
small molecules.
2- Ion Channels All cells specially on excitable cells – Neurons and
muscle cells
 Selective and non selective
 Gated – voltage gated and extracellular agonist or
antagonist gated ex – acetylcholine gated cationic
specific channel at motor end plate of skeletal muscle.
 Conductance- 1-2 picosimens and > 100 picosimens.
 Ex- Na, K, Ca, Cl, Anion , cation.
3.Solute Carriers > 40 types , > 300 transporters.
 three gps-1. Uniporters- single molecule across the
membrane (GLUT )
2. Symporters- Two or more molecules
Ex- Na-k-cl Symporter (Kidney)
Na - Glucose Cotransporter.
3. Antiporters- Two or more molecules in
opposite directions
Ex :Na- H antiporter ( PH regulation)
3Na- Ca , Cl- HCO3
 1. ATPase Ion Transporters
1. P- Type- gate phosphorylted during
transport. Na- K ATP ase.
2. V- Type- Vacuolar H- ATPase – urine
acidification on Vacules like endosomes
and lysosomes.
 2. ATP – binding cassette (ABC) transporters – 7 subgroups
transport diverse group of ions ex- Cl, Cholesterol, bile acids,
drugs, iron and organic anions.
 EX:- Cystic fibrosis transmembrane regulator.
Multidrug Resistance Protein.
organic Anions.
Molecular Motors:
 Kinesin- over the microtubule
 Dynein- retrogate transport
 Myosin- over the microfilaments.- 18 types a
Q-1 all membrane processes, such as pumping and
channelling of molecules are carried out by.
c-nucleic acid
Q-2 Which of the following statement about
membrane transport protein is incorrect
a-carrier proteins are similar to enzymes in that they
show saturation
b-carrier protein can facilitate both active and passive
c-channel protein can facilitate both active and passive
d-the Na+ /Glucose transport protein carries out
secondary active transport.
Q-3 Diffusion across the plasma membrane is
more rapid if a substance is
a-a protein
c-high in its oil : water partition coefficient
d-larger and globular in shape
Q-4 the difference between simple diffusion and
facilitated transport is that facilitated transport.
a-is concentration dependent
b-occurs across plasma membrane
c-require membrane protein
d-utilize a substance moving with its concentration
Q-5 Erythrocyte glucose transporter specifically
transports glucose down its concentration gradient
and exhibit hyperbolic saturation kinetics .This is an
example of
a-active mediated transport
b-passive mediated transport
c-non- mediated transport
d-group translocation
Q-6 which one of the following is a correct
statement for Na-K ATPase.
a-it gives out 3 Na-ions and takes in 2 K-ions
b- it gives out 2 Na-ions and takes in 3 K-ions
c- it gives out 3 Ca-ions and takes in 2 K-ions
d-it gives out 3 Na-ions and takes in 2 Ca-ions
Q7-which of the following effects of the steroid
digitalis is observed after treatment of congestive
heart failure.
a-decrease in cytosolic sodium levels
b-inhibition of Na-K ATPase
c-decrease in the force of heart muscle contraction
d-stimulation of the plasma membrane ion pump.
Q8-you wish to design a new drug which will act as
an ionophore to deliver Ca2+ across the nerve cell
membrane .This drug would most likely be
a-hydrophobic on the outside and hydrophilic on
b-insoluble in lipid
c-soluble in proteins
d-smaller than 0.001 nm in diameter
Q9- the process by which a cell secretes macromolecule by fusing a vesicle to the plasma
membrane is called
Q10- free fatty acids enter cell by
a-passive diffusion
b-active diffusion
c- through carrier protein
d – Active transport
 Q-11 Aquaglyceroporins transport-
a. Water only
b. water and small molecules.
c. Water and Glucose
d. Water and salt.
 Q-12 Which of the fallowing is responsible for PH
Regulationa. Antiporters.
b. Symporters
c. Uniporters.
d. Co-porters.
 Q-13 V type – transporters are
a. ATPase dependent.
b. Symporters.
c. Carrier Proteins.
d. Receptor Proteins.
 Q-14 .GLUT is an example of-
a. Antiporters.
b. Symporters
c. Uniporters.
d. Co-porters.
 Q-15 Presence of Ion channels are must on
a. Excitable tissue.
b. Non excitable tissue.
c. Renal tissue
d. Cardiac muscle.
Q-16. Na- K ATPase transport Naa. Towards Concentration gradient.
b. Against Concentration gradient.
c. Towards electro chemical gradient.
d. Against electrochemical gradient.
 Q-17. Rennin secretion from JG cells is an example of-
a.) Exocytosis
b.) pincocytosis
c.) Vacular movement.
d.) Transcytosis.
 Q.- 18. PTH secretion fro parathyroid glands require-
a.) low intracellular Ca.
b.) high Intracellular Ca.
c.) Low intracellular K.
d.) high Intracellular K.
 Q-19. Transcytosis incudes-
a. Endocytosis and phagocytosis.
b. Endocytosis and pincocytosis.
c. Endocytosis and exocytosis.
d. Endocytosis only.
Q-20. Transcytosis occurs at
a). Epethelial Cells.
b). Endocrine Cells.
c). Nerve cells.
d). None of the above.

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