2. • Transport of various small and large molecules
across the cell membrane, which is relatively
impermeable, occurs by several mechanisms.
• Transport of small molecules
• Passive transport
• Facilitated diffusion. By transporters
By ion channels
5. Transport of large molecules
• By endocytosis
• By exocytosis
• Beside the above, cell membrane is also
involved in signal transduction across the
membrane via receptors and signal
6. • Passive transport-Without the input of any
energy,occurs under the influence of
• Facilitated transport-It is also a passive
transport but it uses specific transport proteins
• Active transport-Occurs against a
concentration gradient and requires the input
of energy as ATP.
8. Membrane transporter
• Transporter are involved in facilitated as well
as active transport of solute.
• Uniport-Transport one type of molecule
• Symport-Transport two types of molecules in
same direction.e.g. Na+ glu.symport
• Antiport-Transport two different molecules in
the opposite direction.e.g. Na+-Ca++
11. Property of a Transporter
• A specific solute binding site
• A saturable system and has a maximum rate of
• An affinity towards the solute (Km) like
• Transporters are different in one important
aspect from enzyme.They do not modify the
solute unlike enzymes which convert the
substrate into product.
13. • Diffusion-Simple diffusion occurs the con.
gradient and its solublity in the hydrophobic
membrane core of the membrane
• Gases co2 and o2 diffuse freely.
• Na+,k+,Cl-,which are poorly soluble in lipid
do not diffuse easily. They require hydration
shell,the size of which is directly proportional
to charge density on ion.
• Na+ has higher charge,large shell of water,
diffuse slowly than K+.
14. • Factors affect Diffusion
• Concentration gradient
• Electric potential across the membrane,solute
moves toward the opposite charge.
• Permeability coefficient
• Hydrostatic pressure gradient
• Temp. Higher temperature increase partial
motion and enhance diffusion.
15. • Facilitated Diffusion
• Some solute are transported across membrane by
specific channels or transporter protein located in
• This specific transporter is saturable and is driven
by transmembrane electrochemical
gradients.They are also show substrate specificity.
• Rate depends upon on concentration gradient of
the solute,availability of the transporter,binding
affinity of solute to transporter and rate of
conformation changes in transporter.
17. • Co-transporters
• They use the gradient created by the active
transport of one substance to derive the
movement of the other solute.The gradient
used may be produced by an ATPase
pump(primary-co-transport) by other
• They are transmembrane protein
• Make pore size of 5-8 nm
• Conduct rapidly
• Composed of many subunits
• Highly specific for the ions they transport.
• They open transiently to allow ion movement.
• Their activity are regulated and these are
conserved in species.
19. MEDIATORS OF ION CHANNELS
• Opening and closing of ion channels is mediated
in several ways depending upon the type of
channels mentioned below.
• By ligand bending in ligand gated channel
• By change in voltage in voltage gated channel
• By mechanical change,pressure in mechanically
• Permeabiltyof ion channel depends upon the
• Size and charge of the ion,
• Degree of hydration of ion
20. • Na+ channel
• Composed of many subunits
• α- subunit is essential,which is a large
protein(1840 a.a.),organised into four domains
clustered togather to make a central pore.
• Each domain has six transmembrane α –helical
• Actual channel is formed by the association of
four domains and has a pore of 5-8 nm dimeter
22. • Helices v and Vl of each domain are critical in
imparting Na+ specficity and pore formation
• Helix lV impart voltage sensitivity to the
• Neuronal and muscle Na+ channels are voltage
• Highly selective for Na+ ions.
23. • K+ channel
• Consist of our subunits of transmembrane
• Each subunit is a dimer.
• The four subunits are arranged to make a
inverted cone like structure.
• Ion selectivity is conferred by the lining of
channel by the carbonyl oxygen atoms of
threonine,tyrosine,glycine and valine residues.
• K+ ion get dehydrated as they enter into the
channel to fit into the channel and pass through
24. • Na+ ion is too small to intract with carbonyl
oxygen in correct alignment and is rejected.
• K+ channel is also voltage gated channel.
• AQUAPORIN THE WATER CHANNEL
• They are a family of integral membrane
proteins which make water channels
• Ten types of aquaporins are known,each with a
• Rate of follow of water molecules through the
different aquaporins is variable.
25. • They permit movement of water molecule but
not hydronium ions.
• Therefore maintaining the pH gradient across
• They are small, hydrophobic, intinsic
• It is highest for AqP1(109 water
molecules/sec,Aqp2 mutation cause Diabetes
26. ACTIVE TRANSPORT
• It require energy(By ATP hydrolysis) to
transport a molecule uphill against the
• Primary active transport-By ATP hydrolysis
and ATP hydrolysis is directly coupled to
transport of a solute.e.g. Na-K+ ATPase pump.
• Secondary active transport-Occurs when uphill
transport of one solute is coupled to downhill
transport of other solute which has been earlier
transported by primary active transport
29. PRIMARY ACTIVE TRANSPORT SYSTEM
• ATP dependent transporters
Type Cellular location and
ABC-transporter ABC-ATP Binding cassette
H+-ATPase;pumps H+ ions into
F-Type F=Coupling Factor
Mitochondrial ATP synthase
Na+-K+ATPase in plasma membrane
Ca++-ATPase in sarcoplasmic reticulm
30. SECONDARY ACTIVE
• Glucose in the intestinal wall cell is
transported by secondary active transport
along with sodium by sodium glucose
• SGT-1 is coupled to Na+-K+ ATPase pump
which maintain the Na+ gradient across the
32. TRANSPORT OF MACRO
• EDOCYTOSIS-It is a process intake of fluid
and substance into cell from sroundind.
• Occurs by invagination of a part of membrane
enclosing a small amount of fluid along with
• The invagination form a vesicle which then
• Subsequent fusion of plasma membrane
restores the cellular membrane continuity.
34. • The vesicle transport its content to other cell
organelles by fusion with lysosome to make
• The enzymes degrade the molecular content
into the consituent molecule.
• It require ATP,Ca++ and contractile element.
• Type of endocytosis
2 Pinocytosis (Two types)
1 Fluid phase pinocytosis
2 Absorptive endocytosis
• Endocytosis undertaken by phagocytes like
macrophages is called phagocytosis.
• Phagocytosis involves the ingestion of large
particulate material like bacteria, viruses, dead
cell, debries etc.
• It play an important role in combating
infectious and removal of other harmful
38. Fluid phase pinocytosis
• It is general mechanism of ingestion, like
endocytosis, undertaken by all cells in a non-
• It is much slower than phagocytosis.
• It does not lead to much change in the volume
or surface area of the cell.
• Ingested membrane is replaced by exocytosis
39. ABSORPTIVE ENDOCYTOSIS
• It is a selective, receptor mediated endocytosis
used to ingest specific substance from
extracellular space without much fluid and
• The substance to be ingested binds to the
receptor and is endocytosed.
• The invaginated vesicle is coated on the
cytoplasmic side with filamentous protein
40. • Clathrin protein is involved in the endocytosis
og ligand-receptor complex internalization as
in case of hormones. Growth factors and other
protein like transferrin.
• All these are internalized as complex with their
• LDL receptors mediated internalization of
LDL occurs through clathrin coated pits.
• Cell release molecules by exocytosis.
• It is often initiated by a signal such as
hormone, which on binding to the receptor
cause a local increase in Ca++ concentration.
• This triggers exocytosis.
43. FUNCTION OF EXO.AND
• It regulate the membrane components, various
transporter and cell function.
• Nutrition intake and secretion of products.
• Cell communication.
• Removal of microbes and antigen.
• Role in research and therapeutics.
• Endocytosis cause some
• Produced by bacteria which facilitate the
transport of ions across the membrane.
• Non-protein compound
• Some are antibiotic in nature.
• Mobile ionophores bind to ion and diffuse
across the membrane.
• Channel ionophores form channel in the
membrane to transport ions.
45. IONOPHORE ION Transport Action
Valinomycin K+ Uniport;electron
Nigrecin K+/H+ Antiport;electron
A 2387 Ca++/2H+ do
Gramicidin H+/K+/Na+ Channel forming
Alamethicin K+ Channel forming