The document discusses various mechanisms of membrane transport, including passive transport, ionophores, porins, ion channels, aquaporins, transport proteins, filtration, and osmosis. Passive transport uses integral membrane proteins to transport larger molecules across cell membranes without energy. Ionophores increase membrane permeability to ions and can exert antibiotic effects. Porins form water-filled pores to transport molecules. Ion channels allow rapid ion passage. Aquaporins transport water and small solutes. Transport proteins may form channels or undergo conformational changes. Filtration and osmosis move water and solutes across membranes.

1. Membrane transport

2. James Danielle
(1911-1984)
Cell Membrane
“Possibly the decisive step
the origin of life] was the
formation of the first cell,
which chain molecules
enclosed by a
membrane which kept
together but let their food

3. Plasma membrane

5. Membrane transport
“The collection of mechanisms that
regulate the passage of solutes such as
ions and small molecules through
biological membranes, which are lipid
bilayers that contain proteins
embedded in them.”

7. Passive Transport
 Passive transport that uses integral
membrane proteins to help larger,
charged, hydrophilic, and polar molecules
across a concentration gradient.
 It does not require cellular energy to
transport molecules across cell
membrane.
 Passive-mediated transport is carried out

8. Ionophores
Ionophores are organic molecules of diverse
types, usually of bacterial origin, that
increase the permeability of membranes to
ions. These molecules often exert an
antibiotic effect by discharging the vital
ion concentration gradients that cells
actively maintain.
1. Carrier ionophores
2. Channel forming ionophores

9. Valinomycin
Gramicidine

10. Porins
Porins are bacterial β-strand proteins that
form a water-filled β-barrel pore within the
outer membrane, either causing a
disruption of the membrane or generating a
means for transporting molecules such as
carbohydrates and amino acids across the
membrane.

11. Ion channels
All cells contain ion-specific channels that
allow the rapid passage of ions such as Na,
K, and Cl. The movement of these ions
through such channels, along with their
movement through active transporters, is
essential for maintaining osmotic balance,
for signal transduction.
1. Mechanosensitive channels
2. Ligand-gated channels
3. Signal-gated channels

13. Aquaporins
Aquaporins (AQP)
are integral
membrane proteins
that serve as
channels in the
transfer of water,
and in some cases,
small solutes across
the membrane. They
are conserved in
bacteria, plants, and

14. Transport proteins
Membrane proteins known as ‘connexins’
also form such channels, in the form of
gap junctions between cells.
However, not all membrane transport
proteins offer a discrete bilayer-spanning
pore. Instead, some proteins undergo
conformational changes to move
substances from one side of the
membrane to the other.

16. Some transport proteins move more than one
substance at a time. Hence, it is useful to
categorize mediated transport according to the
stoichiometry of the transport process.
1. Uniport
2. Symport
3. Antiport

17. Filtration
Filtration is the
process of the
movement of water
and solute molecules
across the cell
membrane due to
hydrostatic pressure
generated by the
system. Depending on
the size of the
membrane pores,

18. Osmosis
• Osmosis is a form of passive transport
that's similar to diffusion and involves a
solvent moving through a selectively
permeable or semipermeable membrane
from an area of higher concentration to
an area of lower concentration.
• the ability of an extracellular solution to
make water move into or out of a cell by
osmosis is known as toncity.