structure and function

1. Department of
Pharmacology
Sub : Pharmacology – 1
Topic: BIOLOGICAL
MEMBRANE

2. •Boundaries around cells (Plasma Membrane)
•Boundaries round distinct sub-cellular compartments
(Nucleus, Mitochondria, Lysosomes, Golgi bodies, etc.)
• Segregate intracellular events, and Separate cells from
one another membranes mediate regulation of cellular
functions by acting as selective barriers, allowing inside
environment of cells or organelles to differ from outside
BIOLOGICAL MEMBRANE
A biological membrane or biomembrane is an enclosing
or separating membrane that acts as a selectively
permeable barrier within living things.

3. Biological membranes- (e.g. the plasma membrane)-
1. fluidity
3. function
The membrane encapsulates
cellular components and
maintains an equal solute
concentration between the
inside and the outside of
the cell.
A biological membranes’
main function is to
segregate chemicals.
Outside
Inside
35-50 Å
Membranes impose barriers to
diffusion

4. Lipids assemble spontaneously into sheets, liposomes and micelles-
A lipid’s chemistry determines its geometric shape
(e.g. cones, cylinder, etc.)
Lipids self-associate without covalent bonding; their tails
cooperate to exclude water

5. •Two basic components:
1. Lipids
2. Proteins
•Some membranes also contain carbohydrate
•Composition of lipid, protein and carbohydrate varies
from one membrane to another
ratio of Lipid to Protein is not fixed in most membranes
•Lipid to Protein ratio in membranes varies widely from
4:1 to 1:4, depending on the specific functions of the
membrane

6. Physiological factors and process involved in
transportation of drug access cell membrane
The principle mechanism for transport of drug molecule
across the cell membrane in order of there importance
are……
• Passive diffusion
• Pure transport
• Facilitation diffusion
• Active transport
• Ionic or electrochemical transport
• Ion pair transport
• Endocytosis

7. Different transport systems in biological membranes

8. Passive transport moves across a concentration gradient,
or a gradual difference in solute concentration between
two areas. Simple diffusion is the diffusion of small,
uncharged, or hydrophobic molecules from an area of
high concentration to an area of low concentration
across the cell membrane
Diffusion across a cell membrane is a type of passive
transport, or transport across the cell membrane that
does not require energy. Remember that the cell
membrane is a phospholipid bilayer. Although the inside
and the outside of a cell are both water-based, there is a
hydrophobic region in the middle, and this is an
important barrier to anything large, charged, or
hydrophilic. Molecules that are hydrophobic, just like the
hydrophobic region, can pass through the cell membrane .

10. •Two types of passive transport:
•Simple Diffusion •Facilitated Diffusion
•Simple Diffusion (unmediated, Carrier-free)
•Small uncharged or hydrophobic molecules (H2O, O2,
CO2, other gases, urea, ethanol, esters, ethers, etc.) cross
the lipid bilayer by simple diffusion
•No membrane proteins are involved, so there is no
specificity Unmediated (Carrier-free) transport proceeds
always in the direction of the concentration gradient
•High to Low concentration

11. •Facilitated (carrier-mediated) diffusion of a molecule across
biological membrane is dependent on specific Integral
Membrane Proteins called Uni-porters
•Uni-porter facilitates translocation of molecules across
membrane in the direction of the concentration gradient without
any supply of energy
•Molecule binds to protein on one side of the membrane, the
protein then undergoes a conformational change, transports the
molecule across the membrane and releases it on the other side
•Molecules transported in this way include: Hydrophilic
molecules such as Glucose, Sugars, Amino Acids

13. •It is movement of molecules across bio-membrane from site
of low to higher concentration
•It requires both a Carrier-Protein and metabolic energy
•Energy for active transport can be derived either from direct
coupling to hydrolysis of ATP or by coupling to th movement
of an ion down its concentration gradient.
Active transport may involve:
•Translocation of a single molecule in one direction (Uni-port)
•Translocation of two molecules in opposite directions (Anti-
port)
•Translocation of two molecules in the same directions
(Symport)
•These processes are also known as COUPLED ACTIVE
TRANSPORT

16. This mechanism explains the absorption of drug
which ionises under all pH conditions..

17. •Bidirectional transport of macromolecules between the
nucleus and the cytoplasm occurs through the nuclear
pore complexes (NPCs) by a signal-mediated mechanism
that is directed by targeting signals (NLSs) residing on
the transported molecules or “cargoes.”
• Nuclear transport starts after interaction of the targeting
signal with soluble cellular receptors. After the formation
of the cargo-receptor complex in the cytosol, this
complex crosses the NPC.
• Herein, we use gold particles of various sizes coated
with cargo-receptor complexes to determine precisely
how large macromolecules crossing the NPC by the
signal-mediated transport mechanism could be.

18. •We found that cargo-receptor-gold complexes with
diameter close to 39 nm could be translocated by the NPC.
• This implies that macromolecules much larger than the
assumed functional NPC diameter of 26 nm can be
transported into the karyoplasm.
•The physiological relevance of this finding was supported
by the observation that intact nucleocapsids of human
hepatitis B virus with diameters of 32 and 36 nm are able
to cross the nuclear pore without disassembly.

20. •There are two types of endocytosis, which differ in the
size of the vesicles formed.
• In pinocytosis (or cell drinking), fluid or small
particlesare taken into small vesicles about 150 nm in
diameter. In phagocytosis (or cell eating), large particles
such as micro-organisms and cell debris are taken into large
vesicles (or vacuoles) about 250 nm in diameter. Most cells
carry out
pinocytosis; only specialized phagocytic cells carry out
phagocytosis.
•Many of the particles taken up by either process end up in
lysosome.Phagocytic vesicles
(phagosomes) fuse directly..

22. Reference :-
Source : Internet
http://www.molbiolcell.org/content/13/2/425.short
https://www.biochemistry.org/Portals/0/Education/Docs/BA
SC08
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4626904/