The document discusses intracellular and extracellular communication through biological membranes. It notes that water makes up 60% of lean body mass and is divided between intracellular and extracellular fluid. Intracellular fluid provides the cell's environment while extracellular fluid acts as a delivery and waste removal system. Cells developed selective barriers called membranes that use pumps to regulate material exchange and maintain internal conditions. The document outlines membrane structure including lipid bilayers and integral and peripheral proteins. It describes membrane transport mechanisms like simple diffusion, facilitated diffusion, active transport, endocytosis, and exocytosis which allow specialized cellular functions.

1. Biochemistry of Extracellular &Biochemistry of Extracellular &
Intracellular CommunicationIntracellular Communication
Membrane Structure &Membrane Structure &
DynamicsDynamics

2. Body FluidsBody Fluids
• Water makes ~ 60% of the lean body mass & is
distributed in 2 large compartments:
– Intracellular Fluid (2/3 of water) & provides the
environment for the cell to 1) make, store & utilize
energy 2) repair 3) replicate 4) perform special
functions
– Extracellular Fluid (1/3 of water). It act as
delivery system that brings to the cell: nutrients,
oxygen, various ions & minerals & hormones. And
removes CO2, waste products, toxic & detoxified
materials from the immediate cellular environment
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3. • Intracellular environment is rich in K+
, Mg+
and
phosphate. While the extracellular fluid is
characterized by high Na+
, Ca+
and Cl-
.
• Based on the biochemical & physiological
actions; cells exchange materials with the its
environment.
• In order to maintain the internal
microenvironment, cells developed barriers
(membranes) with associated pumps.
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4. • Biological membranes are sheet-like structures,
that are composed of protein & lipid molecules
held together by non-covalent interactions
• They have selective permeability
• They create closed compartment (cell or organelle)
• Pnmps & gates regulate the molecular & ionic
compositions of these compartments
• They also control the flow of information between
cells, e.g many membranes have hormone
receptors
• Furthermore, membranes are involved in energy
conversion processes, such as oxidative
phosphorylation
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5. Membrane Lipids:
• Major classes are phospholipids, glycolipids &
cholesterol
• They are amphipathic ( hydrophilic and
hydrophobic ) molecules that spontanously
form extensive bimolecular sheets (lipid
bilayer)
• These lipid bilayers are highly impermeable to
ions & most polar molecules, but they are
quite fluid, which enables them to act as
solvents for membrane proteins
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6. Membrane proteins:
• Distinctive membrane functions such as
transport, communication & energy
transduction are mediated by proteins
• There are 2 types of membrane proteins:
– Integral
– Peripheral
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10. Fluid Mosaic Model
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11. Membrane selectivity allowsMembrane selectivity allows
specialized functionsspecialized functions
• Certain molecules freely diffuse across
membranes, but the movement of others is
restricted because of:
– Size
– Charge
– Solubility
• Plasma membranes are involved in simple &
facilitated diffusion, active transport & other
processes such as endocytosis & exocytosis.
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12. Simple Diffusion:
• Some solutes such as gases enter the cell by
diffusing down an electrochemical gradient &
is limited by:
– Thermal agitation (physics related to
particles in thermodynamic equilibrium ) of
that molecule
– Concentration gradient across the membrane
– The solubility of the solute in the
hydrophobic core of the membrane bilayer
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13. • Molecules that cannot pass freely through the
lipid bilayer membrane by themselves, do so in
association with carrier proteins. This involves 2
procesess:
– Facilitated diffusion
– Active trasnport
# Both processes involve carrier proteins &
show specificity for ions, sugars & amino
acids.
# Active transport needs energy while facilitated
diffusion is not. This is the major difference
between the two processesAMNA MEDANI,2015AMNA MEDANI,2015

14. Endocytosis (phagocytosis & pinocytosis):
• Endocytotic vesicles are generated when
segments of the plasma membrane invaginates,
enclosing a minute volume of extracellular
fluid & its contents. Then it pinches off, fuses
with other membrane structures & thus
transports its contents to other cellular
compartment.
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15. Exocytosis:Exocytosis:
A process by which most cells releaseA process by which most cells release
macromolecules to the exteriormacromolecules to the exterior

16. • Cross-membrane movement of small molecules:
– Diffusion (passive & facilitated)
– Active transport
• Cross-membrane movement of large molecules:
– Endocytosis
– Exocytosis
• Signal transmission across membranes:
– Cell surface receptors:
• Signal transduction
• Signal internalization
– Movement to intracellular receptors
Transfer of material & information across membraneTransfer of material & information across membrane
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