transport of substances through cell membrane

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Transport of Substances through Cell Membranes
DR MUHAMMAD MUQEEM MANGI
MBBS. MPhil PHYSIOLOGY ASSOCIATE
PROFESSOR SULEMAN ROSHAN MEDICAL COLLEGE TANDO
ADAM _at_ HYDERABAD,SINDH PAKISTAN
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Transport of Substances through Cell Membranes

• _at_ the end of slides student have basic concept
  of
• Importance of cell membrane
• Types of Transport mechanisms
• Active transport in detail
• Primary active transport
• Secondary active transport
• Co-transport and Counter transport

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Transport of Substances through Cell Membranes

• The cell perform many functions
• support, transport, communication, recognition
  and acts as selective barriers.
• All these functions are achieved through
  movement across cell membranes.
• There are several mechanisms of transport across
  cellular membranes. Pathways include passive and
  active transport.

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Transport of Substances through Cell Membranes

• The Functions of Cell Membrane
• Protective Function
• Selective permeability
• Absorptive function
• Excretory function
• Exchange of gases
• Maintenance of shape and size of the cell

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Transport of Substances through Cell Membranes

• Differences between composition of intracellular
  and extracellular fluids are caused by transport
  mechanisms of cell membrane.

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Transport across cell membrane
Transport mechanisms
Passive transport (diffusion)
Active transport
Transport of large particles by a)
Endocytosis b) Exoocytosis
Simple diffusion
Facilitated diffusion
Primary
Secondary
Sodium co-transport mechanism
Sodium counter Transport mechanism
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Transport across cell membrane

• Includes passive and active transport.
• Passive transport includes simple and facilitated
  diffusion.
• Active transport includes primary and secondary
  active transport.
• Vesicular transport includes Endocytosis and
  Exocytosis.

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Transport across cell membrane
Membrane transport proteins
2 major classes of transport proteins
Carrier Proteins
Channel Proteins
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Transport across cell membrane
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Transport across cell membrane

• Diffusion
• Means random movement of molecules either thru
  intermolecular spaces in the cell membrane or in
  combination with a carrier protein.
• Energy that causes diffusion is energy of normal
  kinetic motion of matter.

High to Low Concentration
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Transport across cell membrane
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Transport across cell membrane

• Simple diffusion
• Molecules move thru a membrane without binding
  with carrier proteins.
• Does not require energy b/c molecules move across
  the plasma membrane down a concentration gradient
  or electrochemical gradient.

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Transport across cell membrane

• Simple diffusion
• Can occur thru cell membrane by two pathways
  thru the interstices of lipid bilayer and thru
  watery channels in some of the transport
  proteins.
• Transports small non polar molecules (e.g O2 and
  N2) and small uncharged, polar molecules
  (e.g.H2O,CO2,glycerol).

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Transport across cell membrane

• Simple diffusion thru protein channels
• Protein channels are selectively permeable to
  certain substances.
• The channels can be opened or closed by gates.

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Transport across cell membrane

• Gating of protein channels
• Provides a means for controlling the permeability
  of the channels.
• Gates are actual gate like extensions of the
  transport protein molecule.

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Transport across cell membrane

• Opening and closing of gates
• Are controlled in two principal ways
• Voltage gating in this, the molecular
  conformation of the gate responds to the
  electrical potential across the cell membrane.
• Ligand gating some protein channel gates are
  opened by binding of another molecule with the
  protein this causes a conformational change in
  the protein molecule that opens or closes the
  gate.

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Transport across cell membrane
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Transport across cell membrane

• Facilitated diffusion
• Is diffusion of a substance mediated by a
  carrier.
• FD occurs thru ion channels or carrier proteins.
• Is down the electrochemical gradient.

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Transport across cell membrane

• Facilitated diffusion
• Does not require energy.
• Differs from simple diffusion in that the rate of
  diffusion approaches a maximum, called Vmax as
  the conc. of substance increases.

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Transport across cell membrane
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Transport across cell membrane

• Characteristics of Facilitated diffusion
• Specificity
• Vmax

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Transport across cell membrane
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Transport across cell membrane

• Examples of substances transported by facilitated
  diffusion
• Glucose
• Amino acids.
• Mannose
• Galactose
• Xylose
• Arbinose

Examples of substances transported by facilitated
diffusion
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Transport across cell membrane

• Osmosis
• Is the flow of water across a semi permeable
  membrane from a solution with low solute
  concentration to a solution with high solute
  concentration.
• Osmotic pressure is determined by number of
  particles per volume of fluid.

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Transport across cell membrane

• Osmosis is the diffusion of water through a
  selectively permeable membrane like the cell
  membrane
• Water diffuses across a membrane from an area of
  high concentration to an area of low
  concentration.

Semi-permeable membrane is permeable to water,
but not to sugar
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Transport across cell membrane
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Transport across cell membrane

• Osmole, osmolality and osmolarity
• To express the concentration of solution in terms
  of number of particles unit osmole is used.
• Osmolar concentration expressed as osmoles per
  kilogram of solution is osmolality.
• Osmolar concentration expressed as osmoles per
  liter of solution is osmolarity.

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Transport across cell membrane
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Transport across cell membrane

• Active transport
• Occurs in combination of a carrier protein.
• Occurs against the concentration gradient.
• Requires energy.
• Is of two types,
• primary active transport
• secondary active transport.

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Transport across cell membrane

• Primary Active transport
• In primary active transport, energy is derived
  from breakdown of ATP.
• Example is sodium potassium pump.

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Transport across cell membrane
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Transport across cell membrane
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Transport across cell membrane

• Examples of primary active transport
• Sodium ions
• Potassium ions
• Hydrogen ions
• Calcium ions
• Chloride ions

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Transport across cell membrane

• Importance of Na-K pump
• It controls the cell volume by controlling the
  concentration of solutes inside the cell and thus
  minimizing osmotic effects.
• It establishes NaK concentration gradients
  across the plasma membrane of all cells, these
  gradients are critically important in the ability
  of nerve and muscle cells to generate electrical
  signals.

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Transport across cell membrane

• Importance of sodium potassium pump
• The energy used to run the Na K pump also
  indirectly serves as the energy source
• for secondary active transport.

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Transport across cell membrane

• Secondary active transport
• In secondary active transport energy is derived
  by ionic concentration gradient created by
  primary active transport.

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Transport across cell membrane

• Secondary active transport
• Has two types
• Sodium Co-transport mechanism
• Sodium Counter transport mechanism

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Transport across cell membrane

• Sodium Co-transport
• In this mechanism, a substance is transported
  along with sodium in the same direction, and is
  therefore called, sodium co transport mechanism.

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Symport
Transport across cell membrane
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Transport across cell membrane

• Examples of Co-transport
• sodium glucose co-transport.
• sodium amino acids co-transport
• sodium potassium-two chloride co-transport

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Transport across cell membrane

• Sodium counter transport
• In this mechanism, sodium and the other substance
  move in opposite direction.
• Example sodium-calcium counter transport
• Sodium-hydrogen counter transport

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Antiport
Transport across cell membrane

• Two Substrate Bind to the opposite sides of the
  transport.
• One substrate( Na) is travelling downhill will
  energize transport of another substrate ( Ca)
• Transporter changes orientation with respect to
  inner and outer membrane surface
• After being transported across the membrane, both
  substrate are released and the protein is ready
  for an other cycle

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Transport across cell membrane
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Transport across cell membrane

• Endocytosis
• Is the entry of large particles into the cell.
• Occurs in two forms
• Pinocytosis (cell drinking)
• Receptor mediated endocytosis
• Phagocytosis (cell eating)

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Transport across cell membrane

• Pinocytosis
• Occurs in all cells of the body.
• is the only means by which very large
  macromolecules such as protein molecules can
  enter the cell.

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Transport across cell membrane

• Pinocytosis
• Occurs in all cells of the body.
• is the only means by which very large
  macromolecules such as protein molecules can
  enter the cell.

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Receptor mediated Endocytosis
Transport across cell membrane
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Transport across cell membrane
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Transport across cell membrane

• Phagocytosis Involves large particles rather than
  molecules.
• Occurs only in certain cells such as macrophages
  and some of the white blood cells.

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Transport across cell membrane

• Phagocytosis
• In phagocytosis of bacteria, bacteria attach to
  antibodies and then to the receptor. This
  intermediation of antibodies is called
  opsonization.
• Phagocytic vesicle is larger than the pinocytic
  vesicle.

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Transport across cell membrane

• Exocytosis
• Is release of substances originating within the
  cell to the exterior.
• Is the primary mechanism for accomplishing
  secretion.

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Transport across cell membrane

• Exocytosis
• the cell to add specific components to the
  membrane, such as selected carriers, channels or
  receptors.

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THANKS
Transport across cell membrane

• THE END