بسم الله الرحمن الرحيم
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بسم الله الرحمن الرحيم. TRANSPORT ACROSS CELL MEMBRANE. Prepared by Dr.Mohammed Sharique Ahmed Quadri Assistant prof. Physiology Al Maarefa College. Objectives . Define permeability and list factors influencing permeability .

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TRANSPORT ACROSS CELL MEMBRANE

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بسم الله الرحمن الرحيم

TRANSPORT ACROSS CELL MEMBRANE

  • Prepared by

  • Dr.MohammedSharique Ahmed Quadri

  • Assistant prof. Physiology

  • Al Maarefa College


Objectives

  • Define permeability and list factors influencing permeability.

  • Basic principles of various mechanisms of transport across cell membrane (Diffusion, facilitated diffusion, secondary active transport, and primary active transport.)

  • define diffusion and describe the factors that influence the rate of diffusion

  • osmosis, describe the conditions required for it to occur, and explain how osmosis relates to osmolality and osmotic pressure

  • Significance of these mechanisms in various parts of body & and organs


Fluid Mosaic Model of the cell membrane

Polar heads love water & dissolve.

Non-polar tails hide from water.

Carbohydrate cell markers

Proteins


About Cell Membranes (continued)

  • 4. Cell membranes have pores (holes) in it

    • Selectively permeable: Allows some molecules in and keeps other molecules out

    • The structure helps it be selective!

Pores


MEMBRANE TRASPORT

  • Plasma membrane is selectively permeable that means it allows some particles to pass while other can not pass.

  • Things which can pass through Plasma membrane easily are:

    1. Lipid soluble particles e.g. O2, CO2, fatty acid.

    2. Size of the particle—less than 0.8nm.


Weeee!!!

high

low

This is gonna be hard work!!

high

low

Types of Cellular Transport

  • Passive Transport

    cell doesn’t use energy

    • Diffusion

    • Facilitated Diffusion

    • Osmosis

  • Active Transport

    cell does use energy

    • Protein Pumps

    • Endocytosis

    • Exocytosis


Passive Transport

  • Energy is not required

  • Molecules move randomly

  • Molecules spread out from an area of high concentration to an area of low concentration.

    (HighLow)


3 Types of Passive Transport

  • Diffusion

  • Facilitative Diffusion– diffusion with the help of transport proteins

  • Osmosis – diffusion of water


Simple Diffusion

(diffusus means “to spread out”)

  • Molecules/ions are in constant state of random motion due to their thermal energy.

  • Physical process that occurs when

    • Concentration difference across the membrane

    • Membrane is permeableto the diffusing substance.


Passive Transport:1. Diffusion

  • Diffusion: randommovement of particles from an area of high concentration to an area of low concentration.

    (High to Low)

  • Diffusion continues until all molecules are evenly spaced (equilibrium is reached)-Note: molecules will still move around but stay spread out.

http://bio.winona.edu/berg/Free.htm


NetRate of Diffusion

factors affecting net rate of diffusion are

  • Concentration gradient( C)

  • Permeability of membrane (P)

  • Surface area of the membrane (A)

  • Molecular wt of the substance(MW)

  • Thickness of membrane( X)


Fick’s law of diffusion


Diffusion of electrolyte

  • If diffusing sub is an ion or electrolyte there r two consequences

  • Potential difference will alter the net rate of diffusion

  • This diffusion itself generate potential diff acc membrane called a diffusion potential


Electrochemical Gradient

  • When there is Electrical gradient (charge) and Concentration gradient (chemical) for ion it is referred ELECTROCHEMICAL GRADIENT.

  • REMEMBER THREE WORDS

    1. Chemical gradient – concentration of ion

    2. Electrical gradient – charge of ion

    3. Electrochemical gradient – Both Electrical charge and concentration gradient


Passive Transport: 2. Facilitated Diffusion

A

B

2. Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane

  • Transport Proteins are specific – they “select” only certain molecules to cross the membrane

  • Transports larger or charged molecules

Diffusion (Lipid Bilayer)

Facilitated diffusion(Channel Protein)

Carrier-Mediated Transport

Carrier Protein


Passive Transport: 2. Facilitated Diffusion

Glucose

molecules

Cellular Transport From a-

High

High Concentration

Cell Membrane

Protein

channel

Low Concentration

Low

Transport Protein

Through a 

Go to Section:


Diffusion through protein channels &gating of these channels

  • Ion channels are integral proteins, tubular pathway all the way from extra cellular to intracellular fluid, substance can move by simple diffusion directly along these channels

  • These channels are distinguish by two imp characteristics

    -selectively permeable

    -many channels open n closed by gates


Passive Transport: 3. Osmosis

  • 3.Osmosis: diffusion of water through a selectively permeable membrane

  • Water moves from high to low concentrations

  • Water moves freely through pores.

  • Solute (green) to large to move across.


Osmotic Pressure

The force that would have to be exerted to prevent osmosis.


Effects of Osmosis on Life

  • Osmosis- diffusion of water through a selectively permeable membrane

  • Water is so small and there is so much of it the cell can’t control it’s movement through the cell membrane.


Osmolarity

  • Osmoles: concentration of osmotically active particles is expressed as osmoles

  • Osmolarity: number of osmoles per liter of solution

  • Osmolality: number of osmoles per kg of solvent

    osmolarity


Hypotonic Solution

Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water)

Result:Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!


Hypertonic Solution

Hypertonic:The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water)

shrinks

Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!


Isotonic Solution

Isotonic:The concentration of solutes in the solution is equal to the concentration of solutes inside the cell.

Result:Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)


What type of solution are these cells in?

B

C

A

Hypertonic

Isotonic

Hypotonic


References

  • Human physiology by Lauralee Sherwood, fifth edition

  • Text book physiology by Guyton &Hall,11th edition

  • Text book of physiology by Linda .s contanzo,third edition


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