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LECTURE-----4

DR ZAHOOR ALI SHAIKH

MEMBRANE TRANSPORT

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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.

MEMBRANE TRASPORT

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Note – If particles are low lipid soluble and size more than 0.8nm, they can not pass.

MOVEMENT ACROSS CELL MEMBRANE Two Types: 1. Passive transport– No energy is required 2. Active transport– energy is required

MEMBRANE TRANSPORT(CONT)

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DIFFUSIONIf two solutions are separated by permeable

membrane , the movement will take place from high concentration to low concentration

That is down the Concentration Gradient also called CHEMICAL GRADIENT.

No energy is required for this movement It is passive mechanism of Membrane

Transport.Example: O2 transferred across the Lung

membrane is Diffusion.

MEMBRANE TRANSPORT(CONT)

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MEMBRANE TRANSPORT(CONT) DIFFUSION

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NET DIFFUSION It is the difference between Two opposite

movement

MEMBRANE TRANSPORT (CONT)

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Concentration of a substance Lipid solubilitySurface area of membraneThickness of membraneMolecular weight of substance

FACTORS INFLUENCING THE DIFFUSION

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DIFFUSION (cont)

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Ions are electrically charged particles. Movement of ions is also affected by their

electric charge.Cations (positively charged ions) move

towards negatively charged area.Anions (negatively charged ions) move

toward positively charged area.

MOVEMENT ALONG THE ELECTRICAL GRADIENT

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Therefore difference in CHARGE between two adjacent areas produces ELECTRICAL GRADIENT.

ELECTRICAL GRADIENT passively induces movement of ions.

There is ELECTRICAL GRADIENT between Intracellular fluid and Extracellular fluid.

Electrical Gradient (cont)

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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

Electrochemical Gradient

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If two solutions are separated by semi- permeable membrane or selectively permeable membrane, which allows water to cross but does not allow the solute (Na+) to pass, than water will pass from high concentration of water to low concentration of water.

This movement of water from high concentration to low concentration through selectively permeable membrane is called Osmosis.

OSMOSIS

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Tonicity—means concentration of Extracellular fluid.

Isotonic solution– means same concentration. Extracellular fluid (ECF) is isotonic to Intracellular fluid (ICF).

Hypotonic solution – below normal concentration.

Hypertonic solution – above normal concentration.

TONICITY

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Solve the problem

If RED BLOOD CELL (RBC) is put in Hypotonic solution, what will happen?

If RED BLOOD CELL (RBC) is put in Hypertonic solution, what will happen?

TONICITY

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• How poorly lipid soluble molecules e.g. protein, glucose are transported across cell membrane?

• To transport glucose, amino acid in the cell and transport waste products and secretary products out of cell, cell uses TWO different mechanisms.

1. Carrier mediated transport 2. Vesicular transport a). Endocytosis b). Exocytosis

SPECIAL MECHANISM FOR TRASPORT OF SUBSTACE ACROSS PLASMA MEMBRANE

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i. Facilitated Diffusion

ii. Active Transport TWO TYPES: A. Primary Active Transport B. Secondary Active Transport

1. Carrier mediated transport

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Carrier is involved.Carrier facilitates ( assists ) the substance to

move from high concentration to low concentration.

No energy is required.Example – glucose transport in cell.

i. Facilitated Diffusion

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It involves protein carrier to transfer the substance across the membrane.

It is from low concentration to high concentration.

Energy is required.

ii. Active Transport

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TWO TYPES: A. Primary Active Transport B. Secondary Active Transport

ACTIVE TRANSPORT (cont)

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In Primary Active Transport, energy is directly required to move a substance from low concentration to high concentration.

A. Primary Active Transport

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In Secondary Active Transport, when Na+ and glucose are carried together, energy is required for Na+ to move it from lower concentration to higher concentration.

Now if glucose is also carried (co-transported with Na+) by the carrier – glucose gets free ride.

Therefore, glucose transport is called ‘Secondary Active Transport’.

B. Secondary Active Transport

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In Vesicular Transport , material is moved into or out of the cell, wrapped in membrane.

Vesicular Transport is of TWO types: i. Endocytosis ii. Exocytosis

2. Vesicular Transport

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Endocytosis means ‘substances are taken into the cell’.

Endocytosis of fluid is called ‘Pinocytosis’ (cell drinking).

Endocytosis of large particles e.g. bacteria is known as ‘Phagocytosis’ (cell eating).

Once inside the cell, Lysosomes unite the vesicle to kill the bacteria.

i. Endocytosis

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ENDOCYTOSIS

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In Exocytosis, vesicle is formed within the cell. It fuses with plasma membrane then opens up and releases its content outside.

ii. Exocytosis

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You should know 1. Diffusion 2. Osmosis 3. Facilitated Diffusion 4. Primary Active Transport 5. Secondary Active Transport 6. Endocytosis 7. Exocytosis

Methods Of Membrane Transport

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Thank you