LECTURE DR ZAHOOR ALI SHAIKH 1

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. 2

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 3

 DIFFUSION If 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. 4

5

NET DIFFUSION It is the difference between Two opposite movement 6

Concentration of a substance Lipid solubility Surface area of membrane Thickness of membrane Molecular weight of substance 7

8

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. 9

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. 10

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 11

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. 12

13

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. 14

 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? 15

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 16

i. Facilitated Diffusion ii. Active Transport TWO TYPES: A. Primary Active Transport B. Secondary Active Transport 17

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. 18

19

It involves protein carrier to transfer the substance across the membrane. It is from low concentration to high concentration. Energy is required. 20

21

TWO TYPES: A. Primary Active Transport B. Secondary Active Transport 22

In Primary Active Transport, energy is directly required to move a substance from low concentration to high concentration. 23

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’. 24

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 25

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. 26

27

In Exocytosis, vesicle is formed within the cell. It fuses with plasma membrane then opens up and releases its content outside. 28

You should know 1. Diffusion 2. Osmosis 3. Facilitated Diffusion 4. Primary Active Transport 5. Secondary Active Transport 6. Endocytosis 7. Exocytosis 29

30