Transport_across_cell_membrane____. pptx

It is a ppt tells about transport across cell membrane.
It includes transport proteins: channel proteins, carrier proteins.
protein channels characteristics: selectively permeable, gating.
method of transport which include active and passive transport. other method of transport exocytosis, endocytosis, phagocytosis,
pinocytosis.

1. Transport across cell membrane

2. The chemical composition of extracellular fluid (ECF) is quite different from that of intracellular fluid (ICF). The difference is extremely important for the survival of cell. Passage of substances through the cell membrane can be divided into two categories: (a) Direct Passage through the membrane. (b) Passage through carrier proteins and channels. The lipid bilayer of the cell membrane allows lipid – soluble substances such as oxygen, carbon dioxide , nitrogen , and alcohol to pass through it. Lipid insoluble substances such as electrolytes, glucose, and amino acids are selectively transported by protein molecules present in the cell membrane. These proteins are called transport proteins.

3. TRANSPORT PROTEIN CHANNEL PROTEINS CARRIER PROTEINS

4. CHANNEL PROTEINS They have watery spaces through the molecules allow free movements of certain ions and molecules. Ion channels Water channels They are formed by polypeptides subunits. They are called aquaporins. Ions pass from one side of the membrane to the other through pores. Example: sodium channel and potassium channel They are mainly present in kidneys. They also found in liver, spleen, leukocytes, and lacrimal glands.

5. Protein channels have two important characteristics : They are selectively permeable to certain substances. Many of the channels can be opened or closed by gates. voltage gating chemical gating The molecular conformation The molecule are opened of gate responds to changes with the binding of another in the electrical potential across molecule. the cell membrane.

6. CARRIER PROTEINS They bind to substances that are to be transported. This causes movement of substances from one side of the membrane to the other. Uniport Symport Antiport There is transport of only one substances. There is transport of two substances in the same direction. There is movement of two substances in opposite direction. Example : Na channels transport Na+ Example :Sodium and glucose transport Example : Na+ - Ka+ pump

7. METHODS OF TRANSPORT ACTIVE TRANSPORT PASSIVE TRANSPORT The active transport mechanism includes the following: Primary Secondary The passive transport mechanism includes the following: Simple diffusion Facilitated diffusion Osmosis Filtration Bulk flow Solvent drag

8. Other transport mechanisms include the following : 1. Exocytosis 2. Endocytosis 3. Phagocytosis 4. Pinocytosis

9. PASSIVE TRANSPORT Transport occurs downhill (along the electrochemical gradient). It doesn’t require ATP.

10. DIFFUSION It is the continuous movements of molecules among one another in a liquid or in a gaseous state. It is of two types : Simple diffusion Facilitated diffusion The movement of molecules or ions through cell membrane without involvement of carrier proteins. This occur through the lipid bilayer and protein channels. Diffusion depends on the following: Permeability of cell membrane Concentration gradient Electrical gradient Pressure gradient It is also called carrier- mediated diffusion. The substances are transported with the help of specific carrier protein. Features of facilitated diffusion Faster rate of transport Saturation Specificity Competitive inhibition

11. Osmosis It is a special type of diffusion. It is the movement across a semi permeable membrane from a region of lower solute concentration to a region of higher solutes. Filtration It is a process by which fluid is forced through a membrane because of pressure difference on both sides. Bulk flow The process of movement of greater quantities of water. Solvent drag It occurs during bulk flow. In this process, dissolved particles are also carried with water.

12. ACTIVE TRANSPORT It is the process by which molecules or ions move uphill across the cell membrane against a concentration gradient. Uphill transport (occurs against the electrochemical gradient ). Utilisation of energy Exhibits saturation

13. Primary active transport In primary active transport , energy is derived directly from the breakdown of ATP or some other high energy phosphate compounds. Example: Sodium potassium pumps Potassium hydrogen pumps Calcium pumps Secondary active transport The energy derived from the transport of one substances help in the movement of the others substances. This is of two types: Cotransport (symport) Counter transport (antiport)

14. Sodium potassium pump It is present in all the cells of the body. This pump transport sodium ions from inside the cell to the exterior. At the same time , it transport potassium ions from outside to inside of the cell. Potassium hydrogen pump It is present in two places : The parietal cells of gastric glands The renal tubules This pump H+ ions out of the cell. At same time, k+ ions from lumen into the cell. Calcium pump The calcium pump helps in maintaining extremely low concentration of calcium in the intracellular fluid.

15. Cotransport (symport) Two substances are simultaneously transported across the cell membrane in the same direction. Example : sodium glucose co transport Counter transport (antiport) A single carrier is used to transport two substances in opposite directions. Examples: sodium calcium counter transport.

16. Exocytosis It is a process by which intracellular substances are extruded ( force out ) of the cell. The membranes of granules and vesicles fuse with the cell membrane releasing the contents to the exterior. Release of hormones and enzymes by the secretory cells of the body occurs by exocytosis. Endocytosis It is the reverse of exocytosis. It is a process by which substances are taken into the cell. Phagocytosis It is a process in which bacteria, dead tissues, are engulfed by the cells. Attachment of the foreign molecules with the cell membrane Engulfment of the foreign molecules in the form of endocytosis vesicles. Pinocytosis It is similar to phagocytosis. The substance ingested are in fluid form. It is therefore called cell drinking.

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