Plasma membrane or cell membrane (2).pptx

Plasma membrane

1. CELL MEMBRANE The cell membrane also called the plasma membrane or Plasmalemma - separating the interior of a cell from the outside environment. Outside cell Cell interior Plasma membrane

2. Plasma membrane The plasma membrane separates the internal environment of the cell from the external environment . It regulates the entrance and exit of molecules into and out of the cell. It helps the cell and the organism maintain a steady internal environment.

3. History

4. Ernest overtone (1980) recognized that boundary of plants and animals cells was “impregnated” by lipid material. Langmuir studied that if a lipid containing hydrophilic groups is dissolved in highly volatile solvent and several drops then carefully applied to the surface of water , the lipid spreads out to form a thin monomolecular film in which the hydrophilic parts of each molecule project into the water surface and the hydrophobic parts are directed up away from the water. History

5. Gordel and Grendel proposed that cell membrane formed by bimolecular lipid sheet . In 1935 they proposed that plasma membrane itself might be composed of two such lipid – protein bilayers- one facing the interior of the cell and the other facing the external surface of the cell

6. Robertson’s Unit Membrane Model In the late 1950s, Robertson proposed this mode According to the him, the unit membrane consisted of bimolecular lipid sandwich between outer and inner layers of the proteins organized in a pleated sheet configuration. Such arrangement was presumed to be basically the same in all the cells.

7. Fluid mosaic model The plasma membrane is a phospholipid bilayer in which protein molecules are either partially or wholly embedded . The phospholipid bilayer has a fluid consistency. The proteins are scattered either just outside or within the membrane . This description of the plasma membrane is called the fluid-mosaic model of membrane structure .

8. The Fluid Mosaic Model

9. The Fluid Mosaic Model The hydrophilic (water-loving) polar heads of the phospholipid molecules face the outside and inside where water is present. T he hydrophobic (water-fearing) nonpolar tails face each other. Cholesterol is another lipid found in animal plasma membranes . Cholesterol stiffens and strengthens th e membrane, thereby helping to regulate its fluidity.

10. Plasma membrane or cell membrane components Contents 1 plasma membrane structure and function 2 plasma membrane permeability

11. Membrane proteins The proteins in a membrane consist of peripheral proteins and integral proteins. 1. Peripheral protiens Peripheral proteins are associated with only one side of the plasma membrane. Peripheral proteins on the inside of the membrane are often held in place by cytoskeletal filaments .

12. Membrane proteins

13. 2.Integral protiens Integral proteins span the membrane, and can protrude from one or both sides . They are embedded in the membrane, but they can move laterally , changing their position in the membrane.

14. Functions of the Proteins The plasma membranes of various cells and the membranes of various organelles each have their own unique collections of proteins. The peripheral proteins often have a structural role in that they help stabilize and shape the plasma membrane. They may also function in signaling pathways.

15. Types of integral proteins The integral proteins largely determine a membrane’s specific functions. Integral proteins can be of the following types : Channel proteins Carrier proteins Cell recognition proteins Receptor proteins Enzymatic proteins

16. Channel proteins Channel proteins are involved in the passage of molecules through the membrane. They have a channel that allows a substance to simply move across the membrane. For example , A channel protein allows hydrogen ions to flow across the inner mitochondrial membrane . Without this movement of hydrogen ions, ATP would never be produced.

17. Example Channel Protein Allows a particular molecule or ion to cross the plasma membrane freely. Cystic fibrosis, an inherited disorder, is caused by a faulty chloride ( Cl –) channel; a thick mucus collects in airways and in pancreatic and liver ducts.

18. Carrier proteins Carrier proteins are also involved in the passage of molecules through the membrane. They combine with a substance and help it to move across the membrane. For example , a carrier protein transports sodium and potassium ions across a nerve cell membrane. Without this carrier protein, nerve conduction would be impossible.

19. Carrier Protein Selectively interacts with a specific molecule or ion so that it can cross the plasma membrane. The family of GLUT carriers transfers glucose in and out of the various cell types of the body . Different carriers respond differently to blood levels of glucose

20. Cell recognition proteins Cell recognition proteins are glycoproteins Among other functions, these proteins help the body recognize when it is being invaded by pathogens so that an i mmune reaction can occur.

21. Cell Recognition Protein The MHC (major histocompatibility complex) glycoproteins are different for each person, so organ transplants are difficult to achieve . Cells with foreign MHC glycoproteins are attacked by white blood cells responsible for immunity .

22. Receptor proteins Receptor proteins have a shape that allows a specific molecule to bind to it . The binding of this molecule causes the protein to change its shape and thereby bring about a cellular response. The coordination of the body’s organs is totally dependent on such signal molecules. For example, the liver stores glucose after it is signaled to do so by insulin.

23. Receptor Protein Shaped in such a way that a specific molecule can bind to it . Some types of dwarfism result not because the body does not produce enough growth hormone , but because the plasma membrane growth hormone receptors are faulty and cannot interact with growth hormone.

24. Enzymatic proteins Enzymatic proteins carry out metabolic reactions directly . Without the presence of enzymes, some of which are attached to the various membranes of the cell . A cell would never be able to perform the metabolic reactions necessary to its proper function

25. Enzymatic Protein Catalyzes a specific reaction . The membrane protein, adenylate cyclase , is involved in ATP metabolism. Cholera bacteria release a toxin that interferes with the proper functioning of adenylate cyclase , which eventually leads to severe diarrhea .

26. Carbohydrates Both phospholipids and proteins can have attached carbohydrate (sugar) chains. These molecules are called glycolipids and glycoproteins, respectively. The carbohydrate chains occur only on the outside surface . Peripheral proteins occur asymmetrically on one surface or the other, the two halves of the membrane are not identical. .

27. Carbohydrates Certain plasma transporter proteins, hormones, and enzymes are glycoproteins and in these molecules carbohydrates are important to physiological activity. The carbohydrates of glycolipids of the RBC plasma membrane determine weather a person blood type is A, B, AB, O

28. A person having blood type A has an enzyme that adds an N- acetylgalactosamine to the end of the chain. A person blood type B has an enzyme that adds a Galactose to the chain terminus.

29. People with blood type AB posses both enzymes. People with blood group O lack the enzymes capable of attaching either terminal suga r

30. How Cells Talk to One Another Cell Signaling The cells of a multicellular organism “talk” to one another by using signaling molecules, sometimes called chemical messengers. Some messengers are produced at a distance from a target tissue and, in animals, are carried by the circulatory system to various sites around the body. For example, the pancreas releases a hormone called insulin.

31. (a) Some cells signal one another by making direct contact . ( b) In paracrine regulation, a local regulator diffuses to target cells. (c) Neurons transmit signals across synapses. ( d) Many hormones are transported in blood to target cells

32. Receptor: Binds to a signaling molecule, becomes activated and initiates a transduction pathway. 2 . Transduction pathway : Series of relay proteins that ends when a protein is activated. 3. Response: Targeted protein(s) bring about the response(s) noted structural protein enzyme gene regulatory protein Targeted protein: Cellular response Altered shape or movement of cell Altered metabolism or a function of cell Altered gene expression and the amount of a cell protein Cytoplasm plasma membrane

33. The Permeability of the Plasma Membrane charged molecules and ions H2O noncharged molecules macromolecule protein phospholipid molecule

34. Passive Transport Processes Some of the transport process happens "passively" without the cell needing to expend any energy to make them happen. These processes are called "passive transport processes". Passive transport processes includes Osmosis Diffusion Facilitated diffusion

35. Active Transport Active transport refers to a process in which a substance is transported across a membrane by the use of an integral membrane protein (or protein complex) that has ATPase activity. Example: Sodium-Potassium pumps The sodium-potassium pump was discovered in the 1950’s by Jens Christian Skou . It marked an important step forward in our understanding of how ions get into and out of cells, and it has a particular significance for excitable cells such as nervous cells, which depend on it for responding to stimuli and transmitting impulses.

36. ENDOCYTOSIS

37. Exocytosis

38. Co-transport C o-transport is the name of a process in which two substances are simultaneously transported across a membrane by one protein, or protein complex which does not have ATPase activity. Different types of co-transport Symport When both substances are transported in the same direction the transport protein is known as a symport . Antiport When the substances are transported in opposite directions the transport protein is known as an antiport .