Cell Theory


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Continuation of the topic in Cell theory. More of the Passive and Active Transport, etc.

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Cell Theory

  1. 1. CELL MEMBRANE • Outside boundary • Give shape • Surround and protect the cell • Passage way of materials into and out of the cell • Also called “plasma membrane” • Semipermeable membrane (a permeable membrane allows all materials through, while an impermeable membrane does not allow anything through)
  2. 2. • The fluid-mosaic model describes the plasma membrane of animal cells. The plasma membrane that surrounds these cells has two layers (a bilayer) of phospholipids (fats with phosphorous attached), which at body temperature are like vegetable oil (fluid). And the structure of the plasma membrane supports the old saying, “Oil and water don’t mix.” • Each phospholipid molecule has a head that is attracted to water (hydrophilic: hydro = water; philic = loving) and a tail that repels water (hydrophobic: hydro = water; phobic = fearing). Both layers of the plasma membrane have the hydrophilic heads pointing toward the outside; the hydrophobic tails form the inside of the bilayer.
  3. 3. Fluid Mosaic Model According to the fluid mosaic model of S.J. Singer and G.L. Nicolson (1972), which replaced the earlier model of Davson and Danielli, biological membranes can be considered as a two-dimensional liquid in which lipid and protein molecules diffuse more or less easily. Although the lipid bilayers that form the basis of the membranes do indeed form two- dimensional liquids by themselves, the plasma membrane also contains a large quantity of proteins, which provide more structure. Examples of such structures are protein-protein complexes, pickets and fences formed by the actin-based cytoskeleton, and potentially lipid rafts. S.J. Singer G.L. Nicolson
  4. 4. Adolf Eugen Fick (3 September 1829 – 21 August 1901) was a German-born physician and physiologist. In 1855, he introduced Fick's law of diffusion, which governs the diffusion of a gas across a fluid membrane. In 1870, he was the first to measure cardiac output, called the Fick principle.
  5. 5. Diffusion is one of several transport phenomena that occur in nature. A distinguishing feature of diffusion is that it results in mixing or mass transport, without requiring bulk motion. In Latin, "diffundere" means "to spread out".  the process whereby particles of liquids, gases, or solids intermingle as the result of their spontaneous movement caused by thermal agitation and in dissolved substances move from a region of higher to one of lower concentration  a passive process which means that no energy is needed  due to the random movement of particles  plays a part in moving substances in and out of the cell
  6. 6. The concept of diffusion is widely used in: • physics (particle diffusion) • chemistry • biology • sociology • economics • finance (diffusion of people, ideas and of price values). The concept of diffusion is typically applied to any subject matter involving random walks in ensembles of individuals.
  7. 7. The diffusion of water through a selectively permeable membrane is called osmosis. Water helps to dissolve many of the substances involved in cell processes. When water is lost (moves out of the cell) it leaves behind a high concentration of the dissolved substances- when water moves back into the cell, the substances become more diluted and can be used by the cell for its life functions.  Movement of molecules from an area of lower concentration to an area of greater concentration.
  8. 8. Solution is a type of homogenous mixture in which the particles of one or more substances (the solute) are distributed uniformly throughout another substance (the solvent).  A solution typically consists of the dissolved material called the solute and the dissolving agent called the solvent. A common example is sugar (the solute) dissolved in water (the solvent). Isotonic Solution is a solution having the same osmotic pressure as blood; the concentration of the water molecules is the same as that in the cell.  Isotonic solutions are commonly used as intravenously infused fluids in hospitalized patients.
  9. 9. Hypotonic solution refers to any solution which has a lower osmotic pressure than another solution (that is, has a lower concentration of solutes than another solution). In biology, a hypotonic solution refers to a solution that contains less solute (more water) compared to the cytoplasm of the cell. If the solution surrounding the cell is hypotonic osmosis causes water to have a net flow into the cell, thus, resulting in the swelling and expansion of the cell. When an animal cell is set to a hypotonic environment the cell will eventually lyse (rupture) due to the osmotic pressure. In a plant, the cell will not lyse but become turgid because of its cell wall that prevents it from bursting. In fact, it is the osmotic pressure (or turgor pressure) that helps keep the plant from wilting and losing its shape.
  10. 10. Hypertonic solution is a solution that has higher osmotic pressure (or has more solutes) than another solution to which it is compared.  any solution with a higher salt concentration than normal body cells so that the water is drawn out of the cells by osmosis; contains higher concentration of solutes than the cell. Example: Plasmolysis is the process in plant cells where the cytoplasm pulls away from the cell wall due to the loss of water through osmosis. This occurs in a hypertonic solution.
  11. 11. Mediated transport refers to transport mediated by a membrane transport protein. There are three types of mediated transport: uniport, symport, and antiport.  The movement of a solute across a membrane with the assistance of a transport agent, such as a protein, that is specific for certain solutes.  Movement of a solution across a membrane with the aid of a transport agent (e.g., protein).
  12. 12. Passive transport is a movement of biochemicals and other atomic or molecular substances across membranes. Unlike active transport, it does not require an input of chemical energy, being driven by the growth of entropy of the system. The rate of passive transport depends on the (semi-)permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the membrane lipids and proteins. The four main kinds of passive transport are diffusion, facilitated diffusion, filtration and osmosis.  There is no energy required.
  13. 13. Active transport is the movement of all types of molecules across a cell membrane against its concentration gradient (from low to high concentration). In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. If the process uses chemical energy, such as from adenosine triphosphate (ATP), it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient. Active transport uses cellular energy, unlike passive transport, which does not use cellular energy. Active transport is a good example of a process for which cells require energy.  Spend energy  Examples of active transport include the uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of plants.
  14. 14. The process of moving sodium and potassium ions across the cell membrance is an active transport process involving the hydrolysis of ATP to provide the necessary energy. It involves an enzyme referred to as Na+/K+-ATPase. This process is responsible for maintaining the large excessof Na+ outside the cell and the large excess of K+ ions on the inside. A cycle of the transport process is sketched below. It accomplishes the transport of three Na+ to the outside of the cell and the transport of two K+ ions to the inside. This unbalanced charge transfer contributes to the separation of charge across the membrane. The sodium-potassium pump is an important contributer to action potential produced by nerve cells. This pump is called a P-type ion pump because the ATP interactions phosphorylates the transport protein and causes a change in its conformation.
  15. 15. Endocytosis is an energy-using process by which cells absorb molecules (such as proteins) by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane. The process which is the opposite to endocytosis is exocytosis.  Entry into the cell of materials that are too large to get in by mere diffusion.
  16. 16. • In phagocytosis, or "cell eating," the cell engulfs debris, bacteria, or other sizable objects. Phagocytosis occurs in specialized cells called phagocytes, which include macrophages, neutrophils, and other white blood cells. Invagination produces a vesicle called a phagosome, which usually fuses with one or more lysosomes containing hydrolytic enzymes. Materials in the phagosome are broken down by these enzymes and degraded. • Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytosed. • Phagocytosis occurs in our body when some foreign particle enters inside it, our white blood cells engulf it, and then digest it. It is also how some microorganisms like amoeba get their food. • Example: white blood cell engulfing a large, liquid protein droplet.
  17. 17. In pinocytosis, or "cell drinking," the cell engulfs extracellular fluid, including molecules such as sugars and proteins. These materials enter the cell inside a vesicle, although they do not mix with cytoplasm. Epithelial cells in capillaries use pinocytosis to engulf the liquid portion of blood at the capillary surface. The resulting vesicles travel across the capillary cells and release their contents to surrounding tissues, while blood cells remain in the blood. The cell takes in surrounding fluids, including all solutes present. Pinocytosis also works as phagocytosis; the only difference is that phagocytosis is specific in the substances it transports. Phagocytosis engulfs whole particles, which are later broken down by enzymes, such as cathepsins, and absorbed into the cells.
  18. 18. Pinocytosis, on the other hand, is when the cell engulfs already-dissolved or broken-down food. Pinocytosis is non-specific and non-absorptive. Molecule-specific endocytosis is called receptor- mediated endocytosis. Pinocytosis is otherwise known as cell-drinking, fluid endocytosis, and bulk-phase pinocytosis. Example: The uptake of extracellular fluids such as hormones and enzymes by the body cells
  19. 19. • A process of cellular secretion or excretion in which substances contained in vesicles are discharged from the cell by fusion of the vesicular membrane with the outer cell membrane. • Cells expels large molecules. • Golgi bodies • Example: hormone insulin is spilled out into the blood