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Physiology of Cells

Physiology of Cells. Movements through cell membranes. Basics: Movement of molecules will be either Passive or Active Passive processes require no added energy from the cell. Molecules move because of a concentration gradient.

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Physiology of Cells

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  1. Physiology of Cells

  2. Movements through cell membranes • Basics: Movement of molecules will be either • Passive or Active • Passive processes require no added energy • from the cell. Molecules move because of a concentration gradient. • Active transport processes: REQUIRE ENERGY FROM THE CELL.

  3. Examples of PASSIVE transport • SIMPLE DIFFUSION • OSMOSIS • CHANNEL or CARRIER MEDIATED DIFFUSION • FILTRATION

  4. Examples of active transport • Sodium – potassium ‘pump’ • Calcium pump ENDOCYTOSIS, which includes: • Pinocytosis (cell drinking) • Phagocytosis (cell eating)

  5. Diffusion—a passive process • Molecules spread / pass through the membranes • Molecules move from an area of high concentration to an area of low concentration, down a concentration gradient • As molecules diffuse, a state of equilibrium will result High conc. >>> lower conc.

  6. Movement of Substances through Cell Membranes • Simple diffusion • Solute Molecules cross through the phospholipid bilayer • Certain Solutes permeate the membrane; therefore, we call the membrane ‘permeable’ to those molecules • Osmosis • Diffusion of water through a selectively permeable membrane, which limits the diffusion of at least some of the solute particles. Water diffuses freely. • Water pressure that develops as a result of osmosis is called osmotic pressure

  7. OSMOSIS

  8. MOVEMENT OF SUBSTANCES THROUGH CELL MEMBRANES: PASSIVE TRANSPORT (cont.) • Osmosis results in gain of volume on one side of the membrane , and loss of volume on the other side of the membrane, Whereas the osmotic pressure reaches equilibrium between the two sides.

  9. Osmosis • Knowledge of potential osmotic pressure allows prediction of the direction of osmosis and the resulting change in pressure • Isotonic: when two fluids have the SAME potential osmotic pressure • HYPERTONIC (higher pressure): cells placed in solutions that are hypertonic to intracellular fluid always shrivel as water flows out of them; if pathologic conditions, or medical treatment causes the extracellular fluid to become hypertonic to the cells of the body, serious damage may occur • HYPOTONIC (lower pressure): cells placed in a hypotonic solution may swell as water flows into them; • water always osmoses from the hypotonic solution to the hypertonic solution

  10. H2O 2% or Higher saline (also D5W) Hypertonic to the fluid in the cells, Also to the plasma of the blood (hypotonic TO THE FLUID IN the CELLS) .9 % Normal saline --- ISOTONIC to plasma, and to the fluid in the cells

  11. Facilitated diffusion CHANNEL MEDIATED OR CARRIER MEDIATED (passive Transport) • A special kind of diffusion in which movement of molecules is made more efficient by the action of transporters embedded in a cell membrane (something like revolving doors) • The Energy required comes from the natural collision energy of the solute (none required from the cell) • MOVES substances down a concentration gradient • ( from higher to a lower concentration)

  12. Channel-mediated passive transport • Channels are specific; allow only one type of solute to pass through • Gated channels may be open or closed (or inactive); & may be triggered by any of a variety of stimuli (ELECTRICAL, CHEMICAL, MECHANICAL) • Channels allow membranes to be selectively permeable • Aquaporins are water channels that permit rapid osmosis - movement of water

  13. Carrier-mediated passive transport • Carriers attract and bind to the solute, change shape, and release the solute on the other side of the carrier. (but without expending energy) • Carriers are usually reversible depending on the direction of the concentration gradient • (again, it is something like a revolving door - the energy is provided by the natural tendency of the solute to go DOWN the concentration gradient. • It is also something like falling into a basket and sliding DOWN a hill)

  14. 2 special variations of passive transport: dialysis and filtration • DIALYSIS : diffusion of SMALL Solute particles, but NOT Larger Molecules, Through a Selectively permeable membrane; RESULTS In Separation of the large and Small solutes. ( Movement is DOWN the concentration gradient.) ( Dialysis is used as a therapeutic process in kidney failure, to ‘artificially’ cleanse the bloodstream)

  15. filtration • Filtration involves FORCEFUL passing of • WATER and permeable SOLUTES Through a membrane, BY THE FORCE OF HYDROSTATIC PRESSURE . • Hydrostatic pressure is the force, or power of A fluid pushing against a surface. (as in the Water Pressure in a pipe flowing downhill, or the water pressure generated when it is pumped through a hose or pipe.)

  16. Filtration The force of the Hyrostatic Pressure pushes the molecules through the sheet. (so this not dependent on a concentration gradient) A VERY IMPORTANT PROCESS IN THE KIDNEY, Which literally FILTERS the Blood, removing waste products and producing URINE. • (The cardiac PUMP and systemic blood pressure provide the hydrostatic pressure)

  17. SUMMARY OF: MOVEMENT OF SUBSTANCES THROUGH CELL MEMBRANES: PASSIVE TRANSPORT • Role of passive transport processes: • Move substances down a concentration gradient, thus maintaining equilibrium and homeostatic balance • Types of passive transport: • simple DIFFUSION, and Facilitated Diffusion (channels and carriers); • OSMOSIS is a special example of channel-mediated passive transport of water

  18. Movement of Substances through Cell Membranes • ACTIVE TRANSPORT processes—require the expenditure of metabolic energy by the cell • A. Transport by pumps • Pumps are membrane transporters that move a substance against its concentration gradient—(the opposite of diffusion) Examples: SODIUM-POTASSIUM PUMP (Figure 3-19 page 92) and the calcium pump • B. Transport by vesicles—allows substances to enter or leave the interior of a cell without actually moving through its plasma membrane • (ENDOCYTOSIS, EXOCYTOSIS )

  19. THE NA-K PUMP IS IMPT. IN MANY WAYS Most importantly , in establishing and maintaining the TRANS- MEMBRANE POTENTIAL

  20. Calcium pump

  21. Movement of Substances through Cell Membranes Active transport processes (cont.) • Endocytosis—the plasma membrane “traps” some extracellular material and brings it into the cell in a vesicle • Two basic types of endocytosis (Figure 4-10): • Phagocytosis—“condition of cell-eating”; large particles are engulfed by the plasma membrane and enter the cell in vesicles; vesicles fuse with lysosomes, where the particles are digested • Pinocytosis—“condition of cell-drinking”; fluid and the substances dissolved in it enter the cell

  22. (Such as a Bacteria or virus) (Such as a packet of Hormones, OR NEUROTRANSMITTERS)

  23. ‘Phagocytosis’ is for engulfing and digesting unwanted invaders - but there is another type of endocytosis: RECEPTOR-MEDIATED ENDOCYTOSIS- to bring in ‘wanted’, useful molecules, (usually hormones or neurotransmitters) >>>

  24. : ACTIVE TRANSPORT (cont.) EXOCYTOSIS • Exocytosis • Process by which large molecules, notably proteins, can leave the cell even though they are too large to move out through the plasma membrane • Large molecules are enclosed in membranous vesicles and then pulled to the plasma membrane by the cytoskeleton, where the contents are released • Exocytosis also provides a way for new material to be added to the plasma membrane

  25. MOVEMENT OF SUBSTANCES THROUGH CELL MEMBRANES: SUMMARY: ACTIVE TRANSPORT • Role of the active transport processes: • Active transport requires energy use by the membrane, or BY THE CELL • Pumps function to: concentrate substances on one side of a membrane, such as when storing an ion inside an organelle, or establishing an electrical potential across the membrane • Vesicle-mediated (endocytosis, exocytosis): move large volumes of substances at once, such as in secretion of hormones and neurotransmitters

  26. Cellular Metabolism

  27. Cell Metabolism • Metabolism is the set of ALL chemical reactions in a cell • Catabolism—breaks large molecules into smaller ones; usually releases energy • Anabolism—builds large molecules from smaller ones; usually consumes energy

  28. ENZYMES and CHEMICAL REACTIONSsee chapter 2, pp.50- 54 • Role of enzymes ENZYMES are PROTEINS (functional) • Enzymes are chemical catalysts, • They reduce the ACTIVATION ENERGY needed for a reaction , ( while they are not themselves altered or broken down by the reaction)

  29. More on Enzymes • Enzymes regulate cell metabolism (orchestrate) • Chemical structure of enzymes ARE IMPT. • They are Proteins of a complex shape • The active site is where the enzyme molecule fits the substrate molecule — (the lock-and-key model ) • ENZYMES are SPECIFIC in their ACTION, and often several function together in succession

  30. ENZYMES Most enzymatic reactions are REVERSIBLE (both ways) Metabolic PATHWAYS are regulated by a series of ENZYMES

  31. Collegiate ‘chemistry’ analogy: • ANN and CAThy are CATALYSTS (enzymes): • 1. ‘AnnABOLIC’ REACTION: • ANN brings LINDA to meet BILL >>>> • (add energy) . . . marriage , family • 2. ‘CatABOLIC’ REACTION: • TED/BARBARA are a couple …. • TED looks longingly at CAThy walking by ; • Barbara *#**@** TED with HEAT, FIREWORKS (energy released) -- Breakup/Split occurs

  32. Cell Metabolism FYI Classification and naming of enzymes Enzymes usually have an -ase ending, with the first part of the word signifying the substrate or the type of reaction catalyzed specific: lipase, sucrase, etc general - TYPES of reactions/enzymes: Oxidation-reduction enzymes—known as oxidases, hydrogenases, and dehydrogenases; energy release depends on these enzymes Hydrolyzing enzymes—hydrolases; digestive enzymes belong to this group

  33. Various chemical and physical agents known as **allosteric effectors affect enzyme action by changing the shape of the enzyme molecule; examples of allosteric effectors include the following : Temperature Hydrogen ion (H+) concentration (pH) Cofactors (removal , addition, changes) cofactors are nonprotein components of the enyme End products of certain metabolic pathways THIS IS PRIME EXAMPLE OF THE IMPORTANCE OF HOMEOSTASIS !!!!!! ** allosteric: ‘differing shapes’ **

  34. CATABOLISM CELLULAR RESPIRATION, (C/ to pulmonary respiration) • the (complex) pathway in which glucose is broken down to yield its stored energy; is an important example of cell catabolism; cellular respiration has three pathways that are chemically linked : • 1. .Glycolysis (Taking place in cytoplasm) Glucose is broken down to 2 Pyruvate molecules, with 6 ATP produced (in the mitochondria): • 2.Citric acid cycle (Figure 4-19) AEROBIC (uses oxygen) and • 3.Electron transport system (ETS) (Figure 4-20) AEROBIC

  35. RESPIRATION CELLULAR PULMONARY O2 into cell, breakdown of Movement of air in/out of glucose, to release energy Lungs, gas exchange ‘Internal’ respiration External resp. CHEMICAL rxnsVENTILATION MICROMACRO

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