Post Laboratory Notes: The Cell PDF

POST LABORATORY NOTES THE CELL Cell Parts Descrip on Func on Plasma Membrane Lipid bilayer composed of Func ons as the outer phospholipids and cholesterol; boundary of the cell; controls...

POST LABORATORY NOTES THE CELL Cell Parts Descrip on Func on Plasma Membrane Lipid bilayer composed of Func ons as the outer phospholipids and cholesterol; boundary of the cell; controls proteins extend across or are the entry and exit of embedded in either surface of the substances; receptor proteins lipid bilayer func on in intercellular communica on; marker molecules enable cells to recognize one another Nucleus Enclosed by nuclear envelope, a Is the control center of the cell; double membrane with nuclear DNA within the nucleus pores; contains chroma n regulates protein (e.g., (dispersed, thin strands of DNA enzyme) synthesis and and associated proteins), which therefore the chemical condenses to become visible reac ons of the cell mito c chromosomes during cell division; also contains one or more nucleoli, dense bodies consis ng of ribosomal RNA and proteins Cytoplasmic Organelles Ribosome Ribosomal RNA and proteins form Serves as site of protein large and small subunits; some are synthesis atached to endoplasmic re culum, whereas others (free By: Deannise Ann Boco, RMT POST LABORATORY NOTES ribosomes) are distributed throughout the cytoplasm Rough Endoplasmic Membranous tubules and Synthesizes proteins and Re culum flatened sacs with transports them to Golgi atached ribosomes apparatus Smooth Endoplasmic Membranous tubules and Manufactures lipids and Re culum flatened sacs with no atached carbohydrates; detoxifies ribosomes harmful chemicals; stores calcium Golgi Apparatus Flatened membrane sacs stacked Modifies, packages, and on each other distributes proteins and lipids for secre on or internal use Lysosome Membrane-bound vesicle pinched Contains diges ve enzymes off Golgi apparatus Peroxisome Membrane-bound vesicle Serves as one site of lipid and amino acid degrada on; breaks down hydrogen peroxide Proteasomes Tubelike protein complexes in the Break down proteins in the cytoplasm cytoplasm Mitochondria Spherical, rod-shaped, or Are major sites of ATP threadlike structures; synthesis when oxygen is enclosed by double membrane; available inner membrane forms projec ons called cristae Centrioles Pair of cylindrical organelles Serve as centers for consis ng of triplets of parallel microtubule forma on; microtubules; located in the determine cell polarity during centrosome, a specialized area of cell division; form the basal the cytoplasm where microtubule bodies of cilia and flagella forma on occurs Cilia Extensions of the plasma Move materials over the membrane containing doublets of surface of cells parallel microtubules; 10 μm in length Flagellum Extension of the plasma In humans, propels membrane containing doublets of spermatozoa parallel microtubules; 55 μm in length Microvili Extensions of the plasma Increase surface area of the membrane containing plasma membrane for microfilaments absorp on and secre on; modified to form sensory receptors Fluid Mosaic Model By: Deannise Ann Boco, RMT POST LABORATORY NOTES Fluid Mosaic Model: describes the plasma membrane as being neither rigid nor sta c in structure. By: Deannise Ann Boco, RMT POST LABORATORY NOTES MEMBRANE PHYSIOLOGY: FACTORS AFFECTING DIFFUSION: DIFFUSION: a passive process in which the random mixing of par cles in a solu on occurs because of the par cles’ kine c energy. Both the solutes, the dissolved substances and the solvent, the liquid that does the dissolving, undergo diffusion.  If a par cular solute is present in high concentra on in one area of a solu on, and in low concentra on in another area, solute molecules will diffuse toward the area of lower concentra on—they move down their concentra on gradient. FACTORS THAT AFFECT RATE OF DIFFUSION:  Steepness of the concentra on gradient – the greater the difference in concentra on between the two sides of the membrane, the higher is the rate of diffusion.  Temperature – the higher the temperature, the faster the rate of diffusion. (All of the body’s diffusion processes occur more rapidly in a person with a fever)  Surface Area – the larger the membrane surface area available for diffusion, the faster is the diffusion rate. By: Deannise Ann Boco, RMT POST LABORATORY NOTES  Diffusion Distance – the greater the distance over which diffusion must occur, the longer it takes. SIMPLE DIFFUSION:  a passive process in which substances move freely through the lipid bilayer of the plasma membrane of cells without  the help of membrane transport proteins.  Non-polar, hydrophobic molecules move across the lipid bilayer through the process of simple diffusion.  Example: O2, CO2, Nitrogen gases; faty acids; steroids; and fat-soluble vitamins (A, D, E, and K).  Small, uncharged polar molecules such as water, urea, and small alcohols pass through the lipid bilayer by simple diffusion. FACILITATED DIFFUSION:  In this process an integral membrane protein assists a specific substance across the membrane.  Integral membrane protein could either be a membrane channel or a carrier.  Solutes that are too polar or highly charged to move through the lipid bilayer by simple diffusion can cross the plasma membrane through facilitated diffusion. A. CHANNEL-MEDIATED FACILITATED DIFFUSION  A solute moves down its concentra on gradient across the lipid bilayer through a membrane channel.  Most membrane channels are ion channels.  Ion channels are integral membrane proteins that allow passage of small inorganic ions that are too hydrophilic to penetrate the nonpolar interior of the lipid bilayer. Each ion can diffuse across the membrane only at certain sites.  Most ions are selec ve for potassium or chloride ions; fewer channels are available for sodium and calcium ions.  Diffusion of ions through channels is generally slower than free diffusion through the lipid bilayer, due to channels occupying a smaller frac on of the membrane’s total surface area than lipids.  “Gated” channel – when part of the channel protein acts as a “plug” or “gate”, changing its shape in one way to open the port and in another way to close it. Some alternate between open and closed posi ons, while others are regulated by chemical or electrical changes inside and outside of the cell.  When the gates of a channel are open – ions diffuse into or out of the cells down their electrochemical gradients. By: Deannise Ann Boco, RMT POST LABORATORY NOTES B. CARRIER-MEDIATED FACILITATED DIFFUSION  A carrier moves a solute down its concentra on gradient across the plasma membrane.  The solute binds to a specific carrier on one side of the membrane and is released on the other side a er the carrier undergoes a change in shape.  The solute binds more o en to the carrier on the side of the membrane with a higher concentra on of solute.  Once the concentra on is the same on both sides, the solute molecules bind to the carrier on the cystolic side and move out to the extracellular fluid as rapidly as they bind to the carrier on the extracellular side and move into the cytosol.  The rate of carrier-mediated facilitated diffusion is determined by the steepness of the concentra on gradient across the membrane.  The number of carriers available in a plasma membrane places an upper limit, called Transport Maximum.  Once all the carriers are occupied, the transport maximum is reached, the process of carrier- mediated facilitated diffusion exhibits satura on.  Substances: glucose, fructose, galactose, and some vitamins. ACTIVE TRANSPORT: - Considered an ac ve process because energy is required for carrier proteins to move solutes across the membrane against a concentra on gradient. Two sources of cellular energy: A. Energy obtained from hydrolysis of ATP. (Primary Ac ve Transport) B. Energy stored in an ionic concentra on gradient. (Secondary Ac ve Transport) A. PRIMARY ACTIVE TRANSPORT  Energy derived from hydrolysis of ATP changes the shape of a carrier protein, which “pumps” a substance across a plasma membrane against its concentra on gradient.  Pumps – carrier proteins that mediate primary ac ve transport.  Sodium-Potassium Pump – most prevalent primary ac ve transport mechanism that expels sodium ions from cells and brings potassium ions in.  Other name is Sodium-Potassium ATPase.  Maintain a low concentra on of sodium ions in the cytosol by pumping these ions oon to the extracellular fluid against the sodium concentra on gradient. At the same me, the pumps move potassium into the cells against the potassium concentra on gradient. By: Deannise Ann Boco, RMT POST LABORATORY NOTES  The different concentra ons of sodium and potassium in the cytosol and extracellular fluid are crucial for maintaining normal cell volume and for the ability of some cells to generate electrical signals such as ac on poten als. B. SECONDARY ACTIVE TRANSPORT  Mechanisms uses the energy stored in an ionic concentra on gradient. Because primary ac ve transport pumps that hydrolyze ATP maintain the gradient, secondary ac ve transport mechanisms consume ATP indirectly.  A carrier protein simultaneously binds to sodium and another substance and then changes its shape so that both substances cross the membrane at the same me.  Symporters – transporters that move two substances in the same direc on.  An porters – moves two substances in opposite direc on across the membrane. ENDOCYTOSIS Three types of endocytosis: a. Receptor-Mediated Endocytosis- highly selec ve type of endocytosis by which cells take up specific ligands (molecules that bind to specific receptors). PROCESS:  Binding  Vesicle forma on  Uncoa ng  Fusion with endosome  Recycling of receptors to plasma membrane  Degrada on in lysosomes b. Phagocytosis – form of endocytosis in which the cell engulfs large solid par cles, such as worn- out cells, bacteria, or viruses.  Phagocytes – cells that are able to carry out phagocytosis. Two types of Phagocytes:  Macrophages – located in many body ssues.  Neutrophils – a type of WBC. PROCESS:  Par cle binds to a plasma membrane receptor on the phagocyte causing it to extend pseudopods (projec ons of plasma membrane and cytoplasm)  Pseudopods surround the par cle outside the cell, and the membranes fuse to form a vesicle called phagosome.  The phagosome fuses with one or more lysosomes, and lysosomal enzymes break down the ingested material.  Any undigested material in the phagosome remain indefinitely in a vesicle called a residual body.  The residual bodies are then either secreted by the cell via exocytosis or they remain By: Deannise Ann Boco, RMT POST LABORATORY NOTES stored in the cell as lipofuscin granules. c. Bulk-phase endocytosis/Pinocytosis – a form of endocytosis in which ny droplets of extracellular fluid are taken up.  During pinocytosis, the plasma membrane folds inward and forms a vesicle containing a droplet of extracellular fluid. The vesicle detaches or “pinches off” from the plasma membrane and enters the cytosol.  Within the cell, the vesicle fuses with a lysosome, where enzymes degrade the engulfed solutes.  The resul ng smaller molecules, such as amino acids, and FA, leave the lysosome to be used elsewhere in the cell.  Pinocytosis occurs in most cells, especially absorp ve cells in the intes nes and kidneys. Exocytosis  Releases materials from a cell.  All cells carry out exocytosis. Two types of cells: 1. Secretory cells – liberate diges ve enzymes, hormone, mucus, or other secre ons. 2. Nerve cells – release substances called neurotransmiters.  In some cases, wastes are also released by exocytosis.  During exocytosis, membrane-enclosed vesicles called secretory vesicles form inside the cell, fuse with the plasma membrane and release their contents into the extracellular fluid. TRANSCYTOSIS  Vesicles undergo endocytosis on one side of a cell, move across the cell, and then undergo exocytosis on the opposite side. As the vesicles fuse with the plasma membrane, the vesicular contents are released into the extracellular fluid.  Transcytosis occurs most often across the endothelial cells that line blood vessels and is a means for materials to move between blood plasma and interstitial fluid. By: Deannise Ann Boco, RMT POST LABORATORY NOTES OSMOSIS  There is a net movement of a solvent through a selec vely permeable membrane from an area of higher water concentra on to an area of lower water concentra on un l equilibrium is reached.  In living systems, the solvent is water, which moves osmosis across the plasma membranes from an area of higher water concentra on to an area of lower water concentra on.  During osmosis, water molecules pass through a plasma membrane in two ways: a. By moving between neighboring phospholipid molecules in the lipid bilayer via simple diffusion. b. By moving through aquaporins, integral membrane proteins that func on as water channels.  Osmosis occurs only when a membrane is permeable to water but is not permeable to certain solutes PRINCIPLE OF OSMOSIS  Water molecules move through the selec vely permeable membrane; solute molecules cannot. a) Water molecules move from the le arm into the right arm down the water concentra on gradient. b) The volume of water in the le arm has decreased and the volume of solu on in the right arm has increased. c) Pressure applied to the solu on in the right arm restores the star ng condi ons.  ISOSMOTIC – solutions having the same or equal osmotic pressure.  Osmotic pressure – the pressure that must be applied to the solution side to stop fluid movement when a semipermeable membrane separates a solution from water. By: Deannise Ann Boco, RMT POST LABORATORY NOTES TONICITY – a solution’s tonicity is a measure of the solution’s ability to change the volume of cells by altering their water content. A. ISOTONIC SOLUTION – concentra ons of solutes that cannot cross the plasma membrane are the same on both sides of the membrane.  Our RBC maintains its normal shape and volume in an isotonic solu on.  Normal saline solu on or 0.9% NaCl solu ons is an isotonic solu on which contains 0.9% grams of NaCl in 100 ml of solu on.  When RBCs are bathed in 0.9% NaCl, water molecules enter and exit at the same rate, allowing RBCs to keep their normal shape and volume. B. HYPOTONIC SOLUTION – a solu on that has a lower concentra on of solutes than the cytosol inside the RBCs.  In this case, water molecules enter the cells faster than they leave, causing the RBCs to swell and eventually burst.  Hemolysis – rupture of RBCs in the manner.  Pure water is very hypotonic and causes rapid hemolysis. C. HYPERTONIC SOLUTION – a solu on with higher concentra on of solutes than does the cytosol inside the RBCs.  In such solu on, water molecules move out of the cells faster than they enter, causing the cells to shrink.  Crenation – shrinkage of cells. By: Deannise Ann Boco, RMT POST LABORATORY NOTES DIALYSIS:  a process in which a solu on containing par cles of different sizes is placed a bag made of a semipermeable membrane. The bag is placed into a solvent or solu on containing only small molecules. The solu on in the bag reaches equilibrium with the solvent outside, allowing the small molecules to diffuse across the membrane but retaining the large molecules.  An osmo c semipermeable membrane allows only solvent and not solute molecules to pass. If, however, the openings in the membrane are somewhat larger, then small solute molecules can also get through, but large solute molecules, such as macromolecular and colloidal par cles, cannot. Colloids: are stable mixtures despite the rela vely large size of the colloidal par cles. The stability results from the solva on layer that cushions the colloid’s par cles from direct collisions and from the electric charge on the surface of colloidal par cles. Crystalloid: have small, highly soluble molecules, such as glucose, that are easily dialyzed. They can be charged or neutral and go into solu on because of their microscopic size. Dialysate: the part of a mixture which passes through the membrane in dialysis. By: Deannise Ann Boco, RMT