what is pH dependent endocytosis?
113839
Endocytosis is when a cell takes outside material inside it.  The cell membrane is a phospholipid bilayer.  This means that that outer and inner surfaces of the memberane like to be with water and the center of the memberane likes to be with oil.    The cell membrane deforms to surround whatever it is trying to bring into the cell.  The membrance then closes around the stuff that it is engulfing.  At this point the cell is still completely surrounded by the membrane; however, there is a new, smaller membrane bound pocket inside of the cell.  That is endocytosis.  If the endocytosis is pH dependent, that means that this cellular process happens in a manner that is related to how acidic or basic the outside enviroment is.\n\nThis question might get a more detailed answer in the biology catagory.
768732
pH at pKa +- 1 unit. from henderson hasselbalch\npH = pKa + log [base]/[acid] \ngiving +- 1 when the ratios are 1/10 or 10/1 in concentration\nthe capacity of a buffer is achieved when the ratio of weak acid to conjugate base exceeds 10:1 or vice versa. \nDoes that help?
184683
pH is the measure of acidity or basicity(alkalinity) of a solution. When pH increases, the solution is more alkaline and when pH decreases the solution is more acidic. A pH of 7 implies that the solution is neither basic(alkaline) nor acidic but neutral. Check the answer to one of the similar questions on Yahoo answers at the following page.
168314
Ionic strength of isolated protein depends on the pH of the medium. At pI i.e. isoelectric pH ionic strenght would be 0.\n\nHope this helps.
975413
Passive Transport does not require chemical energy to allow molecules across the membrane.  \n\nOne method of passive transport is simple diffusion.  Diffusion is the movement of molecules across a membrane from areas of high concentration to low concentration or along the concentration gradient.  These molecules can pass readily directly through the membrane.\n\nAnother method is facilitated diffusion.  This method is dependant on structures called transport proteins.  These proteins are simply pore like structures that span the width of the membrane.  The two types are pores and gated channels.  Pores always remain open, but gated channels can open and close in response to stimuli.  Also, these pores can only transport molecules down the concentration gradient.  Some transport proteins are also substrate specific, meaning that they can only transport a specific type of molecule.
576639
With facilitated diffusion, proteins are needed to make an opening in the cell membrane.  However, once this opening is there, particles diffuse from the side which has the higher concentration to the side with the lower concentration, just like regular diffusion.  (The difference in concentrations is called the concentration gradient.)\n\nIn active transport, much more effort is needed to make it happen.  For example, in phagocytosis, the cell wall actually engulfs a particle and brings it inside the cell.  The difference is between the transport being facilitated or being forced.
1117081
c. Na - HCO3- reabsorption\nCOnserving FIltered Bicarbonate Ions: bicarbonate reabsorption:\nBicarbonate ions HCO3- are an important part of the bicarbonate bufffer sysem, the most important inorganic blood buffer. If this resevoir of base, or alkaline reserve, is to be maintained, the kidneys must do more than just eliminate enough Hydrogen ions to counter rising blood H+ levels. DEpleted stores of HCO3- have to be replenished. Dissociation of carbonic acid liberates HCO-3 as well as H+. WHile the tubule cells cannot reclaim HCO3- directly from the filtrate, they can and do shunt HCO3- generated within them as a result of H2CO3 splitting into the peritubular capillary blood. Accompanying HCO3- in the blood is the Na+ that enters the tubule cell as H- is pumped out. Thus reabsorption of HCO3- depends on the active secretion of H+ via an H+ -ATPase and more importantly NA+-H+ antiporter, which uses the lumen-to-tubule cell NA+ gradient to drive the transport process. In the filtrate H+ combines with filtered HCO3- generated within the tubule cells enters the blood- a one-for-one exchange. WHen large amounts of H+ are secreted, corresponding large amounts of HCO3- enter the peritubular blood, and the net effect is that HCO3- is almost completely removede from the filtrate.\nAdditional information abou the kidneys********below\nStep 3: TUbular Secretion:\nThe failure of tubule cells to reabsorb some solutes is an important means of clearing plasma of unwanted substances. A second such mechanism is tubular secretion-- essentially reabsorption in reverse. Substances such as H+,K+,NH4+, creatine and certaine organic acids move eithre from the blood of the pertibular capillaries through the tubule cells or directly from the tubule cells in the filtrate, Thus, the urine eventually excreted contains both filtrated and secreted substances. Tubular secretion is important for:\n1. Disposing of substances not already in the filtrate-certain drugs.\n2.ELiminating undesirab;e substances or end products that have been reabsorped by passive processes(urea and uric acid)\n3. Ridding the body of excess K+\n4. Controlling blood ph-----when blood ph drops toward the acidic end of its homeostatic rang the renal tubule cells actively secrete more H+ into the filtrate and retain more HCO3- and K+. as a result the blood pH rises and the urine drains off the excess H+
675531
It depends.  \n\nTable salt, NaCl, theoretically doesn't effect the pH, strong electrolytes are weak acids and bases, however in practice I believe that it slighty basic.  However salts can be either Basic, like soduim cyanide, NaCN, or acidic, like ammonium cloride, NH4Cl.\n\nSugar does effect the pH because of the acidic proton on the alcohol portion of the sugar.  This does not mean that a sugar is acidic, but it means that if sugar is put with a strong base the pH will go down because some of the base will react with the sugar.
868421
7.3 to 7.4\nBlood pH. The pH in which body cells can survive and function best.
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buffer solution ?\nBuffer solution is  solution of which the pH does not change significantly on the addition of a little acid or base.\n\nBuffer are also important in many industrial processes.Certain processed food has to be prepared in a buffered form so that when consumed does not cuase undue changes in pH.
1113665
The wall of the intestine has many tiny finger like projections called Villae, these make the surface area very large.  Glucose moves throught the epithelial cells on the walls of the villae by "active transfer" a type of osmosis.  Glucose levels are maintained by the action of the hormone Insulin, failure in this system leads to the disorder Diabetes.  Search on some of these words in  google and you'll find loads of articles at different levels.  There are two site below to get you started.
1038925
Lysosomes are organelles that contain digestive enzymes (acid hydrolases) to digest macromolecules. They are found in both plant and animal cells, and are built in the Golgi apparatus. At pH 4.8, the interior of the lysosomes is more acidic than the cytosol (pH 7). The lysosome single membrane stabilizes the low pH by pumping in protons (H+) from the cytosol, and also protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. The digestive enzymes need the acidic environment of the lysosome to function correctly. For this reason, should a lysosome's acid hydrolases leak into the cytosol, their potential to damage the cell will be reduced, because they will not be at their optimum pH. All these enzymes are produced in the endoplasmic reticulum, and transported and processed through the Golgi apparatus. The Golgi apparatus produces lysosomes by budding. Each acid hydrolase is then targeted to a lysosome by phosphorylation. The lysosome itself is likely safe from enzymatic action due to having proteins in the inner membrane which has a three-dimensional molecular structure that protects vulnerable bonds from enzymatic attack[1
577726
a BASE is a proton acceptor; an ACID is a proton donator\n\nweak base - has low tendency to accept protons\nweak acid - has low tendency to donate protons - doesn't fully dissociate (reaction stays incomplete, in equilibrium)\n\n\nBuffer solutions are made up of weak acids, so an equilbrium is set up:\n\nHA  <==> H+ + A-\n(HA - acid; H+ - protons; A- - base)\n\nThe pH stays constant because, if an acid (donating H+ ions) is added, the extra A- ions will react with them to form HA. If more base is added, there are plenty of HA molecules to give up the H+ and react with them.  Therefore the amount of H+ ions in solution is constant.  Since pH is a measure of H+ ions in solution, pH stays constant too.
736186
Facilitated diffusion (or transport) is the diffusion across a membrane which is aided by a membrane protein usually by a channel or pore this allows molecules that cannot pass through the lipid bilayer to enter the cell. The process still occurs down a concentration gradient, like normal diffusion and it requires no energy unlike active transport. For more information you could try looking up passive transport.\n\nI hope this helps
731164
pH: pH is a measure of the acidity or hydrogen ion concentration of a solution. It is measured on a scale of 0-14 with pH values below 7 being acidic, values above 7 being basic and a value around 7 is neutral. As the pH drops into the acidic range an enzyme tends to gain hydrogen ions from the solution. As the pH moves into the basic range the enzyme tends to lose hydrogen ions to the solution. In both cases the changes produced in the chemical bonds of the enzyme molecule result in a change in conformation that decreases enzyme activity.\n\nHope this helps :)
1146467
As cells grow the surface area/volume ratio goes down.  This inhibits their ability to uptake nutrients.
236505
Glucose, sodium ions and choride ions are just a few examples of molecules and ions that must efficently get across the plasma membrane but to which the lipid bilayer of the membrane is virtually impermiable. Their transport must therefore be "facilitated" by proteins that span the membrane and provide an alternative route or bypass. Facilitated diffusion is the name given this process. It is similar to simple diffusion in the sense that it does not require expenditure of metabolic energy and transport is again down an electrochemical gradient. \n\nTwo major groups of integral membrane proteins are involved in facilitated diffusion: \n\nCarrier proteins(also known as permeases or transporters) bind a specific type of solute and are thereby induced to undergo a series of conformational changes which has the effect of carrying the solute to the other side of the membrane. The carrier then discharges the solute and, through another conformational change, reorients in the membrane to its original state. Typically, a given carrier will transport only a small group of related molecules.\n\nSome important and illustrative groups of transporters are: \nCertain of the hexose transporters, which transport glucose and similar monosaccharides into and out of cells.\n \nBand 3, the anion transporter, which facilitates transport of bicarbonate and chloride ions \n\n\nIon Channels do not really bind the solute, but are like hydrophilic pores through the membrane that open and allow certain types of solutes, usually inorganic ions, to pass through. In general, channels are quite specific for the type of solute they will transport and transport through channels is quite a bit faster than by carrier proteins. Additionally, many channels contain a "gate" which is functions to control the channel's permiability. When the gate is open, the channel transports, and when the gate is closed, the channel is closed. Such gates can be controlled either by voltage across the membrane (voltage-gated channels) or have a binding site for a ligand which, when bound, causes the channels to open (ligand-gated channels).\n\nIon channels allow currents the be carried across the membrane and are thus of particular importance in the physiology of excitable cells like neurons and muscle cells.