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| Frage | Antworten |
| What molecules are capable of penetrating the plasma membrane? Which molecules aren't? | - Can penetrate: Small, NON-POLAR substances. - Partially penetrate: Small/medium UNCHARGED, polar substances. - Cannot penetrate: Large or charged. |
| Give some examples of substances which can penetrate the plasma membrane, and are FULLY permeable. Why? | Carbon dioxide and Oxygen - small, hydrophobic, non-polar, lipophilic compounds. |
| What is meant by lipophilic? | The ability of a substance to dissolve in lipids i.e. the plasma membrane. |
| Why are small, POLAR molecules moderately permeant? | Depending on their charge distribution and their size, many are able to pass through. |
| Name some substances which cannot cross across the membrane i.e. they are impermeant. Why? How do these molecules get into the cell? | Ions such as Na+, K+ and Cl-, and molecules such as ATP, glucose and amino acids. They are too large and/or they have a very significant charge. Membrane transport proteins i.e. aquaporins for water. |
| Describe osmosis in terms of solute concentration. | Osmosis is the movement of water from a region of low solute concentration to a region of high solute concentration until solute concentrations are equal in both compartments separated by a water-permeable membrane. |
| If water flows throughout a water-permeable membranes from a region of high solute concentration to a region of low solute concentration until solute concentrations in both compartments are EQUAL, how does this affect the volume in each compartment? | - Region with initially lower solute concentration DECREASES in volume... - Region with initially higher solute concentration INCREASES in volume as water flows in. |
| What is a hyposomotic solution (describe in terms of osmosis)? | A hyposmotic solution is one that contains a lower concentration of solute than the solution on the other side of the water-permeable membrane and therefore water will move away from an area of hyposomolarity until concentration are equal. |
| What is a hyperosmotic solution (describe in terms of osmosis)? | A hyperosmotic solution is one which has a higher concentration of solutes than the solution on the other side of the water permeable membrane, thus water moves towards an area of hyperosmolarity until concentrations are equal. |
| What is a isomotic solution (describe in terms of osmosis)? | Isosmotic solutions contain equal concentrations either side of the water-permeable membrane, thus no net movement of water. |
| Define osM (osmotic effect of a solution) in biochemistry terms. | The sum of the molar concentration of individual molecular species or individual ionic species (osmolytes) in the solution. |
| How many moles of Glycerol does a 0.3osM solution of Glycerol contain? Why? | Contains 0.3 M Glycerol because glycerol is a single molecular species - it does not dissociate in water. |
| What is meant by a single molecular species? | One which does not dissociate in water. |
| How many moles of ions is in 1 mole of fully dissociated KCl? Therefore, how many moles of KCl is in a 0.3osM solution? | If fully dissociated there will be 1 mole of K+ ions and 1 mole of Cl- ions = 2 moles of ions in solution. Therefore... since the osM is the sum of the individual moles of the molecular species/ osmolytes; 0.3osM accounts for both sets of moles of ions in solution, thereofore there are 0.15 M KCl. |
| Therefore, how many moles of MgCl2 is in a 0.3osM solution? | 1 mole of MgCl2 = 3 moles of ions. 0.3osM contains 0.1 M MgCl2 |
| How do red blood cells appear if they are presented in a very hypotonic solution? | Swollen - water flows from region of low solute concentration to region of high solute concentration (inside the RBC). |
| How do red blood cells appear if they are presented in a hypertonic solution? | Crenated/ Shrivelled = Water flows from region of low solute concentration (inside RBC) to region of high solute concentration, and cell shrinks. |
| How do red blood cells appear if they are presented in an isotonic solution? | Normal. |
| How do red blood cells appear if they are presented in a very hypotonic solution? | Lysed - too much water flows in. |
| What is meant by tonicity? | Tonicity only considers impermeant solutes, whereas osmolarity takes both impermeant and permeant solutes into account. |
| What is considered a region of low osmolarity to a RBC and why? | < 0.3osM since RBCs have an intracellular osmolarity of about 0.3osM so anything less than this will induce the flow of water into the cell since the region outside of the RBC has a lower solute concentration. |
| What is meant by osmotic haemolysis in RBCs? | This is when RBCs are placed into a region of osM of less than 0.3 (this indicates the region has a low solute concentration in comparison to RBCs) - this causes water to flow into the cell by osmosis. Initially, the cell expands and accounts for the initial flow of water into the cell, but once regulatory mechanisms are overcome, the plasma membrane will rupture and the contents of the cell will equilibrate with the external solution. |
| How can the extent of haemolysis be measured? | By centrifuging out any intact cells and measuring the haemoglobin released from the cells by its absorbance at 420nm in the spectrophotometer. |
| What is an osmotic fragility test? | When blood samples are taken and are exposed to a variety of osmolyte concentrations to measure how easily they break. |
| If a RBC is placed in a solution containing 0 osM impermeant solute, will its volume increase, decrease or not change? Why? | Increase, because there is a higher osM of 0.3 in the RBC, therefore more ions in the RBC. Water will move from low ion concentration to high ion concentration and move into the cell, increasing the cell volume. |
| If a RBC is placed in a solution containing 1.0 osM impermeant solute, will its volume increase, decrease or not change? Why? | Decrease. This means that the solution has a higher osM than within the RBC, thus more ions in solution. Water will flow from region of low solute concentration to region of high solute concentration - water flows out of RBC. |
| If a RBC is placed in a solution containing 0.3 osM impermeant solute, will its volume increase, decrease or not change? Why? | Stay the same. osM is equal for both regions and therefore there is not net movement of water. |
| What happens if RBCs are placed in a 0.3osM solution of permeant solute? | The solute will enter the cells until its intracellular concentration [P] is the same as that in the medium. |
| Describe why the intracellular osmolarity of a RBC becomes greater than that of the medium when RBCs are placed into a medium of permeant solutes. | - Intracellular osmolarity = [Impermeant cellular osmolytes already in cell], I + [Permeant solute], P - Extracellular osmolarity = [Permeant solute], P - Overall: Intracellular osmolarity (P+I) > Extracellular osmolarity (P) |
| How can Hameolysis be used to determine whether a a RBC membrane is permeable to a particular compound? | If a RBC is permeable to a particular compound, the permeant solute will flow into the RBC until concentrations inside the cell are equal to medium. [Permeant solute] + [Impermeant osmolytes] can cause cell lysis thus indicate that there is a substance present which is permeant. |
| If a RBC is placed in a solution containing 0.3osM impermeant solute, will its volume increase, decrease or stay the same? | Stay the same - at iso-omolar concentrations of impermeant substances, water will neither travel in or out of cells. |
| If a RBC is placed in a solution containing 0.3osM permeant solute, will its volume increase, decrease or stay the same? | The permeant solute will travel from its region of high concentration in the medium, through the membrane, into its region of low concentration in the RBC until concentrations are equal. However, the [permeant solute] + [impermeant solutes] = Higher conc. inside RBC, therefore water flows in. |
| What is the osmolarity of a solution containing 200mM Na2PO4? | 200mM = 0.2 M Na2PO4 = 3 ions Therefore osM = 0.6 |
| What is the osmolarity of a solution containing 200mM NaCl? | 200mM = 0.2 M NaCl = 2 ions osM = 0.4 M. |
| What is the osmolarity of a solution containing 0.1 M sucrose? | 0.1 osM (does not dissociate in solution - remains a single species). |
| What is the osmolarity of a solution containing 200mM NaCl and 0.1M Na2HPO4? | 200mM NaCl (2) = 0.2 M = 0.4 osM Na2HPO4 (3) = 0.1 M = 0.3 osM = 0.7osM |
| Placing red blood cells in which of the following solutions is likely to lead to haemolysis? - 0.3 M Sucrose - 0.1 M MgCl2 - 0.1 M NaCl - 0.2 M MgCl2 - 0.1 Na2PO4 | - 0.3 M Sucrose, therefore osM = 0.3 - 0.1 M MgCl2 = 0.3 osM - 0.1 M NaCl = 0.2 osM - 0.2 M MgCl2 = 0.6 osM - 0.1 Na2PO4 = 0.3 osM Therefore Sucrose. |
| Will adding a concentrated solution of ethanol to a red blood cell suspension cause haemolysis in the cells? What is your reasoning? | Yes, because it is permeable and will flow into the cell, and water will follow it (osmotically active). |
| Why is ethanol permeable? | Ethanol is sufficiently small and non-polar to pass through the cell membrane. |
| Describe the 5 stages that would follow from adding a permeant substance with high osmolarity to a red blood cell (including any tests as the end) | - The permeant solute would flow into the RBC until the concentrations of the permeant solute are equal both inside the RBC and in the medium. - RBCs now have a higher overall solute concentration (concentration of impermeable osmolytes + permeant solutes). - Water follows the solutes into the RBC by osmosis down the water conc. gradient. - Cell swells and haemolysis occurs. - Any haemoglobin lysed from damaged RBCs will remain in supematent after centrifugation to be assayed at 420nm. |
| Describe out of the following 3 species; NaCl, Sucrose and Na2HPO4 which one requires the most moles to generate haemolysis in RBCs. | In solution, all of these molecules break down into different amounts of species. NaCl = 2 Na2HPO4 = 3 Sucrose = 1 Therefore, Sucrose requires the MOST amount of moles in order to create the same level of haemolysis as the other 2 molecules since for NaCl for example, twice the amount of species are present in solution when it dissociates. in comparison to Sucrose with just one |
| What chemical structures and properties make substances more permeable to lipid bilayer membranes? | Small, non-polar substances are much more permeable than large and/ or charged substances. Small/medium uncharged, polar substances can also pass through. |
| Which of the following molecules are able to pass across the RBC membrane and enter the cell? - describe the rate at which they diffuse in if they do and their rate of haemolysis. | - All molecules can diffuse across except Tetraethylammonium chloride. - Urea, Glycerol and ethanol are structurally related, all 3 are polar (but uncharged)... the more hydroxyl groups present, the slower the rate of entry > ethanol enters more quickly and causes more cells to lyse in the time frame. However, urea is so small that diffusion is also very fast. - Tetraethylammonium chloride dissociates into a +vely charged tetraethylammonium ion and negatively charged chloride ion which cannot enter the cell. - Whereas the tetraethylammonium hydrochloride, like the ammonium chloride, forms a more neutral, mor elipophilic species on dissociation (due to the loss of a proton) which can enter the cell. |
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