Selective Permeability ⌂ Selective permeability- the cell membrane’s ability to allow some substances to enter/ exit but not all. ⌂ Two processes that allow substances to enter/exit: Passive transport – energy from kinetic energy and concentration gradient. Active transport-ATP
Diffusion ⌂ Process depends on concentration gradient. Particles will never stop moving, but when equilibrium is reached there will be no net change in their concentration. Movement of particles is from [high] to [low] concentration. Dependent on four factors: diameter, temperature, electrical charge (when applicable), and the concentration gradient. Majority of materials enter cell through diffusion…energy conservation for other processes.
Osmosis ⌂ Diffusion of water. ⌂ Water always travels from hypotonic to hypertonic ⌂ Solute always travels in opposite direction of water. ⌂ Osmosis Animation Osmosis Animation
Isotonic Solutions ⌂ Isotonic solutions-the same amount of solute exists inside and outside the cell. ⌂ Water moves in and out at the same rate.
Hypertonic Solutions ⌂ Hypertonic solutions- have more solutes in solution than inside the cell. ⌂ Water moves out of the cell to achieve equilibrium.
Hypotonic Solutions ⌂ Hypotonic solutions- have less solutes in them than inside the cell. ⌂ Water will enter the cell to try and achieve equilibrium. ⌂ Cells may lyse if too much water enters. ⌂ Plants combat this risk with their cell wall, and turgor pressure results.
Water Potential- water’s ability to do work when going through the C.M. ⌂ Pressure Potential Positive pressure is the cell being pushed Negative Pressure- the cell being pulled (eg transpiration) ⌂ Solute Potential- based on solute concentration
Solute Potential ΨS = -iCRT -i (ionization constant) C (molar concentration) R (pressure constant) T (temperature in Kelvin)
Turgor pressure is ~100psi, much more than a tire. The pressure is so great that plant cells would detach from one another if not for adhesive molecules known as pectins.
Facilitated Diffusion with Channel Proteins ⌂ Facilitated diffusion- within the cell membrane are channel proteins that allow materials to pass into the cell. ⌂ Aquaporins- channel proteins that allow water to pass through, in addition to simple diffusion. In kidneys and plants where water is essential Channel Protein Animation
FD with Ion Channel Proteins ⌂ Channel protein let in ions. ⌂ When the protein shape changes, the gate will open. ⌂ Ions pass through based on size and charge. ⌂ Can be ligand gated or voltage gated. ⌂ Voltage gated channels depend on two things: Concentration gradient of K Concentration of K (usually higher inside cell) Membrane potential due to charge imbalance.
Facilitated Diffusion with Carrier Proteins ⌂ Carrier proteins transport polar substances like amino acids and sugars. ⌂ When the carrier proteins become saturated the rate of diffusion is maxed out. ⌂ Animation: How Facilitated Diffusion Works Animation: How Facilitated Diffusion Works
Figure 5.12 A Carrier Protein Facilitates Diffusion (Part 1)
Filtration ⌂ Filtration- pressure driven system that pushes water and nutrients across cell membranes. ⌂ This is how urine is produced ⌂ Does not require energy.
Active Transport is Directional ⌂ Active transport always works against the concentration gradient. Going from a lower to higher concentration. ⌂ Requires energy. ⌂ Two types: primary and secondary active transport.
Membrane Proteins associated with Active Transport ⌂ Cell Pumps: ⌂ Uniports move a single substance in one direction. ⌂ Symports – move two substances in the same direction. ⌂ Antiports - move two substances in opposite directions. One into the cell, and one out of the cell. e.g. NaK pump Coupled transporters are those that move two substances. Which of these are coupled?
Figure 5.13 Three Types of Proteins for Active Transport
Primary Active Transport ⌂ ATP is hydrolyzed and drives the movement of ions against the concentration gradient. ⌂ Sodium potassium pump is an example of 1 AT. Because the ions move against the concentration gradient. (Na leaves cell, although more Na outside cell, same with K more in cell, but K still enters) ⌂ NaK Pump located in all animal cells; antiport; coupled transporter ⌂ NaK Pump Simple Animation NaK Pump Simple Animation ⌂ Na K Pump Animation Na K Pump Animation
Figure 5.14 Primary Active Transport: The Sodium–Potassium Pump
Membrane Potential ⌂ Membrane Potential aka Voltage Gradient allows the cell to do work. ⌂ DNA is negative inside cell(-), NaK pumps extra Na out of the cell (+). ⌂ Difference in charge allows molecules to be transported using ATP. ⌂ E.g. glucose enters through because of membrane potential ⌂ Secondary AT Animation Secondary AT Animation
H Pumps ⌂ Most important pump for cell respiration and photosynthesis. ⌂ H+ pumped out of cell, and ions can now diffuse in ⌂ Pumping H requires little energy, and they help sugars enter the cell by AT
What if the macromolecules are too large, charged, or polar to enter through the membrane? ⌂ Is this a good problem or not? ⌂ Which organelle is responsible for substance transport?
Endocytosis ⌂ Processes that bring substances into the cell such as macromolecules and smaller cells. ⌂ Three types of endocytosis: Phagocytosis Pinocytosis Receptor-Mediated Endocytosis
Figure 5.16 Endocytosis and Exocytosis (A) Phagocytosis Cell eating Part of cell membrane engulfs particles/cells Phagosome fuses with a lysosome and digestion occurs
Endocytosis ⌂ Phagocytosis- process fairly nonspecific ⌂ Only a few cells can do this ex. WBC Must be able to change shape and form pseudopodia. WBC will attach to bacteria engulf bacteria with pseudopodia lysosomes with enzymes digest it residual waste is exocytosed. Pinocytosis- same process just with liquids. Also fairly nonspecific. WBC and Phagocytosis Animation
Receptor-Mediated Endocytosis ⌂ Specific process that utilizes integral membrane proteins to bind to specific molecules in the cell’s environment. ⌂ Receptor proteins are substance specific, aka coated pits. Coated with protein, formed by CM depressions. ⌂ When a ligand binds to the receptor protein, it invaginates and forms a vesicle. ⌂ E.g. cholesterol uptake in mammals rd. 113-114
Figure 5.17 Formation of a Coated Vesicle (Part 1)
Figure 5.17 Formation of a Coated Vesicle (Part 2) Receptors will form a new vesicle and be recycled back to plasma membrane.
Exocytosis ⌂ Anything that comes in must go out. ⌂ Materials are packaged into vesicles, which fuse with the cell membrane via a membrane protein. ⌂ The two membranes fuse, contents expelled, and the CM incorporates vesicle membrane.
Endocytosis and Exocytosis Animation Hyper,Hypo,Iso
Other Cell Membrane Functions ⌂ Some organelle membranes help transform energy. ⌂ Some membrane proteins organize chemical reactions. ⌂ Some membrane proteins process information.
Plasmolysis ⌂ Net loss of a cell’s volume due to a hypertonic environment. ⌂ Plasmolysis Animation Plasmolysis Animation
Water Potential ⌂ Tendency of water to leave one place in favor of another. ⌂ Always moves from higher to lower water potential. ⌂ Affected by pressure and solute ⌂ Water potential ( ) = pressure potential ( p) + solute potential ( s) ⌂ Solute Potential = s=–iCRT i = The number of particles the molecule will make in water; for NaCl this would be 2; for sucrose or glucose, this number is 1 C = Molar concentration (from your experimental data) R = Pressure constant = 0.0831 liter bar/mole K T = Temperature in degrees Kelvin = 273 + °C of solution
Lab: Plasmolysis ⌂ Perform a serial dilution of salt (100, 50, 25, 0% solution) ⌂ Predict which solution will yield the fastest plasmolysis results. ⌂ Perform Experiment with each solution and time results.
Lab: Water Potential ⌂ Perform a serial dilution of sugar ( 100, 50, 25, 0). Label solutions. ⌂ Core equal lengths of 2 vegetables. ⌂ Record lengths, mass, and vegetable type in table. ⌂ Predict what will happen to length and mass by tomorrow.