Cell Transport Notes PDF

CELL TRANSPORT Types of Transport Across the Cell Membrane In order for the cell to stay alive, it must meet the characteristics of life which include taking nutrients in and eliminating wastes and other by- products of metabolism. Several mechanisms allow cells to carry...

CELL TRANSPORT Types of Transport Across the Cell Membrane In order for the cell to stay alive, it must meet the characteristics of life which include taking nutrients in and eliminating wastes and other by- products of metabolism. Several mechanisms allow cells to carry out these processes. All of the cell’s activities are, in one way or another, tied to the membrane that separates its interior from the environment.  ACTIVITY 1 Spray a cologne in one corner of the room Questions:  Who among the class were able to smell the air freshener first?  Who among the class were the last ones to smell the air freshener?  How would you explain the phenomenon wherein people in the same classroom smelled the scent of the cologne at different times?  ACTIVITY 2 What comes to your mind when you see two men who are of the same age but one is 7.5 feet tall and the other is 3.5 feet tall? the two men are similar in the sense that they are both abnormal. Growth in both men is abnormal such that one is too big in size while the other one is too small. Both men have abnormal growth. Both have defective membranes. Insufficient amount of growth hormones pass through a pygmy’s body while an excessive amount of growth hormones is released in a giant. Cell Membrane/Plasma membrane Plasma membranes—are made up of a phospholipid bilayer in an aqueous environment. Phospholipids are the foundation of all known biological membranes. The lipid bilayer forms as a result of the interaction between the non-polar (hydrophobic or water-fearing) phospholipid tails, the polar (hydrophilic or water-loving) phospholipid heads, and the surrounding water. Phospholipids Phosphate “attracted to water” Phosphate head hydrophilic Fatty acid tails Fatty acid hydrophobic Arranged as a bilayer “repelled by water” Aaaah, one of those structure–function examples Arranged as a Phospholipid bilayer Serves as a cellular barrier / border sugar H2O salt polar hydrophilic heads nonpolar hydrophobic impermeable to polar molecules tails polar hydrophilic heads waste lipids Cell membrane defines cell Cell membrane separates living cell from aqueous environment thin barrier = 8nm thick Controls traffic in & out of the cell allows some substances to cross more easily than others hydrophobic (nonpolar) vs. hydrophilic (polar)  Permeability to polar molecules? Membrane becomes semi-permeable via protein channels specific channels allow specific material across cell membrane inside cell H2O aa sugar NH3 salt outside cell Cell membrane is more than lipids… Transmembrane proteins embedded in phospholipid bilayer create semi-permeabe channels lipid bilayer protein channels membrane in lipid bilyer membrane  Why are proteins the perfect molecule to build structures in the cell membrane? 2007-2008 Classes of amino acids What do these amino acids have in common? nonpolar & hydrophobic  Classes of amino acids What do these amino acids have in common? I like the polar ones the best! polar & hydrophilic Proteins domains anchor molecule Polar areas Within membrane of protein nonpolar amino acids hydrophobic anchors protein into membrane On outer surfaces of membrane in fluid polar amino acids hydrophilic extend into extracellular fluid & into cytosol Nonpolar areas of protein  H H+ + Examples Retinal chromophore NH2 aquaporin = water channel in bacteria Porin monomer H2O -pleated sheets Bacterial Nonpolar outer (hydrophobic) COOH membrane -helices in the Cytoplasm cell membrane H H+ + proton pump channel in photosynthetic bacteria function through conformational change = H2O protein changes shape Membrane Proteins  Proteins determine membrane’s specific functions  cell membrane & organelle membranes each have unique collections of proteins  Classes of membrane proteins:  peripheral proteins loosely bound to surface of membrane ex: cell surface identity marker (antigens)  integral proteins penetrate lipid bilayer, usually across whole membrane transmembrane protein ex: transport proteins channels, permeases (pumps) Cell membrane must be more than lipids… In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model! Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Glycoprotein Extracellular fluid Glycolipid Phospholipids Cholesterol Transmembrane proteins Peripheral protein Cytoplasm Filaments of cytoskeleton 1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model Membrane carbohydrates Play a key role in cell-cell recognition ability of a cell to distinguish one cell from another antigens important in organ & tissue development basis for rejection of foreign cells by immune system Any Questions??  Movement across the Cell Membrane 2007-2008 Diffusion 2nd Law of Thermodynamics governs biological systems universe tends towards disorder (entropy)  Diffusion  movement from HIGH LOW concentration Why is it that when you leave an ice cube at room temperature, it begins to melt? Why do we get older and never younger? And, why is it whenever rooms are cleaned, they become messy again in the future? Certain things happen in one direction and not the other, this is called the "arrow of time" and it encompasses every area of science. The thermodynamic arrow of time (entropy) is the measurement of disorder within a system. Denoted as ΔS, the change of entropy suggests that time itself is asymmetric with respect to order of an isolated system, meaning: a system will become more disordered, as time increases. Simple Diffusion Move from HIGH to LOW concentration “passive transport” no energy needed movement of water diffusion osmosis Facilitated Diffusion Diffusion through protein channels  channels move specific molecules across cell membrane facilitated = with help  no energy needed open channel = fast transport HIGH LOW “The Bouncer” Active Transport  Cells may need to move molecules against concentration gradient  conformational shape change transports solute from one side of membrane to other  protein “pump”  “costs” energy = ATP adenosine triphosphate conformational change LOW ATP HIGH “The Doorman” Active transport Many models & mechanisms ATP ATP antiport symport Getting through cell membrane  Passive Transport  Simple diffusion diffusion of nonpolar, hydrophobic molecules lipids HIGH LOW concentration gradient  Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel HIGH LOW concentration gradient  Active transport  diffusion against concentration gradient LOW HIGH  uses a protein pump ATP  requires ATP Transport summary simple diffusion facilitated diffusion active ATP transport How about large molecules? Moving large molecules into & out of cell through vesicles & vacuoles endocytosis phagocytosis = “cellular eating” pinocytosis = “cellular drinking” exocytosis exocytosis Endocytosis fuse with phagocytosis lysosome for digestion pinocytosis non-specific process receptor-mediated triggered by endocytosis molecular signal  The Special Case of Water Movement of water across the cell membrane 2007-2008 Osmosis is just diffusion of water Water is very important to life, so we talk about water separately Diffusion of water from HIGH concentration of water to LOW concentration of water  across a semi-permeable membrane Concentration of water Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water water hypotonic hypertonic net movement of water Managing water balance Cell survival depends on balancing water uptake & loss freshwater balanced saltwater 1 Managing water balance  Hypotonic  a cell in fresh water  high concentration of water around cell problem: cell gains water, swells & can burst KABOOM! example: Paramecium ex: water continually enters Paramecium cell solution: contractile vacuole ATP pumps water out of cell ATP No problem,  plant cells here turgid = full cell wall protects from bursting freshwater Pumping water out Contractile vacuole in Paramecium ATP 2 Managing water balance Hypertonic I’m shrinking, a cell in salt water I’m shrinking! low concentration of water around cell problem: cell loses water & can die example: shellfish solution: take up water or pump out salt I will plant cells survive! plasmolysis = wilt can recover saltwater 3 Managing water balance  Isotonic That’s  animal cell immersed in perfect! mild salt solution  no difference in concentration of water between cell & environment problem: none no net movement of water  flows across membrane equally, in both directions cell in equilibrium I could be better… volume of cell is stable example: blood cells in blood plasma slightly salty IV solution in hospital balanced  1991 | 2003 Aquaporins Water moves rapidly into & out of cells evidence that there were water channels protein channels allowing flow of water across cell membrane Peter Agre Roderick MacKinnon John Hopkins Rockefeller Do you understand Osmosis….05 M.03 M Cell (compared to beaker) hypertonic or hypotonic Beaker (compared to cell) hypertonic or hypotonic Which way does the water flow? in or out of cell Any Questions??