Membrane Transport PDF

Membrane Transport  Passive Transport The movement of materials across a cell membrane without the use of energy (ATP) Movement of particles along a concentration gradient → from an area of higher concentration to an area of lower concentration (WITH a concentration gradient)...

Membrane Transport  Passive Transport The movement of materials across a cell membrane without the use of energy (ATP) Movement of particles along a concentration gradient → from an area of higher concentration to an area of lower concentration (WITH a concentration gradient) Diffusion 2nd Law of Thermodynamics governs biological systems – universe tends towards disorder (entropy) ▪ Diffusion ◆ movement from HIGH → LOW concentration Simple Diffusion Movement of particles from HIGH to LOW concentration areas – “passive transport” – no energy needed – Will continue until equilibrium is achieved movement of water diffusion osmosis Example: Movement of O2 into cells and CO2 out of cells Facilitated Diffusion Molecules too large for simple diffusion or are hydrophilic 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” Example: Glucose is constantly being used up inside the cell so the concentration gradient is maintained; Small ions  Osmosis Water is very important to life, so we talk about water separately Diffusion of WATER through a selectively permeable membrane from an area of HIGH concentration of water to an area of LOW concentration of water – Water moves from an area of lower solute concentration to an area of higher solute concentration Osmosis is important to aquatic organisms. Kidney’s use osmosis to regulate water balance in the blood. 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 1 Managing water balance Hypotonic – a cell in fresh water – high concentration of water around cell problem: cell gains water, swells & can burst example: Paramecium KABOOM! solution: contractile vacuole – pumps water out of cell – Uses ATP – plant cells turgid = full No problem, cell wall protects from burstinghere ATP freshwater 2 Managing water balance Hypertonic – a cell in salt water I’m shrinking, – low concentration of waterI’m shrinking! around cell problem: cell loses water & can die example: shellfish solution: take up water or pump out salt – plant cells I will survive! plasmolysis = wilt can recover saltwater 3 Managing water balance Isotonic – animal cell immersed in mild salt solution – no difference in concentration of water between cell & environment That’s problem: none perfect! –no net movement of water –cell in equilibrium –volume of cell is stable example: blood cells in blood plasma be Ibetter… could –slightly salty IV solution in hospital balanced  Aquaporins 1991 | 2003 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 Active Transport Uses ATP (energy) to move materials across a cell membrane against a concentration gradient. – conformational shape change transports solute from one side of membrane to other – protein “pump” – “costs” energy = ATP conformational change LOW ATP HIGH “The Doorman”  Active transport Many models & mechanisms ATP ATP antiport symport  Na+/K+ pump Membrane transport proteins pump Na+out of the cell and K+ into the cell against the concentration gradient. Uses ATP! Nerve cells must maintain a higher concentration of Na+ outside the cell and K+ inside the cell to function.  Getting through cell membrane Passive Transport – Simple diffusion nonpolar, hydrophobic molecules –HIGH → LOW concentration gradient – Facilitated transport polar, hydrophilic molecules through a protein channel –HIGH → LOW concentration gradient Active transport – against concentration gradient LOW → HIGH ATP – uses a protein pump (requires ATP) What about large molecules? Moving large molecules into & out of cell – through vesicles & vacuoles Endocytosis – moving materials INTO the cell phagocytosis = “cellular eating” pinocytosis = “cellular drinking” receptor-mediated endocytosis – Molecules bind to receptors on the outside of the cell membrane. Exocytosis – moving materials OUT of the cell Insulin released from the pancreas into the bloodstream exocytosis  Endocytosis White blood cells (macrophages) take in bacteria. phagocytosis fuse with lysosome for digestion. Invagination End products (pinching) of pinocytosis of digestion. cell membrane non-specific forms a vesicle process inside the cell. receptor-mediated endocytosis LDL’s taken into cell. triggered by molecular signal Transport summary simple diffusion facilitated diffusion active ATP transport Any Questions??