AP Biology Cell Membrane and the Movement across it!

AP Biology Cell (plasma) membrane  Cells need an inside & an outside…  separate cell from its environment  cell membrane is the boundary IN food carbohydrates sugars, proteins amino acids lipids salts, O 2, H 2 O OUT waste ammonia salts CO 2 H 2 O products cell needs materials in & products or waste out IN OUT Can it be an impenetrable boundary? NO!

AP Biology Lipids of cell membrane  Membrane is made of phospholipids  phospholipid bilayer phosphate lipid hydrophilic hydrophobic inside cell outside cell

AP Biology Phospholipid bilayer  What molecules can get through directly? inside cell outside cell fats & other lipids can slip directly through the phospholipid cell membrane, but… what about other stuff? lipid salt aa H2OH2O sugar NH 3

AP Biology A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

AP Biology Membrane Proteins  Proteins determine most of membrane’s specific functions  cell membrane & organelle membranes each have unique collections of proteins  Membrane proteins:  peripheral proteins = loosely bound to surface of membrane  integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane proteins

AP Biology Membrane Protein Types  Channel proteins – wide open passage  Ion channels – gated  Aquaporins – water only, kidney and plant root only  Carrier proteins – change shape  Transport proteins – require ATP  Recognition proteins - glycoproteins  Adhesion proteins – anchors  Receptor proteins - hormones

AP Biology Membrane Carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish neighboring cells from another  important in organ & tissue development  basis for rejection of foreign cells by immune system

AP Biology Cholesterol  Provides stability in animal cells  “temperature buffer” quality for membrane  Replaced with sterols in plant cells

AP Biology Getting through cell membrane  Passive transport  No energy needed  Movement down concentration gradient  Active transport  Movement against concentration gradient  low  high  requires ATP

AP Biology Diffusion  2nd Law of Thermodynamics - Universe tends towards disorder  Diffusion  movement from high  low concentration

AP Biology Simple diffusion across membrane inside cell outside cell Which way will lipid move? low high  lipid

AP Biology Diffusion of 2 solutes  Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances

AP Biology When is Diffusion Needed?  Respiratory and Circulatory systems  Oxygen/CO 2 transport into and out of bloodstream  Skins, gills, alveoli, capillaries  Excretory systems  Movement of wastes into or out of blood  Skin, nephridia, nephrons, gills  What do these systems have in common for diffusion to occur?

AP Biology Overcoming limitations of diffusion O2O2 CHO aa CH CO 2 NH 3 aa O2O2 CH aa CO 2 NH 3 O2O2 aa CH aa CHO O2O2  Diffusion is not adequate for moving material across more than 1-cell barrier

AP Biology Gas exchange in many forms… one-celledamphibiansechinoderms insectsfishmammals endotherm vs. ectotherm size cilia water vs. land

AP Biology Counter current exchange system  Water carrying gas flows in one direction, blood flows in opposite direction just keep swimming….

AP Biology  Blood & water flow in opposite directions  maintains diffusion gradient over whole length of gill capillary  maximizing O 2 transfer from water to blood water blood How counter current exchange works front back blood 100% 15% 5% 90% 70%40% 60%30% 100% 5% 50% 70% 30% water counter- current concurrent

AP Biology Gas Exchange on Land  Advantages of terrestrial life  air has many advantages over water  higher concentration of O 2  O 2 & CO 2 diffuse much faster through air  respiratory surfaces exposed to air do not have to be ventilated as thoroughly as gills  air is much lighter than water & therefore much easier to pump  expend less energy moving air in & out  Disadvantages  keeping large respiratory surface moist causes high water loss  reduce water loss by keeping lungs internal

AP Biology Facilitated diffusion  Move from HIGH to LOW concentration through a protein channel  passive transport  no energy needed  facilitated = with help

AP Biology Gated channels  Some channel proteins open only in presence of stimulus (signal)  stimulus usually different from transported molecule  ex: ion-gated channels when neurotransmitters bind to a specific gated channels on a neuron, these channels open = allows Na + ions to enter nerve cell  ex: voltage-gated channels change in electrical charge across membrane causes channel to open or close

AP Biology Active transport  Cells may need molecules to move against concentration situation  need to pump against concentration  protein pump  requires energy  ATP Na+/K+ pump in nerve cell membranes

AP Biology Transport summary

AP Biology How about large molecules?  Moving large molecules into & out of cell requires ATP(energy)!  through vesicles & vacuoles  endocytosis  phagocytosis = “cellular eating”  pinocytosis = “cellular drinking”  receptor-mediated endocytosis  exocytosis exocytosis

AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by ligand signal

AP Biology The Special Case of Water Movement of water across the cell membrane

AP Biology Osmosis is diffusion of water  Diffusion of water from high concentration of water to low concentration of water  across a semi-permeable membrane

AP Biology 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 hypotonichypertonic water net movement of water

AP Biology Managing water balance  Cell survival depends on balancing water uptake & loss freshwaterbalancedsaltwater

AP Biology Hypotonicity  animal cell in hypotonic solution will gain water, swell & possibly burst (cytolysis)  Paramecium vs. pond water  Paramecium is hypertonic  H 2 O continually enters cell  contractile vacuole - pumps H 2 O out of cell = ATP  plant cell  Turgid (turgor pressure)  Cell wall

AP Biology Hypertonicity  animal cell in hypertonic solution will loose water, shrivel & probably die  salt water organisms are hypotonic compared to their environment  they have to take up water & pump out salt  plant cells  plasmolysis = wilt

AP Biology 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.05 M.03 M Osmosis…

AP Biology Water Potential  Water moves from a place of greater water potential to a place of lesser water potential (net).  As the concentration of a solute increases in a solution, the water potential will decrease accordingly.  Which has the greater water potential: .2M or.8M?  Which has the greater water potential:  20% or 80% water?

AP Biology intracellular waste Animal systems evolved to support multicellular life O2O2 CHO aa CH CO 2 NH 3 aa O2O2 CH O2O2 aa CO 2 NH 3 O2O2 aa CH aa CHO O2O2 Diffusion too slow! single cell but what if the cells are clustered? for nutrients in & waste out extracellular waste

AP Biology Overcoming limitations of diffusion  Evolution of exchange systems for  distributing nutrients  circulatory system  removing wastes  excretory system systems to support multicellular organisms aa CO 2 NH 3 O2O2 aa CH aa CHO O2O2

AP Biology Intracellular Waste  What waste products are made inside of cells?  what do we digest our food into…  carbohydrates = CHO  lipids = CHO  proteins = CHON  nucleic acids = CHOPN CO 2 + H 2 O NH 2 = ammonia  CO 2 + H 2 O  CO 2 + H 2 O + N  CO 2 + H 2 O + P + N | ||| H H N C–OH O R H –C– Animals poison themselves from the inside by digesting proteins! cellular digestion… cellular waste

AP Biology Nitrogen waste  Aquatic organisms  can afford to lose water  ammonia  most toxic  Terrestrial  need to conserve water  urea  less toxic  Terrestrial egg layers  need to conserve water  need to protect embryo in egg  uric acid  least toxic

AP Biology Land animals  Nitrogen waste disposal on land  need to conserve water  must process ammonia so less toxic  urea = larger molecule = less soluble = less toxic  2NH 2 + CO 2 = urea  produced in liver  kidney  filter solutes out of blood  reabsorb H 2 O (+ any useful solutes)  excrete waste  urine = urea, salts, excess sugar & H 2 O urine is very concentrated concentrated NH 3 would be too toxic O C H N H H N H Urea costs energy to synthesize, but it’s worth it! mammals

AP Biology Animal Osmoregulation (blood solute levels)  Kidneys – generate urine by filtering wastes from blood  Nephrons – basic unit of kidney  Water will move towards urine or blood as it becomes hypertonic via AQUAPORINS  Anti-Diuretic Hormone increases water movement back to blood….why?  Blood pressure is highly regulated by the kidney because without pressure, there is no filtration = toxic blood = death!!!

AP Biology Osmotic control in nephron  How is all this re-absorption achieved?  tight osmotic control to reduce the energy cost of excretion  use diffusion instead of active transport wherever possible the value of a counter current exchange system

AP Biology Osmoregulation Why do all land animals have to conserve water?  always lose water (breathing & waste)  may lose life while searching for water  Water balance vs. Habitat  freshwater  hypotonic to body fluids  water flow into cells & salt loss  saltwater  hypertonic to body fluids  water loss from cells  land  dry environment  need to conserve water  may also need to conserve salt hypotonic hypertonic