1 Big Idea: The plasma membrane allows the cell to separate the extracellular (outside cell) environment from the inside of the cell while still allowing nutrients in the cell and wastes out of the cell.
2 Plasma Membrane A selectively permeable membrane about 8 nm thick, allows certain molecules in/out easier than others. Structure: Made mostly of phospholipids & other lipids, but also contains many different types of proteins and carbs Amphipathic: Most phospholipids and other lipids & proteins in membrane have a hydrophobic & hydrophilic component to them. Fluid Mosaic Model: Proteins are embedded in or attached to the phospholipid bilayer.
3 History of Membrane The sandwich model was proposed by Davson & Danielli in 1935 and was the dominant view until Structure: phospholipid bilayer sandwiched by a protein layer on both sides of membrane.
4 Modern View of Membranes Fluid Mosaic model the new view of the plasma membrane that electron microscopy and freeze fracture research contributed to Accepted view since the 1970 s
5 Membranes are Fluid Lipids & proteins can drift laterally, but not flip- flop because a hydrophilic region would have to pass through a hydrophobic region. Lipids move rapidly (2 micrometers per second) Proteins move more slowly connected to cytoskeleton where motor proteins move membrane proteins. Some proteins are stationary
6 Temperature Affects Membrane Fluidity Big Idea: Membranes work best when they are fluid because as membranes solidify the permeability changes and enzyme proteins become inactive. Unsaturated hydrocarbons of phospholipids increase fluidity at lower temperatures. (VEGETABLE OILS) Cholesterol decreases fluidity at body temp, but increase fluidity at lower temps. Cold tolerant plants change phospholipids to unsaturated hydrocarbons before cold season Ex: Winter wheat changes over in the fall
7 Fluid versus Viscous Membrane
8 Membrane Structure Integral proteins: span the membrane, have a hydrophobic & 2 hydrophilic regions. Hydrophobic region consists of nonpolar amino acids that make alpha helices. Often attached to cytoskeleton. Ex: Integrins Peripheral proteins: proteins not embedded in lipid bilayer, typically loosely attached to membrane proteins. Ex: collagen, fibronectin Proteins, lipids & carbs are directional made for inside or outside of cell. Made in the ER (inside of ER = outside of plasma membrane)
9 What level of protein structure is alpha helical?
10 Membrane Structure Oligosaccharides: Short polysaccharides attached to membrane proteins (glycoproteins) or lipids (glycolipids) These allow for diversity in the surface molecules of different organisms or cells within organisms.
11 Oligosaccharides and Blood Type
12 FuncDons of Membrane Proteins figure 8.9 in your book Transport (Integral proteins) Enzyme Activity Signal Transduction (chemical messengers) Intercellular Joining Cell to Cell Recognition Attachment to cytoskeleton or ECM
13 Transport Proteins Integral proteins that open hydrophilic channels or hydrolyze ATP to pump ions across membrane. What is the structure of the integral proteins?
14 Enzyme AcDvity Active site exposed to cytoplasm or ECM where substrate attaches. Often occur in metabolic pathways where product from enzyme is reactant for nearby enzyme.
15 Signal TransducDon Protein on ECM may have a binding site that changes the shape of the protein which relays message to the inside of the cell. Chemical messengers: Hormones insulin, glucagon, TSH, etc
16 Intercellular Joining Membrane proteins may hook cells together. What are some examples? Tight junctions Desmosomes
17 Cell to Cell RecogniDon Some glycoproteins serve as identification tags specifically recognized by other cells
18 APachment to cytoskeleton & ECM Proteins bond to microfilaments or other parts of cytoskeleton to maintain cell shape or coordinate intra/extra- cellular changes
19 Many individual molecules (proteins, lipids, carbs) work together towards regulating transport.
20 Permeability of the Lipid Bilayer Hydrophobic molecules can dissolve in the lipid bilayer and cross w/ ease, such as hydrocarbons, & CO 2 Hydrophilic molecules like ions & polar molecules (sugars- - glucose, amino acids) are impeded by the hydrophobic core of the membrane Can water move in easily?
21 Transport Proteins H 2 O, ions, & other polar molecules can pass through transport proteins that span the membrane. Hydrophilic channels are specific to certain molecules Proteins can also physically move molecules across Example: transport proteins of liver cells move glucose rapidly but exclude the structural isomer fructose Why would glucose need to be transported rapidly into liver & muscle cells?
22 Transport Proteins what drives the movement of molecules?
23 Passive Transport Diffusion: the thermal motion or tendency for solutes to spread out evenly into available space. Spontaneous process decreases free energy In a population of molecules, directionality occurs from high to low concentration (concentration gradient) until dynamic equilibrium occurs equal movement of molecule in both directions. Regardless of other molecules present, each substance diffuses down its own concentration gradient.
24 Diffusion Much of the membrane traffic occurs from diffusion Example: In cell respiration, O 2 diffuses across the membrane continuously because it is used up quickly. No energy is necessary for this process, in fact, potential energy is stored in the concentration gradient, which drives diffusion.
26 Diffusion AnimaDon hill.com/sites/ / student_view0/chapter2/ animation how_diffusion_works.html
27 Osmosis Passive Transport of H 2 O Hypertonic high solute concentration Hyper means more Hypotonic low solute concentration ( Hypo = less ) The cell will have a hyper & hypotonic side (comparison) Isotonic solutions that have equal solute concentrations on both sides of a membrane. Direction of osmosis: water moves from hypo to hypertonic side
28 A nurse hooks a patient up to an IV, the solution is hypertonic to the patients body. What happens? How about if it is hypotonic to patient? A roadside plant is shriveled up after a winter of salting the roads. Why?
29 Cells & Balancing Water Uptake What do animal cells do in isotonic solutions? No net movement of water in/out What do animal cells do in hypertonic solutions? Net movement of water out Cell typically shrivels and likely dies Ex: blood cell & dehydration, salinity change affects homeostasis (Great Salt Lake) Most marine animals have cells that are isotonic to seawater
30 Plant & Animal Cells
31 Cell Walls & Water Transport Become turgid (firm) in hypotonic solution because water will come in only until pressure from the cell wall (turgor pressure) pushes back Isotonic environ: plant becomes flaccid (limp) Hypertonic environ: Plasmolysis lethal Non- woody plants rely on firmness (turgidity) to stand upright.
32 OsmoregulaDon Control of water balance in organisms w/out cell walls that live in hypotonic environments Paramecium uses a contractile vacuole to deal with water uptake
33 Facilitated Diffusion NO ENERGY REQUIRED Uses concentration gradient to drive diffusion of polar molecules and ions that cannot cross membrane. Proteins behave like enzymes: Protein is specific to a solute (like enzyme/substrate) Protein may have a binding site (like active site) Limited proteins specific to a solute in the membrane, so there is a maximum speed of transfer (reaction rate) Imposter solute can compete w/ normal solute (competitive inhibitor) Difference is: Physical vs Chemical process
34 Channel Proteins Corridor for ions or small molecules hydrophilic channel Aquaporins: allow fast movement of lots of H 2 O Gated channels: open/ close based on a stimulus. Ex: Nerve cells & NT, allow Na+ ions into cell
36 Shape Changers Solute binds to binding site, changing shape of transport protein & it unloads solute inside Changes back after Disorder cystinuria Doesn t allow for reabsorption of cystine & other amino acids makes kidney stones
37 Facilitated Diffusion AnimaDon hill.com/sites/ / student_view0/chapter2/ animation how_facilitated_diffusion_works.html
38 AcDve Transport The pumping of a solute against the concentration gradient (low to high) An uphill process; not spontaneous; requires work NEEDS ENERGY INPUT Allows cell to increase or decrease solutes in comparison to the outside of the cell. Performed by specific proteins in membrane in conjunction w/ ATP transfers a P i to the protein, causing a shape change, brings solute across the membrane
39 Sodium- Potassium Pump Na+ in cytoplasm attaches to binding sites which stimulates phosphorylation P i causes the protein to change shape expels Na+ out Na+ leaving opens K+ binding site; K+ attaches causing P i to release P i loss restores the original shape, causing release of K+ inside of the cell. An exchange of Na+ for K+ against both concentration gradients
40 Na+/K+ Pump hill.com/sites/ / student_view0/chapter2/ animation how_the_sodium_potassium_pump_wor ks.html
41 Voltage Across Membranes Membrane Potential: cytoplasm is more negative than extracellular fluid resulting in voltage across the membrane. Which way will cations & anions like to travel? Anions out & cations in Electrochemical gradient: combination of forces acting on ion s movement Chemical force: ion s concentration gradient Electrical force: effect of membrane potential
42 Voltage Across Membrane Electrogenic Pump: Na+/K+ is the major type in animal cells where 3Na+ ions go out & 2K+ ions move in. This makes the inside negative. STORES ELECTRICAL PE FOR CELL WORK Proton Pump: main electrogenic pump of plants, bacteria, & fungi Transfer H+ ions out of cell stores electrical PE
43 Proton Pump AnimaDon hill.com/olcweb/cgi/ pluginpop.cgi?it=swf::535::535::/sites/dl/free/ /120072/bio13.swf::Photosynthetic %20Electron%20Transport%20and%20ATP %20Synthesis
44 Transport of Large Molecules Exocytosis: secretion of macromolecules by fusion of vesicles w/ the plasma membrane Vesicle moves from Golgi to membrane. How does it move from Golgi to membrane?? Examples: Pancreatic cells release insulin into blood Neuron releasing neurotransmitters to stimulate other neurons or muscle cells. In plants, carbs released to help build cell walls
45 Endocytosis Vesicle forming from plasma membrane pinching inward taking in intended contents. Types: Phagocytosis how does cell accomplish this? Pinocytosis cell drinking (forms tiny vesicles) Receptor mediated endocytosis: Specific receptor sites in membrane bind to target molecules Form in coated pits where proteins on cytoplasmic side have a fuzzy layer of protein in the groove Allows cell to bring in unconcentrated substances from extracellular fluid
46 Endo/Exocytosis AnimaDon hill.com/olcweb/cgi/ pluginpop.cgi?it=swf::535::535::/sites/dl/free/ /120068/bio02.swf::Endocytosis%20and %20Exocytosis