Presentation on theme: "Unit 3: Cells and Cellular Communication"— Presentation transcript:
1Unit 3: Cells and Cellular Communication Chapters 6-7,11
2“I’m talking to you!...You’re so…so…so thick-membraned sometimes.”
3CHAPTER 8 Cell Membrane Structure and Function Cell Memranes are… Selectively permeableFluid
4Discovering Membrane Sructure Memorizing this timeline is unnecessary- Important concept is that each researcher worked from previous ideas, up to the currently accepted theory.Discovering Membrane SructureMade of lipids and proteinsEvidence:1895 substances that dissolve in lipids enter cells fastest (Overton)1917 man-made membrane of phospholipids created (Langmuir)1925 proposal that memranes are phospholipid bilayers (Gorter + Grendel)
5Discovering Membrane Structure 1935 theory that proteins surround both sides of the phospholipid bilayer (Davson +Danielli)1950’s + 60’s Questions about this model because membrane proteins have large hydrophobic sections, not all membranes are the same1972 fluid mosaic model proposed- and still in use in 2008 (Singer + Nicolson)
6Fluid Mosaic Model of Membranes Insert pic of model
7Chemistry: phospholipids Insert picAmphipathic molecules = has a hydrophobic region and a hydrophilic region
8Fluidity within the membrane Movement of lipids2 µm/sSame size as bacterial cell
9Movement of Phospholipids is controlled by Cytoskeleton- some are immobile because of itTemp- as temp ↓ movement ↓ until it solidifiesCholesterol- at 37C it limits fluidity, but it allows the membrane to be fluid at lower than normal temp b/c it blocks the packing of lipidsCells- can change lipid composition to adjust to tempTemp for solid memb depends on types of ipids. More unsaturated = fluid longer
10Cholesterol in membranes Insert pic of cholesterol blocking movement
11Mosaic= huge variety of molecules 50+ types of proteins in membranes of RBC’s!Integral proteins- cross into the hydrophobic coreTransmembrane proteins- span entire membPeripheral proteins- stuck to the surface
12A Transmembrane Protein with 7 passes through the membrane
13Inside ≠ Outside of Membrane Membrane showing all types labeled
14Carbs in the Membrane cell-cell recognition “Name Tags” Branched oligosaccharides (less than 15 monosaccharides)Uses:Correct placement of cells as embryo developsImmune system defenses
15Glycolipids and Glycoproteins Insert image of glycolipid and label parts
16Structure + Function = moving things across the cell membrane SugarAmino acidswaterOxygenNa+K+Ca2+Cl-OUTCarbon DioxideWaterOther waste productsNa+K+Ca2+Cl-
17How to Cross a Membrane Hydrophobics: Dissolve in the lipid bilayer and pass throughHydrocarbonsCarbon dioxideOxygen
18What if you are hydrophilic?? Transport proteinsLet water, ions, and polar molecules through“toll gate”Some are just tunnels, others carry a molecule through
19Passive Transport Diffusion – [high] [low] Concentration gradient- the natural direction of flow (different for each molecule)
20Passive Transport for Life: Cellular Respiration Oxygen diffuses INTO a cell as long as C.R. is happeningWater diffuses in/out of cells freely through transport proteinsNo energy needed!
21OSMOSISDIFFUSION OF WATERPic of hypo, hyper, isotonic solns
23OsmoregulationControl of water balance in organisms without cell wallsParamecium live in ponds that are hypotonic compared to their cell.Adaptation- Contractile Vacuole collects water and forces it out.Pic Of contractile vacuole in para.
24Water Balance With Cell Walls When surrounded by incoming rain water, it is in a hypotonic solution.Turgid- cell membrane pushed up against cell wall- normal for plantsFlaccid- cell membrane pulls in from cell wall- plant wiltsPlasmolysis- water leaves cell, cell shrivels, fatal to cell
25Facilitated Diffusion Passive transportHydrophilic molec. diffuse via transport proteins
26Transport Proteins are Like Enzymes Specific match to molecules they transportSome have specific active sitesRate of transport slows down when it becomes saturatedInhibited by “imitation” moleculesCatalyze movement of molecules instead of reactions
27Gated ChannelsExample: Neurotransmitter arrives at a nerve cell, causes Na+ to enter the cellChannel ProteinExample: Aquaporins
28Some proteins have “induced fit” like an enzyme Triggered by binding/release of the molecule to be moved
29How can transport proteins affect your health? CystinuriaBody is unable to make memb. Proteins that transport cystine and other A.A. out of the kidney cellsAffect: chronic kidney stones
30Active Transport Movement AGAINST the concentration gradient Requires Energy!ATP is the keyAllows cells to have a different internal environment than surroundingsMore K+ and less Na+ inside than outside
31Na-K Pump Well studied example of active transport Exchanges Na+ for K+ across plasma membrane of animal cells
33Very important concept that will be used in examples all year long. Membrane PotentialElectrical voltage formed when there is an unequal distribution of ions across a membraneInside is negative compared to outside-50mV to -200mV
34Electrochemical Gradient Combination of concentration gradient and electrical forceInside a cell more negative than outside THEREFOREPassive transport will move cations IN and anions OUT
35How this works in a Neuron Stimulated by triggerResting nerve cellGated channels openNa+ enters following electrochemical gradient
36Electrogenic Pumps Na-K pump does not give equal trade of ions 3Na+ OUT and 2K+ INResult: storing energy every time the pump cycles for other jobsANIMALS use Na-K pumpsPLANTS, BACTERIA, FUNGI use Proton pumps
37Proton Pump is the main electrogenic pump in plants, fungi, and bacteria
38ContransportA single ATP pump works, and then diffusion of the same substance assists in moving a molecule AGAINST the concentration gradient
39Moving Very Large Molecules that don’t fit through transport proteins OUT exocytosisInsulin created in pancreatic cells is secreted into the bloodCarbs finished in Golgi Apparatus moved outside plant cells to make a new cell wallIN endocytosisProcess: Vesicles containing molecules fuse with the membrane and release contents
40Ligand- extracellular substances that bind to receptors
41Why should you care? Receptor Mediated Endocytosis Cholesterol carried in blood in Low Density Lipoproteins (LDL’s)Receptors on cell membranes bind to LDL’sVesicle brings cholesterol into cellIf LDL receptor proteins are defective cholesterol accumulates in blood- atherosclerosis…VERY BAD
42CHAPTER 7 A TOUR OF THE CELL We will do this very quickly as 95% is review!If you need extra time see me ASAP! I am happy to help you catch up!
60Signal transduction pathway Process of a signal converted to cellular responseyeast + animal cells similar processPlant + bacterial cells similar processTHEREFORE…APPROXIMATELY WHEN DID THIS EVOLVE???
62Messages over short distances Local regulatorsParacrine signalingGrowth factors sent out to all nearby cellsBenefits of this method?NeurotransmittersElectrical signal secretion of neurotransmitter into synapse message to one immediate neighbor only
63Long Distance Communication: Hormones Endocrine signalingTravel in blood in animalsTravel in by diffusion, or through cells in plantsLess known about these mechanismsEthylene- causes fruit to ripen is a gas C2H4
671971 Nobel Prize Work: Earl W. Sutherland Hormone epinephrine stimulates depolymerization of glycogen in liver and skeletal muscles cellsDepolymerization relases glucose-1-phosphateCell converts it to glucose-6-phosphateCell uses it for glycolysis (make energy)
68Conclusion 11 effect of epinephrine secreted from adrenal gland in times of stress is to quickly mobilize fuel for cells
69Mechanism Shown by Sutherland Epinephrine activates enzyme glycogen phosphorylase that starts depolymerization of glycogenExperimentEpinephrine + enzyme + substrate = no reactionOnly worked in living cells
70Conclusion 2 Epinephrine does not directly work with the enzyme Plasma membrane must be involved in the process
72Induced fit of Membrane Receptor Proteins Each cell has ID tags so the message doesn’t get to the wrong cell.Ligand- a small molecule that specifically binds to a larger moleculeThe induced fit is the trigger to cause another molecular interaction
73Signal molecues do not need to enter the cell to start the chain reaction of events!! Epinephrine is HUGE, it will never get into the cell!
77G Protein act can as GTPase Enzyme that hydrolizes GTP GDPFunction= shut down reaction when the extracellular signal is gone
78WHY do we care????Studies of some G proteins show that if a mouse is conceived and lacks a certain G- protein, blood vessels form incorrectly, mouse is never born.Human vision and smell depend on G proteinsCholera bacteria form toxins that interfere with G proteins
79FYI from the CDC What is cholera? Cholera is an acute, diarrheal illness caused by infection of the intestine with the bacterium Vibrio cholerae. The infection is often mild or without symptoms, but sometimes it can be severe. Approximately one in 20 infected persons has severe disease characterized by profuse watery diarrhea, vomiting, and leg cramps. In these persons, rapid loss of body fluids leads to dehydration and shock. Without treatment, death can occur within hours.
80Tyrosine-Kinase receptors Used for growth factorsCytoplasmic side= enzyme tyrosine kinase.Catalyzes transfer of phosphate group from ATP to tyrosine (AA) on a substrate proteinExtra cellular side = tyrosine kinase receptorAttach phosphates to tyrosines on proteins
822 steps to the T-K Receptor reaction 1. ligan binding causes 2 receptor polypeptides to aggregate (dimer)2. activates the T-K parts of polypeptides , which adds phosphates to the tyrosine on the tail of the 2nd polypeptideAP exam word: phosphorylation
83T-K receptors vs. G protein receptors T-K receptors can trigger many different reaction pathwaysG protein receptors are more specificSome cancers form when the T-K receptors aggregate w/o the ligand
84Ligand gated ion channels Protein pores in membrane that open/close in response to signals from ions (Ca+, Na+)Important for the nervous system cell to cell communication
85When a specific ligand binds to the protein, the channel opens for ions to pass through.
86Intracellular receptors Some receptors are inside the cellSteroiods, ex testosterone works this way.Activated testosterone receptor is a transcription factor to regulate specific genes.
87Steroid hormone goes through membrane Hormone binds to receptorHormone+ receptor enter nucleus binds to specific genesStarts transcription of the geneTranslation of mRNA completed
88Signal Transduction Pathway Once the chain reaction has started there are multiple intermediate stepsCan amplify the message being sentBetter regulation of chemicalprocesses
89Relay molecules are usually proteins Phosphorylation is often the way that a message is passed from one molecule to the next(Add a phosphate group from ATP to the next molecule in line)Enzymes that do this are protein kinases
90THIS IS A HYPOTHETICAL MECHANISM!!!! NOT A REAL ONE!!
91Importance of Protein Kinases 1% of your genes are for protein kinases1 cell can have hundreds of different protein kinasesAbnormal activity of those regulating cell division contributes to cancer
92Turning OFF a signal transduction pathway Protein phosphatease- enzyme that remove phosphate groups from proteins
93Second MessengersIons, or water soluble molecules that help carry on the chain reactionMove by diffusion through the cellUsed in G protein linked receptors and T-K receptorsCa2+ and cAMP most common
95Links back to epinephrine Sutherland observed that the binding of epinephrine caused and increase in the production of cAMP.Converted back to inactive AMP almost immediately after the epinephrine leaves the receptor
97Application: Cholera Infections Vibrio cholerae enters body in waterBacteria colonize in small intestineBacteria form a toxin, that modifies a G protein that regulates salt and water secretionGTP never made into GDPAdenylyl cyclase never stops making cAMPIntestinal cells continue to excrete water and saltdiarrhea
98Ca2+ as second messenger Always in cells, BUT there is more than 10,000X more in the blood and extracellular fluidProtein pumps move it out of the cell or into the ERA signal molecule tells the cell to release Ca2+ from the ER
102Epinephrine sends different signals to different cells Liver cells- break down glycogenHeart cells- contraction, rapid heartbeatThe combination of proteins in each type of cell determine the message
104Scaffolding proteinsLarge proteins that “hold” other proteins in the correct order so they are ready for a chain reaction.In the brain, there are permanent scaffolding proteins that keep synapse proteins in place
105Signal molecules are only present for a short time BIG problems if the molecule stays too long!Go back to cholera example!
107Practice Essay Question Cell to cell communication is vital for a multicellular organism.A. Discuss the ways that cells communicate locally and over long distances.B. Describe the importance of multistep pathways using one of the following:Tyrosine kinase receptorsG protein linked receptors