Exam 1 Notes
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Date Created: 10/04/15
Lecture 1 Earth History Chem Review Atoms elements Isotopes 2 atoms with same protons but different neutrons ex C12 vs C13 Halflife the time it takes for half of an atom to decay Formation of the Universe occurred 137 billion years ago 0 The Big Bang was the birth of our universe 0 The rst stars were formed within a couple hundred million years from the hydrogen and helium created by the Big Bang 0 All 100 billion galaxies including ours were formed in the rst billion years after the big bang Formation of atoms 0 All atoms have been made inside of stars fusion of like elements to form larger elements until star can t handle energy and explodes o All matter was created billions of years ago from the gravitational collapse of quotcosmic dustquot nebula from supernovas Everything we know is made from these atoms stardust Formation of our solar system Sun Planets SUN Our sun is a second generation star that formed about 5 billion years ago from the supernova dust of a rst generation star that blew up in our galaxy 1 Gravity caused this cosmic dust to collapse into a rotating disk shape 2 The center of the disk became superheated and former a new star our sun made of burning hydrogen 3 In the rotating disk individual planets began to form around our sun by the action of local gravitational attraction 0 Proof We know that our solar system formed about 45 billion years ago because of the known decay rate of certain radioactive elements like Uranium238 This isotope undergoes radioactive decay with a halflife of 45 billion years to form the stable isotope Lead206 so by measuring the amount of uranium and lead isotopes in a piece of rock we can tell how old the rock is In the oldest rocks we nd approx equal amounts of lead and uranium meaning that the rock is about 45 billion years old many meteorites have been analyzed and were found to be the same age 0 EARTH 1 2 3 The earth grew in size as small celestial bodies collide with earth As earth s mass grew so did its gravitational force and the earth began to compress itself into a smaller denser body This compression in the interior began to heat up the earth s core causing the interior to melt a lot of this heat was generated by the radioactive decay of heavy elements 4 Because iron is really heavy large globs of molten iron fell by gravity into the center of the earth MOON o The moon was formed by material from the outer mantle of the 0 early earth blown off into space by a collision Because of this the moon unlike the earth does not have an iron core 0 Modern Earth 0 00 Earth still has an iron core solid iron in the center molten iron above that Above the iron core is hot molten rock called the mantle The outermost layer of cold hard rock is called the crust The heat in the interior of the earth comes mostly from radioactive decay Physical Changes on Earth 0 Plate tectonics movement of the Earth s crust Plates move because of convection in the underlying mantle Convection occurs because heat rises and cool dense mantle will sink by gravity causing a circular motion 0 North Am South Am Africa and Europe are all on different moving plates of crust previously all the plates were connected and formed the supercontinent Pangea 0 These plates have been moving for millions of years and continue to move 0 Plate tectonics explains why we see fossil remains of the same ancient animal restricted to certain areas of both Africa and South America Life on Earth 0 The earth is 45 billion years old but the earliest fossil remains of cells are found in sedimentary rocks that are about 35 billion years old Rocks 38 billion years old have been found with numerous specks of carbon which appear to be carbonized cells which are most likely the remains of cells because of the Carbon12Carbon13 ratios they contain 0 Living organisms x the Carbon12 isotope preferentially over the Carbon13 isotope leading to a signature C12C13 ratio TIMELINE 137 bya Universe forms Big bang 45 bya Solar system forms 38 bya possible fossil evidence of cells 35 bya de nite fossil evidence of cells Lecture 2 The Beginning of Life on Earth Chemical Evolution the series of reactions by which a set of molecules present of the early earth chemically reacted with each other to form amino acids and nucleotides the building blocks of life Hypothesis of how life formed 1923 Oparin amp Haldane proposed in 1923 that the early earth would be composed of water H20 hydrogen H2 ammonia NH3 and methane CH4 because are abundant in space and are the main gases on Jupiter and Saturn but early earth had no free oxygen Oparin amp Haldane proposed that under the action of heat and lightning these molecules H2 CH4 H20 and NH3 would react to produce reduced organic molecules which would then react to form sugars amino acids nucleotides etc which would accumulate in the oceans forming a quotPrebiotic Soupquot 0 Building blocks of life Amino acids l Proteins Nucleotides l DNA RNA Sugars l Polysaccharides Ultimately biological macromolecules would be formed which would then become encased in a membrane forming the rst protocells 0 Fatty acids and lipids spontaneously form to enclose things This process is known as chemical evolution Experiment to show how life formed 1953Miller amp Urey Experiments 3 1st quotFalse positivequot 0 Miller and Urey created a device to mimic the conditions on the early earth by making sparks for lightning in an atmosphere of H2 CH4 H20 and NH3 0 Within a week much of the starting material has been converted into amino acids and purine nucleotides 0 Later though scientists concluded that the early atmosphere of earth would have been dominated by volcanic gases C02 H20 and N2 meaning that there would not have been a large amount of methane or ammonia o 2nOI Negative 0 When the Miller amp Urey experiment was repeated with these gases nothing formed 0 3rd Positive o It was later found out that when volcanic gases are irradiated with UV light as would have happened when there was no ozone layer to block UV radiation reduced molecules like H2CO formaldehyde and HCN hydrogen cyanide are formed 0 When these reduced molecules were added to the experiment amino acids nucleotides and sugars formed How did these molecules form What was the real life mechanism of what miller and urey s experiment showed 3 proposals 0 Process of Forming Molecules on Early Earth 1 Undersea volcanoes erupt releasing gases enclosed in bubbles 2 The gases in the bubbles reacted to produce simple organic molecules 3 The bubbles rose to surface and popped releasing contents into air 4 Simple organic molecules turned into complex org molecules when hit with UV radiation from the sun 5 The more complex organic molecule fell back into the sea as raindrops 6 They could then be reenclosed and begin the process again 0 Black Smokers 0 quotBlack smokersquot and geothermal vents are located deep under the sea near ridge crests 0 Ocean water is heated by magma underneath and circulates through the crust extracting rich reduced chemical compounds and producing reduced organic molecules 0 Life forms resembling early life are abundant at these sites 0 Meteorites import 0 Reduced organic molecules such as amino acids are abundantly produced in interstellar space 0 Earth bombarded with meteorites with organic molecules on them Simple Complex Molecules o The amino acids and nucleotides that accumulated in the oceans bind to the surface of certain clays and when heated polymerize to form proteins and nucleic acids o Clays have catalytic properties that cause amino acids to form chains Problems with Chemical Evolution 1 Purine nucleotides readily form A amp G but not pyrimidine nucleotides 2 T amp C It is dif cult to nd conditions that permit ef cient synthesis of more ribose than deoxyribose quotthe ribose problemquot proven later that can with phosphate Too coincidental to not be proof The basic components of living cells are polymeric macromolecules such as proteins phospholipids polysaccharides and nucleic acids The building blocks of these form spontaneously in conditions that mimic those of early earth These building blocks polymerize under circumstances that mimic the early earth to form the basic components of living cells The First 3 Billion Years All cell development occurred in the rst 3 billion years First prokaryotes no nucleus 0 Probably same size as modern day bacteria fossil record Oily surface membrane lipid membrane Some kind of cell wall No nuclear membrane Genes were probably made of RNA instead of DNA and they probably used RNA to catalyze chemical reactions quotRNA WORLDquot lnstead of DNA RNA l protein ogenetic info RNA l RNA l catalytic RNA Evolutionary divergence A As time went by these early prokaryotic cells evolved internal membranes which they used to increase their ability to oxidize food molecules and capture the energy of the food molecules to build their own body molecules premitochondria B Cell able to synthesize chlorophyll photosynthesis use light to make food and oxygen C Development of a nuclear membrane and ER which makes it possible to regulate the expression of genes These 3 types of cells evolved into a single cell with chloroplasts and mitochondria OOOO o C ate A and B and couldn t digest it so A and B became organelles Prearchea evolved into eukaryotic cells which then learned how to live as multicellular organisms such as algae and sponges Photosynthesis by algae begins to create a lot of oxygen which is rst used up oxidizing all the iron in the ocean water After this iron is oxidized the concentration of oxygen rises and permits the evolution of worms and shell sh All the animals we know of appear in the Phanerozoic period the 3rd Eon Evolution at a Molecular Level Carl Woese clari ed the understanding of the family tree by sequencing the gene for the small subunit SSU of ribosomal RNA Woese founded the 3 domains Bacteria Archaea and Eukarya Bacteria and Archea differ in that archea DNA is organized around proteins like eukaryotes and their transcription machinery resemble that of eukaryotes Phylogenetic analysis looking at the relatedness of organisms Phylogenies found by nucleotide sequencing are consistent with the fossil record Chemistry Review 2 types of energy Energy the capacity to do work 0 Potential Energy energy by position 0 Kinetic Energy motion energy 0 Conversion tofrom PEKE follows 2 laws of thermodynamics 2 Laws of Thermodynamics 1 Energy is conserved 2 Every energy transfer increases the entropy of the universe Redox reactions Reductionoxidation o Oxidation Loss of electrons 0 Reduction Gain of electronsreduction of charge 0 Ex Photosynthesis many basic biological processes Exothermic vs Endothermic o Exothermic gives off heat the heat given off is H enthalpy which equals AE o Endothermic absorb heat from surrounding 0 Most reactions that will go to completion are exothermic enthalpy as a driving force 0 In the NaCl and H20 endothermic reaction the driving force for this reaction is the increase in entropy of the system cause by the dissolution of the salt crystals Spontaneity 0 Some reactions are nonspontaneous require an outside source to occur ex CH4 and 02 0 Spark gets molecules moving fast enough so that when they hit each other they have enough energy to rearrange by breaking chemical bonds Gibbs invented the concept of Free Energy and wrote an equation which determines whether a chemical reaction will proceed as written 0 Temp in Kelvin Celsius 27315 0 Reactions with a AG are called exergonic and are spontaneous will proceed as written 0 AG endergonic reverse reaction will proceed Lecture 34 Biological Macromolecules Biological macromolecules DNA RNA protein and polysaccharides Physicist Max Delbruck hoped that looking at life at its deepest level might reveal new laws Delbruck and Luria set out to discover how bacterial viruses bacteriophages replicate Delbruck and Luria are considered the quotfathers of molecular biologyquot Was disappointed to nd that all life in an application of the laws of physics and chemistry and that no new laws are required to understand a living cell Polysaccharides Proteins and Nucleic Acids Sugars amino acids and nucleotides can polymerize polymerization the bonding together of monomers to form macromolecules called polysaccharides proteins and nucleic acids the building blocks of cells 0 A polymer consists of a chain of monomer subunits Condensation water is released 0 Polymerization is a condensation reaction Hydrolysis adding H20 0 A monomer is broken off the chain during hydrolysis resulting in a shorter polymer Polysaccha rides The structure of glucose 6 carbon sugar one particular example of a sugar Sugars are de ned by the presence of a carbonyl group CO and multiple hydroxyl groups OH Sugars are chiral molecules the right handed quotDquot isomers predominate in cells Sugars like glucose can exist in both linear and ring forms Glucose 0 When glucose forms a ring the hydroxyl group can take two different positions to form either the alpha form or beta form of glucose The alpha and beta forms are catalyzed by different enzymes 0 To use the sugars in this an enzyme catalyzes hydrolysis to use the individual sugars 0 Starch polymerized alpha glucose alpha 14 linkage garches are quotstorage polysaccharidesquot They are a reserve form of sugar for times when free sugar in the diet is absent Starch is helical chains 3 types of starches amylose and pectin are the storage polysaccharides found in plants glycogen highly branched is the storage polysaccharide found in animal cells 0 Cellulose polymerized beta glucose beta 14 linkage Animals don t have enzymes that can catalyze the hydrolysis metabolize of the beta glucose in cellulose Cellulose is a quotstructural polysaccharidequot Long linear strand In plants long strands of cellulose bundle together to form micro brils found in cell wall 0 Chitin other important structural polysaccharide beta 14 Makes up the exoskeleton of insects and crustaceans o Peptidoglycan other important structural polysaccharide beta 14 Makes up bacterial cell wall Proteins polypeptide Protein string of amino acids on a quotpeptide backbonequot string of carbon and nitrogen Peptide short string of amino acids gt30 amino acids 0 The sequence of amino acids is called the primary structure of a protein 0 Proteins are synthesized beginning with the amino terminus quotN termina right Amino Acids General structure of an amino acid eft and ending with the carboxy terminus quotCterminal 0 Amino acids are chiral like sugars but the lefthanded form is the form that s found in cells 0 Some amino acids have hydrophobic side chains not soluble in water and some have hydrophilic side chains watersoluble Amino acid A R ends Polar Charge Other b in d Lysine Lys K NH3 Y Y Basic Arginine Arg R NH2 and Y Y Basic NH2 Glutamate Glu COO39 Y Y Acidic Serine Ser S OH Y N Cysteine Cys C SH Y N 2 cysteines react to form a disul de bond that act like quotmolecular staplesquot to stabilize the folded structure of a protein Isoleucine lie I CH3 N N Phenylalanine F Benzene N N Phe ng Protein Folding structure 0 Proteins will fold to o maximize amino acid interactions 0 put hydrophobic amino acids in the interior and hydrophilic outside to hydrogen bond with water 0 most thermodynamically stable state 0 Secondary structure alpha helix or beta sheet 0 Formed by hydrogen bonds between the carbonyl oxygen and amide hydrogens on adjacent regions of the peptide backbone o Discovered by Linus Pauling TertiaryOther interactions hydrophobic interactionsdisulfide bonds among the side chains of the amino acids govern the overall folded structure of the protein called tertiary structure 0 The linear sequence of amino acids determines the 3D folded structure of the protein 0 19SOsChristian Anfinsen performed a classic experiment that demonstrated that the linear sequence of amino acids in a protein determines the folded structure of that protein Using a chemical called urea he denatured unfolded a protein and then removed the chemical he used to denature it and it refolded back to its original shape and regained full enzymatic activity From this experiment we can conclude that the information from the complete correct folding of a protein is contained in the linear amino acid sequence of that protein Quaternary structure shape produced by 2 or more proteins ex structure of the dimer trimer tetramer etc Protein function 0 Proteins basically perform all the biochemical functions of cells 0 Cells are basically a quotbag of proteinsquot 0 Important function of proteins catalysts for biochemical reactions These proteins that serve as catalysts are called enzymes Enzymes end in quotasequot o Crevices on protein align with reactive part of amino acids l Binding speci city quotlock and keyquot o Enzymes lower the activation energy Ea by stabilizing the transition state of the reaction Ex reactions can occur at lower temperatures etc 0 Proteins can serve as structural elements in the cell Proteins called actin and tubulin polymerize to form laments that function as part of the cytoskeleton Also antibodies motor proteins receptor signal or transport proteins etc 0 DNA is made of 2 chains of nucleotides twisted around each other in a double helix 0 DNA 2 Deoxyribose Nucleic Acid 0 RNA Ribose Nucleic Acid 0 Nucleic acid string of nucleotides 0 Nucleotide phosphate group P04 5 carbon sugar nitrogenous base 0 The 5 carbon sugar can either be ribose in RNA or deoxyribose in DNA 0 Sugarphosphate backbone bases in between as the rungs of theladder o Nitrogenous Bases A T G or C in DNA orA U G orC in RNA 0 Pyrimidines one ring C U and T o Purines two rings A amp G Cytosine can become uracil loss of NH3 and addition of H20 0 A strand of DNA is made by attaching nucleotides onto one another into a strand 0 3 phosphates on end to add one lose 2 phosphates 3rCI phosphate because a phosphodiester bond with the 3 OH on the previous nucleotide in a condensation reaction Nucleic acids are synthesized 5 l 3 The complementary strands of DNA can speci cally pair with each other because the bases form speci c hydrogen bonds 0 The 2 sugarphosphate backbone strands are antiparallel When a cell is going to divide via mitosis it rst makes a copy of its DNA DNA replication each of the two strands serves as a template for making a sister strand 0 First the parental strands are separated 0 Then an enzyme runs along each template strand making a copy sister strand daughter strand assembling the bonding base to the existing one ex G to an existing C that creates a complementary strand of DNA 0 The original molecule has then been duplicated each of which contains one old strand and one new strand DNA is the genetic material in a cell Experiment added viruses to bacteria and noticed that the DNA was injected into the bacterial shells and the protein stayed outside later new viruses were released from the bacterium Discovering the structure of DNA 0 1952 Rosalind Franklin was able to make semicrystalline bers of DNA and take pictures of the xray diffraction pictures of these crystals 0 Watson amp Crick saw it Crick built a model structure that t with all the known DNA facts which turned out the be a correct model in which they correctly paired AampT and GampCwhich they later found would explain quotChargaff s Rulequot Chargaff found that the percentage of AT and percentage of CG Crick almost singlehandedly worked out the fundamental concepts of molecular biology in the 10 years after he and Watson solved the structure of DNA quotCentral Dogmaquot 0 DNA is transcribed to make messenger RNAs with the help of transfer RNAs mRNAs are translated on ribosomes to make proteins 0 The genetic code is a triplet sequence of nucleotides 0 Watson played an important role in the formulation of the concept of messenger RNAs RNA The structure of RNA is similar to that of DNA except 0 the nucleotide subunits have ribose rather than deoxyribose as the sugar 0 Uridine is substituted for thymidine 0 RNA is generally found as a singlestranded molecule in cells esp in animals RNA can basepair with itself to form stemloop structures 0 ex transfer RNA has stemloop structure RNA can form complex structures with pockets of their surface like proteins Also like proteins RNA can catalyze chemical reactions function as enzymes 0 quotRibozymequot Since it was discovered that RNA can function catalytically the idea of the quotRNA worldquot that existed before DNA came into the picture was developed where RNA played the roles that DNA and proteins currently play Types of RNA all encoded by genes on DNA 0 rRNA ribosomal ribosomal proteins translate mRNA 0 mRNA encodes AA quotproteincoding o tRNA transfer brings AA to ribosome o snRNAljcomplex w protein to process RNA Lecture 5 Cellular Membranes Membranes are made of lipids and proteins 0 The current molecular model for the structure of biological membranes is the SingerNicholson uid mosaic model Lipids Lipids are quotwaterinsoluble hydrocarbonsquot 0 There are three major types of lipids found in cells Fats phosphoipids and cholesterol Fats Found as droplets inside ces food storage form Fats 3 fatty acid molecules 1 glycerol backbone o Formed in esteri cation reaction making an ester 0 Ester RCOOR Fats triglycerides triacygycero Fatty acidsfats generally insoube Some are amphipathic o Amphipathic have a watersoluble region and an insoluble region 0 In a fatty acid the hydrocarbon quottailquot is insoluble in water hydrophobic the carboxyl head is soluble in water hydrophiic Fatty acids form micelles when they are added to water the tails go to the interior away from the water and the heads are on the surface able to hydrogenbond with water 0 May also form a thin surface layer with the hydrophiic head touching the surface of the water Fatty acids and other amphipathic molecules function as detergents soaps to solubilize fats and oils Saturated unsaturated or polyunsaturated Saturated fatty acid has no CC double bonds 0 Largely saturated fatty acids fat is solid at room temp Pack closely together Ex typicay animal fats Unsaturated fatty acid has 1 CC o Cismethyl groups on same side or trans methyl groups on opposite sides Cis is energetically unfavorable because the two methyl groups tend to bump into each other which is found in cellular lipids cause a kink in the fatty acid hydrocarbon chain Trans is favorable but less common because there is no steric hindrance no kink in the chain 0 Trans fatty acids heating many cis CC bonds allows them to isomerize into the more stable trans con guration This process is called hydrogenation so quotpartially hydrogenated vegetable oilsquot are rich in trans fatty acids 0 Trans fatty acids are quotbadquot because they re not found in nature and so our bodies are not able to metabolize them well 0 Largely unsaturated fatty acids fat is liquid at room temperature Not packed as closely together because of kinks Polyunsaturated fatty acid has two or more CC bonds 0 Polyunsaturated fatty acids There are 2 polyunsaturated fatty acids that cannot be synthesized by mammals and therefore must be taken in by the diet these two essential fatty acids are linoleic acid quotomega6 bc CC bond is 6 carbons away from the omega carbon last carbon and alphalinolenic acid quotomega 3quot Phospholipids Only two hydroxyl groups are esteri ed to fatty acids while the third one is esteri ed to phosphoric acid 0 Fats all 3 hydroxyl groups on glycerol esteri ed to fatty acids 0 Structure Polar head glycerol phosphoric acid and another polar group nonpolar tail the 2 long chain fatty acids 0 Phospholipids amphipathic hydrophiic polar at one end hydrophobic nonpolar on the other Spontaneously form phospholipids bilayers 0 Don t form micelles like fatty acids mostly due to the shape fatty acids are cone shaped and thus pack together well into a sphere while phospholipids pack well into layers because they re tubular o Bilayer l vesicle Bilayers are not energetically favorable so they spontaneously close to form quothollowquot water lled vessels Liposomes arti cially created phospholipid vessels 0 Properties of the bilayer o The phospholipid bilayer is a twodimensional uid phospholipid molecules can diffuse in the plane of the membrane the molecules can ex rotate or rarely ip op o Phospholipid bilayers can melt or freeze depending on the temperature More cis unsaturated fatty acids more uid membrane Kink cis double bonds make it more dif cult to pack the chains closely together 0 Bacteria and coldblooded organisms like sh can adjust the ratio of saturated to unsaturated phospholipids in their surface membrane according to temperature to prevent the membrane from freezing or becoming too permeable Cholesterol 0 Small polar head hydroxyl group large nonpolar tail I greasy molecule 0 Not water soluble very hydrophobic 0 Cholesterol lls in the spaces in lipid bilayers containing cis unsaturated fatty acids 0 Animal cell membranes have a high percentage of lipids with unsaturated fatty acids Because of this they are very uid so in the absence of cholesterol they would be too uidpermeable cholesterol quotplugsquot the holes caused by kinks Lipid bilayers with unsaturated fatty are too permeable Lipid bilayers with 100 saturated fatty acids are too impermeable Adding cholesterol to lipid bilayers with unsaturated fatty acids decreases the permeability of the bilayer to an appropriate leve a reasonable amount of cholesterol quottoughens upquot the bilayers The SingerNicholson model has been modi ed to include cholesterol rich patches of particular lipids called quotlipid raftsquot Proteins 1940s Davson and Danielli Proposed that the protein associated with membranes coated both sides of the lipid bilayer o DavsonDanielli quotproteinlipid sandwichquot model was the working model for membrane structure through the 19605 1972 Singer and Nicholson 0 Proposed the quot uidmosaicquot model named so because the lipids are a 2D uid in which both proteins and lipids can diffuse and because the proteins form a discrete mosaic pattern 0 Proof Freeze fracture experiments showed that membranes have a smooth surface the lipid bilayer with bumps membrane proteins Experiment including striking the frozen cell with a knife and observing the split lipid bilayer under a microscope Proposed that a hydrophobic sequence of amino acids would fold into an alpha helix to cross the lipid bilayer 0 Approx 20 amino acids are required to be long enough to traverse the bilayer Singlepass membrane protein 0 Glycophorin A a red blood cell membrane protein 0 Only one alpha helix segment that crosses bilayer Multipass proteins 0 Multiple alpha helices that cross bilayer multiple times lntegral membrane proteins in membrane only detergents can solubilize Peripheral membrane proteins can be extracted from membranes by treating them with high salt or pH extremes interact noncovalently 0 Ex cytochrome Membrane proteins are glycosylated on their external surface meaning that they have short chains of sugars attached to them at multiple locations along the external part of the polypeptide chain glycoproteins Lipids can also become glycosylated glycolipids Lecture 6 Permeability of membranes and transport of molecules across them Diffusion Results in an even distribution of molecules through the solvent 0 If there are two different molecules on opposite sides of a lipid bilayer membrane there will be an equal concentration of both types of molecule on both sides of the membrane at equilibrium Osmosis Solute on one side of the membrane membrane is permeable to water but impermeable to the solute o The water will ow from the area of low concentration to high concentration of solute in an attempt to dilute the solute 0 Higher concentration of free water molecules on the side with less solute water tries to even out this concentration by passing free water molecules to the highsolute side DiffusionOsmosis in life 0 The cytoplasm of a cell is approximately 015M in solute o If an animal cell is placed in salt of higher molarity hypertonic to the cell the cell will shrink because water flows out of the cells in an attempt to dilute the surrounding medium 0 If the cell is placed in 001M hypotonic to the cell the cell will osmotically swell and burst lyse as the medium attempts to dilute the cell 0 ln isotonic solution same concentration as cell the cell will be unaffected o Permeability of phospholipid bilayers o Hydrophobic and small uncharged polar molecules pass through the lipid bilayer 02 C02 N2 H20 glycerol 0 Large polar molecules and ions are unable to pass through the lipid bilayer sugars H HCO3 Na Cl etc Sugars and amino acids enter the cell through membrane proteins Transport 0 3 classes of membrane proteins 0 ATP powered pumps Pumps move solute against a concentration gradient Requires work Active transport Ex Sodium Potassium Pump NaK pumps Na out of the cell higher concentration outside and K into higher concentration inside both against solute gradient 0 Ion channels Mediate quotfacilitated diffusionquot Permit solute to diffuse down the concentration gradient Passive transport CFTR Cystic Fibrosis Transmembrane Conductance Regulator can act as an ion channel or an ATPpowered chloride ion pump 0 Transporters Mediate quotfacilitated diffusionquot Permit solute to diffuse down the concentration gradient Passive transport Ex GLUT 1Wi only enter the cell when there is a higher concentration of glucose outside the cell than inside Water can enter cells via simple diffusion but there are also channel proteins aquaporin that only allow water to pass through
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