Chapter 5-7 Book Note Bundle
Chapter 5-7 Book Note Bundle BSC 118
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Date Created: 10/04/15
Chapter 5 Thursday October 1 2015 1108 AM Macromolecules carbohydrates proteins and nucleic acids notable mention lipids not actually large enough to be macromolecules but important building block polymers long molecule consisting of many similar or identical building blocks linked by covalent bonds 0 made of repeating units called monomers 0 4050 common monomers create unlimited number of polymers 0 arrangementlinearsequence is key cells make and break polymers constantly o enzymes are the macromolecules that speed up chemical reactions 0 dehydration reaction two monomers are covalently bonded due to the loss of a water molecule I water is released one monomer provides OH while other provides H o hydrolysis dissembling polymers I water is added in order to break bonds I opposite of dehydration reaction Carbohydrates o monosaccharides simple sugars generally follow CHZO formulamultiples vary I carbonylCO group and multiple hydroxyOH I aldosealdehyde sugar or ketoseketone sugar I many sugars are 6 carbonhexoses or 3 ctrioses or 5 cpentoses I spatial arrangement of asymmetric carbons a carbon attached to 4 different atoms a difference in spatial arrangementvariety I in aqueous solutions glucose molecules form rings major fuel for cell work also carbon skeleton serve as raw materials for synthesis of amino acids and fatty acids 0 disaccharides double sugars w covalent bond I 2 monosaccharidesjoined by glycosidic linkage after dehydration reaction a most known is a sucrosetable sugar o polysaccharides macromolecules with few hundredthousand monosaccharides linked together I Storage D Starch polymer of glucose monomers plants use as storage for energy 0 stored mainly in chloroplasts in plastids 0 allows plants to stockpile surplus glucose and use as a bank to be later drawn out by hydrolysis when needed a Glycogen animal form of stored glucose 0 stored mainly in liver and muscle cells 9 depletes easily in one day unless replenished by food I Structural a Cellulose 0 cell walls made of formula similar to glucose 0 hydroxyl group attaches to the b configuration while starch is a configuration 0 never brandedhydroxyls are free to hydrogen bond to other hydroxyls 0 enzymes digesting starch with a can t digest starch with b linkages El Chitin 9 used by arthropods to build their skeleton 9 similar to cellulose except glucose monomer chitin has nitrogencontaining appendage Lipids 0 not true polymers I grouped together because all mix poorly with water 0 Fats I 2 smaller molecules glycerol and fatty acids a fatty acid has long carbon skeleton and attaches to glycerol 9 one end of carbon chain is carboxylCOOH group which gives the acid part of fatty acid a triacylglycerol 3fatty acids 1 glycerol molecule I saturated v unsaturated a saturated with hydrogen aka NO 2x bonds 0 more single bonds to be taken with hydrogen 0 solid at room temperature bc they pack close together 0 very unhealthy known to cause cardiovascular disease a unsaturated without hydrogen aka 1 2x bonds 9 2x bonds are cis 2x bonds which causes a kink in hydrocarbon chain 0 this prevents fats from being too close together and makes it liquid at room temperature 9 can be trans double bonded 0 super unhealthy and contribute to atherosclerosis I main function energy storage B 1g of fat 2x 1g starch a humans store fat in adipose cells 0 swell and shrink as fat enters and exits o Phospholipids I major constituents of cell membranes I similar to fat but only has 2 fatty acid attached to glycerol a 3rd hydroxyl group is attached to phosphate group charge I think phospholipid bilayer hydrophobic tails are in the center whie hydrophilic phosphate heads face outwards creating a cell membrane 0 Steroids I carbon skeleton consisting of 4 fused rings a different steroids based off which chemical group is attached to rings I Cholesterol crucial in animals a common in cell membranes precursor form which other steroids can be synthesized a saturated and trans fats negatively affect health by changing cholesterol levels Proteins o biologically functional molecule made up of 1 polypeptides each folded and coiled into a specific 3D figure I polypeptide bonds between amino acids are peptides multiple pep des I made from 20 amino acids linked in unbranched polymers 0 many proteins are enzymes I catalysts chemical agents that selectively speed up chemical reactions wo being consumed by reaction 0 accountfor more than 50 of dry mass of most ces 0 Amino Acids organic molecule with both an amino group amp carboxyl group I alpha carbonasymmetric carbon atom attached to amino group carboxyl group hydrogen atom and variable R group a R groupside chain differs with each amino acid 9 properties come from side chain 9 some amino acids have nonpolar side chains which means they are hydrophobic 9 acidic amino acids are those with side chains that are generally negative in charge 0 have polar side chains 0 this is bc the carboxyl group usually dissociates at cellular pH 0 because it is charged acidic and basic chains are hydrophilic o polypeptides are formed when the carboxyl group of one amino acid is adjacent to the amino group of the other uses dehydration reaction to form peptide bond I polypeptide backbone chain of polypeptides one end is free amino end other is free carboxyl end a attached to backbone are different side chainsR groups 9 side chains outnumber terminal groups so the chemical nature is determined by the m and sequence of side chains 0 structure and function I activities result from intricate 3D architecture a simplest level is amino acid sequence I chain may fold spontaneously this is driven by formation of bonds in chain a globular proteins spherical shape a fibrous proteins long fibers I 4 Levels primary secondary tertiary quaternary a primary sequence of amino acids 0 inherited genetic information a secondary coilsfolds 9 result of hydrogen bonds between repeating constituents of backbonenot side chains alpha helix coil held bw every fourth amino acid 9 beta pleated sheet parallel chain segments of backbone a tertiary overall shape of polypeptide due to side chainR group interactions 9 hydrobhobic interaction van der Waals forces hold nonpolar hydrophobic parts together 9 disulfide bridges covalent bonds that reinforce shape 0 form where two cysteine monomerscontaining SH are brought together due to folding a quaternary 2 polypeptide chains aggregate together I function affects proteins ability to function a sickle cell disease inherited blood disorder a substitution of amino acid valine for glutamic acid 0 affects hemoglobin which carries oxygen in red blood cells a change makes protein aggregate into chains and forms a sickle shape 0 this makes cells unable to carry oxygen as well or even at all 39 structure depends on physical and chemical conditions of protein s environment El change in environment can lead to protein denaturation 9 causes protein to unravel and lose native shape 0 makes protein biologically inactive D disruptions 0 transferring from aqueous to nonpolar solvent refolds so hydrophobic regions face outward O chemicals thatdisrupt hydrogen bonds ionic bonds and disulfide bridges these maintain shape 9 excessive heat overpowers weak interactions that stabilize 0 think fevers being fatal blood proteins denature a denaturing can sometimes be reversible I protein folding a most go through several structures on their way to the final shape 0 refolded many times D chaperonins protein molecules that assist in the proper folding of other proteins 0 segregate polypeptides from outside environment until they spontaneously fold 9 shelter 9 have systems which check misfolded proteins for refold or destruction a misfolding lead to many serious problems 9 cystic fibrosis alzheimer s parkinson s mad cow senile dementia a determining folding pattern of protein 0 XRay crystallography O NMRnuclear magnetic resonance spectroscopy 0 bioinformatics Nucleic Acids 0 genes unit of inheritance that codes amino acid sequence made of up DNA which is a nucleic acid a nucleic acid made of monomers called nucleotides 0 DNA V RNA enable organisms to reproduce from one generation to the next gene expression DNA provides directions for its own replication and also directs RNA synthesis and controls protein synthesis through RNA DNA doesn t run ces it is just a scanner that proteins base off to implement genetic programs mRNAmessenger directed by gene along a DNA molecule a interacts with cell s proteinsynthesizing to produce polypeptide D DNARNAprotein protein synthesis happens at ribosomes a mRNA brings info from DNA outside of nucleus to ribosomes o poynucleotides polymers consisting of nucleotide monomers nucleotide 5c sugar nitrogencontainingnitrogenous base 1 phosphate groups a each nitrogenous base has 1 or 2 rings act as bases bc they tend to take H from solutions 0 pyrimidine 6 member carbon amp nitrogen atoms 0 Cytosine Thymine Uracil b TDNA b URNA O purine 6c fused to 5c 0 Adenine and Guanine a sugar 9 DNAdeoxyribose El 0 lacks oxygen on 2nd carbon in ring 0 RNAribose attach phosphate group 9 attached to 5th carbon of sugar each monomer has 1 phosphate group El portion wo is called nucleoside nucleotides are linked by dehydration reaction into polynucleotides El El adjacent nucleotides joined by phosphodiester linkage 0 phosphate group that links sugars of 2 nucleotides repeating pattern turns into sugarphosphate backbone backbone has 2 free ends 0 phosphate attached 5 carbon and other has hydroxyl group attached to 3 end 0 build in directionality from 5 to 339 O kinda like a one way street o Structure of DNA and RNA DNA El El RNA 2 polynucleotides form a double helix one runs 5 to 3 while other runs 3 to 539 0 antiparallel sugar phosphate backbones on outside of helix nitrogenous bases on inside hydrogen bonds between base pairs hold strands together Adenine pairs with Thymine Guanine pairs with Cytosine 9 base pairing rules tell us that one stretch of 5 to 3 is complementary to 3 to 539 0 ie TCCAAGGT 0 allows cells to generate 2 identical copies of DNA before dividing single strands base pairing in this instance allows it to take 3D shape necessary for function 0 ie transferRNAtRNA brings amino acids to ribosome during synthesis of polypeptides ltgt functiontal shape results from base pairing between complementary stretches of molecule running antiparallel together Adenine with Uracil Cytosine with Guanine 0 no T in RNA DNA mnv hnvn nrnnnrlnrl DNA I I II I IIIuy a very versatile IIuVV VI vvvuvu I II l o Genome entire sequence of the full complement DNA of an organism Human Genome Project a prompted development of bioinformatics genomics looking at problems by analyzing large sets of genes or even comparing whole genomes of different species a similar analysis of proteins proteomics allowed us to better understand evolution a allowed us to find relationships among different groups of organisms molecular genealogy expectation that 2 species closely related on anatomical evidence share a greater proportion of DNA and protein sequences than less closely related species Chapter 6 Thursday October 1 2015 Cells 1105 AM cytosol jellylike substance inside all cells where organelles are suspended 0 makes up cytoplasm all contain chromosomescarry genes in DNA form all have ribosomesmake proteins eukaryotic almost all of the DNA is inside the nucleusdouble membrane enclosed has organelles prokaryotic DNA is in nucleoidnot membrane enclosed have no organelles but instead organized regions of cytoplasm generally smaller than eukaryotic cells plasma membrane selective barrier allowing passage of oxygen nutrients and waste in and out of cell 0 because of this SAV ratio is critical 0 SA must be large enough to support cell 0 larger organisms don t have larger cells just more cells 0 microvilli increase surface area without increasing volume long thin projections nucleus contains most of genes in eukaryotic cell 0 nuclear envelope encloses nucleus from cytoplasm 0 double membrane each lipid bilayer I pore complex protein structure that regulates entry and exit of RNA and proteins nuclear lamina netlike array of protein filaments that maintain shape of nucleus by supporting nuclear envelope chromosomes carry genetic informationDNA I complex of DNA proteins chromatin nucleolus inside nondividing nucleus rRNA synthesized from DNA instructions I proteins imported from cytoplasm assembled with rRNA into large and small ribosomal subunits nucleus synthesizes mRNA which is then transported through nuclear pores and into cytoplasm which then translates into primary structure of polypeptide ribosomes cellular components that carrv out protein synthesis 0 not membrane bounded so not organelles 0 free suspended in cytosol function within cytosol o bound attached to endoplasmic reticulum or nuclear envelope make proteins destined for packaging with certain organelleslike lysosomes or for insertion into membranes 0 ribosomes can alternate between two roles endomembrane system all related by direct contact or transfer of vesiclessacs made of membrane 0 nuclear envelope 0 endoplasmic reticulum extensive network of membranes that is 12 total membrane in cell network of tubules and sacs called cisternae ER membrane separates internal ER lumencisterna space from cytosol Smooth lacks ribosomes El El El El synthesis of lipids metabolism of carbs detoxification of drugs and toxins storage of calcium ions examples cells that make hormones are rich in smooth ER enzymes of smooth ER help synthesis of lipids oils steroids and new membrane phospholipids detoxification in liver cells involves adding hydroxyl groups to drug molecules making them more soluble Rough studded with ribosomes El El as polypeptide grows from bound ribosome chain threaded through lumen through a pore formed by a protein complex in membrane protein is folded into functional shape here most secretory proteins are glycoproteins proteins with carbs covalently bonded to them 0 depart from ER wrapped in transport vesicles membrane factory for cell 9 grows in place by adding proteins and phospholipids to its own membrane 0 anchored into ER membrane by hydrophobic portions 9 as it expands and portions are transferred in form of transport vesicles to other components of endomembrane system 0 Golgi apparatus think warehouse for receiving sorting shipping products of ER are modified and stored and sent I consists of cisternae flattened membranous sacs a structural directionality cis face and trans face 0 cis near ER the receiving side 9 trans opposite vesicles pinch off and travel shipping side I also manufactures some macromolecules a many polysaccharides I cisternal maturation model cisternae actually progress forward from cis to trans face carrying and modifying cargo as it moves I sorts products and targets them for certain cells D ID tags such as phosphate groups added as quotzip codesquot 0 ysosomes membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest macromolecules I hydrolytic enzymes and ysosoma membrane made by rough ER and golgi apparatus I intracellular digestion a phagocytosis engulfing food or smaller organisms 9 food vacuole formed when fuses with ysosome a digests simple sugars amino acids monomers 9 pass into cytosol and become nutrients for cell a recycle cells organic material autophagy 9 2x membrane surrounds damaged organelle or cytosol and ysosome fuses to membrane 0 organic compounds are released for reuse 9 cell renews itself I Tay Sachs Disease lack ysosomes a can tdigest lipids and brain becomes impaired o Vacuoles large vesicles derived from endoplasmic reticulum and Golgi apparatus storage I Food vacuoles formed by phagocytosis I contractile vacuoles pump excess water out of cell I plants have large central vacuole a stores cell sap plant cells main repository of inorganic ions a major roll in growth of plant which enlarges when water is absorbed 0 plasma membrane Mitochondria and Chloroplasts o mitochondria sites of cellular respiration metabolic process that uses oxygen to drive creation of ATP I 2x membranes have phospholipid bilayer with unique embedded Droteins D outer is smooth D inner has cristae infoldings dividing mitochondrion into intermembrane space and mitochondrial matrix 0 gives large surface area which enhances cellular respiration rates 0 chloroplasts sites of photosynthesis process converts solar energy to chemical energy by absorbing sunlight and using it to create synthesis of organic compounds such as sugars from 002 and H20 I contain chlorophyll I 2 membranes separated by narrow inter membrane space a thylakoids membranous system in form of flattened interconnected sacs 9 each stackpoker chip style is a granum 9 contains fluid called stroma 0 holds DNA ribosomes and enzymes I 3 spaces intermembrane space stroma thylakoid space mobile along tracks of cytoskeleton I member of plastid family a amyloplast colorless stores starch a chromoplast pigments give fruitsflowers orange and yellow hues o peroxisome oxidative organelle I specialized metabolic compartment bounded by a single membrane I contains enzymes that remove hydrogen atoms and transfers them to oxygen a produces H202hydrogen peroxide 0 toxic but organelle contains enzyme to convert it to water I glyoxysomes specialized peroxisomes found in fatstoring tissues of plant seeds initiate the conversion of fatty acids to sugar a uses as energy until it can preform photosynthesis o endosymbiont theory eukaryotic cells engulfed oxygenusing non photosynthetic prokaryotic cell this eventually turned into eukaryotic cell with mitochondrion Cytoskeleton network of fibers extending throughout cytoplasm 0 cell motility changes in cell location and movement of cell parts I motor proteins 0 microtubules thickest of fibers making up cytoskeleton compression rolequot hollow rods constructed from globular protein called tubulin a each protein is a dimer molecule made up of 2 subunits alpha and beta tubulin shape and support the cell and serve as tracks where motor proteins can move along Centrosomes and Centrioles a microtubules grow out of a centrosome 9 inside centrosome is pair of centrioles 9 sets of triplet microtubules arranged in a ring Cilia and Flagella a microtubule extensions that project from some cells acting as locomotor appendages 9 group of microtubules sheathed in an extension of the plasma membrane 0 9 doublets arranged in ring with 2 single microtubules in center92 0 anchored to cell by basal body similar to a centriole with microtubule triplets in a 90 pattern a flagella beats like the tail of a fish cilia like oars with alternating power and recovery strokes 0 bending movements involves dyneins large motor proteins that are attached to outer microtubule doublet 0 uses 2 feet to walk and uses ATP for energy a cilium may also act as signalrecieivng antenna for cell if cell has this function it is generally nonmotile and only 1 perceH 0 crucial to brain function and embryonic development 0 are 90 0 intermediate filaments fibers in middle range only found in some cells of animals vertebrates specialized for bearing tension very diverse class constructed from molecular subunit belonging to a family of proteinsincluding keratins a only one that varies in diameter size and composition more permanent fixtures of cells a makes cel retain its shape a especially sturdy 9 nucleus sits in cage made of intermediate filaments 9 also make up nuclear lamina a supporting shapehelps cel carry out specific function o microfilaments thinnest fibers also called actin filaments bear tensionquot I thin solid rods made from actina globular protein a twisted double chain of actin subunits can form a structural network a adds branches as proteins bind along side of filament a 3D inside plasma membrane supports cell shape a cortex outer cytoplasmic layer ofa cell has the consistency of a geldue to microfilaments role in motility myosincauses contraction of muscle cells psuedopodia cellular extensionsthatallow cell to crawl cytoplasmic streaming actinmyosin interactions in plants allow a circular flow of cytoplasm within cells 0 Cell Walls of Plants 0 cell wall extracellular structure that protects cell maintains shape and prevents excessive uptake of water I thickerthan plasma membranes I made of microfibrils made out of polysaccharide cellulose a synthesized by enzyme cellulose synthase and become embedded in matrix of other polysaccharides and proteins I primary cell wall relatively thin and flexible wall I middle lamella thin layer rich in pectinsstick polysaccharides in between cell walls a acts as glue a stops growing when ce matures and strengthens wall I secondary wall deposited in several laminated layers a strong durable matrix that affords protection and support for cell ECMExtracellular Matrix of Animal Cell 0 glycoproteins I collagenforms strong fibers outside of cell a embedded in a network woven out of proteoglycans secreted by cells 9 proteoglycans small core protein with many carb chains covalently attached I fibronectin bind to cellsurface receptor proteins called integrinsbuilt into plasma membrane 0 ECM can regulate cell s behavior by communication via integrins Cell Junctions o plasmodesmata in plant cells I cell walls perforated by channels that connect cells a cytosol passing through join internal chemical environments of adjacent cells I unify most of cell into one living continuum I molecules move freely along cytoskeleton to reach plasmodesmata 0 Tight Junctions I plasma membranes of neighboring cells pressed tightly I bound by specific proteins I forms continuous seal that establishes a barrier which prevents leaked of extracellular fluid across epithelial cells a formed between skin cells makes us watertight o Desmosomes I function like rivets a fasten cells into strong sheets I intermediate filaments made of keratin anchor desmosomes into cytoplasm I attach muscle cells to other muscle 0 Gap Junctions communicatingjunctionsquot I cytoplasmic channels between cells and function similar to plasmodesmata I membrane proteins that surround a pore and allow communication between cells a many types of tissues a allows ions sugars amino acids and other small molecules to pass through Chapter 7 Thursday October 1 2015 104 PM Membrane Structures and Functions Selective permeability allows some substances to cross more easily than others 0 Cellular membranes are fluid mosaics of lipids and proteins 0 Lipids proteins carbohydrates make up membranes 0 Amphipathic molecule has both a hydrophobic region and a hydrophilic region 39 Most membrane proteins are I Phospholipids are 0 Fluid mosaic model membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids 39 Proteins are often associated into special patches groups that all carry out similar function 39 Lipids form defined regions 0 The fluidity of membranes 0 Membrane is held together by hydrophobicinteractions 39 These are way weaker than covalent o Remains fluid while temperature decreases until phospholipids settle into a close arrangement solidifying membrane 39 Solidifying temp depends on type of lipids III Fluidity at lower temp rich in phospholipids with unsaturated tails III Steroid cholesterol less fluid at high temps lowers temperature for solidification Good at resisting change quotfluidity bufferquot 0 Must be fluid to work properly 39 Affects permeability and motility of membrane proteins 39 Natural selection has favored organisms with mix of membrane lipids that ensures an appropriate level of membrane fluidity Membrane proteins and their functions 0 Phospholipidsform the main fabric of membrane but proteins determine function 39 Integral proteins penetrate hydrophobicinterior of lipid bilayer III Transmembrane proteins span membrane III Others only extend partwayinto hydrophobicinterior III Hydrophobic portions of proteins consist of 1 stretches of nonpolaramino acids Usually coiled into alpha helices I Peripheral proteins not embedded in the lipid bilayer appendages loosely bound to surface of membrane often exposed to integral proteins 39 On the cytoplasmic side some membrane proteins are held in place by attachment to cytoskeleton 39 On extracellular side some are attached to fibers of extracellular matrix III Give animal cells strongerframework than the plasma membrane alone could provide 0 Membrane is not only structural mosaic but also functional mosaic 39 Transport proteins I Enzymatic activity 39 Signal transduction 39 Cellcell recognition 39 Intercellular joining 39 Attachment to cytoskeleton and ECMextra cellular matrix 0 The role of membrane carbohydrates in CellCell recognition 0 Cell39s ability to distinguish one type of neighboring cell from another 39 Crucial to functioning ofan organism 0 Cells bind to moleculeswith carbs on ECM of plasma membrane 39 Membrane carbs are shorter chains with 15 or less sugar units 39 Glycolipids carbslipid via covalent bond 39 Glycoproteins carbsprotein via covalent bond Membrane structure results in selective permeability o Steady traffic of small molecules and ions moves across the plasma membrane in both directions 0 Cell able to take up some small ions and molecules and exclude others 0 The Permeability of the Lipid Bilayer o NonpolarmoleculesCOZ OZ hydrocarbons are hydrophobic 39 Will dissolve in lipid bilayer and cross easily 0 Polar moleculesglucose sugars water pass super slowly 0 Charged atom or molecules and surrounding shell of water 39 Very unlikely to penetrate hydrophobicinterior of membrane Transport Proteins 0 Channel proteins hydrophilic channel that certain molecules or atomic ions use as tunnel 39 Ie water molecules use aquaporins 0 Carrier proteins hold onto passengers and change shapein a way that shuttles them across the membrane 0 Proteins are specific in that they only allow certain substances to cross a membrane 39 Specific per protein 0 Selective permeability depends on bilayer AND specific proteins in membrane Passive transport is diffusion ofa substance across a membrane with no energy investment 0 Diffusion movement of particles ofany substance so they spread out into available space 39 A substance will diffusefrom where there is more concentration to less concentration III Diffuses down concentration gradient Region along which the density ofa chemical substance increases or decreases Substance diffuses down own concentration gradient unaffected by other substances 0 Passive Transport diffusion ofa substance across a biological membrane without the cell expending energy 39 Concentration gradient itself represents potential energy 0 Osmosis diffusion offree water across a selectively permeable membrane cellular or artificial 39 Based offfree water aka water with no dissolved solute Water balance of Cells without Cell Walls 0 Tonicity ability ofa surrounding solution to cause a cell to gain or lose vvater I Depends in part on concentration of nonpenetrating solutes relative to inside cell 0 Cells without cell walls 39 Isotonic if cell is put in environmentthat is isotonic to the cell no net movment of water III Water is diffusing at same rate in both directions IILA erl II 3 ILLIL IALELLI II IIypertonlc IT tne ceII IS In scluuon tnat IS nypertonIc to me cell cell will lose water sh rivel and die D Hypermorereferring to nonpenetrating solutes 39 Hypotonic if the cell is in a solution that is hypotonicto the cell water enters cell and it swells and lyses III Hypoless 39 Cells without rigid cell walls cant tolerate excessive uptake or water loss III Osmoregulation control of solute concentrations and water balance Cells with Cell Walls 39 Tu rgor pressure opposes further water uptake III Inelastic cell wall will only expand so much before it exerts a back pressure III Cell becomes turgid which is healthy for most plant cells 9 Very firm III Isotonic no net tendency for water to enter cell becomes flaccid III Hypertonic plasmolysisplantwilts and normally dies 7 r Ecross the 2125 immersed in 122 Wall helps malntaln the cell s a o at 11151 water for exam 3 der 3 plant cell L1ke an ammal cell 1 metra mg ConSI osiS Fi ure I e l to leave water b31311 as Water enters by 05m H in 69X 7125 plant cell SW6 Slatively inelastic cell wa W th Palrlld 0111 he r6 on e ce 151m Howeverl tf re it exerts a back pressure H y y 2 Called lilelzkog39 SO mUCh 39 At this r quot Hypotonic solution ell An 0 I fares best H2 nic environ s it has otations he osmo r loss of V Lysed 39 Plasma Cell Wani Vf membrane 7t cells and tiest 1 WW the is quoted 79 water balance of ii 7eir environm a entde39 IOOd cell do n 0 Facilitated Diffusion Passive TransportAided by Proteins o Facilitated diffusion many polar molecules and ions impeded by the lipid bilayer diffuse passively with the help of transport proteins 39 Channel proteins simply provide corridors III Allow specific molecules to cross III Ion channels function as gated channels which open or close in response to stimuli 39 Carrier proteins undergo subtle change in shape to translocate the solutebinding site across membrane III Those involved in facilitated diffusion result in net movement down concentration gradient 0 Active Transport uses energy to move solutes against their gradients o Enables a cell to maintain internal concentrations ofsmall solutes that differ from concentrations in environment 0 ATP supplies energy 39 Example sodiumpotassium pump III Exchanges Na for K against concentration gradient 0 How Ion Pumps Maintain Membrane Potential 0 Voltage is electrical PE separation ofopposite charges 39 Called membrane potential ranges from 50 to 200 mV III Voltage across membrane 0 2 forces that drive diffusion of ions 39 Chemical and electrical 39 Electrochemical gradient III Ions diffuse down electrochemical gradient o Electrogenic pump transport protein that generates voltage across a membrane 0 Proton pump actively transports protonsH out of cell Cotransport Coupled Transport bya Membrane Protein 0 Cotransport a transport protein can couple the quotdownhillquot diffusion of the solute to the quotuphillquot transport of a second substance against its own concentration gradient Exocytosis 0 Cell secretes molecules by fusion of vesicles with the plasma membrane 39 When membrane and vesicle come in contact proteins rearrange lipid molecules so the membranes fuse spilling contents ofvesicles out of cell Endocytosis 0 Cell takes in molecules and particulate matter by forming new vesicles from plasma membrane 39 Small pocket forms in membrane pocket pinches in o Phagocytosis eating larger molcules o Pinocytosis drinking smaller molcules 0 Receptor Mediated form of pinocytosis 39 Take in cholesterol for membrane synthesis and the synthesis of other steroids 39 Use ligands molecules that bind specifically to a receptor site
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