2Why are cells so small? Why can’t they be as huge as an hippo?
3Overview: The Fundamental Units of Life All organisms are made of cellsThe cell is the simplest collection of matter that can be aliveCell structure is correlated to cellular functionFor the Discovery Video Cells, go to Animation and Video Files.
4-Lenses refract (bend) the light, so that the image is magnified Concept 6.1: Biologists use microscopes and the tools of biochemistry to study cellsIn a light microscope (LM), visible light is passed through a specimen and then through glass lenses-Lenses refract (bend) the light, so that the image is magnifiedScanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-DScanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D
5Figure 6.2 The size range of cells. Human height1 mLength of some nerve and muscle cells0.1 mUnaided eyeChicken egg1 cmFrog egg1 mmHuman egg100 mMost plant and animal cellsLight microscopy10 mNucleusMost bacteriaMitochondrion1 mFigure 6.2 The size range of cells.Smallest bacteriaSuper- resolution microscopyElectron microscopy100 nmVirusesRibosomes10 nmProteinsLipids1 nmSmall molecules0.1 nmAtoms
6Cell FractionationCell fractionation takes cells apart and separates the major organelles from one another
7Figure 6.4 Research Method: Cell Fractionation TECHNIQUEHomogenizationTissue cellsHomogenateCentrifuged at 1,000 g (1,000 times the force of gravity) for 10 minCentrifugationSupernatant poured into next tubeDifferential centrifugation20,000 g20 min80,000 g60 minPellet rich in nuclei and cellular debrisFigure 6.4 Research Method: Cell Fractionation150,000 g3 hrPellet rich in mitochondria (and chloro- plasts if cells are from a plant)Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes)Pellet rich in ribosomes
8What limits cell size? Surface to volume ratio as cell gets bigger its volume increases faster than its surface areasmaller objects have greater ratio of surface area to volumeAlka-seltzer DemoAs cell gets larger, volume increases cubically, but surface area only increases by the square.The volume of the cell is demanding… it needs exchange. The surface area is the exchange system… as cell gets larger, the surface area cannot keep up with demand.Instead of getting bigger, cell divides -- mitosis.s:v6:1~1:16:1
9Cell characteristics All cells: surrounded by a plasma membrane have cytosolsemi-fluid substance within the membranecytoplasm = cytosol + organellescontain chromosomes which have genes in the form of DNAhave ribosomestiny “organelles” that make proteins using instructions contained in genes
10Prokaryote bacteria cells Eukaryote animal cells Types of cells- no organelles- organellesEukaryote animal cellsEukaryote plant cells
11Types of cells Prokaryotic vs. eukaryotic cells Prokaryotic cell DNA in nucleoid region, without a membrane separating it from rest of cellCell wall present in all (type differs)Eukaryotic cellchromosomes in nucleus, membrane-enclosed organelleCell walls present in fungi and plants onlyMore complexMembrane bound organelles present
12The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.
13Why organelles? mitochondria chloroplast Golgi ER Specialized structuresspecialized functionscilia or flagella for locomotionContainerspartition cell into compartmentscreate different local environmentsseparate pH, or concentration of materialsdistinct & incompatible functionslysosome & its digestive enzymesMembranes as sites for chemical reactionsunique combinations of lipids & proteinsembedded enzymes & reaction centerschloroplasts & mitochondriachloroplastGolgiWhy organelles?There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Second, membrane bound organelles can act as containers, separating parts of the cell from other parts of the cell. Third, the membranes of organelles can act as sites for chemical reactions.Organelles as specialized structuresAn example of the first type of organelle is cilia, these short filaments act as "paddles" to help some cells move.Organelles as ContainersNothing ever invented by man is as complex as a living cell. At any one time hundreds of incompatible chemical reactions may be occurring in a cell. If the cell contained a uniform mixture of all the chemicals it would not be able to survive. Organelles surrounded by membranes act as individual compartments for these chemical reactions. An example of the second type of organelle is the lysosome. This structure contains digestive enzymes, these enzymes if allowed to float free in the cell would kill it.Organelle membranes as sites for chemical reactionsAn example of the third type of organelle is the chloroplast. The molecules that conduct the light reactions of photosynthesis are found embedded in the membranes of the chloroplast.ER
14Cells gotta work to live! What jobs do cells have to do?make proteinsproteins control every cell functionmake energyfor daily lifefor growthmake more cellsgrowthrepairrenewal
17Nucleolus Function ribosome production build ribosome subunits from rRNA & proteinsexit through nuclear pores to cytoplasm & combine to form functional ribosomessmallsubunitlarge subunitribosomerRNA &proteinsnucleolus
18Types of Ribosomes Free ribosomes Bound ribosomes suspended in cytosol synthesize proteins that function in cytosolBound ribosomesattached to endoplasmic reticulumsynthesize proteins for export or for membranesmembrane proteins
19Rough ER functionFinalize protein formation and prepare for export out of cell (protein folding)protein secreting cells will have lotspackaged into transport vesicles to golgiWhich cells have a lot of ER?protein production cells like pancreas = production of digestive enzymes (rough endoplasmic reticulum from a cell of exocrine pancreas (88000X))
20Golgi Apparatus Function finishes, sorts, tags & ships cell products like “UPS shipping department”ships products in vesiclesmembrane sacs“UPS trucks”transport vesiclessecretoryvesiclesCells specialized for secretion?endocrine glands: produce hormonespituitary, pancreas, adrenal, testes, ovariesexocrine glands: produce digestive enzymes & other productspancreas, mammary glands, sweat glands
22Smooth ER function Membrane production Many metabolic processes synthesissynthesize lipidsoils, phospholipids, steroids & sex hormoneshydrolysishydrolyze glycogen into glucosein liverdetoxify drugs & poisonsex. alcohol & barbiturates
23Lysosomes Function Structure little “stomach” of the cell digests macromolecules“clean up crew” of the cellcleans up broken down organellesStructurevesicles of digestive enzymessynthesized by rER, transferred to Golgionly inanimal cells
24Cellular digestion Lysosomes fuse with food vacuoles polymers digested into monomerspass to cytosol to become nutrients of cellvacuolelyso– = breaking things apart–some = body
25When cells need to die…Lysosomes can be used to kill cells when they are supposed to be destroyedsome cells have to die for proper development in an organismapoptosis“auto-destruct” processlysosomes break open & kill cellex: tadpole tail gets re-absorbed when it turns into a frogex: loss of webbing between your fingers during fetal developmentFeedback mechanismThere are sensors in the cell that monitor growth. They trigger self-destruct when they sense processes.Brown spots on leaves too.Virus infected plant cell auto-destructs and even cells around it to wall off virus.
26Making EnergyCells must convert incoming energy to forms that they can use for workmitochondria: from glucose to ATPchloroplasts: from sunlight to ATP & carbohydratesATP = active energycarbohydrates = stored energyATPATP+
27Mitochondria & Chloroplasts Important to see the similaritiestransform energygenerate ATPdouble membranes = 2 membranessemi-autonomous organellesmove, change shape, divideinternal ribosomes, DNA & enzymes
28Mitochondria Function cellular respiration generate ATP from breakdown of sugars, fats & other fuelsin the presence of oxygenbreak down larger molecules into smaller to generate energy = catabolismgenerate energy in presence of O2 = aerobic respiration
29Mitochondria Almost all eukaryotic cells have mitochondria there may be 1 very large mitochondrion or 100s to 1000s of individual mitochondrianumber of mitochondria is correlated with aerobic metabolic activitymore activity = more energy needed = more mitochondriaWhat cells would have a lot of mitochondria?active cells:• muscle cells• nerve cells
30Chloroplasts Chloroplasts are plant organelles class of plant structures = plastidsamyloplastsstore starch in roots & tuberschromoplastsstore pigments for fruits & flowerschloroplastsstore chlorophyll & function in photosynthesisin leaves, other green structures of plants & in eukaryotic algae
31Who else divides like that? ChloroplastsFunctionphotosynthesisgenerate ATP & synthesize sugarstransform solar energy into chemical energyproduce sugars from CO2 & H2OSemi-autonomousmoving, changing shape & dividingcan reproduce by pinching in twoWho else divides like that?bacteria!
32Mitochondria & chloroplasts are different Organelles not part of endomembrane systemGrow & reproducesemi-autonomous organellesProteins primarily from free ribosomes in cytosol & a few from their own ribosomesOwn circular chromosomedirects synthesis of proteins produced by own internal ribosomesribosomes like bacterial ribosomesWho else has a circular chromosome not bound within a nucleus?bacteria
33Endosymbiosis theoryMitochondria & chloroplasts were once free living bacteriaengulfed by ancestral eukaryoteEndosymbiontcell that lives within another cell (host)as a partnershipevolutionary advantage for bothone supplies energythe other supplies raw materials & protectionLynn MargulisFrom hypothesis to theory!Paradigm shifting ideas in evolutionary biology.Lynn MargulisU of M, Amherst
34Evolution of eukaryotes Endosymbiosis theoryEvolution of eukaryotes
35Food & water storage plant cells animal cells food vacuoles central vacuoleanimal cellscontractile vacuole
36Vacuoles & vesicles Function little “transfer ships” Food vacuoles phagocytosis, fuse with lysosomesContractile vacuolesin freshwater protists, pump excess H2O out of cellCentral vacuolesin many mature plant cells
37Vacuoles in plants Functions storage stockpiling proteins or inorganic ionsdepositing metabolic byproductsstoring pigmentsstoring defensive compounds against herbivoresselective membranecontrol what comes in or goes out
38Putting it all together, try labeling.. animal cellsplant cells