2Why are cells so small? Why can’t they be as huge as an hippo?
3What 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 volumeWhat cell organelle governs this?Alka-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.Why is a huge single-celled creature not possible?s:v6:11.2:16:1
4Limits to cell size Metabolic requirements set upper limit in large cell, cannot move material in & out of cell fast enough to support lifeaaaaWhat process is this?CHNH3aaCHOO2CHCHOCO2CHOCO2CO2What process is this?diffusionWhat’s the solution?cell dividesmake a multi-celled creature = lots of little cell, rather than one BIG cellaaNH3O2NH3O2CHONH3aaCO2CHaaCHO2aaO2What’s the solution?
5How to get bigger? Become multi-cellular (cell divides) aa aa aa O2 aa But what challenges do you have to solve now?CO2CO2O2NH3aaNH3aaCO2NH3O2CO2CO2CHCHOCO2NH3Larger organisms do not generally have larger cells than smaller organisms — simply more cellsWhat’s challenges do you have to solve now?how to bathe all cells in fluid that brings nutrients to each & removes wastes from eachaaO2NH3NH3CO2CO2CO2CHOaaNH3NH3NH3CHCHOCO2CO2O2aaaaCH
6Cell 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
7Prokaryote bacteria cells Eukaryote animal cells Types of cells- no organelles- organellesEukaryote animal cellsEukaryote plant cells
8Types 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
9The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.
10Why 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
11Cells gotta work to live! What jobs do cells have to do?make proteinsproteins control every cell functionmake energyfor daily lifefor growthmake more cellsgrowthrepairrenewal
14Nucleolus Function ribosome production build ribosome subunits from rRNA & proteinsexit through nuclear pores to cytoplasm & combine to form functional ribosomessmallsubunitlarge subunitribosomerRNA &proteinsnucleolus
15Types 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
16Which cells have lot of rough ER? Rough 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 lot of rough ER?Which 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))
17Which cells have lots of Golgi? Golgi ApparatusFunctionfinishes, sorts, tags & ships cell productslike “UPS shipping department”ships products in vesiclesmembrane sacs“UPS trucks”transport vesiclessecretoryvesiclesWhich cells have lots of Golgi?Cells specialized for secretion?endocrine glands: produce hormonespituitary, pancreas, adrenal, testes, ovariesexocrine glands: produce digestive enzymes & other productspancreas, mammary glands, sweat glands
19Smooth ER function Membrane production Many metabolic processes synthesissynthesize lipidsoils, phospholipids, steroids & sex hormoneshydrolysishydrolyze glycogen into glucosein liverdetoxify drugs & poisonsex. alcohol & barbiturates
20Where old organelles go to die! LysosomesFunctionlittle “stomach” of the celldigests macromolecules“clean up crew” of the cellcleans up broken down organellesStructurevesicles of digestive enzymessynthesized by rER, transferred to Golgionly inanimal cells
21Cellular digestion Lysosomes fuse with food vacuoles polymers digested into monomerspass to cytosol to become nutrients of cellvacuolelyso– = breaking things apart–some = body
22When 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.
24Making 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+
25Mitochondria & Chloroplasts Important to see the similaritiestransform energygenerate ATPdouble membranes = 2 membranessemi-autonomous organellesmove, change shape, divideinternal ribosomes, DNA & enzymes
26Mitochondria 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
27Mitochondria 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
28Chloroplasts 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
29Who 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!
30Mitochondria & 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
31Food & water storage plant cells animal cells food vacuoles central vacuoleanimal cellscontractile vacuole
32Vacuoles & 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
33Vacuoles in plants Functions storage stockpiling proteins or inorganic ionsdepositing metabolic byproductsstoring pigmentsstoring defensive compounds against herbivoresselective membranecontrol what comes in or goes out