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Intro to Cell & Molecular Biology • How do we study cell biology? – Reductionist view • Cells as tiny complex machines • Sum of parts = whole • Your goal: – be able to explain the roles various molecular parts play in cell biological processes – With the same comfort and familiarity as with macroscopic items (trains, stoves, bicycles, etc…) Intro to Cell & Molecular Biology • How do we study cell biology? – Parsimony • the simplest explanation for all relevant data is preferred over more complex explanations • The most parsimonious answer is not necessarily perfectly correct • More data could make us revise it Intro to Cell & Molecular Biology • An example of parsimony in action – How did I get to class today? • Data: Someone saw me in the parking garage • Data: You can see that I’m here now • More parsimonious answer – Drove to campus, walked straight to class • Less parsimonious answer – Drove to campus, went to Starbucks, checked email in office, wandered around Salazar Hall lost for awhile, finally found classroom Intro to Cell & Molecular Biology • However, if someone else can add more observations: • Data: I have a cup from Starbucks • Data: I was seen in my office before class • More parsimonious answer – Drove to campus, went to Starbucks, checked email in office, found classroom • Still less parsimonious to include – wandered around Salazar Hall lost for awhile …unless someone has additional data to add… The Discovery of Cells • Cell theory was articulated in the mid1800s by Schleiden, Schwann and Virchow. – All organisms are composed or one or more cell. – The cell is the structural unit of life. – Cells arise from pre-existing cells by division. The Discovery of Cells • An early timeline of important tools – Microscopes, ~1650s • Robert Hooke & • Anton van Leeuwenhoek, – Human cell culture, 1951 • Henrietta Lacks = HeLa cells – In vitro (within the glass) experiments are conducted outside the living organism or with isolated parts of the organism – In vivo (within the living) experiments are conducted on the whole living organism Intro to Cell & Molecular Biology • Basic properties of cells – Complex and organized – Able to capture and use energy – Chemical factories – Genetically programmed – Responsive to stimuli – Capable of mechanical work – Reproductive – Capable of self-regulation Intro to Cell & Molecular Biology • Two structural classes of cells – Prokaryotic • “Before” nucleus Intro to Cell & Molecular Biology • Two structural classes of cells – Eukaryotic • “True” nucleus A generic animal cell • Our primary focus of study, comparative approach with bacteria • A very sophisticated micro-machine Types of prokaryotes • Archaea – Extremophiles (methanogens, halophiles, thermophiles) • Bacteria (what “prokaryote” makes most people think about) – Cyanobacteria – Mycoplasma Fix CO2 --> CH2O, Fix N2 --> NH3 Smallest living organisms – Total carbon in bacteria ~ total carbon in plants cyanobacterium Types of Eukaryotes • Single-celled – Performs all functions for viability • Multicellular – Individual cells specialize via differentiation • • • • Neurons Hepatocytes Myotubes Sperm, Egg So, who are the prokaryotes? • Both the Bacteria and the Archaea are prokaryotes • And they are quite different from each other Intro to Cell & Molecular Biology • Two structural classes of cells – Prokaryotic • “Before” nucleus – Eukaryotic • “True” nucleus – No known intermediates, – Common evolutionary ancestry Model for common evolutionary ancestry • Anaerobic heterotrophic prokaryote phagocytoses an aerobic heterotrophic prokaryote • The aerobic heterotroph escapes into the cytosol of the “host” • A symbiotic relationship gives rise to an aerobic heterotrophic prokaryote Model for common evolutionary ancestry • Plasma membrane invaginations cluster genomic DNA into a cellcentral location • Pinching membrane off yields a double membrane structure surrounding the genomic DNA Model for common evolutionary ancestry • Further elaboration of the double membrane enclosure yields the modern nucleus and endoplasmic reticulum • Symbiotic capture of a photosynthetic bacteria and elaboration of a cell wall yields plant cells Evidence for common evolutionary ancestry • Evidence to support endosymbiont theory – Absence of eukaryote species with organelles in an intermediate stage of evolution. – Many symbiotic relations are known among different organisms. – Organelles of eukaryotic cells contain their own DNA. – Organelles duplicate independently of nucleus. – Nucleotide sequences of rRNAs from eukaryotic organelles resembles that of prokaryotes. Parsimony Stem cells for use in cell replacement therapy • Two fundamental stem cell types – Adult • Hematopoietic, muscle, etc • Very limited potential – Embryonic • Pluripotent stem cells • Very broad potential Muscle stem cell Stem cells for use in cell replacement therapy 1. Isolate nucleus from a normal somatic cell 2. Inject it into an enucleated oocyte 3. Grow in vitro to blastocyst stage 4. Isolate ES cells and grow more in vitro 5. Induce differentiation in vitro to yield desired cell type 6. Transplant new cells back into patient Stem cells for use in cell replacement therapy • Induced pluripotent (iPS) cells has been demonstrated in culture. – Involves reprogramming a fully differentiated cell into a pluripotent stem cell. – These cells have been used to correct certain disease conditions in experimental animals. – Studies to reveal the mechanism of iPS could have significant medical applications. Steps taken to generate iPS for use in correcting the inherited disease sickle cell anemia in mice 1. 2. 3. 4. 5. 6. Collect skin cells Reprogram into iPS cells (+ 4 txn factors) Correct mutation by genetic engineering Recover corrected iPS cells Differentiate into hematopoietic stem cells Transplant corrected cells back into host Cell Size • • • • • Eukaryote Nucleus Mitochondria Ribosome DNA 10-30 um diameter 5-10 um diameter 2 um long 30 nm diameter 2 nm wide • Why are cells so small? – Limited by diffusion rates • O2 diffuses 1um in 100 microseconds • It takes 106 longer to travel 1 mm • As Volume increases, • Surface area becomes limiting Cell Size • Limited by diffusion rates – S/V = 3/r surface/volume – As Volume increases • V= 4/3 π r3 – Surface area becomes limiting • S = 4 π r2 4 3 2 1 0 0 10 20 radius, r 30 Cells find ways to get around the Surface/Volume problem Line A: Line B: • Which line is longer? – Cells apply the same idea to plasma membrane topology An epithelial cell surface Line A: Line B: