Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Chapter 1:Introduction to Cells• the cell theory• the origin of organic molecules• self-replicating molecules• the first cells• surface area to volume ratio• prokaryotic & eukaryotic cells• the evolution of cells• the basic properties of cells• model organismsReferences 4th ed: p. 1-36; 261-264(3rd ed: p. 1-36; 253-256)• All living organisms are made of one or more cells.• The cell is the fundamental unit of structure and function in all living organisms.• All cells are essentially the same in chemical composition.The Cell TheoryThe flow of genetic information in all living cellsThe Miller-Urey experiments recreated the conditions thought to exist in the atmosphere of the primitive earth.7 simple molecules (all gases): water vapor, nitrogen (N2), ammonia (NH3), CO2, CO, methane (CH4), and hydrogen (H2)• no oxygen!• heat: evaporates water• electric discharge: provides energy to rearrange thesimple gas molecules into more complex structures• cooling system condenses molecules into liquid form The Miller-Urey experiments (1950’s)The Miller-Urey experimentsHeat simulates sunElectric discharge = lightningSimple organicmolecules1. aldehydes2. simple acids3. more complex acids (including amino acids), many of them found in living systems todayThese experiments suggested that organic molecules couldform under the abiotic conditions that existed on primitive earth.With each round of heating, energy radiation, and cooling, more complex organic molecules were formed:The Miller-Urey experimentsResultsThe formation of self-replicating macromoleculesThe advent of self-replicating macromolecules was the next step in the origin of life.• necessary for:• present day:Reference: p. 261-264The RNA worldThe first genetic system might have been RNA-based.Evidence for the RNA world:1.) Some RNA molecules (ribozymes) have enzymaticactivity.Observed in:• genome replication in some RNA viruses• intron splicing• ribosome function in translationRibozyme-catalyzed reactionsRibozyme-catalyzed RNA cleavageEvidence for the RNA world:2.) RNA can catalyze the polymerization of nucleotides, including the synthesis of complementary RNA,using itself as template (this is not observed in DNA).Self-replication of RNA(in a test tube)Self-replication of RNA(In the hypothetical RNA world)The ribozyme and the substrate may be two domains of the same RNA molecule.RNA may have predated DNAand proteins in evolutionA self-replicating RNA and other life-promoting moleculesinside a phospholipid membrane.The first cellCell radiusSurface areaVolume1 cm12.57 cm24.189 cm310 cm1257 cm24189 cm3=10X=100X=1000XWhat constrains the size of a cell?The ratio of surface area to volumeSmaller cells have a greater surface area to volume ratio• as r increases, v increase is greater than sa increase• high sa : v ratio means more membrane per unit of volume: important for the cell to interact with its environment• smaller cells can interact with surroundings more efficiently• smaller cells are more likely to lose energy as heat totheir surroundingssmaller animals eat more (as % of their own mass) thanlarger animalsr = 1 cm surface area : volume ratio is ~3:1r = 10 cm surface area : volume ratio is ~1:3The surface area to volume ratioPresent day cellsProkaryotesEukaryotesEscherichia coli• no nucleus• no organelles• single chromosome(in nucleoid area) + plasmids• cell wall• capsuleProkaryotic cellsProkaryotes are the most diverse of cellsBacteria come in different shapes and sizes.Photosynthetic bacteria obtain energy from sunlight.• these cells have an internal system of membranes wherephotosynthesis occurs (in photosynthetic eukaryotes suchas plants, this system of membranes is an organelle, thechloroplast)A) Anabaena cylindrica form filaments of specialized cells:• nitrogen-fixing (H, incorporate atmospheric N2 into organic compounds)• photosynthetic (V, incorporate atmospheric CO2 into organic compounds using sunlight energy)• weather-resistant spores (S)B) Phormidium laminosum contain intracellular membranes where photosynthesis occurs Prokaryotes are the most diverse of cellsProkaryotes are the most diverse of cellsChemosynthetic = derive energy from oxidation of H2S.Prokaryotes are the most diverse of cellsSome prokaryotes live in extreme environments.The filamentous bacteria Beggiatoa can live in hydrogen sulfide-contaminated marine environments.The eukaryotic cell nucleusThe nucleus is thedistinguishing featureof eukaryotic cells.It contains most of theDNA in the cell.Eukaryotic organellesMitochondria are organelles found in eukaryotic cells and generate most of the cell's supply of usable energy.• DNA-containing organelles (they are endosymbionts)• enclosed by a double membraneChloroplasts are organelles found in plant cells and eukaryotic algae. They harvest energy from sunlight by photosynthesis.• DNA-containing organelles• larger than mitochondria• two membranes + a 3rd membrane system, the thylakoid,which contains the photosynthetic pigment chlorophyllThe mitochondrionThe chloroplastEukaryotic cellsMembrane-enclosedorganellesCytosolCells engage in endocytosis and exocytosisA continual exchange of materialswith the environment involves theplasma membrane, small vesicles,the endoplasmic reticulum, theGolgi apparatus, and the lysosomes.Endocytosis: import mediated by theformation of endocytic vesiclesExocytosis: exportFrom prokaryote to eukaryoteReference: p. 499Origin of organelles in eukaryotic cellsEndosymbiosis:Evidence for endosymbiosis:• resemble present-day prokaryotes in size• organelles contain their own DNA (organelle genomes)• organelle genomic sequences resemble those of present-dayprokaryotes• organelles can divide independent of mitosis & cell division• organelles are enclosed by double membranesMitochondria and chloroplasts were prokaryotes that entered eukaryotic cells and became specialized to perform specific cellular functions.Evolution of cellsMitochondria enteredinto the eukaryotecell lineage.Endosymbiosis: