Eukaryotic cells have organelles. The chief distinguishing feature of eukaryotic cells is the presence of a nucleus, a membrane-bound structure that contains linear strands of DNA. In addition to a nucleus, eukaryotic cells usually contain in their cytoplasm several other specialized structures, called organelles, many of which are enclosed separately within their own lipid membranes. Eukaryotic cells are also about 10 times larger than prokaryotes. All of these physical differences make it easy to distinguish eukaryotes from prokaryotes under a microscope (Figure 3-5 Comparison of eukaryotic and prokaryotic cells).  1

Eukaryotic Cells Eukaryotes differ from prokaryotes in several ways: 1) separation of nucleus from cytoplasm by double membrane (nuclear envelope) 2) DNA organized into distinct chromosomes (X-shaped) 3) complex membrane-bound organelles (e.g., mitochondria)

Three Functional Categories of Eukaryotic Organelles Manufacturing Nucleus – genetic control center - DNA & RNA synthesis and ribosome assemble ribosomes: assemble amino acids into polypeptides (proteins/enzymes)

Three Functional Categories of Eukaryotic Organelles Manufacturing Rough Endoplasmic Reticulum (Rough ER) - network of interconnected membrane- bound sacs - “rough” appearance because ribosomes stuck to membrane surface

Three Functional Categories of Eukaryotic Organelles Manufacturing Golgi Apparatus (GA) “cell’s warehouse/factory” - stacks of membrane-bound sacs - work in close association with ER - receive, store, modify products of ER

Three Functional Categories of Eukaryotic Organelles 2) Breakdown of Material Lysosomes - produced by Rough ER & GA - digest nutrients within cell Vacuoles - plant cells - digest nutrients & storage sac

Three Functional Categories of Eukaryotic Organelles 3) Energy Processing Chloroplasts - plant cells - site of photosynthesis - absorb sun light & transform this energy to food - light absorbed in grana (stacked “solar packs”)

Three Functional Categories of Eukaryotic Organelles 3) Energy Processing Mitochondria – “cell powerhouse” - cellular respiration - double membrane - folds (cristae) of inner membrane - matrix is the inner fluid

Advantages of membrane-bound organelles 1. compartments 2. unique chemistry in different compartments 3. membranes themselves have enzymes embedded) 4. provides localized environment

Advantages of membrane-bound organelles 1. compartments 2. unique chemistry in different compartments 3. membranes themselves have enzymes embedded) 4. provides localized environment

Origin of Eukaryotic Cells from Prokaryotes – Additional Evidence Supporting the Endosymbiotic Hypothesis 1. Mitochondria and Chloroplasts contain DNA and ribosomes similar to bacteria 2.Double membrane 3. Circular DNA 4. Looks like bacteria 5. Reproduces by binary fission

Road to Modern Organisms 1st life was bacteria unicellular prokaryotes Photosynthesis changed Earth’s atmosphere released O2 - cyanobacteria!!!! 2nd was unicellular eukaryotes Endosymbiotic Theory 3rd was multicellular organisms

Origin of Eukaryotic cells The endosymbiotic theory is a theory that eukaryotic cells formed from a symbiosis among several different prokaryotic organisms