n Chapter 6, II ~ A Tour of the Cell Other membranous organelles, I n Mitochondria Quantity in cell correlated with metabolic activity; Cellular respiration; Double membranous (phospholipid); Cristae folds in inner membrane - surface area n Studded w/ stalked particles site of ATP synthesis Matrix intermembrane space; Contain own circular DNA Other membranous organelles, II n Chloroplast plants, algae - photosynthesis type of plastid; double membranous; thylakoids (flattened disks); grana (stacked thylakoids); stroma (space w/in); own circular DNA Endosymbiotic Theory n It is thought that eukaryotic cell organelles like mitochondria and chloroplasts are derived from prokaryotic cells that became incorporated inside larger prokaryotic cells. This idea is called endosymbiosis, and is supported by these observations: organelles contain circular DNA, like bacteria cells organelles have double membranes, as though a single-membrane cell had been engulfed and surrounded by a larger cell Endosymbiotic Theory cont. n Two processes can be combined to explain eukaryotic origin: n 1. Autogeny - Extensive inpocketing of the external plasma membrane formed a complex internal network of membranes. n 2. Endosymbiosis First proposed by Lynn Margulis (University of Massachusetts), this model proposes that small, energy-transducing prokaryotes were either ingested as prey or internal symbionts inside larger prokaryotes, where they survived and thrived. Eventually, host and symbiont became inextricably linked in a symbiotic relationship. Primary endosymbiosis is believed to have given rise to heterotrophs, and secondary endosymbiosis is believed to have given rise to the photoautotrophic eukaryotes. Peroxisomes n Single membrane n Metabolism of fatty acids; detoxification of alcohol (liver) n Produce hydrogen peroxide in cells n Contain catalase that converts H 2 O 2 to water The Cytoskeleton n Fibrous network in cytoplasm n Support, cell motility, biochemical regulation n 3 types Microtubules: tubulin protein Microfilaments: actin protein Intermediate filaments: keratin Centrosomes/centrioles n Centrosome: region near nucleus where microtubules grow n Centrioles: 9 sets of triplet microtubules in a ring; used in cell replication form mitotic spindles; only in animal cells Cilia/flagella n Locomotive appendages n Extension of cystoplasm, surrounded by the cell membrane n Ultrastructure: 9+2 9 doublets of microtubules in a ring 2 single microtubules in center Connected by radial spokes Motor proteins allow movement Cell Walls n Not in animal cells n Protection, shape, regulation n Freely permeable to solutes n Plants made mainly of cellulose, but can also contain pectin, lignin and other polysaccharides. n Fungal cell walls are made of chitin. Extracellular matrix (ECM) n Found in animal cells outside plasma membrane n Act in cell communication/ recognition n Glycoproteins, collagen (50% of protein in human body), fibronectins Intracellular junctions n PLANTS: Plasmodesmata cell wall perforations; water and solute passage in plants n ANIMALS: Tight junctions fusion of neighboring cells; prevents leakage between cells Desmosomes riveted, anchoring junction; strong sheets of cells Gap junctions protein (connexon) channels; allows passage of materials or current between cells; cardiac muscle, animal embryos