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