Chapter 6: A Tour of the CellObjectives for Lecture 9• Light microscope- 1590-1600’s, visible light is passed through the specimen and then through glass lenses. The lenses bend light in such a way that the image of the specimen is magnified as it is projected into the eye onto the screen. Cant detail finer than .2 micrometers-Magnification- is the ratio of an objects image size to its real size.-Resolution- is a measure of the clarity of the image-Contrast- differences in parts of the sample-can use live cells• Organelles- membrane enclosed compartments within cells• Electron microscope- 1950s, focuses a beam of electrons through the specimen or onto its surface. -resolution is inversely related to the wavelength of the radiation a microscope uses for imaging-electron beams have shorter wavelengths than visible light-“cell ultrastructure”-kills cells• Cell Fractionation- takes cells apart and separates the major organelles and other subcellular structures from one another.-Centrifuge- spins test tubes at various speeds-allows researchers to prepare specific cell components in bulk and identify their functions. • All cells have plasma membrane-enclosed in the membrane is the cytosol (organelles are found)• All cells have ribosomes (tiny complexes that make proteins according to instructions from genes)• Cell cells have chromosomes (carry genes in the form of DNA)• Eukaryotic cell- most DNA is in the nucleus, which is bounded by a double membrane-most organisms including fungi, animals, and plants-have internal, membrane bound organelles-generally larger (size relates to function)-typically 10-100 micrometers• Prokaryotic cell- DNA is concentrated in a region that isn’t membrane enclosed, the nucleoid.-bacteria (Eubacteria and Archaea)-typically 1-5 micrometers• Endomembrane system-synthesis of proteins and their transport into membranes and organelles or out of the cell-metabolism and movement of lipids-detoxification of poisons-transfer of membrane segments as tiny vesicles (sacs made of membrane)-INCLUDES: nuclear envelope, ER, golgi apparatus, lysosomes, various kinds of vacuoles, and the plasma membrane• Cytoplasm- region between the nucleus and the plasma membrane of a Eukaryotic cell(organelles are within); also the interior of a Prokaryotic cell• Plasma membrane- at the boundary of every cell, functions as a selective barrier that allows sufficient passage of oxygen, nutrients, and wastes to service the entire cell. -as a cell increases in size, its volume grows proportionally more than its surface area. -a smaller object has a greater ratio of surface area to volume• Nucleus:-Nuclear envelope- double membrane enclosing the nucleus; perforated by pores; continuous with the ER-Nucleolus- structure involved in production of ribosomes; a nucleus has one or more nucleoli Ribosomal rRNA is synthesized here from instructions in the DNA Proteins imported from the cytoplasm are assembled with rRNA into large and small ribosomal subunits These subunits exit the nucleolus through nuclear pores to the cytoplasm where the subunits assemble into ribosomes-Chromatin- material consisting of DNA and proteins; visible as individual chromosomes in a diving cell-Nuclear matrix- framework of fibers extending throughout the nuclear interior• Ribosomes- complexes that make proteins; free in cytosol or bound to rough ER or nuclear envelope Free ribosomes- suspended in cytosol. Most function with cytosol: ex) enzymes that catalyze the first steps of sugar breakdown Bound ribosomes- are attached to the outside of the ER or nuclear envelope. Generally make up proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes, or for the export from the cell (secretion)• Cell wall- outer layer that maintains cells shape and protects cell from mechanical damage; made out of cellulose, other polysaccharides, and protein-prevents excessive uptake of water-hold up the plant against gravity-much thicker than the plasma membrane-Microfibrils made up of cellulose are synthesized by an enzyme called cellulose synthase and secreted to the extracellular space where they become embedded in a matrix of other polysaccharides and proteins. -microtubules affect the growth pattern of the cells-The Extracellular Matrix (ECM) Main ingredients are glycoproteins secreted by the cells Collagen- most abundant glycoprotein. Forms strong fibers outside the cells. Accounts for about 40% of the total protein in the human body The collagen fibers are embedded in a network woven from proteoglycans (consist of a small core protein with many carbohydrate chains covalently attached• Endoplasmic Reticulum- network of membranous sacs and tubes; active in membrane synthesis and other synthetic and metabolic processes; rough & smooth-consists of a network of membranous tubules and sacs called cisternae-Smooth ER- outer surface lacks ribosomes Synthesis of lipids- ex) sex and steroid hormones Metabolism of carbohydrates Detoxification of drugs and poisons- especially in liver cells Stores calcium ions- trigger contractions of the muscle cell-Rough ER- has ribosomes on outer surface Form secretory proteins- pancreatic cells synthesize insulin on the ER and secrete this hormone into the bloodstream Most secretory proteins are glycoproteins Transport vesicles- vesicles in transit from one part of the cell to another Grows membrane by adding membrane proteins and phospholipids to its own membrane Makes its own membrane phospholipids- enzymes built into the ER membrane assemble phospholipids from precursors in the cytosol• Golgi apparatus- organelle active in synthesis, modification, sorting, and secretion of cell products-products of the ER such as proteins are modified and stored and then sent to other destinations Extensive in cells specialized for secretion-Distinct structural polarity Cis face- usually located near the ER; transport vesicles move material from ER to golgi apparatus; a vesicle that buds from the ER can add its membrane and the contents of its lumen to the cis face by fusing to the golgi membrane Trans face- gives rise to vesicles, which pinch off and travel to other sites-Also manufactures certain macromolecules by itself- many polysaccharides-Cisternal maturation model- the cisternae of the Golgi actually progress forward from the cis to trans face of the Golgi,
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