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Chapter 2

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Matthew Smith

 2.1 - Basic Features of Cell Structure  Cell theory o All organisms made of 1+ cells o Cell is basic structural and functional unit of all living organisms o Cells arise from division of pre-existing cells  Three domains of life: o Bacteria o Archaea o Eukarya  Cells are too small to be seen by naked eye; see cells and structures using microscopy o Light microscopy--> use light to illuminate specimen  Bright-field  light passes directly through specimen; usually insufficient contrast to be discerned; stained w/ dye to enhance contrast  Dark-field  light illuminates specimen at angle , only light scattered by specimen reaches viewing lens of microscope; gives bright image of cell against black background  Phase-contrast  differences in refraction (way light is bent) caused by variation in density of specimen are visualized as difference in contrast; otherwise invisible structures are visible using this technique  Nomarski (differential interference contrast)  similar to phase-contrast microscopy, special lenses enhance differences in density; gives cell 3D appearance  Fluorescence  fluorescent dye used to help w/ visibility when illuminated with UV light; view emitted visible light  Confocal laser scanning  lasers scan fluorescently stained specimen; computer focuses light to show single plane through cell; provides sharper 3D image than other light microscopy techniques o Electron microscopy --> uses electrons to illuminate specimen  Transmission electron (TEM)  beam of electrons focused on thin section of specimen in vacuum; electrons that pass through form the image; structures that scatter electrons appear dark  Scanning electron (SEM)  Beam of electrons scanned across whole cell/organism; electrons excited on specimen surface are converted to a 3D-appearing image  Cells bound by plasma membrane (bilayer of lipids with embedded protein molecules)  Cytoplasm contains organelles, cytosol, and cytoskeleton  Cytosol is aqueous (water) sol'n containing ions and various organic molecules  Cytoskeleton is protein-based framework of filamentous structures that helps maintain proper cell shape and plays key roles in cell division and chromosome segregation  Many of cell's vital activities occur in cytoplasm  Nucleoid is DNA-containing central region of cell  2.2 - Prokaryotic Cells  Two major groups: o Bacteria o Archaea  Most common shapes: spherical, rod-like, spiral  Genetic material of archaea and bacteria located in nucleoid  Prokaryotic chromosomes are generally circular  Ribosomes use info from mRNA to assemble amino acids into proteins  Cell wall outside plasma membrane o Cell wall provides rigidity and structure  Glycocalyx is a "sugar coating"; it's a slime layer when loosely associated w/ cells; it's a capsule when more firmly attached to cells  Plasma membrane o Transports material into and out of cell o Contains most of molecular systems that metabolize food molecules into ATP  Bacterial flagellum o Helically shaped; rotates in socket in plasma membrane and cell wall  2.3 - Eukaryotic Cells  Four major groups: o Protists o Fungi o Animals o Plants  Nucleus separated from cytoplasm by nuclear envelope which consists of two membranes (one layered just inside the other and separated by narrow space)  Nuclear pore complex is a large structure formed from many proteins (nucleoporins) o Nucleoporins prevent transport of material not meant to cross nuclear membrane; exchanges components b/w nucleus and cytoplasm  A nuclear pore is a channel/complex that assists exchange of large molecules such as proteins and RNA molecules w/ cytoplasm o Small molecules pass through nuclear envelope w/o assistance from nuclear pore complexes o Protein/RNA molecule (cargo) associates w/ transport molecule (which acts as a shuttle) in order to pass through the nuclear pore complex and ultimately through the nuclear envelope  A nuclear localization signal distinguishes b/w proteins that
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