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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