Wednesday, March 07, 2007

Bio 101:4

Okay, now we're at Chapter 4.
Cells, the Fucking Unit of Life.
1. Cell: The structural and functional unit of life. All cells consist of living matter, or protoplasm, bounded by an outer membrane. Each cell exhibits the characteristics of life. Organisms may be unicellular or multicellular.
2. The Cell Theory states that all life is composed of cells, that cells are the functional units of life, and that all cells come from preexisting cells. Many illnesses result from abnormalities at the cellular level.
3. Prokaryotic organisms are unicellular and include bacteria and cyanobacteria. A prokaryotic cell lacks a nucleus and has DNA, ribosomes (structures that help manufacture proteins), enzymes for obtaining energy, and various other biochemicals. A cell membrane and usually a rigid cell wall enclose the cell contents. Prokaryotes are abundant and ancient.
4. The more complex eukaryotic cells sequester certain biochemical activities in organelles (specialized structures in eukaryotic cells that carry out specific functions). A eukaryotic cell houses DNA in a membrane-bounded nucleus; snythesizes, stores, transports, and releases molecules along a network of organelles (endoplasmic reticulum, Golgi bodies, vesicles); degrades wastes in lysomes (a sac in which molecules and worn-out organelles are enzymatically dismantled); processes toxins and oxygen in peroxisomes; extracts energy from nutrients in mitochondria (organelles in which the reactions of cellular metabolism occur); and in plants, extracts solar energy in chloroplasts. A cell membrane surrounds eukaryotic cells. Cell walls protect and support cells of many organisms, except animals.
5. Archea are a third form of life that share some characteristics with prokaryotes and eukaryotes but also have unique structures and biochemistry.
6. Simpler than cells are viruses, viroids, and prions. Viruses: nucleic acid cores, protein capsids, and in some cases, envelopes. Viruses require a host cell to reproduce and have varied effects on specific species. Viroids are infectious RNA and prions are infectious glycoproteins.
7. Endosymbient theory: Choloroplasts and mitochondria evolved from once free-living prokaryotes engulfed by larger prokaryotes- chloroplasts descend from cyanobacteria and mitochondria descend from aerobic bacteria. Evidence for the endosymbiont theory is that mitochondria and chloroplasts resemble small bacteria in size, shape, and membrane structure and in the ways their DNA, RNA, and ribosomes interact to manufacture proteins.

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