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What is a cell.docx

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Richard B Day

January 7 , 2013 Biology 2B03: Cell Biology What is a Cell? What is a Cell? - an autonomous biological unit - smallest living unit - individual cells can grow, reproduce, process information, respond to stimuli, communicate, carry out chemical reactions - individual cells carry hereditary material in the form of DNA (chromosome) confined in an area of the cell, transcribed to become proteins which serve different functions - individual cells are surrounded by plasma membranes - can reproduce, divide and produce two daughter cells identical to each other and to the mother cell Classification of Living Organisms: Eukaryotes or Prokaryotes - prokaryotes:  single-celled bacteria and cyanobacteria  study of transcription and DNA replication - eukaryotes:  these comprise all multicellular plants and animals  fungi (multicellular moulds and unicellular yeast)  protozoans (unicellular)  communication, cell division and organisation Fundamental Differences - prokaryotes: cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments, compartmentalized functions that are not membrane-bound - eukaryotes: cell containing a membrane-bound nucleus that carries most of the genetic information (chromosomes) and a wide-array of membrane- bound organelles that perform discrete functions. Can distinguish specific functions within an organelle and increase it’s activity. Because they are compartmentalizing these functions they can become larger Prokaryotic Cells have a Simple Internal Organization - single closed compartment surrounded by a plasma membrane (1 or 2/single or double) - the nucleoid consists of a single circular DNA molecular and it is not enclosed within its own membrane - reproduce by a simplified cell division (fission, replicate their genome, not highly regulated like mitosis) - electron micrograph: high resolution image of a cell Prokaryotes - dividing eubacteria: lactococcus lactis - a colony archeabacteria: methanosarcina - prokaryotes may be unicellular or exist as colonies - is a colony the same as a multicellular organism? Eukaryotic Cells Have a Complex Internal Organization - eukaryotes contain a membrane-bound nucleus containing (most of) the genetic material of the cells; (eu-true; karyon-nucleus) - single membrane - activities are compartmentalized; an extensive internal membrane enclose various compartments = organelles Despite Their Apparent Differences, The Two Cell Types Have a lot in Common - both have selectively-permeable plasma membranes that separate the interior of the cell from the exterior of the cell - both contain an aqueous medium called cytoplasm - both contain DNA that carries the genetic information of the cell. Both contain ribosomes that translate genetic information into proteins - essential metabolic reactions are identical All Cells Share a Common Ancestor: We Can Learn Many Lessons by Looking at Cellular Evolution - eukaryotes share common proteins, macromolecules, organelles and cellular processes - conservation of protein and DNA sequences…and thus molecular mechanisms - we share many biochemical pathways with all organisms even though we look very different from one another - the proteins in different cells are often chemically similar and functionally identical
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