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What is a Cell

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Kathleen Gilmour

Topic 1: Introduction to Cell Biology Slide 2: What is a cell? -a cell is the fundamental unit of life -every organism either consists of a group of cells or is a single cell itself -is membrane bound -contains genetic information -some cells can communicate with other cells -can self-replicate -a cell is the structural and reproductive unit of life -can respond to stimulus -can metabolize -contains water based fluids, salts, organic molecules, etc. Slide 3: The Cell Theory 1) All organisms consist of one or more cells (cells are the fundamental unit of life) 2) The cell is the basic unit of structure for all organisms (Theodor Schwann and Matthias Schleiden) 3) All cells arise only from pre-existing cells (cells are the basic unit of reproduction) (Rudolf Virchow) The generally accepted parts of modern cell theory include: 1) All known living things are made up of one or more cells. 2) All living cells arise from pre-existing cells by division. 3) The cell is the fundamental unit of structure and function in all living organisms. 4) The activity of an organism depends on the total activity of independent cells. 5) Energy flow (metabolism and biochemistry) occurs within cells. 6) Cells contain hereditary information (DNA) which is passed from cell to cell during cell division. 7) All cells are basically the same in chemical composition in organisms of similar species. Slide 5: -cells are diverse but have similar basic chemistry -they have similar basic chemistry -contain similar macromolecules that are common across all cells -genetic material is highly conserved across all organisms; the similarities are greater than differences -all cells are capable of metabolism (i.e.: oxidizing sugars into ATP / the common currency of energy) -we rely on similarities to make generalizations -diversity includes: -simple to complex shapes -shapes that reflect function (i.e.: intestinal cells = square shaped, which increases surface area for digestion) -range in size (from 200nm to 13cm to over 1m long in neurons / muscle cells) -some can carry out all functions of life (i.e.: single-celled organisms) or can be extremely specialized (i.e.: differentiated cells in multi-cellular organisms) Slide 6: Cell Size 1nm = 10^-9 m 1 micro m = 10^-6 m = 1 µm 1 angstrom = 10^-10 m -prokaryote size ranges from 1-5 micro m -eukaryote size ranges from 10 - 30 micro m -molecules are typically in the angstrom size range -ribosomes = 30 nm -nucleus = 0.006 mm -mitochondria = 3 x 10^-6 m -axon length of giraffe = 1 x 10^6 µm -microfilament diameter = 0.007 µm Why are cells small? -there are limitations on cell size: 1) SA:V Ratio -volume tells how much nutrients the cell needs and how much waste it produces -surface area represents the area available for exchange -larger cell size = smaller ratio (i.e.: more volume and less surface area) -a larger cell has more requirements but less access to contents and less ability for the movement of waste 2) Rates of Diffusion and Diffusion Distance -a small distance = quick diffusion -cells rely on diffusion to move things around 3) Adequate Concentrations or Synthetic capacity -for reactions to occur, you need a correct amount of substrate and catalyst -larger cells may not be able to synthesize the correct concentrations and no reactions would occur Slide 8: -prokaryotic and eukaryotic cells differ in their solutions to the problem of size Prokaryotes -smaller and simpler cells than eukaryotes -plasma membranes are bound by the cell wall with cytosol, ribosomes for protein synthesis, and genetic material (a single, circular chromosome) is condensed into an area of genetic material (i.e.: the nucleoid) -prokaryotic cells stay small and live with their limitations -prokarytoes are divided into bacteria and archaea (extremophiles) -they can be used for bio-remediation and bio-engineering using their special pathways Eukaryotes -have a true nucleus (a membrane bound nucleus) -are larger than prokaryotic cells -in order to overcome limitations: -eukaryotic cells elaborates membrane systems (i.e.: more complex membrane system for compartmentalization and to increase surface area) -uses a transport system (that is not necessarily diffusion) -the vast majority are single-celled protists -fungi, animal, and plants = multicellular eukaryotic organisms -they start from single cells, grow and divide, and differentiate even though each cell contains the same genetic information -model organisms are used for their simplicity (i.e.: small genome), utility, practicality, and their commonality (with multicellular organisms) -e.g.: yeast, rabidopsis, fruit fly, mouse -these organisms all have a small and simple genome, reproduce quickly, mature quickly, and grow easily under lab conditions -model eukaryotes: -Arabidopsis thaliana = the flower the Dr. Johnson uses in his studies -Caenorhabditis elegans = a round worm (C. elegans) -Danio rerio = zebra fish -Drosophila melongaster = fr
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