BS 161 1st Edition Lecture 10 Outline of Last Lecture I Lipids and membranes Outline of Current Lecture II A tour of the cell Current Lecture Fundamental units of life all organisms are made of cells the cell is the simplest collection of matter that can live cell structure is correlated to cellular function all cells arise from pre existing cells Prokaryotic cells that don t have a nucleus bacteria archaea lumped together with prokaryotes bacteria example organisms that live in extreme envionments Eukaryotic cells with a nucleus protists single celled eukaryotes Composition of a cell Wet weight 70 water 25 macromolecules 5 ions and small molecules Dry weight 60 proteins 25 nucleic acids 10 carbohydrates 5 lipids majority of nucleic acids in a cell are RNA The logistics of carrying out cellular metabolism sets limits on the size of cells The surface area to volume ratio is critical as the surface area increase by a factor of n2 the volume increases by a factor of n3 Basic features of all cells 1 small want a high surface area to volume ratio 2 obtain energy from environment autotrophs self feeders plants convert light into chemical energy heterotrophs feed on other things everything other than plants 3 selective in what comes in goes out membrane allows passage of certain materials selective permeability 4 use genetic material to reproduce DNA The plasma membrane is a selective barrier that allows sufficient passage of oxygen nutrients and waste to service the volume of every cell Hydrophobic molecules ex Hydrocarbons can dissolve in the lipid bilayer and pass through the membrane rapidly Polar molecules ex sugars do not cross the membrane easily If a molecule cannot easily pass through but is needed transport proteins are used to convey it through a space within a dedicated transmembrane protein Five types of transport across membranes 1 Passive transport movement of a permeable molecule across the membrane in unaided diffusion 2 Osmosis the passive diffusion of water across a membrane which has impermeable molecules 3 Facilitated transport net diffusion movement of an impermeable molecule across the membrane using a transporter 4 Active transport movement of an impermeable molecule from low to high concentration sides using energy 5 Bulk transport carrying the impermeable molecule across in a vesicle phagocytosis
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