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Lecture 2

BIOL 2021 Lecture 2: L2 Chapter 9b & 10a

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York University
BIOL 2021
Patricia Lakin- Thomas

Chapter 9 continued… Electron microscopy - 2 types o TEM (transmission EM) – needs thin slices of specimen (in sections) -> soak in stain -> add heavy metal (mag)  Allows electrons to pass through  Stained areas = dark  Membrane made up of heavy metal o Scanning EM – electrons scattered from surface  Still need to add heavy metal to specimen  Thin on surface -> stain only on surface  Scan areas = 3D image  Membranes tend to be seen b/c heavy metals bind there alot o Eg. Yeast cell (thin slice)  TEM + SEM  With SEM can only see outside of cell -> 3D surface picture  With TEM can see inside of cell o STAINING IS NEEDED FOR EM  Also needs heavy metal to scatter the electron or bounce off them  Without it electrons would just pass though specimen not creating an image o EM uses electrons instead of light (photon beams) to view specimen Imaging cells - Blood vessels o What’s wrong with video shown  Its not closely packed (should be bumping into eachother)  Things are moving as if they know where to go  Should move randomly - David S. Goodseel painting o Green membrane o Highly packed-> no room for water Chapter 10: Membrane Structure Eukaryotic cell - Almost ALL important things happen with or at the membrane o There are many types of membranes Membrane Function - Barrier to water soluble molecules - Separates the inside from the outside of cell o Cell vs environment o Organelles vs cytosol - Maintains ion gradient (energy conversions) - Used for signalling -> plasma membrane receptors Membrane Structure - TEM of red blood cell o Big bay of hemoglobin o Plasma membrane double to create a lipid bilayer o FIGURE 10-1a - Lipid bilayer + proteins o Held together by non-covalent interactions o 50:50 ratio by weight of protein to lipid  but there are more lipids in # then are proteins o FIGURE 10-1b  - lipids o fatty molecules o amphiphilic -> half hydrophobic and half phobic (love and hate water) o Categories of lipids (animal cells)  Phospholipids  Phosphoglycerides o Glyceride backbone with 2 fatty acid on 2 OH groups o Other OH has phosphate with something else attached LAST (head group) o Straight chain  are 4 major phospholipids in mammalian plasma membrane o 3 phosphoglycerides: Ptd-Etn, Ptd-Ser, Ptd-Cho  =different head groups  Ptd-Ser negatively charged, others are neutral  Sphingo lipids (mostly sphingomyelin) o **about sphingomyelin**… sphingosine backbone (has nitrogen) + 1 fatty acid tail (via amino group) + Choline head  Sterols (cholesterol)  Rigid ring structure that doesn’t bind or move around +Polar head group (OH) +Non-polar tail  Glycolipids (have sugar in them)  Sphinosine backbone (animals) + 6 membered ring sugar + fatty
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