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UW-Madison BIOLOGY 151 - Lipid Bilayer and Permeability

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BIOLOGY 151 1st Edition Lecture 7 Outline of Last Lecture 1. Protein structure and shape2. Almost all enzymes are proteins3. Proteins can be...4. Protein folding can be altered5. Shape changes can cause disease6. Membranes7. Lipids8. Membrane lipids9. Hydrophobic interactionsOutline of Current Lecture 1. Dissolved molecules can...2. Permeability of lipid bilayer3. Concentration of dissolved solutes outside cells can be...4. Cells in fresh (hypotonic) water5. What if the cell wants something else inside or outside?6. Exocytosis and endocytosis Current Lecture - 2/4/15- cell membrane made of lipid bilayer- lipids can spontaneously form cell-like liposomesDissolved molecules can...- diffuse between parts of a cellPermeability of lipid bilayer:- permeable to --large and small nonpolar molecules-small polar molecules (including water, although very slow)-gases (O2, CO2, N2)-glycerol- largely impermeable to --larger polar molecules-small and large ions-glucose, sucrose- steroids - cholesterol in animal cell membranesConcentration of dissolved solutes outside cells can be:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- isotonic - solute concentration is the same (iso-) outside and inside cell -like sea water- hypotonic - solute concentration is lower (hypo-) outside cell-high concentration of water inside-like fresh water- hypertonic - solute concentration is higher (hyper-) outside cell-higher concentration of water outside-like evaporated sea water- osmosis - diffusion of water across membrane from region of high water concentration to low water concentrationCells in fresh (hypotonic) water:- 1. Use still cell wall external to cell membrane - creates turgor pressure - 2. Use contractile vacuole - pumps out waterWhat if the cell wants something else inside or outside?:- add cholesterol (partly polar, partly nonpolar)- endocytosis (outside to inside)- exocytosis (inside to outside)- bulk transport- eukaryotic cells are capable of thisExocytosis and endocytosis:- membrane vesicles = small membrane-bound compartments inside cells- can fuse with or pinch off from cell membrane- fusion releases vesicle contents outside cell = exocytosis- pinching off captures substance from outside cell = endocytosis (pinocytosis = small, phagocytosis = large)- can control membrane permeability with proteins- embedded in membrane = trans-membrane proteins- fluid mosaic model- facilitated diffusion vs. active transport- facilitated diffusion - allows diffusion (region of high concentration to region of low concentration)a) through channels/pores (protein pores)b) carrier proteins --particular solutes, very sensitive-source of energy comes from movement of high concentration to low concentration- active transport - against concentration difference, needs energy from a) cotransport - diffusion of one molecule drives active transport of secondb) chemical reactions --pump against concentration gradient-breaking energy bonds,


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