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Biology Midterm #2 Notes -Biological Membranes.pdf

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BIOL 130
Heidi Engelhardt

Biological Membranes▯ ▯ General:▯ • all cells have plasma membrane which encloses the entire cell contents▯ • most common cells are eukaryotic cells (membrane bound organelles)▯ - golgi apparatus▯oplasmic reticulum▯ - lysosomes/vacuoles▯ - transport vesicles▯ • cell membrane plays an essential role in maintaining homeostasis by controlling what enters and leaves the cell▯ ▯ •eselectively permeablees:▯ membranes - they allow particular things to enter and prevent others from entering in the cell▯ • transport solutes (exchanging • responding to externalane)▯ signals, from a distance or from near by cells▯ • energy transduction- converting energy from one creating separate • environments for specific activities▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ phosphate( Phospholipids▯ glycerol( # ▯ polar&head&group& i ▯ a ▯ % • Phosphatidyl Choline (PC)▯ • Phosphatidyl Serine (PS)▯ • Phosphatidyl Ethanolamine (PE)▯ • Phosphatidyl Inositol (PI)▯ ▯ **AMPIPATHIC MEMBRANE**▯ ▯ ▯ Phospholipid composition and Membrane Fluidity▯ • Membrane fluidity- how easily lipid can move in and ▯ ▯ ▯ ▯ out of leaflet▯ • Tightly packed tails -> membrane is more vicious▯ ▯ ▯ ▯ and less fluid▯ • freely moving tails -> higher fluidity▯ ▯ *What parts of the phospholipid composition influence▯ membrane fluidity?▯ - length of fatty acids (14-24 carbons, 18-20 carbons)▯ - degree of saturation of FA -> # of double bonds▯ typically one saturated FA and one with one or more ▯ double bonds▯ ▯ Cholesterol and Membrane Fluidity▯ Membrane can become much stiffer and less fluid filled▯ ▯ -can make up to 50% of plasma membrane lipid▯ ▯ Temperature and Membrane Fluidity▯ There are two types of membrane fluidity temperatures▯ ▯ 1. above room temperature- membrane is fluid and moves freely▯ ▯ 2. as temp is dropping- fluidity decreases (permeability)▯ ▯ 3. low temps- hydrophobic tails are packed together and membrane ‘GELS’ ▯ ▯ ▯ In order for a cell to function normally…▯ ▯luid s- change composition▯ed▯ ▯ - alter phospholipids▯ ▯ -change length of FA chains (yeast and bacteria)▯ ▯ -adjust amounts of cholesterol (animals)▯ ▯ ▯ ▯ Examples of where the above listed have been used are : ▯ ▯ -pond fish▯ ▯ -cold resistant plants▯ ▯ -winter wheat▯bacteria living in hot springs▯ ▯ -sperm reduce their cholesterol just before fertilization▯ ▯ Asymmetry of Lipid Bilayer▯ ▯ sphingomyelin ▯ phosphatidyl choline (PC) ▯ ▯ ▯ ▯ ▯ ▯ ▯ phosphatidyl inositol (PI)tidyl serine (PS) ▯ phosphatidyl ethanolamine (PE) ▯ ▯ If PS is on the outer leaflet of membrane = cell is going to die▯ Human RBCs as “Model Organisms” for Plasma Membrane▯ -already present in single cell suspension▯ -no nucleus, endoplasmic reticulum, mitochondria, lysosomes (pure preps of plasma ▯embranes)▯ **asymmetry is preserved during membrane transport**▯ ▯ -they are embedded in the fluid matrix of the lipid bilayer (50 different kinds found)▯ -phospholipids form the main fabric of the membranes but proteins determine most of the membranes functions▯ ▯ ▯ ▯ ▯ ▯ ▯ junctions between cells ▯unctions of Membrane Proteins▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ cytoskeleton Transporters: protein that spans the membrane providing hydrophilic channel (small polar substances + water). Each protein provides a private passageway across the membrane for a particular class of molecule (ions, sugars, amino acids), they can also its own characteristic set of transport proteins. ▯rough. Each type of membrane has **transporters allow passage only to those molecules or ions that fit into a binding site on the protein, then transfers molecules/ions across membrane one at a time by ▯hanging its conformation**▯ - transporter proteins common: passageway for particular molecules or classes of molecules (muti-pass protein)▯ - transporter proteins in contrast: detect size and charge as long as its open, carriers ▯ require that molecules ▯ Channels: discriminate on the basis of size and electric charge ▯ ▯ Signal Transduction: some bind with specific hormones to cause effect in cell▯ Cell to Cell recognition: serves as identification▯ ▯ ▯roteins Associate with membranes …▯ ▯1. Barrel 2. Leaflet ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ Polypeptide Chains usually cross as Alpha ▯ helices ▯ ▯ hydrophobic (aids in creating a mess)▯ ▯ ▯ Eukaryotic Cells are coated with sugars; “glyco calyx”▯ ▯ -ummary:▯ - lipid molecules TEND to block passage of polar molecules (water soluble)▯ - ways substances can enter a cell▯ 1. directly through lipid bilayer▯ 2. transported across bilayer by membrane proteins acting as carriers and channels▯ ▯ 3. being engulfed by the cell▯ How do molecules move: Diffusion▯ Diffusion: movement of molecules from area of high [ ] to an area of lower concentration (CO 2and O 2move across membranes by diffusion)▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ ▯ Key terms: concentration gradient, and dynamicnergy equilibrium▯ ▯ Concentration Gradient: [ ] of water is equal total solute is also equal as longas water allowed to cross is too▯ ▯ Osmosis: The diffusion of WATER across a semi permeable membrane, water follows the concentration gradient. It moves towards a higher solute concentration. Once water = on both sides no net movement of water. ▯ ▯ ▯ ▯ ▯ ▯ Osmosis and Cells▯ - water is constant moving through cell membrane (both directions)▯ ▯ Three different types of solutions:▯ ▯ 1. Isotonic Solution: the same amount of water on outside compared to inside of ▯ ▯ cell▯ ▯ 2. Hypotonic Solution: has a lower concentration of solute and therefore higher ▯ ▯ concentration of water than inside the cell ▯ ▯ 3. Hypertonic Solution: more solute or less water than inside the cell▯ ▯ Osmotic effects in RBCs▯ ▯ ▯ ▯ ▯ net water gain, cell no net gain or loss net water loss, cell ▯ swells shrinks Osmotic effects on cells with walls▯ ▯ ▯ An▯mal Cells ▯ ▯ -water enters -water leaves ▯ cell and it will
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