Chapter 6 Cell Membranes PDF

Ch 6: Cell Membranes Membrane biology and transport across cell membrane The plasma membrane : boundary of a cell : Compartmentalizat ion Cell signaling through membrane Phospholipid bilayer Hydrophobic environment Eukaryotic Cell: m...

Ch 6: Cell Membranes Membrane biology and transport across cell membrane The plasma membrane : boundary of a cell : Compartmentalizat ion Cell signaling through membrane Phospholipid bilayer Hydrophobic environment Eukaryotic Cell: membrane-enclosed organelles system (dm: double membrane) (sm structure: liposome-like (dm structure) (sm: ) Other organelles single (ER, Golgi, membran lysosome, e) peroxisome, transport (secretory) vesicles: (sm) (dm (sm ) ) chloroplast in plants (dm) (micelle: monolayer) The fluid mosaic model Dynamic cell membrane: Fluidity is controlled Fatty acids composition (Saturated fatty (Unsaturated fatty acid) acid) More fluidity (Very rare) Cholesterol content Integral membrane proteins Cell membrane carbohydrates/lipids are the recognition sites (Glycobiology) Glycoprotein example Cell recognition and adhesion Protein-protein interactions  Cell junctions link animal cells together Epithelial tissue Integrins (anchor proteins) and the ECM Mediating the attachment of cells to the ECM  Transport across membrane Substances can cross membranes by passive process Diffusion Small molecules’ and ions’ Permeability of phospholipid bilayers Membrane permeability: summary Diffusion may be aided by channel (or carrier/transporter) proteins Membrane transport: Passive vs Active (ATP) Facilitated diffusion Doesn’t require concentration gradient Concentration gradient is not required A gated channel: ligand-gated e.g. K+ , Ca2+ Dipole-ion interaction A gated channel: e.g. Voltage-gated ion channel Na , K , Ca + + 2+ A carrier protein (transporter) Osmosis: movement of solvent (water) Active transport: 3 types Primary active transport: Na+- K+ pump: antiporter Sodium ion out Potassium ion in Secondary active transport: symporter Na+-Glucose co-transporter Large molecules enter and leave a cell through vesicles Liposome –like structure (Polar molecules) Transport (secretory) vesicles: endocytosis vs exocytosis Secretory vesicles (granules): Secretory pathways Micelle-like structure can transport nonpolar molecules LDL: Low Density Lipoprotein Micell HDL: High Density Lipoprotein e Transporting nonpolar molecules Receptor-mediated endocytosis Summary: endocytosis and exocytosis Nuclear Pore Complex at the Nuclear envelope (Hugh protein Controls nuclear trafficking complex: quaternary structure) -mRNA out -Proteins (transcription factors, enzymes, proteins,…) in Summary: Osmosis and osmotic pressure Isotonic hypotonic solution hypertonic solution solution 1. Which of the following statements regarding cellular membranes is not true? a. The hydrophobic nature of the phospholipid tails limits the migration of polar molecules across the membrane. b. Integral proteins and phospholipids move laterally throughout the membrane, thereby contributing membrane fluidity. c. Membrane phospholipids flip back and forth rapidly from one side of the bilayer to the other. d. Glycolipids and glycoproteins serve as recognition sites on the cell membrane. 2. Which of the following statements regarding osmosis is not true? a. Osmosis refers to the movement of water along a concentration gradient. b. In osmosis, water moves to equalize solute concentrations on either side of the membrane. c. Osmosis refers to the movement of solutes from high to low concentration solution. d. The movement of water across a semipermeable membrane can affect the turgor pressure of some cells. 3. Sodium-potassium pumps are common in many cells. Which of the following are necessary for the pumps to work? a. ATP b. A channel protein c. No concentration gradient d. All of the above 4. Which statement about ion channels is not true? a. They form pores in the membrane. b. They are proteins. c. All ions pass through the same type of channel. d. Movement through them is from regions of high concentration to regions of low concentration. e. Movement through them is by diffusion.