* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Plasma membrane
Protein moonlighting wikipedia , lookup
Lipid bilayer wikipedia , lookup
Epitranscriptome wikipedia , lookup
Membrane potential wikipedia , lookup
Model lipid bilayer wikipedia , lookup
Gene expression wikipedia , lookup
Expanded genetic code wikipedia , lookup
SNARE (protein) wikipedia , lookup
Magnesium transporter wikipedia , lookup
Genetic code wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Protein adsorption wikipedia , lookup
Two-hybrid screening wikipedia , lookup
Biosynthesis wikipedia , lookup
Signal transduction wikipedia , lookup
Biochemistry wikipedia , lookup
Proteolysis wikipedia , lookup
Western blot wikipedia , lookup
Cell-penetrating peptide wikipedia , lookup
Cell membrane wikipedia , lookup
I. Plasma Membrane Structure Plasma membrane – Boundary that separates living cells from their nonliving surroundings. - Apprx. 8 nm thick - Composed chiefly of lipids and proteins - Surrounds the cell and controls chemical traffic in/out of cell - Is semi-permeable Enables cells to maintain internal environment different from external environment Phospholipid bilayer -Composed of 2 layers of phospholipids -Heads are hydrophillic -Tails are hydrophobic Membrane Structure (Fluid Mosaic Model) • Membrane proteins embedded in phospholipid bilayer • Give membrane ‘fluidity’ similar to salad oil • Phospholipids & proteins can drift laterally (2 um / sec) Membranes must be fluid to work properly ! - solidification causes changes in permeability and enzyme deactivation How do cells control membrane fluidity ? 1. Unsaturated hydrocarbon tails 2. Adding cholesterol makes membrane: - Decreases fluidity at low temps by restraining phospholipid movement - Increases fluidity at high temps by preventing close packing of phospholipids So, how do the plant overcome the winter? winter wheat • Increase the percentage of cholesterol in phospholipids • Prevents membrane from solidifying in cold weather Proteins in Plasma Membrane - Mosaic of proteins ‘bobbing’ in a fluid lipid bilayer - Proteins determine a membrane’s specific function: Two types 1. Integral proteins (‘transmembrane’, or embedded) 2. Peripheral proteins (bound to surface of membrane) Some Functions of Membrane Proteins Transport – protein provides channel across membrane for particular solutes Enzymatic activity – proteins may be enzymes that catalyze steps in metabolic pathway Signal transduction – protein is a receptor for chemical messenger (hormone). Conformational change in protein relays message to inside of cell Intercellular joining – membrane proteins of adjacent cells join together for strength (epithelium) Cell-cell recognition – glycoproteins act as I.D. tags that are recognized by other cells (e.g. RBCs) Regulating Traffic Across Membranes II. Passive Transport: Diffusion and Facilitated diffusion Diffusion : net movement of a substance down a concentration gradient. • Solutes diffuse from high to low concentration. • Continues until a dynamic equilibrium is reached. • No requirement for energy expense (passive) • Examples: - Uptake of O2 by cell performing respiration - Elimination of CO2 from cell Diffusion of solutes across a membrane Each dye diffuses down its own concentration gradient. • • • Facilitated diffusion Passive transport Transport proteins speed the movement of molecules across the plasma membrane. Channel protein and Carrier protein required a) Channel protein : aquaporins, ion channels b) Carrier protein Osmosis • Diffusion (passive transport) of water across a selectively permeable membrane • Direction of water movement is determined by the difference in total solute concentration, regardless of type or diversity of solutes. • Water moves always from high concentration solution to low concentration solution. Water balance of living cells • Tonicity : the ability of a solution to cause a cell to gain or lose water - Isotonic: no net movement of water across the membrane (normal). - Hypertonic : the cell loses water to its environment (crenation). - Hypotonic : the cell gains water from its environment (lysis). Questions An artificial cell consisting of an aqueous solution enclosed in a selectively permeable membrane has just been immersed in a beaker containing a different solution. The membrane is permeable to water and to the simple sugars glucose and fructose but completely impermeable to sucrose. 1. Glucose? 2. Fructose? 3. Hypotonic/Hyp ertonic? 4. Water? Active Transport • Requires the cell to expend energy: ATP • Transport proteins pump molecules across a membrane against their concentration gradient. • “Uphill” transport • Maintain steep ionic gradients across the cell membrane (Na+ , K+ , Ca++ , Mg++ , Cl-) Na+ Na+ Na+ Na+ Na+ Na+ Na+ inside Na+ Na+ Na+ outside An Example of Active Transport: The Sodium-Potassium Pump Passive and Active Transport More examples of active transport • Exocytosis – Removing large particles out of the cell with a vesicle • Endocytosis – Ingesting large particles – Pinocytosis: “Cell drinking” – Phagocytosis: “Cell eating” Protein Synthesis • The process of using DNA to form proteins • Involves two steps: – Transcription – Translation Genetic Information • Uses 2 main forms of genetic information: – DNA Deoxyribonucleic Acid • • • • Double stranded Sugar: Deoxyribose Stays in the nucleus Bases: A T G C – RNA Ribonucleic Acid • • • • Single stranded Sugar: Ribose Can leave the nucleus Bases: A U G C Transcription • DNA unwinds • One strand of the double helix is used as a template • Nucleotides line up along the DNA and form a copy, called mRNA • Once completed, DNA winds back up and mRNA leaves • mRNA must be spliced before it leaves the nucleus ( immature RNA) – Enzymes remove noncoding areas called introns, and coding regions called exons are spliced back together – The result is a shorter, coding strand of mRNA – Every 3 bases on mRNA is a codon Codons • Codes for amino acids • 64 codons can code for 20 different amino acids Translation • mRNA binds to a ribosome • tRNA binds to ribosome along the codon and reads which amino acid it codes for • tRNA finds the specific amino acids • For every codon, the tRNA brings the amino acids • Amino acids link together forming a proteins • Peptide bonds link each amino acid together.