Membrane Transport Facilitative Diffusion

Membrane Transport Facilitative Diffusion Membrane Transport Examples: Facilitative Diffusion Ionophore Maltoporins GLUT1 transprter Aquaporin Selective ion channel for potassium (K-channels) Active Transport Primary (1°) Na+/K+ ABC Secondary (2°) Na+/Glc Bicarb/Cl– Lactose/H+ Group Translocation Bacterial phosphotransferase system (PTS) 1 Membrane Transport Active Transport Membrane Transport Examples of Active Transport Two Types 2 Membrane Transport One of the best and most important examples of Active Transport (primary): The sodium–potassium (Na+–K+) pump is primary active transport. Found in all animal cells. The pump is an integral membrane glycoprotein (an antiporter). Membrane Transport Sodium– potassium (Na+– K+) pump a2b2g pentamer 3 Membrane Transport Sodium– potassium (Na+–K+) pump Due to b subunit Membrane Transport Sodium– potassium (Na+– K+) pump 4 Membrane Transport Sodium– potassium (Na+– K+) pump Membrane Transport Sodium– potassium (Na+– K+) pump 5 Membrane Transport ABC Transporters Use ATP Hydrolysis to Drive Transport of Substrates OUT Membrane Transport ABC Transporters Use ATP Hydrolysis to Drive Transport of Substrates IN 6 Membrane Transport Failure of ABC-Transporters Can Lead to Human Disease • Mutations in the human CFTR transporter (an ABC-type transporter-like channel for chloride ions)(cystic fibrosis transmembrane-conductance regulator) result in the human disease cystic fibrosis. • Single-amino-acid mutations can render the protein misfolded and/or unable to transport chloride ions, resulting in an imbalance of water across the membrane. Regulated Facilitative Diffusion • Phosphorylated by PKA • Puts it in cycle Membrane Transport Examples of Secondary Active Transport Bicarbonate Transporter is an Antiporter Maintains the electrochemical potential across the membrane 7 Membrane Transport The bacterial Lactose Transporter is an Symporter Uses the power of a proton gradient across the plasma membrane Membrane Transport Efficient Import of Glucose uses Multiple Glucose Transporters • A Na+-glucose symporter and a glucose uniporter operate on opposite sides of epithelial cells to facilitate movement of glucose from the intestine to the blood. • Uses the Na/K gradient set up by “the pump.” 8 Membrane Transport Efficient Import of Glucose uses Multiple Glucose Transporters • A Na+-glucose symporter and a glucose uniporter operate on opposite sides of epithelial cells to facilitate movement of glucose from the intestine to the blood. • Uses the Na/K gradient set up by “the pump.” Membrane Transport Summary We learned that: •membrane proteins play a important functional role in the transport of solutes across the membrane •Transport is mediated or non-mediated. •In mediated transport there is a facilitative diffusion mechanism or an active transport mechanism •active transport is either primary or secondary •Primary active transport of solutes across membranes requires ATP •The most important and one of the best examples of primary active transport is the Na/K ATPase. •Secondary active transport but can be accomplished in many different ways, but uses the potential energy established by primary active transport 9 CATABOLISM Glycogen-o-lysis Glyco-lysis Pyruvate Oxidation Krebs' Cycle First, let’s discuss how crucial glucose is for cellular metabolism Phosphorylation Oxidative CATABOLISM Glucose Importance: • Glucose is an excellent fuel. – yields good amount of energy upon oxidation • −2840 kJ/mol glucose (–678 kcal/mol) – can be efficiently stored in the polymeric form – Many organisms and tissues can meet their energy needs on glucose only. • Glucose is a versatile biochemical precursor. – Many organisms can use glucose to generate: • • • • • all the amino acids membrane lipids nucleotides in DNA and RNA cofactors needed for the metabolism of EVERYTHING IOW, EVERYTHING!! 1 CATABOLISM Glucose Utilization: • Storage – can be stored in the polymeric form (starch, glycogen) – used for later energy needs • Energy production – generates energy via oxidation of glucose – short-term energy needs • Production of NADPH and pentoses – generates NADPH for use in relieving oxidative stress and synthesizing fatty acids, amino acids, etc. (anabolism) – generates pentose phosphates for use in DNA/RNA biosynthesis • Structural carbohydrate production – used for generation of alternate carbohydrates used in cell walls of bacteria, fungi, and plants CATABOLISM Glucose Utilization: Four Major Fates of Glucose What if you need glucose for cellular metabolism and energy? NADPH / 2 Glucose is Stored for Later Use as Glycogen (animals) or Starch (plants) • Glycogen/starch are branched polymers of α(1à4)-linked glucose with α(1à6) linkages (glycogen every 8-12 glucose units; starch every 24-30 glucose units). • Glycogen storage occurs mainly in the liver and muscle. Digestion • Starch storage occurs mainly in the leaves and seeds. maltose maltase Digestion versus intra-cellular utilization glucose (isomaltase) Glycogenolysis is performed mainly by Glycogen Phosphorylase intra-cellular utilization 3 Glycogenolysis is performed mainly by Glycogen Phosphorylase intra-cellular utilization a-D Glycogenolysis is performed mainly by Glycogen Phosphorylase 4 Glycogenolysis is performed mainly by Glycogen Phosphorylase Mechanism Carbocation (carbonium ion) intermediate 1 Acid catalysis a Base catalysis Glycogenolysis is performed mainly by Glycogen Phosphorylase Mechanism Carbocation (carbonium ion) intermediate 1 Acid catalysis a Base catalysis 5